Jugular Foramen

CHAPTER 9

Jugular Foramen Albert L. Rhoton, Jr., M.D. Department of Neurological Surgery, University of Florida, Gainesville, Florida Key words: Cranial base, Cranial nerves, Jugular foramen, Microsurgical anatomy, Occipital bone, Skull base, Temporal bone, Venous sinuses

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he jugular foramen is difficult to understand and to access surgically (3, 11, 15, 19, 24, 28). It is difficult to conceptualize because it varies in size and shape in different crania, from side to side in the same cranium, and from its intracranial to extracranial end in the same foramen, and because of its complex irregular shape, its curved course, its formation by two bones, and the numerous nerves and venous channels that pass through it (Fig. 9.1). The difficulties in exposing this foramen are created by its deep location and the surrounding structures, such as the carotid artery anteriorly, the facial nerve laterally, the hypoglossal nerve medially, and the vertebral artery inferiorly, all of which block access to the foramen and require careful management. The jugular foramen is divided into three compartments: two venous and a neural or intrajugular compartment. The venous compartments consist of a larger posterolateral venous channel, the sigmoid part, which receives the flow of the sigmoid sinus, and a smaller anteromedial venous channel, the petrosal part, which receives the drainage of the inferior petrosal sinus. The petrosal part forms a characteristic venous confluens by also receiving tributaries from the hypoglossal canal, petroclival fissure, and vertebral venous plexus. The petrosal part empties into the sigmoid part through an opening in the medial wall of the jugular bulb between the glossopharyngeal nerve anteriorly and the vagus and accessory nerves posteriorly. The intrajugular or neural part, through which the glossopharyngeal, vagus, and accessory nerves course, is located between the sigmoid and petrosal parts at the site of the intrajugular processes of the temporal and occipital bones, which are joined by a fibrous or osseous bridge. The glossopharyngeal, vagus, and accessory nerves penetrate the dura on the medial margin of the intrajugular process of the temporal bone to reach the medial wall of the internal jugular vein. The operative approaches that access various aspects of the foramen and adjacent areas are the postauricular transtemporal, retrosigmoid, extreme lateral transcondylar, and preauricular subtemporal-infratemporal approaches.

OSSEOUS RELATIONSHIPS The jugular foramen is located between the temporal bone and the occipital bone (Figs. 9.1 and 9.2). The right foramen is

usually larger than the left. In a previous study, we observed that the right foramen was larger than the left in 68% of the cases, equal to the left in 12%, and smaller than the left in 20% (24). The foramen is configured around the sigmoid and inferior petrosal sinuses. It can be regarded as a hiatus between the temporal and the occipital bones. The structures that traverse the jugular foramen are the sigmoid sinus and jugular bulb, the inferior petrosal sinus, meningeal branches of the ascending pharyngeal and occipital arteries, the glossopharyngeal, vagus, and accessory nerves with their ganglia, the tympanic branch of the glossopharyngeal nerve (Jacobson’s nerve), the auricular branch of the vagus nerve (Arnold’s nerve), and the cochlear aqueduct. The foramen is situated so that its long axis is directed from posterolateral to anteromedial, giving it an anterolateral margin formed by the temporal bone and a posteromedial margin formed by the occipital bone. From the intracranial end, it is directed forward, medially, and downward. One cannot see through the foramen when viewing the skull from directly above or below because of its roof, formed by the lower surface of the petrous part of the temporal bone. The foramen, when viewed from the intracranial side in a posterior to anterior direction, has a large oval lateral component, referred to as the sigmoid part, because it receives the drainage of the sigmoid sinus, and a small medial part, called the petrosal part, because it receives the drainage of the inferior petrosal sinus. The view through the foramen from directly below reveals the part of the temporal bone forming the dome of the jugular bulb, rather than a clear opening. The junction of the sigmoid and petrosal parts is the site of bony prominences on the opposing surfaces of the temporal and occipital bones, called the intrajugular processes, which are joined by a fibrous, or less commonly, and osseous bridge, the intrajugular septum, separating the sigmoid and petrosal part of the foramen. Although the margins of the jugular foramen are formed by the petrosal part of the temporal bone and the condylar part of the occipital bone, the other parts of these bones also have important relationships to the jugular foramen. The petroclival fissure, the fissure between the lateral edge of the clival part of the occipital bone and the petrous part of the temporal bone, intersects the anteromedial edge of the foramen, and the occipitomastoid suture, the suture between the mastoid por-

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FIGURE 9.1. A–D. Osseous relationships. A, the jugular foramen is located between the temporal and occipital bones. One cannot see directly through the foramen from above, as shown, because it is directed forward under the temporal bone. The sigmoid groove descends along the mastoid and crosses the occipitomastoid suture where it turns forward on the upper surface of the jugular process of the occipital bone and enters the foramen by passing under the posterior part of the petrous temporal bone. B, the view directed from posterior and superior shows the shape of the foramen, which is not seen on the direct superior view. The foramen has a larger lateral sigmoid part through which the sigmoid sinus empties and a smaller anteromedial petrosal part through which the inferior petrosal sinus empties. The two parts are separated by the intrajugular processes of the occipital and temporal bones. The glossopharyngeal, vagus, and accessory nerves pass through the intrajugular portion of the foramen located between the sigmoid and petrosal parts. The foramen is asymmetric from side to side with the right side often being larger as shown. The cochlear aqueduct opens just above the anterior edge of the petrosal part. The vestibular aqueduct opens into the endolymphatic sac, which sits on the back of the temporal bone superolateral to the sigmoid part of the jugular foramen. C, jugular foramen viewed from directly below. One cannot see directly through the foramen from below because the foramen is covered above by the part of the petrous temporal bone forming the jugular fossa, which houses the jugular bulb. The entrance into the carotid canal is located directly in front of the medial half of the jugular foramen. The stylomastoid foramen is located lateral and the anterior half of the occipital condyle medial to the jugular foramen. The posterior condylar foramen is transversed by an emissary vein, which joins the sigmoid sinus. The hypoglossal canal passes above the middle third of the occipital condyle and opens laterally into the interval between the jugular foramen and carotid canal. D, the view directed from anterior and backward reveals the shape of the jugular foramen. The roof over the foramen formed by the jugular fossa of the temporal bone is shaped to accommodate the jugular bulb. The posterior margin of the foramen is formed by the jugular process of the occipital bone, which connects the basal (clival) part of the occipital bone to the squamosal part. The petroclival fissure intersects the anteromedial margin of the petrosal part of the foramen. Ac., acoustic; Car., carotid; Coch., cochlear; Cond., condyle; Fiss., fissure; For., foramen; Hypogl., hypoglossal; Int., internal; Intrajug., intrajugular; Jug., jugular; Mast., mastoid; Occip., occipital; Pet., petrous; Petrocliv., petroclival; Post., posterior; Proc., process; Sig., sigmoid; Squam., squamosal; Stylomast., stylomastoid; Temp., temporal; Vest., vestibular. tion of the temporal bone and the condylar part of the occipital bone, intersects its posterolateral edge. The intrajugular processes of the temporal and occipital bones divide the anterior and posterior edges of the foramen

between the sigmoid and petrosal parts. The intrajugular process of the temporal bone protrudes farther into the jugular foramen than the opposite process from the occipital bone, and may infrequently reach the smaller intrajugular process


