Far Lateral and Transcondylar Approaches

CHAPTER 11

FAR LATERAL AND TRANSCONDYLAR APPROACHES Neurosurgery 61:S4-211–S4-228, 2007

DOI: 10.1227/01.NEU.0000280028.00006.98

The basic far lateral approach is a low suboccipital approach that extends up to, but does not include removal of, part of the atlantal or occipital condyles. The far lateral approach usually includes a suboccipital craniectomy or craniotomy with removal of at least half of the posterior arch of the atlas, dissection of the muscles along the posterolateral aspect of the craniocervical junction to permit an adequate exposure of the Cl transverse process and the suboccipital triangle, and early identification of the vertebral artery either above the posterior arch of the atlas or in its ascending course between the transverse processes of the atlas and axis. The far lateral approach provides access for the following three approaches: 1) the transcondylar approach directed through the occipital condyle or the atlanto-occipital joint and adjoining parts of the condyles, 2) the supracondylar approach directed through the part of the occipital bone above the occipital condyle, and 3) the paracondylar exposure directed through the area lateral to the occipital condyle. The transcondylar extension, accomplished by drilling the occipital condyle, allows a more lateral approach and provides access to the lower clivus and premedullary area. The supracondylar approach provides access to the region of and medial to the hypoglossal canal and jugular tubercle. The paracondylar approach, which includes drilling of the jugular process of the occipital bone in the area lateral to the occipital condyle, accesses the posterior part of the jugular foramen, and, if needed, the posterior aspect of the facial nerve and mastoid on the lateral side of the jugular foramen. The basic far lateral approach without drilling of the occipital condyle may be all that is required to reach some lesions located along the anterolateral margin of the foramen magnum. However, it also provides a route through which the transcondylar, supracondylar, and paracondylar approaches and several modifications of these approaches can be completed. The transcondylar exposures can be categorized into several variants. One variant is an atlanto-occipital transarticular approach, in which the adjacent posterior part of the occipital condyle and/or the superior articular facet of C1 is removed to facilitate completion of a circular dural incision, permitting the vertebral artery with the surrounding cuff of dura to be mobilized. A more extensive removal of the articular surfaces and condyles can be performed to gain access to extradural lesions situated along the anterior and lateral margins of the foramen magnum. Another variant, the occipital transcondylar variant, is directed above the atlanto-occipital joint through the occipital condyle and below the hypoglossal canal to access the lower clivus and the area in front of the medulla. The supracondylar approach directed above the occipital condyle can also be varied, depending on the pathology to be exposed. The supracondylar exposure can be directed above the occipital condyle to the hypoglossal canal or both above and below the hypoglossal canal to the lateral side of the clivus. In the transtubercular variant of the supracondylar approach, the prominence of the jugular tubercle that blocks access to the brainstem and cistern in front of the glossopharyngeal, vagus, and accessory nerves is removed extradurally to increase visualization of the area in front of the brainstem and to expose the origin of a posterior inferior cerebellar artery that arises from the distal part of the vertebral artery near the midline. The paracondylar approach also has several variants. In the transjugular variant, the exposure is directed lateral to the condyle through the jugular process of the occipital bone to the posterior surface of the jugular bulb. The approach can also be extended lateral to the jugular foramen into the posterior aspect of the mastoid to access the mastoid segment of the facial nerve and the stylomastoid foramen.