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FIGURE 9.1. E–H. E and F, another jugular foramen. Left side: E, the sutures have been forced open to show the relationship of the foramen to the petroclival and occipitomastoid sutures. The jugular foramen has a larger lateral part, the sigmoid part, which receives the drainage of the sigmoid sinus, and a smaller medial part, the petrosal part, which receives the drainage of the inferior petrosal sinus. The intrajugular process of the occipital bone is somewhat more prominent than shown in C and projects forward toward the intrajugular process of the temporal bone. The hamate process normally extends along the medial edge of the petrosal part of the foramen to the adjacent part of the temporal bone, but in this case the sutures were forced open, leaving an interval between the hamate process and the temporal bone. F, enlarged view. G and H, another jugular foramen. G, the intrajugular process of the temporal bone projects into the interval between the sigmoid and petrosal parts of the foramen. A ridge, the intrajugular ridge, extends forward from the intrajugular process along the medial side of the jugular bulb. The glossopharyngeal nerve passes forward along the medial side of the intrajugular process and ridge. The vagus and accessory nerves enter the dura on the medial side of the process, but quickly descend and do not pass forward along the medial edge of the ridge as does the glossopharyngeal nerve. The jugular process of the occipital bone often has a small prominence on its surface that projects toward the intrajugular process of the temporal bone, and in some foramina, the intrajugular processes of the two bones are joined by an osseous bridge that converts the foramen into two osseous foramina. In this case, the intrajugular process of the occipital bone is absent. H, enlarged view. The cochlear aqueduct opens above the petrosal part of the foramen and the site where the glossopharyngeal nerve enters the intrajugular part of the foramen on the medial side of the intrajugular process. The vestibular aqueduct opens onto the posterior surface of the temporal bone superolateral to the jugular foramen. of the occipital bone, dividing the jugular foramen into two bony foramina. A ridge, the intrajugular ridge, extends forward from the intrajugular process of the temporal bone along the medial edge of the jugular bulb (Fig. 9.1). The glossopharyngeal nerve courses along its medial edge. Occasionally, the edge of this ridge extends medially toward the adjacent part of the temporal bone to create a deep groove in which the nerve courses or it may reach the temporal bone to

form a canal, which surrounds the glossopharyngeal nerve as it passes through the jugular foramen. The drainage of the sigmoid sinus is directed forward into the sigmoid portion of the foramen, where a high domed recess, the jugular fossa, forms a roof over the top of the jugular bulb (Figs. 9.1 and 9.3). This recess, which has its summit slightly lateral to the entrance of the sigmoid sinus, is usually larger on the right side of the skull, reflecting the larger sigmoid sinus on


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FIGURE 9.2. Osseous relationships. A, lateral view. The styloid process projects downward and the facial nerve exits the stylomastoid foramen on the lateral side, and both block lateral access to the jugular foramen. The mandibular condyle blocks access to the foramen from anteriorly and the vertebral artery ascending through the C1 transverse process limits access from behind. The transverse process of C1 sits behind and often indents the posterior wall of the internal jugular vein. B, inferior view of the jugular foramen. The jugular foramen is located lateral to the anterior half of the occipital condyle. The temporal bone forms the dome over the jugular bulb. The jugular process of the occipital bone forms the posterior margin of the jugular foramen. The jugular foramen and carotid canal are separated by a narrow bony ridge, which is penetrated medially by the tympanic canaliculus through which passes the tympanic branch of the glossopharyngeal nerve (Jacobson’s nerve). This branch of the nerve passes forward across the promontory in the medial part of the tympanic cavity, then crosses the floor of the middle fossa as the lesser petrosal nerve, and eventually reaches the otic ganglion, providing parasympathetic innervation to the parotid gland. The anterior wall of the sigmoid part of the foramen is the site of a shallow groove across which the auricular branch of the vagus nerve (Arnold’s nerve) passes to enter the mastoid canaliculus. It exits the mastoid through the tympanomastoid suture. C, lateral view of the left temporal bone. A small fiber (arrow) placed in the tympanic canaliculus, shown in B, exits the canaliculus in the middle ear where the fibers of the tympanic branch of the glossopharyngeal nerve cross the promontory, and then regroup to cross the floor of the middle fossa as the lesser petrosal nerve. The styloid process projects downward lateral to the jugular foramen. Aur., auricular; Br., branch; Canalic., canaliculus; Car., carotid; CN, cranial nerve; Cond., condyle; Ext., external; Fiss., fissure; For., foramen; Jug., jugular; Mandib., mandibular; Occip., occipital; Petrotymp., petrotympanic; Proc., process; Trans., transverse; Tymp., tympanic. that side. The dome of the recess is usually smooth as it conforms to the jugular bulb, but the summit may also be ridged and irregular. A small triangular recess, the pyramidal fossa, extends forward on the medial side of the intrajugular process of the temporal bone along the anterior wall of the petrosal part of the

foramen. The external aperture of the cochlear canaliculus, which houses the perilymphatic duct and a tubular prolongation of the dura mater, opens into the anterior apex of the pyramidal fossa. The glossopharyngeal nerve enters this fossa below the point at which the cochlear aqueduct joins its apex.


Jugular Foramen The jugular process of the condylar portion of the occipital bone, which extends behind the jugular foramen and connects the clival and squamosal parts of the occipital bone, forms the posteromedial wall of the foramen. This process extends laterally from the area above the posterior half of the occipital condyle and is penetrated by the hypoglossal canal. The upper surface of the jugular process of the occipital bone in the area superomedial to the foramen presents an oval prominence, the jugular tubercle, which is located above the hypoglossal canal. The jugular tubercle often has a shallow furrow marking the site of passage of the glossopharyngeal, vagus, and accessory nerves across its surface. The terminal end of the sigmoid sinus courses forward on the superior surface of the jugular process in a deep hook-like groove, the sigmoid sulcus, which is directed medially into the sigmoid portion of the jugular foramen. On the lateral wall of the jugular foramen, a few millimeters inside the external edge, just behind the point at which the occipitomastoid suture crosses the lateral edge of the foramen, is a small foramen, the mastoid canaliculus, and a shallow groove leading from medial to lateral across the anterior wall of the sigmoid part to the mastoid canaliculus (Figs. 9.2 and 9.3). The auricular branch of the vagus nerve (Arnold’s nerve) courses along the groove and enters the canaliculus. The nerve passes through the mastoid and exits the bone in the inferolateral part of the tympanomastoid suture. At the site where the intrajugular ridge of the temporal bone meets the carotid ridge, a small canal, the tympanic canaliculus, is directed upward, leading the tympanic branch arising from the inferior glossopharyngeal ganglion (Jacobson’s nerve) to the tympanic cavity (Figs. 9.2). Looking from below at the extracranial orifice of the jugular foramen, it can be recognized that the glossopharyngeal nerve courses along the medial side of the intrajugular process and ridge to reach the area below the tympanic canaliculus.

ADJACENT BONY STRUCTURES On the intracranial side, the petrosal part of the foramen is located approximately 5 mm below the porus of the internal canal and 5 mm above the intracranial orifice of the hypoglossal canal (Figs. 9.2 and 9.4). The lateral edge of the foramen is located below and in approximately the sagittal plane through the lateral end of the internal acoustic meatus. The jugular tubercle, a rounded prominence located at the junction of the basal and condylar parts of the occipital bone, is situated approximately 8 mm medial to the medial edge of the jugular foramen. The otic capsule, which is situated in the petrous part of the temporal bone and which contains the semicircular canals and cochlea, is located superior to the dome of the jugular bulb. The occipital condyle is located along the lateral margin of the anterior half of the foramen magnum in the area below and medial to the jugular foramen. The hypoglossal canals, which pass through the condylar part of the occipital bone in the area above the occipital condyles, are located medial to the jugular foramina (Figs. 9.1 and 9.3). The intracranial end of the hypoglossal canal is situated below the jugular tubercle approximately 5 mm inferomedial to the petrosal part of the jugular foramen and several millimeters below the lower part of the petroclival

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fissure. A more detailed review is included in the chapter on the far-lateral approach. The anterior margin of the jugular foramen, when viewed extracranially, is formed by the narrow ridge of temporal bone, the carotid ridge, which separates the foramen and the carotid canal (Figs. 9.1 and 9.2). The tympanic canaliculus opens on or near the medial part of the carotid ridge. The styloid process and the stylomastoid foramen are located lateral to the outer orifice of the jugular foramen, with the styloid process being located slightly anteromedial to the stylomastoid foramen. The facial nerve exits the stylomastoid foramen approximately 5 mm lateral to the lateral edge of the jugular foramen. The anterior margin of the jugular foramen is located just behind the part of the tympanic bone that forms the posterior wall of the temporomandibular joint and the anterior and inferior wall of the external auditory canal. The vaginal process of the tympanic bone, which separates both the carotid canal and sigmoid part of the foramen from the glenoid fossa, is the site of attachment of the styloid process to the skull base. The styloid process projects downward from the vaginal process of the tympanic bone, lateral to the foramen. The digastric groove is directed posteriorly from the styloid process along the medial margin of the mastoid process. Access to the jugular foramen is blocked laterally by mastoid and styloid processes, the transverse process of the atlas, and the mandibular ramus (Figs. 9.3 and 9.4). The tympanic cavity, which is located medial to the tympanic membrane, is situated above and lateral to the jugular bulb and the sharp right-angled curve, called the lateral bend, at the junction of the vertical and horizontal segments of the petrous carotid artery (Fig. 9.4). Several structures that may be exposed during surgery for lesions in the jugular foramen are the vertical and horizontal segments of the petrous portion of the internal carotid artery, the eustachian tube, and the tensor tympani muscle. Both the cochlea and semicircular canals are located in the petrous part of the temporal bone above the dome of the jugular bulb (Fig. 9.4). The facial nerve in the temporal bone, which often blocks access to lesions in the jugular foramen, descends through the mastoid lateral to the jugular bulb. The endolymphatic sac is situated on the posterior surface of the petrous bone between the two layers of the dura in the corner at which the sigmoid sinus changes its course from a vertical direction to a horizontal one (Figs. 9.3 and 9.5).