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In the standard posterior and posterolateral approaches, an understanding of the individual suboccipital muscles is not essential. However, these muscles provide important landmarks for the far lateral approach and its modifications. In this description, the muscles are reflected separately, but, during an operation, the scalp and muscles superficial to the muscles forming the suboccipital triangle are reflected from the suboccipital area in a single layer, leaving a musculofascial cuff attached along the superior nuchal line for closure. The procedure has been performed through either a horseshoe type suboccipital flap, a Cshaped retroauricular incision similar to that shown in the section on the jugular foramen, or a hockey stick incision that has a vertical lateral limb behind the ear with a medial extension along the superior nuchal line. We prefer the horseshoe scalp flap that begins in the midline, approximately 5 cm below the external occipital protuberance, is directed upward to the external occipital protuberance, turns laterally just below the superior nuchal line, reaches the mastoid area, and turns downward in front of the posterior border of the sternocleidomastoid muscle onto the lateral aspect of the neck below the mastoid tip and where the transverse process of the atlas can be palpated through the skin. The scalp flap is reflected downward with the muscular layer that includes the sternocleidomastoid, trapezius, and splenius, longissimus, and semispinalis capitis muscles. The three muscles, the superior and inferior oblique and the rectus capitis posterior, forming the suboccipital triangle are reflected separately to expose the vertebral artery. The vertebral artery, above the transverse foramen of the axis, veers laterally to reach the transverse foramen of the atlas, which is situated further lateral than the transverse foramen of the axis. The artery, after ascending through the transverse process of the atlas, is located on the medial side of the rectus capitis lateralis muscle. From here, the artery turns medially behind the lateral mass of the atlas and the atlanto-occipital joint and is pressed into the groove on the upper surface of the posterior arch of the atlas, where it courses in the floor of the suboccipital triangle and is covered behind the triangle by the semispinalis capitis muscle. The first cervical nerve courses on the lower surface of the artery between the artery and the posterior arch of the atlas. After passing medially above the lateral part of the posterior arch of the atlas, the artery enters the vertebral canal by passing below the lower, arched border of the posterior atlanto-occipital membrane, which transforms the sulcus in which the artery courses on the upper edge of the posterior arch of the atlas into an osseofibrous casing that may ossify, transforming it into a complete or incomplete bony canal surrounding the artery. The third segment of the vertebral artery, the segment located between the C1 transverse process and the dural entrance, gives rise to muscular branches and the posterior meningeal artery. The muscular branches arise as the artery exits the transverse foramen of C1 and courses behind the lateral mass of the atlas to supply the deep muscles and anastomose with the occipital and ascending and deep cervical arteries. Some of the muscular branches may need to be divided to mobilize and transpose the vertebral artery. The posterior meningeal artery arises from the posterior surface of the vertebral artery as it passes behind the lateral mass or above the posterior arch of the atlas or just before penetrating the dura in the region of the foramen magnum, but it may also have an intradural origin from the vertebral artery, in which case it pierces the arachnoid over the cisterna magna to reach the dura. Six to eight percent of posterior inferior cerebellar arteries arise extradurally and penetrate the dura with the vertebral artery.

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RHOTON

FIGURE 11-1. Far lateral and transcondylar approaches. The far lateral approach involves a dissection of the muscles along the posterolateral aspect of the craniocervical junction to permit exposure of the C1 transverse process and the vertebral artery in the suboccipital triangle. The insert in the lower right illustration shows the scalp incision. A suboccipital horseshoe type flap is commonly selected for the far lateral exposure. The medial limb extends downward in the midline so that an upper cervical laminectomy can be completed if needed. The lateral limb extends below the C1 transverse process, which can be palpated between the mastoid tip and the angle of the jaw. The lateral limb of the incision provides access to the vertebral artery as it ascends through the C1 transverse process and passes medially along the upper surface of the posterior arch of C1. In this section, the muscles are dissected separately to show the anatomy, however, during an operation, the muscles superficial to the suboccipital triangle can be reflected in a single layer with the scalp flap while leaving a cuff of fascia along the superior nuchal line, to which the

S4-212 | VOLUME 61 | NUMBER 4 | OCTOBER 2007 SUPPLEMENT 4

reflected muscles can be attached during the closure. The illustrations on the lower left in Figures 11-1 to 11-4 show the unilateral exposure on the right side. The scalp flap has been reflected to expose the sternocleidomastoid and trapezius muscles, the edges of which form the margins of the posterior triangle of the neck. The splenius and semispinalis capitis are in the floor of the triangle. The three-dimensional illustration above and the orienting illustration on the lower right show the superficial muscles bilaterally.