Dural architecture At the intracranial orifice, the jugular foramen is divided into three compartments by the dura mater: the petrosal compartment situated anteromedially, the sigmoid compartment situated posterolaterally, and the intrajugular or neural compartment situated between the petrosal and sigmoid parts at the site of the intrajugular processes of the temporal and occipital bones, the intrajugular septum, and the glossopharyngeal, vagus, and accessory nerves (Figs. 9.3 and 9.5). The dura over the intrajugular part of the foramen, which is located anteromedial to the sigmoid part, has two characteristic perforations, a glossopharyngeal meatus, through which the glossopharyngeal nerve passes, and a vagal meatus, through which the vagus and accessory nerves pass (Figs. 9.5


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FIGURE 9.3. A, posterior superior view of the jugular foramen. The sigmoid sulcus makes a sharp turn just before emptying into the sigmoid portion of the jugular foramen. The inferior petrosal sinus extends along the petroclival fissure and enters the petrosal part of the foramen. The nerves enter the intrajugular part of the foramen located between the sigmoid and petrosal parts. The outlined area shows the approximate site from which B to F were taken. B, the sigmoid sinus descends in the sigmoid sulcus and makes a sharp anterior turn to enter the jugular foramen. The jugular bulb extends upward under the petrous temporal bone toward the internal acoustic meatus. The endolymphatic sac is located above the lower portion of the sigmoid sinus on the back of the temporal bone and opens above through the vestibular aqueduct into the vestibule. The glossopharyngeal, vagus and accessory nerves penetrate the dura on the medial side of the intrajugular process. C, the dura covering the jugular foramen and the jugular bulb have been removed. The nerves penetrate the dura on the medial side of the intrajugular process of the temporal bone. The intrajugular ridge extends forward along the medial side of the jugular bulb. D, enlarged view. The glossopharyngeal nerve passes forward along the medial side of the intrajugular ridge, but the vagus and accessory nerves, although entering the dura on the medial side of the intrajugular process, almost immediately turn downward and do not course along the medial edge of the intrajugular ridge in the medial wall of the jugular bulb, as


Jugular Foramen and 9.6) (24). Both meatus are located on the medial side of the intrajugular processes and septum. The glossopharyngeal and vagal meatus are consistently separated by a dural septum ranging in width from 0.5 to 4.9 mm (13). The only intradural site at which the glossopharyngeal nerve is consistently distinguishable from the vagus nerve is just proximal to this dural septum. The close origins of the glossopharyngeal and vagus nerves at the brainstem, and the arachnoidal adhesions between the two in their course through the subarachnoid space may make separation difficult except in the area just proximal to the dural septum. The superior glossopharyngeal ganglion is easily visible intracranially in about one-third of nerves. The superior ganglion of the vagus can be seen intracranially in only one-sixth of nerves. Although the cranial and spinal portions of the accessory nerve most frequently enter the vagal meatus together, a dural septum may separate them. The upper and lateral margins of the intrajugular part of the foramen are the site of a characteristic thick dural fold that forms a roof or lip that projects inferiorly and medially to partially cover the glossopharyngeal and vagal meatus (Figs. 9.5 and 9.6). This structure, called the jugular dural fold, was ossified on both sides in one specimen (13, 16, 17, 24, 31). The lip projects most prominently over the glossopharyngeal meatus and is comparable to, but smaller than, the posterior lip of the internal acoustic meatus. It is either predominantly bony or fibrous and may project a maximum of 2.5 mm over the margin of the glossopharyngeal meatus. The vagal lip is less prominent, projecting a maximum of 1 mm over the lateral margin of the vagal meatus.

Neural relationships The glossopharyngeal, vagus, and accessory nerves arise from the medulla as a line of rootlets situated along the posterior edge of the inferior olive in the postolivary sulcus (Figs. 9.3 and 9.5). The hypoglossal nerve arises as a line of rootlets that exit the brainstem along the anterior margin of the lower two-thirds of the olive in the preolivary sulcus, a groove between the olive and medullary pyramid. The glossopharyngeal nerve, at the point at which it penetrates the dural glossopharyngeal meatus, turns abruptly forward and then downward and courses through the jugular foramen in the groove leading from the pyramidal fossa below the opening of the cochlear aqueduct and along the

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medial side of the intrajugular ridge. After the nerve exits the jugular foramen, it turns forward, crossing the lateral surface of the internal carotid artery deep to the styloid process. As the nerve transverses the jugular foramen, it expands at the site of its superior and inferior ganglia (Fig. 9.5). At the external orifice of the jugular foramen, it gives rise to the tympanic branch (Jacobson’s nerve), which traverses the tympanic canaliculus to enter the tympanic cavity where it gives rise to the tympanic plexus, the fibers of which course in shallow grooves on the promontory and regroup to form the lesser petrosal nerve, providing parasympathetic innervation by way of the otic ganglion to the parotid gland. The vagal rootlets enter the dural subcompartment, called the vagal meatus, inferior to the glossopharyngeal meatus from which it is separated by a dural septum (Figs. 9.5 and 9.6). It is joined by the accessory nerve as it enters the dura. After its rootlets gather in the intracranial orifice of the foramen, the vagus nerve expands at the superior ganglion, which is about 2.5 mm in length, and ends below the extracranial orifice of the foramen. It sits on the dura, covering the jugular foramen, and there, along the medial side of the intrajugular process of the temporal bone, it turns downward. At the superior ganglion, the vagus nerve communicates with the accessory nerve, a portion of which blends into the ganglion. The auricular branch (Arnold’s nerve) arises at the level of the superior vagal ganglion and is joined by a branch from the inferior glossopharyngeal ganglion (Fig. 9.3). The auricular branch passes laterally in a shallow groove on the anterior wall of the jugular bulb to reach the lateral wall of the jugular fossa, where it enters the mastoid canaliculus and ascends toward the vertical (mastoid) segment of the facial canal, giving off an ascending branch to the facial nerve as it crosses lateral to it before turning downward to exit the temporal bone through the tympanomastoid fissure. The main trunk of the vagus nerve (or, more accurately, the superior ganglion) courses anterior and inferior as it crosses below the midportion of the intrajugular process of the temporal bone (Figs. 9.3 and 9.5). At the intracranial orifice of the foramen, the intrajugular process of the temporal bone separates the ganglion from the sigmoid sinus. In most cases, in the area immediately below the dura at the level of the intrajugular processes, there are no fibrous bands between the glossopharyngeal nerve and the vagal ganglion.

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does the glossopharyngeal nerve. The auricular branch of the vagus nerve (Arnold’s Nerve) arises from the vagus nerve, passes along the groove in the anterior wall of the jugular fossa, and penetrates the mastoid canaliculus in the lateral wall of the fossa. E, the nerves entering the jugular foramen have been displaced downward. The intrajugular process of the temporal bone projects backward to join the intrajugular process of the occipital bone, thus forming an osseous bridge that divides the foramen into two parts. The vagus and accessory nerves pass lateral to the osseous bridge and the inferior petrosal sinus descends below the bridge to open into the internal jugular vein. F, the hypoglossal nerve has been exposed on the lateral side of the occipital condyle. It exits the hypoglossal canal and joins the glossopharyngeal, vagus, and accessory nerves below the jugular foramen in the interval between the internal carotid artery and internal jugular vein. A., artery; Ac., acoustic; Aur., auricular; Br., branch; Car., carotid; CN, cranial nerve; Cond., condyle; Endolymph., endolymphatic; Gang., ganglion; Inf., inferior; Intrajug., intrajugular; Jug., jugular; Occip., occipital; Pet., petrosal, petrous; Petrocliv., petroclival; Proc., process; Sig., sigmoid; Sup., superior; Temp., temporal; Vert., vertebral; Vestib., vestibular.


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FIGURE 9.4. A–D. Stepwise dissection of the structures superficial to and surrounding the jugular foramen. A, the skin and scalp around the ear have been reflected to expose the area lateral to the jugular foramen. The sternocleidomastoid is exposed behind and the parotid gland in front of the ear. The greater occipital nerve and occipital artery reach the subcutaneous tissues by passing between the attachment of the trapezius and sternocleidomastoid muscles to the superior nuchal line. The external acoustic meatus is located a little forward of the deep site of the jugular bulb. B, removal of the superficial muscles and parotid gland exposes the facial nerve, temporalis and masseter muscles, posterior belly of the digastric, and the internal jugular vein. The sternocleidomastoid muscle has been reflected backward to expose the accessory nerve entering its deep surface. C, the mandibular ramus and condyle, medial and lateral pterygoid muscles, and posterior belly of the digastric have been removed to expose the styloid process, which is located lateral to the jugular foramen. The internal carotid artery ascends to enter the carotid canal in front of the jugular foramen. Both the jugular foramen and carotid canal are situated behind the tympanic part of the temporal bone, which forms the posterior wall of the condylar fossa. The tensor and levator vela palatini muscles are attached to the eustachian tube in the area below the horizontal segment of the petrous carotid. The infratemporal fossa is located below the greater wing of the sphenoid. The mandibular nerve passes through the foramen ovale to enter the upper part of the infratemporal fossa. Branches of the ascending pharyngeal artery pass through the jugular foramen to supply the surrounding dura. The hypoglossal nerve passes forward across the external and internal carotid artery. D, the styloid process has been removed to expose the glossopharyngeal, vagus, accessory, and hypoglossal nerves descending between the internal carotid artery and the internal jugular vein in the area immediately below the jugular foramen. The glossopharyngeal nerve descends along the lateral side of the internal carotid artery. The accessory nerve passes backward across the lateral surface of the internal jugular vein. The hypoglossal nerve passes through the hypoglossal canal, which is located below and medial to the jugular foramen, and descends with the nerves exiting the jugular foramen. The occipital artery gives rise to a meningeal branch, which passes through the jugular foramen to supply the surrounding dura, and to the stylomastoid artery, which passes through the stylomastoid foramen with the facial nerve. A., artery; Asc., ascending; Aur., auricular; Br., branch; Cap., capitis; Car., carotid; Chor. Tymp., chorda tympani; CN, cranial nerve; Cond., condylar; Dors., dorsal; Eust., eustachian; Ext., external; Fiss., fissure; Gl., gland; Gr., greater; Inf., inferior; Int., internal; Jug., jugular; Laryn., laryngeal; Lat., lateral, lateralis; Lev., levator; Long., longus; M., muscle; Mast., mastoid; Men., meningeal; N., nerve; Obl., oblique; Occip., occipital; Pal., palatini; Pet., petrosal, petrous; Pharyn., pharyngeal; Post., posterior; Proc., process; Pteryg., pterygoid; Rec., rectus; Retromandib., retromandibular; Scap., scapulae; Seg., segment; Semicirc., semicircular; Sig., sigmoid; Squamotymp., squamotympanic; Sternocleidomast., sternocleidomastoid; Stylogloss., styloglossus; Stylomast., stylomastoid; Stylophar., stylopharyngeus; Submandib., submandibular; Sup., superior; Temp., temporal; Tens., tensor; TM., temporomandibular; Trans., transverse; Tymp., tympanic, tympany; V., vein; Vel., veli; Vent., ventral; Vert., vertebral.


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FIGURE 9.4. E–H. E, the superior and inferior oblique have been exposed by reflecting the more superficial muscles. The C1 transverse process and rectus capitis lateralis rest against the posterior surface of the internal jugular vein. The rectus capitis lateralis attaches to the jugular process of the occipital bone at the posterior margin of the jugular foramen. Retracting the levator scapulae exposes the segment of the vertebral artery ascending through the C2 transverse foramen in front of the ventral ramus of the C2 nerve root. The vertebral artery, as it passes medially along the upper surface of the posterior arch of the atlas, is situated in the floor of the suboccipital triangle located between the superior and inferior oblique and rectus capitis posterior major. F, the internal carotid artery has been displaced posteriorly to expose the branches of the ascending pharyngeal, which pass through the foramen lacerum, jugular foramen, and hypoglossal canal to supply the surrounding dura. The chorda tympani exits the skull in the medial part of the condylar fossa by first passing through the petrotympanic and then along the squamotympanic sutures. G, the tympanic bone forming the lower and anterior margin of the external meatus has been removed, but the tympanic sulcus to which the tympanic membrane attaches has been preserved. The surface of the temporal and occipital bones surrounding the jugular foramen and carotid canal have an irregular surface that serves as the attachment of the upper end of the carotid sheath. The mastoid segment of the facial nerve and the stylomastoid foramen are situated lateral to the jugular bulb. The chorda tympani arises from the mastoid segment of the facial nerve and courses along the deep side of the tympanic membrane crossing the neck of the malleus. It exits the skull by passing through the petrotympanic and squamotympanic sutures and joins the lingual branch of the mandibular nerve distally. The carotid ridge separates the carotid canal and jugular foramen. Meningeal branches of the ascending pharyngeal and occipital arteries enter the jugular foramen. The glossopharyngeal, vagus, and accessory nerves pass through the jugular foramen on the medial side of the jugular bulb. H, the tympanic ring and bone lateral to the tympanic cavity have been removed. The internal carotid artery has been displaced forward out of the carotid canal to expose the carotid sympathetic nerves that ascend with the artery. The glossopharyngeal, vagus, accessory, and hypoglossal nerves exit the skull on the medial side of the internal carotid artery and jugular vein. The glossopharyngeal and hypoglossal nerves pass forward along the lateral surface of the internal carotid artery, and the accessory nerve descends posteriorly across the lateral surface of the internal jugular vein. The vagus nerve descends in the carotid sheath. The vagus nerve exits the jugular foramen vertically, retaining an intimate relationship to the accessory nerve (Figs. 9.3– 9.5). At the level the two nerves exit the jugular foramen, they are located behind the glossopharyngeal nerve on the pos-

teromedial wall of the internal jugular vein. As the vagus nerve passes lateral to the outer orifice of the hypoglossal canal, it is joined by the hypoglossal nerve medially. The vagus nerve begins to expand at the site of the inferior vagal


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FIGURE 9.4. I–N. I, lateral view of mastoid and tympanic cavity before removing the tympanic ring. The tympanic segment of the facial nerve passes below the lateral semicircular canal and turns downward as the mastoid segment to exit the stylomastoid foramen. The stylomastoid foramen and the mastoid segment are located lateral to the jugular bulb. The semicircular canals are located above the jugular bulb. J, a probe has been placed in the eustachian tube, which passes downward, forward, and medially from the tympanic cavity and across the front of the petrous carotid. The third trigeminal division passes through the foramen ovale on the lateral side of the eustachian tube. K, enlarged view of the tympanic ring with the tympanic membrane removed. The tensor tympany muscle passes backward above the eustachian tube and gives rise to a tendon that turns sharply lateral around the trochleiform process to attach to the malleus. The chorda tympani crosses the inner surface of the tympanic membrane and neck of the malleus. The round window opens into the vestibule. The stapes sit in the oval window. The promontory is located lateral to the basal turn of the cochlea. L, the floor of the middle fossa and the tympanic sulcus have been removed to expose the jugular bulb and petrous carotid. The greater petrosal nerve courses along the floor of the middle fossa on the upper surface of the petrous carotid. The deep petrosal nerve arises from the sympathetic bundles on the internal carotid artery. The deep and greater petrosal nerves join to form the vidian nerve, which passes forward through the vidian canal to join the maxillary nerve and pterygopalatine ganglion in the pterygopalatine fossa. The pharyngobasilar fascia and upper part of the


Jugular Foramen ganglion just below the foramen and is approximately 2.5 cm in length.

Accessory nerve Although the cranial and spinal portions of the accessory nerve most frequently enter the vagal meatus together, they may infrequently be separated by a dural septum. The spinal portion ascends toward the foramen magnum by crawling along the surface of the dura and may even be buried in the dura below the foramen magnum (Figs. 9.3, 9.5, and 9.6). At the dural orifice of the jugular foramen, the nerve is often indistinguishable from the vagus nerve. The accessory nerve usually enters the same dural subcompartment as the vagus nerve and often adheres and blends into the vagus nerve at the level of the superior vagal ganglion. The accessory nerve departs the vagal ganglion after it exits the jugular foramen and descends obliquely laterally between the internal carotid artery and internal jugular vein and then backward across the lateral surface of the vein to reach its muscles. Approximately 30% of nerves descend along the medial, rather than the lateral, surface of the internal jugular vein (8).