FAR LATERAL APPROACHES

FIGURE 11-2. The sternocleidomastoid and trapezius muscles have been detached from the superior nuchal line. The sternocleidomastoid has been

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reflected laterally and the trapezius downward to expose the splenius and semispinalis capitis, which are attached just below the superior nuchal line.


RHOTON

FIGURE 11-3. The splenius capitis has been reflected downward to expose the longissimus and the semispinalis capitis muscles. The occipital artery on the left


passes deep and the right passes superficial to the longissimus capitis. The deep cervical fascia has been preserved in the illustration on the lower left.



FIGURE 11-4. The longissimus and semispinalis have been reflected to expose the suboccipital triangle formed by the superior and inferior oblique and rectus capitis posterior major muscles. The superior oblique extends from the occipital bone to the transverse process of C1; the inferior oblique muscle extends from the

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transverse process of C1 to the spinous process of C2; and the rectus capitis posterior major extends from the occipital bone to the spinous process of C2. The vertebral artery crosses behind the atlanto-occipital joint and across the upper surface of the posterior arch of C1 in the depths of the suboccipital triangle.


RHOTON

FIGURE 11-5. The right superior oblique muscle has been reflected laterally. The rectus capitis posterior major extends from the occipital bone to the C2 spinous process. The rectus capitis posterior minor extends from the occipital bone to the midline tubercle on the posterior arch of C1. The inferior oblique


muscle extends from the C2 spinous process to the transverse process of C1. The occipital artery passes medial to the digastric muscle. The dense venous plexus in the suboccipital triangle surrounds the vertebral artery as it passes behind the atlanto-occipital joint. The lower left shows the right unilateral exposure.



FIGURE 11-6. The rectus capitis posterior major and the adjacent part of the rectus capitis posterior minor have been reflected inferior and medially. The superior and inferior oblique muscles have been reflected downward. The vertebral artery passes behind the atlantal condyle, gives rise to a posterior meningeal branch, and passes deep to the posterior atlantooccipital membrane to enter the dura. The rectus capitis lateralis extends from the transverse process of C1 to the occipital bone behind the jugular foramen.

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RHOTON

FIGURE 11-7. The muscles forming the margins of the suboccipital triangle have been removed while preserving the rectus capitis posterior minor, which extends from the part of the occipital bone just above the foramen magnum to the posterior tubercle on C1. The vertebral artery gives off muscular branches and passes medially on the upper surface of the posterior arch of C1, where it is partially encased in a bony ring. The venous plexus around the vertebral artery has been removed.




FIGURE 11-8. The vertebral artery gives origin to the posterior meningeal artery, which ascends through the foramen magnum and along the occipital dura. Several muscular branches of the vertebral artery have been divided. The C1 nerve passes between the vertebral artery and the posterior arch of C1.

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RHOTON

FIGURE 11-9. A suboccipital craniotomy has been completed and the posterior arch of C1 has been removed. The vertebral artery passes behind and partially hides the atlanto-occipital joint. The facial and vestibulocochlear nerves enter the internal acoustic meatus. The glossopharyngeal, vagus, and accessory nerves enter the jugular foramen. The rootlets of the hypoglossal nerve are stretched around the posterior surface of the vertebral artery. The rectus capitis lateralis muscle extends from the occipital bone behind the jugular bulb to the transverse process of C1. The posterior inferior cerebellar artery rises just outside the dura and penetrates the dura with the vertebral artery. The dentate ligament and spinal accessory nerve ascend through the foramen magnum. The rostral attachment of the dentate ligament is at the level of the foramen magnum.




FIGURE 11-10. The vertebral artery has been depressed to expose the atlanto-occipital joint. Drilling above the occipital condyle has exposed the hypoglossal canal and the venous plexus accompanying the hypoglossal nerve through the canal. The rectus capitis lateralis has been reflected and bone has been removed in the paracondylar area to expose the posterior surface of the jugular bulb. The occipital artery and facial nerve are exposed below the stylomastoid foramen in the paracondylar region lateral to the jugular bulb. A posterior condylar vein connects the venous plexus around the vertebral artery to the jugular bulb and venous plexus in the hypoglossal canal.