Hypoglossal nerve The hypoglossal nerve does not traverse the jugular foramen (Figs. 9.3–9.5). However, it joins the nerves exiting the jugular foramen just below the skull and runs with them in the carotid sheath. The nerve exits the inferolateral part of the hypoglossal canal and passes adjacent to the vagus nerve, descends between the internal carotid artery and the internal jugular vein to the level of the transverse process of the atlas, where it turns abruptly forward along the lateral surface of the internal carotid artery toward the tongue, leaving only the ansa cervicalis to descend with the major vessels.

ARTERIAL RELATIONSHIPS The arteries that may be involved in pathological abnormalities at the jugular foramen include the upper cervical and petrous portions of the internal carotid artery, the posteriorly directed branches of the external carotid artery, and the upper portion of the vertebral artery (Fig. 9.4).

Internal carotid artery The internal carotid artery passes, almost straightly upward, posterior to the external carotid artery and anteromedial to the internal jugular vein, to reach the carotid canal (Fig. 9.4). At the level of the skull base, the internal jugular vein courses just posterior to the internal carotid artery, being separated from it by the carotid ridge. Between them, the

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glossopharyngeal nerve is located laterally and the vagus, accessory, and hypoglossal nerves medially. After the internal carotid artery enters the carotid canal with the carotid sympathetic nerves and surrounding venous plexus, it ascends a short distance (the vertical segment), reaching the area below and slightly behind the cochlea, where it turns anteromedially at a right angle (the site of the lateral bend) and courses horizontally (the horizontal segment) toward the petrous apex (Fig. 9.4). At the medial edge of the foramen lacerum, it turns sharply upward at the site of the medial bend to enter the posterior part of the cavernous sinus.

External carotid artery The external carotid artery ascends anterior to the internal carotid artery. Proximal to its terminal bifurcation into the maxillary and the superficial temporal arteries, it gives rise to six branches, which can be divided into anterior and posterior groups according to their directions. The latter group is related to the jugular foramen. The ascending pharyngeal artery, the first branch of the posterior group, often provides the most prominent supply to the meninges around the jugular foramen (Fig. 9.4) (18). It arises either at the bifurcation or from the lowest part of the external or internal carotid arteries. Rarely it arises from the origin of the occipital artery. It courses upward between the internal and the external carotid arteries, giving rise to numerous branches to neighboring muscles, nerves, and lymph nodes. Its meningeal branches pass through the foramen lacerum to be distributed to the dura lining the middle fossa and through the jugular foramen or the hypoglossal canal to supply the surrounding dura of the posterior cranial fossa. The ascending pharyngeal artery also gives rise to the inferior tympanic artery, which reaches the tympanic cavity by way of the tympanic canaliculus along with the tympanic branch of the glossopharyngeal nerve. The occipital artery, the second and largest branch of the posterior group, arises from the posterior surface of the external carotid artery and courses obliquely upward between the posterior belly of the digastric muscle and the internal jugular vein (Fig. 9.4). Its meningeal branches, which enter the posterior fossa through the jugular foramen or the condylar canal, may make a significant contribution to tumors of the jugular foramen. The posterior auricular artery, the last branch in the posterior group, arises above the posterior belly of the digastric muscle and travels between the parotid gland and the styloid process. At the anterior margin of the mastoid process, it divides into auricular and occipital branches, which are dis-

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longus capitis have been reflected downward to expose the lower margin of the clivus. M, the jugular bulb has been removed from the jugular fossa located below the vestibule and semicircular canals. The vertical segment of the petrous carotid has been removed. The cochlea, which has been opened, is located above the lateral genu of the petrous carotid. The tympanic segment of the facial nerve passes posteriorly below the lateral semicircular canal. N, the retrosigmoid and presigmoid dura have been opened. The lateral wall of the vestibule and cochlea have been removed. The vestibule, semicircular canals, and cochlea are exposed above the jugular bulb and lateral genu of the petrous carotid.


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FIGURE 9.5. A, posterior view of the intracranial aspect of the left jugular foramen. The glossopharyngeal, vagus, and accessory nerves pierce the dural roof of the jugular foramen. The glossopharyngeal nerve is separated from the vagus nerve by a narrow dural septum. The jugular dural fold projects downward and medially from the lateral and upper margin of the jugular foramen over the site at which the nerves enter the dura roof of the foramen. The facial and vestibulocochlear nerves and labyrinthine artery enter the internal acoustic meatus. The subarcuate branch of the anteroinferior cerebellar artery enters the subarcuate fossa. The endolymphatic sac is located between the dural layers lateral to the jugular foramen. A bridging vein from the medulla joins the inferior petrosal sinus on the medial side of the jugular bulb. B, the dura has been removed from the posterior surface of the temporal bone. The intrajugular processes of the temporal and occipital bones, which are connected by a fibrous bridge, the intrajugular septum, separates the sigmoid and petrosal parts of the foramen. The glossopharyngeal, vagus, and accessory nerves enter the intrajugular part of the foramen by penetrating the dura on the medial side of the intrajugular process of the temporal bone. C, the glossopharyngeal nerve enters the jugular foramen below the cochlear aqueduct. The vagus nerve enters the jugular foramen behind the glossopharyngeal nerve. The auricular branch of the vagus nerve (Arnold’s nerve) arises at the level of the superior ganglion and passes around the anterior wall of the jugular bulb. The accessory nerve is formed by multiple rootlets, which arise from the medulla and spinal cord. The accessory rootlets collect together to form a bundle that blends into the lower margin of the vagus nerve at the level of the jugular foramen. The lower vagal and accessory roots pass across the surface of the jugular tubercle. D, enlarged view. The glossopharyngeal nerve expands at the site of the superior and inferior ganglia. The superior ganglion of the vagus nerve is located at the level of or just below the dural roof of the foramen, and the inferior ganglion is located below the foramen at the level of the atlanto-occipital joint. A., artery; Atl., atlanto-; Aur., auricular; Br., branch; Bridg., bridging; Car., carotid; CN, cranial nerve; Coch., cochlear; Cond., condyle; Endolymph., endolymphatic; Gang., ganglion; Glossophar., glossopharyngeal; Hypogl., hypoglossal; Inf., inferior; Int., internal; Intrajug., intrajugular; Jug., jugular; Labyr., labyrinthine; Lat., lateral; Occip., occipital; Pet., petrosal; Proc., process; Sig., sigmoid; Subarc., subarcuate; Sup., superior; Temp., temporal; Vert., vertebral. tributed to the postauricular and the occipital regions respectively. The stylomastoid branch, which arises below the stylomastoid foramen, enters the stylomastoid foramen to supply the facial nerve. Its loss can lead to a facial palsy even though

it anastomoses with the petrosal branch of the middle meningeal artery. The posterior auricular branch may share a common trunk with the occipital artery, or sometimes it is absent, in which case, the occipital artery gives rise to the


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FIGURE 9.6. Retrosigmoid approach to jugular foramen. A, the detail shows the site of the vertical scalp incision and right retrosigmoid craniotomy. The cerebellum has been elevated to expose the nerves in the right cerebellopontine angle. The glossopharyngeal and vagal nerves are separated by the dural septum at the level of the dural roof of the jugular foramen. The glossopharyngeal nerve enters the glossopharyngeal meatus and the vagus nerve enters the vagal meatus with the branches of the accessory nerve. Both meatus are very shallow compared with the internal acoustic meatus. The superior and lateral margins of both meatus project downward and medially over the nerves entering the meatus. The vertebral artery displaces the hypoglossal rootlets of Cranial Nerve XII posteriorly so that they intermingle with the rootlets of the accessory nerve. B, another specimen showing the relationship of the rhomboid lip and choroid plexus protruding from the foramen of Luschka to the glossopharyngeal and vagus nerves. The choroid plexus protrudes laterally behind the glossopharyngeal nerves. The rhomboid lip is a thin layer of neural tissue that forms the ventral margin of the foramen of Luschka at the outer end of the lateral recess. C and D, enlarged view of two jugular foramina. The glossopharyngeal and vagus nerves are consistently separated by a dural septum at the level of the roof over the jugular foramen. The jugular dural fold projects downward and medially over the lateral edge of the glossopharyngeal and vagal meatus and over the site at which the nerves penetrate the dura. A., artery; A.I.C.A., anteroinferior cerebellar artery; Chor., choroid; CN, cranial nerve; Glossophar., glossopharyngeal; Jug., jugular; Plex., plexus; Vert., vertebral. stylomastoid artery. Members of the anterior group, whose origins may be visualized in exposing lesions of the jugular foramen, include the superior thyroid, lingual, and facial arteries.

the meningeal, posterior spinal, and posteroinferior cerebellar artery.

VENOUS RELATIONSHIPS Vertebral artery The vertebral artery, as it ascends to reach and pass through the transverse foramen of the atlas, is located below and behind the jugular foramen (Fig. 9.4). Branches encountered in approaches to lesions of the jugular foramen include

The jugular bulb and adjacent part of the internal jugular vein receives drainage from both intracranial and extracranial sources, which include the sigmoid and inferior petrosal sinuses, the vertebral venous plexus, the venous plexus of the hypoglossal canal, the posterior condylar emissary vein, and


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the vein coursing along the inferior aspect of the petroclival fissure (Figs. 9.4 and 9.5).

Sigmoid sinus and jugular bulb The sigmoid sinus is the largest channel emptying into the jugular foramen (Figs. 9.1 and 9.3–9.5). After coursing down the sigmoid sulcus, the sinus turns anteriorly toward the jugular foramen, crossing the occipitomastoid suture immediately proximal to the foramen. From there, the sinus is directed forward below the petrous temporal bone at the site of the jugular bulb. The upward bulging of the superior margin of the jugular bulb creates a rounded fossa in the lower surface of the temporal bone below the internal auditory canal. The dome of the jugular bulb may extend upward in the posterior wall of the internal auditory canal to the level of the upper margin of the canal. The bulb is usually larger on the right side, reflecting the larger diameter of the sigmoid sinus on that side. From the level of the jugular bulb, flow is directed downward behind the tympanic bone and the carotid canal into the internal jugular vein.

Inferior petrosal sinus and venous confluens The foramen also receives the inflow from the inferior petrosal sinus and the venous confluens in the petrosal part of the foramen. The inferior petrosal sinus, which courses on the intracranial surface of the petroclival fissure, communicates the cavernous sinus and basilar venous plexus at its upper end and with the jugular bulb at its lower end (Figs. 9.3 and 9.5). The inferior petrosal sinus, as it enters the petrosal part of the jugular foramen, forms a plexiform confluens with the venous plexus of the hypoglossal canal, the inferior petroclival vein, and tributaries from the vertebral venous plexus and posterior condylar emissary vein. This confluens, which fills the petrosal part of the foramen, usually consists of a main channel, 2 to 3 mm in diameter, and several smaller channels, less than 1 mm in diameter. It empties into the medial aspect of the jugular bulb through one or two openings in the venous walls between the glossopharyngeal and vagus nerves or into the internal jugular vein below the extracranial orifice. The inferior petroclival vein courses along the extracranial surface of the petroclival fissure and is a mirror image of the inferior petrosal sinus, which courses along the intracranial surface of the fissure (Fig. 9.5). It empties into the venous confluens at the lower end of the inferior petrosal sinus at or just below the extracranial orifice of the jugular foramen or even above it, through bony clefts between the temporal and occipital bones.

Bridging veins A bridging vein, which courses posterior to the glossopharyngeal, vagus, and accessory nerves from the dorsolateral medulla to the lower end of the sigmoid sinus, is present in about one-third of cerebellopontine angles (Fig. 9.5, also see Fig. 3.12). Infrequently, a bridging vein extends from the ventral medulla to the lower margin of the inferior petrosal sinus in front of the nerves.

MUSCULAR RELATIONSHIPS Several muscles that are encountered in the surgical approaches to the jugular foramen and that provide important landmarks in the approach are reviewed in detail in the chapters on the foramen magnum and temporal bone (Fig. 9.4). These include the sternocleidomastoid, situated superficially in the lateral neck, and the splenius capitis, longissimus capitis, levator scapulae, and scalenus medius muscles in a deeper muscular layer. More anteriorly is the posterior belly of the digastric muscle, which arises in the digastric groove located medial to the mastoid process and the longissimus capitis. The styloid process and its attached muscles appear in the triangular zone bounded by the posterior belly of the digastric, the external auditory canal, and the mandibular ramus. Reflecting the digastric muscle exposes the transverse process of the atlas, which is covered by the attachments of numerous muscles, including the superior and inferior obliques, which form the upper and lower margin of the suboccipital triangle. The rectus capitis lateralis muscle is the muscle most intimately related to the jugular foramen. It extends vertically behind the internal jugular vein from the transverse process of the atlas to the jugular process of the occipital bone. On the posterior neck are the trapezius muscle, splenius capitis, and semispinalis capitis. Beneath the semispinalis capitis muscle, three muscles arise between the inferior nuchal line and the margin of the foramen magnum: the rectus capitis posterior major and minor and the superior oblique muscle. The suboccipital triangle, an area defined by the opposing margins of the rectus capitis posterior major and the superior and inferior oblique muscles, is the site at which the vertebral artery courses along the upper posterior surface of the atlas.

SURGICAL APPROACHES Postauricular transtemporal approach The postauricular transtemporal approach accesses the region from laterally, through the mastoid, and from below, through the neck (Fig. 9.7) (2, 4, 5). A C-shaped postauricular skin incision provides the exposure for a mastoidectomy and the neck dissection. The external auditory canal is either preserved or transected, depending on the anterior extent of the pathological abnormality. The neck dissection is completed initially to gain control of the major vessels and the branches supplying the tumor. The internal carotid artery, branches of the external carotid artery, internal jugular vein, and lower cranial nerves are exposed in the carotid sheath. A mastoidectomy with extensive drilling of the infralabyrinthine region accesses the jugular bulb. A limited mastoidectomy confined to the area behind the stylomastoid foramen and mastoid segment of the facial nerve, combined with removal of the adjacent part of the jugular process of the temporal bone, will provide access to the posterior and posterolateral aspect of the jugular foramen. Three obstacles to exposure of the full lateral half of the jugular foramen, the facial nerve, styloid process, and rectus capitis lateralis muscle are dealt with by transposing the facial nerve, removing the styloid process, and divid-


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FIGURE 9.7. A–D. Postauricular exposure of the jugular foramen. A, the detail shows the site of the scalp incision. The C-shaped retroauricular incision provides access for the mastoidectomy, neck dissection, and parotid gland displacement. The scalp flap has been reflected forward to expose the sternocleidomastoid and the posterior part of the parotid gland. B, the more superficial muscles and the posterior belly of the digastric have been reflected to expose the internal jugular vein and the attachment of the superior and inferior oblique to the transverse process of C1. A mastoidectomy has been completed to expose the facial nerve, sigmoid sinus, and capsule of the semicircular canals. C, enlarged view of the mastoidectomy. The jugular bulb is exposed below the semicircular canals. The chorda tympani arises from the mastoid segment of the facial nerve and passes upward and forward. The tympanic segment of the facial nerve courses below the lateral canal. D, enlarged view of the caudal part of the exposure shown in C. The facial nerve and styloid process cover the extracranial orifice of the jugular foramen. The facial nerve crosses the lateral surface of the styloid process. The stylomastoid artery arises from the postauricular artery. The rectus capitis lateralis attaches to the jugular process of the occipital bone behind the jugular foramen. A., artery; Aur., auricular; Cap., capitis; Car., carotid; Chor. Tymp., chorda tympani; CN, cranial nerve; Coch., cochlear; Gl., gland; Gr., greater; Inf., inferior; Int., internal; Intrajug., intrajugular; Jug., jugular; Laryn., laryngeal; Lat., lateral, lateralis; M., muscle; Med., medial; Mid., middle; N., nerve; Obl., oblique; Occip., occipital; Pet., petrosal, petrous; Post., posterior; Proc., process; Rec., rectus; Semicirc., semicircular; Sig., sigmoid; Sternocleidomast., sternocleidomastoid; Stylomast., stylomastoid; Sup., superior; Symp., sympathetic; Tr., trunk; Trans., transverse; V., vein. ing the rectus capitis lateralis muscle. Anterior extensions of the pathological abnormality are reached by sacrificing the external and the middle ear structures. Sensorineural hearing can be preserved by maintaining the foot plate of the stapes in the oval window to avoid opening the labyrinth. Intracranial extensions of the lesion are reached by the retrosigmoid or presigmoid approaches after adding a suboccipital craniectomy. The lesion can be removed by a transtemporal infralabyrinthine approach directed through the temporal bone below the labyrinth without the neck dissection, if the extracranial extension of the lesion is not prominent. The expo-

sure can be extended by opening the otic capsule (translabyrinthine approach).