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RHOTON

FIGURE 11-11. The dural incision completely encircles the vertebral artery, leaving a narrow dural cuff on the artery, thus, allowing the artery to be mobilized. The drilling in the supracondylar area exposes the hypoglossal nerve in the hypoglossal canal and can be extended extradurally to the level of the jugular tubercles to increase access to the front of the brainstem and clivus.




FIGURE 11-12. Comparison of exposure with the far lateral and transcondylar approaches. The far lateral exposure on the right side extends to the posterior margin of the atlantal and occipital condyles and the atlanto-occipital joint. The prominence of the condyles on the right side limits the exposure along the anterolateral margin of the foramen magnum. On the left side, a transcondylar exposure has been completed by removing the upper part of the occipital condyle. The dura can be reflected further laterally with the transcondylar approach than with the far lateral approach. The condylar drilling provides an increased angle of view and additional space for exposure and dissection. The dentate ligament and accessory nerve ascend through the foramen magnum. The rostral attachment of the dentate ligament is at the level of the foramen magnum.

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RHOTON

FIGURE 11-13. The part of the left occipital condyle above the atlanto-occipital joint has been drilled to expose the hypoglossal nerve in the hypoglossal canal. The glossopharyngeal and vagus nerves descend behind the jugular tubercle. Drilling the condyle above and below the hypoglossal canal provides entry into the lower part of the clivus medial to the condyle. A cuff of dura has been left on the vertebral artery.




FIGURE 11-14. The right occipital condyle and bone above the atlanto-occipital condyle joint have been drilled to expose the hypoglossal nerve in the hypoglossal canal. The C1 nerve root passes laterally between the vertebral artery and the posterior arch of C1.

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RHOTON

FIGURE 11-15. Another specimen with the brainstem removed. The bone above the occipital condyle has been removed to expose the hypoglossal nerve in the hypoglossal canal. The glossopharyngeal, vagus, and accessory nerves cross the jugular tubercle. The jugular bulb is located lateral to the occipital condyle and can be exposed by drilling the occipital bone in the paracondylar area.




FIGURE 11-16. The medial part of the right occipital condyle and the posterior arch of C1 have been removed. The extradural segment of the right vertebral artery, which normally courses above the C1 nerve root, has been retracted below the level of the C1 nerve root. The intradural segment of the right vertebral artery has been retracted posteriorly to provide access to the cervicomedullary region. The contralateral vertebral artery is exposed anterior to the medulla. The hypoglossal nerve passes behind the vertebral artery. The drilling has provided wide access to the lower clivus adjacent to the occipital condyle and also to the lateral and anterior aspects of the brainstem.

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RHOTON

FIGURE 11-17. The bone lateral to the occipital condyle has been removed to expose the jugular bulb. The occipital and atlantal condyles have been drilled to provide access to the clivus. The condylar emissary vein connects the jugular bulb and vertebral venous plexus. The hypoglossal nerve, in the hypoglossal canal, has been exposed. A., artery; Atl., atlanto; Bas., basilar; Br., branch; Cap., capitis; Cerv., cervical; CN, cranial nerve; Cond., condylar, condyle; Dent., dentate; Digast., digastric; Dors., dorsal; Flocc., flocculus; Gr., greater; Hypogloss., hypoglossal; Inf., inferior; Int., internal; Jug., jugular; Lat., lateralis; Lev., levator; Lig., ligament; Longiss., longissimus; M., muscle; Maj., major; Memb., membrane; Men., meningeal; Min., minor; Musc., muscular; N., nerve; Obl., oblique; Occip., occipital; P.I.C.A., posterior inferior cerebellar artery; Plex., plexus; Post., posterior; Proc., process; Rec., rectus; Scap., scapulae; Semispin., semispinalis; Sig., sigmoid; Splen., splenius; Sternocleidomast., sternocleidomastoid; Suboccip., suboccipital; Sup., superior; Trans., transverse; Triang., triangle; V., vein; Vent., ventral, ventricle; Vert., vertebral.



Far Lateral and Transcondylar Approaches

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