Retrosigmoid approach A pathological abnormality located predominantly intradurally can be resected by the retrosigmoid approach (Fig. 9.6). A lateral suboccipital craniectomy exposes the dura behind the sigmoid sinus. The dura is opened, and the cerebellum is gently elevated away from the posterior surface of the temporal bone to expose the cisterns in the cerebellopontine


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FIGURE 9.7. E–H. E, the external auditory canal has been transected and the middle ear structures have been removed, except the stapes, which has been left in the oval window. The lateral edge of the jugular foramen has been exposed by completing the mastoidectomy, transposing the facial nerve anteriorly, and fracturing the styloid process across its base and reflecting it caudally. The rectus capitis lateralis has been detached from the jugular process of the occipital bone. The petrous carotid is surrounded in the carotid canal by a venous plexus. F, a segment of the sigmoid sinus, jugular bulb, and internal jugular vein have been removed. The lateral wall of the jugular bulb has been removed while preserving the medial wall and exposing the opening of the inferior petrosal sinus into the jugular bulb. Removing the venous wall exposes the glossopharyngeal, vagus, accessory, and hypoglossal nerves, which are hidden deep to the vein. The main inflow from the petrosal confluens is directed between the glossopharyngeal and vagus nerves. G, the medial venous wall of the jugular bulb has been removed. The intrajugular ridge extends forward from the intrajugular process, which divides the jugular foramen between the sigmoid and petrosal parts. The glossopharyngeal, vagus, and accessory nerves enter the dura on the medial side of the intrajugular process, but only the glossopharyngeal nerve courses through the foramen entirely on the medial side of the intrajugular ridge. The vagus nerve also enters the dura on the medial side of the intrajugular process, but does not course along the medial side of the intrajugular ridge. H, the intrajugular process and ridge have been removed to expose the passage of the glossopharyngeal, vagus, and accessory nerves through the jugular foramen. The tip of a right-angle probe identifies the junction of the cochlear aqueduct with the pyramidal fossa, just above where the glossopharyngeal nerve penetrates the dura. angle and the intracranial aspect of the cranial nerves entering the jugular foramen, hypoglossal canal, and internal acoustic meatus.

Far-lateral approach An extended modification of the retrosigmoid approach, the far-lateral approach, the subject of another chapter in this issue, may be selected if the tumor extends down to the foramen

magnum in front of or lateral to the lower brainstem (10, 30, 32, 33). In this approach, the jugular foramen is opened from behind. The dura is opened and the cerebellum elevated to expose the intracranial extension of the pathological abnormality at the lower clivus and at the foramen magnum. Several variations, depending on the location and extent of the pathological abnormality, include drilling the jugular tubercle extradurally and removing bone above without disturbing the condyle (21, 33). The extradural reduction of the jugular tubercle aids in minimiz-


Jugular Foramen ing the retraction of the brainstem needed to reach the area anterior to the medulla and pontomedullary junction.

Preauricular subtemporal-infratemporal approach The preauricular subtemporal-infratemporal approach, reviewed in detail in the chapter on the temporal bone (see Figs. 8.10 and 8.18), exposes the jugular foramen anteriorly. It may be selected for tumors that extend along the petrous portion of the internal carotid artery, through the eustachian tube, or through the cancellous portion of the petrous apex (29). A preauricular hemicoronal scalp incision is extended down to at least the level of the tragus and possibly into the cervical region, depending on the extent of the pathological finding and whether a neck dissection is needed. The zygomatic arch is removed or reflected downward with the temporalis muscle, taking care to preserve the frontal branch of the facial nerve. A frontotemporal bone flap, which may include the superior or lateral orbital rim, is elevated, and the glenoid fossa and the mandibular condyle with the joint capsule are either dislocated inferiorly or removed. The dura is elevated, and the bone of the middle fossa medial to the glenoid fossa is removed until the carotid canal is opened. The eustachian tube and the tensor tympani muscle, which course anterior to the carotid canal, are sacrificed during this procedure, taking care to protect the lower cranial nerves as they exit the jugular foramen. The styloid process is divided at its base, and the internal carotid artery is reflected anteriorly to gain access to the clivus and anterior aspect of the jugular foramen. Drilling can be extended to the posterior fossa through Kawase’s triangle or through the clivus to the contralateral internal carotid artery (14).

DISCUSSION Pathologies Tumors are the most common lesions to affect the jugular foramen; the majority are chemodectomas (glomus jugulare tumor), neurinomas, and meningiomas, with a small percentage of other tumors, such as chondrosarcomas and chordomas (12, 25). The glomus jugulare tumor arises either in the adventitia of the jugular dome or from the intumescences along the tympanic branch of the glossopharyngeal nerve or the auricular branch of the vagus nerve in the jugular foramen (9). Tumors of the same nature that arise in the tympanic cavity or in the mastoid on branches of these nerves are referred to as glomus tympanicum tumors. Small glomus jugulare tumors remain confined within the jugular foramen. However, the tumor can extend as follows: 1) along the eustachian tube into the nasopharynx and through the foramina at the base of the skull, 2) along the carotid artery to the middle fossa, 3) through the intracranial orifice of the jugular foramen or along the hypoglossal canal to the posterior fossa, 4) through the tegmen tympani to the floor of the middle fossa, 5) through the round window and the internal acoustic meatus to the cerebellopontine angle, and 6) through the extracranial orifice of the jugular foramen to the upper cervical region.

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Neuromas arise either from the glossopharyngeal, vagus, or the accessory nerves, and meningiomas from arachnoid granulations in the jugular bulb or venous sinuses. Although each tumor has characteristic patterns of invasion and destruction, the basic anatomic environment is similar to that of the glomus jugulare tumor.

Selection of surgical approach The approaches to the jugular foramen can be categorized into three groups: 1) a lateral group directed through the mastoid bone, 2) a posterior group directed through the posterior cranial fossa, and 3) an anterior group directed through the tympanic bone. This categorization is based on the anatomic fact that the block of the temporal bone, excluding the squamous part, is regarded as an irregular pyramid, having its base on the mastoid surface. In addition, the middle fossa approaches could be categorized as in the “superior group” and the neck dissection upward to the jugular foramen as in the “inferior group.” However, the latter approaches are usually not suitable when used alone for pathological abnormalities of the jugular foramen.

Lateral approach The lateral approach directed through a mastoidectomy, used alone or in combination with other approaches, is the route most commonly selected for lesions extending through the jugular foramen (7, 12, 22). Because the jugular foramen is situated under the otic capsule, the approach basic to this group is called the infralabyrinthine approach. The facial nerve is frequently transposed anteriorly to drill the bone inferior to the labyrinth. Avoiding injury to the facial nerve is one of the key points in the lateral approaches (1). Even with special care, some degree of transient facial palsy is common, possibly because of disturbance to the nerve’s vasculature. The surgical field can be widened anteriorly by sacrificing the external auditory canal and middle ear structures or medially by drilling away the otic capsule (translabyrinthine approach) or cochlea (transcochlear approach). The postauricular transtemporal approach, when combined with a neck dissection, provides satisfactory exposure of the jugular foramen, mastoid air cells, tympanic cavity, and the extracranial structures in and around the carotid sheath. Removal of the styloid process along with transposition of the facial nerve facilitates wide opening of the extracranial orifice of the jugular foramen and provides access to the lower part of the petrous portion of the internal carotid artery. A wider exposure for the extracranial tumor can be obtained by removing the transverse process of the atlas or dislocating or resecting the mandibular condyle. The intracranial extension of the tumor is approached either retrosigmoidally or presigmoidally after adding a lateral suboccipital craniectomy or craniotomy (4, 6, 10, 26, 27).

Posterior approach This group includes the retrosigmoid approach and its more extensive far-lateral and transcondylar variants. These approaches are suited to the intracranial portion of the tu-


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mors. The conventional retrosigmoid approach provides access to the cerebellopontine angle and the intracranial orifice of the jugular foramen. However, extensions of the tumor through the foramen magnum or medially into the clivus are beyond the reach of this approach. The far-lateral and transcondylar modifications access these areas, providing an upward view from below by opening the posterolateral quarter of the foramen magnum and removing the posterior part of the occipital condyle. The posterior and posterolateral margin of the jugular foramen can be accessed by removing the part of the jugular process of the occipital bone located behind the jugular foramen and the portion of the mastoid located behind the mastoid segment of the facial nerve and stylomastoid foramen. A flatter view toward the midline clivus is obtained by additional extradural drilling of the jugular tubercle, although drilling in front of these nerves risks damaging the nerves as they cross the jugular tubercle (21, 23).

Anterior approach The preauricular subtemporal-infratemporal approach is a major variant of this group of approaches. It uses the pathway anterior to the external auditory canal and through the tympanic bone, which are exposed by removal or displacement of the glenoid fossa and the temporomandibular joint. The approach alone can access the anterior part of the jugular foramen after reflecting the petrous portion of the internal carotid artery anteriorly. Further extensive drilling will expose the middle to upper clivus anteriorly. However, this approach is most often combined with a lateral approach to access an anterior extension of the pathology (22). Fisch et al. call this combined approach the infratemporal fossa approach, Type B or C according to the anterior extension of the exposure (4). The selection of the optimal approach requires an understanding of the nature and the extension of the lesion. The combination of two or three approaches may be needed either in stages or in combination in one operative procedure (4, 25). Preoperative embolization will often reduce the blood loss with a vascular tumor. Intraoperative electrophysiological monitoring is of great help in avoiding nerve injury, in locating the neural trajectory in and around the tumor, or in predicting postoperative neural function (3, 20). Carefully planned reconstruction is required to reduce postoperative complications, especially leakage of cerebrospinal fluid, and to achieve a satisfactory cosmetic result. Reprint requests: Albert L. Rhoton, Jr., M.D., Department of Neurological Surgery, University of Florida Brain Institute, P.O. Box 100265, 100 S. Newell Drive, Building 59, L2–100, Gainesville, FL 32610-0265.

REFERENCES 1. Brackmann DE: The facial nerve in the infratemporal approach. Otolaryngol Head Neck Surg 97:15–17, 1987. 2. Brackmann DE, Arriaga MA: Surgery for glomus tumors, in Brackmann DE (ed): Otologic Surgery. Philadelphia, W.B. Saunders Co., 1994, pp 579–593. 3. DiChiro G, Fischer RL, Nelson KB: The jugular foramen. J Neurosurg 21:447–460, 1964.

4. Fisch U, Fagan P, Valavanis A: The infratemporal fossa approach for the lateral skull base. Otolaryngol Clin N Am 17:513–552, 1984. 5. Gardner G, Cocke EW, Robertson JT, Trumbull ML, Palmer RE: Combined approach surgery for removal of glomus jugulare tumors. Laryngoscope 87:665–688, 1977. 6. Gardner G, Robertson JT, Robertson JH, Cocke EW, Clark WC: Glomus jugulare tumors: Skull base surgery, in Schmidek HH, Sweet WH (eds): Operative Neurological Techniques. Philadelphia, W.B. Saunders Co., 1988, ed 2, pp 739–752. 7. Goldenberg RA, Gardner G: Tumors of the jugular foramen: Surgical preservation of neural function. Otolaryngol Head Neck Surg 104:129, 1991. 8. Grant JCB: An Atlas of Anatomy. Baltimore, Williams & Wilkins, 1951. 9. Guild SR: Glomus jugulare in man. Ann Otol Rhinol Laryngol 62:1045–1071, 1953. 10. Hakuba A, Hashi K, Fujitani K, Ikuno H, Nakamura T, Inoue Y: Jugular foramen neurinomas. Surg Neurol 11:83–94, 1979. 11. Hovelacque A: Osteologie. Paris, G Doin and Cie, 1967, vol 2, pp 155–156. 12. Jackson CG, Cueva RA, Thedinger BA, Glasscock ME III: Cranial nerve preservation in lesions of the jugular fossa. Otolaryngol Head Neck Surg 105:687–693, 1991. 13. Katsuta T, Rhoton AL Jr, Matsushima T: The jugular foramen: Microsurgical anatomy and operative approaches. Neurosurgery 41:149–202, 1997. 14. Kawase T, Toya S, Shiobara R, Mine S: Transpetrosal approach for aneurysms of the lower basilar artery. J Neurosurg 63:857–867, 1985. 15. Kveton JF, Cooper MH: Microsurgical anatomy of the jugular foramen region. Am J Otol 9:109–112, 1988. 16. Lang J: Anatomy in and on the jugular foramen, in Frowein RA, Brock M, Klinger M (eds): Advances in Neurosurgery. Berlin, Springer-Verlag, 1989, vol 17, pp 125–132. 17. Lang J: Clinical Anatomy of the Posterior Cranial Fossa and its Foramina. New York, Thieme Medical Publishers, 1991, pp 92–95. 18. Lang J: Anatomy of the posterior cranial fossa, in Sekhar LN, Janecka IP (eds): Surgery of Cranial Base Tumors. New York, Raven Press, 1993, pp 131–146. 19. Lang J, Weigel M: Nerve-vessel relations in the region of the jugular foramen. Anat Clin 5:41–56, 1983. 20. Leonetti JP, Brackmann DE, Prass RL: Improved preservation of facial nerve function in the infratemporal approach to the skull base. Otolaryngol Head Neck Surg 101:74–78, 1989. 21. Matsushima, T, Ikezaki K, Nagata S, Inoue T, Natori Y, Fukui M, Rhoton AL Jr: Microsurgical anatomy for lateral approaches to the foramen magnum: With special reference to the far-lateral approach and the transcondylar approach, in Nakagawa H (ed): Surgical Anatomy for Microneurosurgery VII. Tokyo, SciMed Publications, 1995, pp 81–89. 22. Patel SJ, Sekhar LN, Cass SP, Hirsch BE: Combined approaches for resection of extensive glomus jugulare tumors: A review of 12 cases. J Neurosurg 80:1026–1038, 1994. 23. Perneczky A: The posterolateral approach to the foramen magnum, in Samii M (ed): Surgery in and around the Brain Stem and the Third Ventricle. Berlin, Springer-Verlag, 1986, pp 460–466. 24. Rhoton AL Jr, Buza R: Microsurgical anatomy of the jugular foramen. J Neurosurg 42:541–550, 1975. 25. Samii M, Bini W: Surgical strategy for jugular foramen tumors, in Sekhar LN, Janecka IP (eds): Surgery of Cranial Base Tumors. New York, Raven Press, 1993, pp 379–387. 26. Samii M, Draf W: Surgery of the middle skull base, in Samii M, Dwarf W (eds): Surgery of the Skull Base: An Interdisciplinary Approach. New York, Springer-Verlag, 1989, pp 234–359.


Jugular Foramen 27. Samii M, Babu RP, Tatagiba M, Sepehrnia A: Surgical treatment of jugular foramen schwannomas. J Neurosurg 82:924–932, 1995. 28. Schwaber MK, Netterville JL, Maciunas R: Microsurgical anatomy of the skull base: A morphometric analysis. Am J Otol 11:401–405, 1990. 29. Sekhar LN, Schramm VL Jr, Jones NF: Subtemporal-preauricular infratemporal fossa approach to large lateral and posterior cranial base neoplasms. J Neurosurg 67:488–499, 1987. 30. Sen CN, Sekhar LN: An extreme lateral approach to intradural lesions of the cervical spine and foramen magnum. Neurosurgery 27:197–204, 1990.

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31. Silverstein H, Willcox TO, Rosenberg SI, Seidman MD: The jugular dural fold: A helpful base landmark to the cranial nerves. Skull Base Surg 5:57–61, 1995. 32. Spetzler RF, Grahm TW: The far-lateral approach to the inferior clivus and the upper cervical region: Technical note. Barrow Neurol Inst Q 6:35–38, 1990. 33. Wen HT, Rhoton AL Jr, Katsuta T, de Oliveira E: Microsurgical anatomy of the transcondylar, supracondylar, and paracondylar extensions of the far-lateral approach. J Neurosurg 87:555–585, 1997.

Cranial cavity with posterior fossa structures, including cerebellum and cranial nerves, from, Andreas Vesalius, De Humani Corporis Fabrica. Basel, Ex officina Ioannis Oporini, 1543. Courtesy, Rare Book Room, Norris Medical Library, Keck School of Medicine, Los Angeles, California. (Also see pages S27, S68, and S209.)


Jugular Foramen

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