Neurosurg Rev (2012) 35:341–349 DOI 10.1007/s10143-011-0371-0
ORIGINAL ARTICLE
Endoscopic telovelar approach to the fourth ventricle: anatomic study Antonio Di Ieva & Mika Komatsu & Fuminari Komatsu & Manfred Tschabitscher
Received: 18 May 2011 / Revised: 24 August 2011 / Accepted: 8 October 2011 / Published online: 15 December 2011 # Springer-Verlag 2011
Abstract The telovelar approach allows reliable access to the fourth ventricle and avoids the splitting of the vermis and its associated “posterior vermal split syndrome.” Our objective was to describe the endoscopic topographical anatomy of the telovelum approach to the fourth ventricle as accessed by the cerebellomedullary corridor. A series of 20 fresh and fixed injected anatomical specimens were used. The endoscopic equipment consisted of rigid endoscopes with different lens angles, while the extradural step required the use of the microscope and/or the exoscope. All the anatomical landmarks and relationships within the fourth ventricle and the cerebellomedullary fissure were identified by means of the endoscopic microscope/exoscope-assisted telovelar approach. In conclusion, we showed that the endoscope is a valid tool to gain an anatomic understanding of the fourth ventricle reached by means of the telovelar approach.
ventricle. This method avoids splitting the vermis or removing part of the cerebellum [26, 27, 29, 31, 37], therefore avoiding the associated “posterior vermal split syndrome” [2, 5, 9, 19]. The anatomical key to this approach is the telovelum, the sheet formed by the tela choroidea and the inferior medullary velum that covers the lower part of the roof of the fourth ventricle. The telovelum can be reached and explored also endoscopically through the cerebellomedullary fissure, the natural cleft between the tonsils, the vermis, and the medulla. Within this study, we describe the endoscopic topographical anatomy of the telovelum approach to the fourth ventricle accessed via the cerebellomedullary corridor.
Keywords Anatomy . Cerebellomedullary fissure . Endoscopy . Exoscopy . Telovelar approach . Fourth ventricle
This anatomic study was performed in the Microsurgical and Endoscopic Laboratory of the Department of Systematic Anatomy at the Medical University of Vienna, Austria. A series of 20 fresh and fixed anatomical specimens were used. The arteries were injected with red silicon; in some specimens the veins were also injected with blue silicon. One specimen was not injected in order to study the syntopy of the telovelum, focusing on its endoscopic relationship with the surrounding anatomical structures. The endoscopic equipment consisted of 2.7- or 4-mmdiameter rigid endoscopes with various viewing angles (0°, 30°, 45°, and 70°) (Karl Storz Endoscopy, Tuttlingen, Germany). For the extradural macroscopic step, an exoscope was used (VITOM SPINE, model E1051–1, Karl Storz, Tuttlingen, Germany) fixed to a mechanical holder 20– 40 cm far from the field. The exoscope was left in situ for the described maneuvers so that the intracranial steps were exoscope assisted. In some cases, an operative microscope
Introduction In the last few years, the telovelar approach has been demonstrated as a reliable approach to access the fourth A. Di Ieva (*) : M. Komatsu : F. Komatsu : M. Tschabitscher Center for Anatomy and Cell Biology, Department of Systematic Anatomy, Medical University of Vienna, Waehringerstrasse 13, 1090 Vienna, Austria e-mail:
[email protected] A. Di Ieva Department of Neurosurgery, Medical University of Vienna, Vienna, Austria
Materials
342
was used for the extradural step and to follow the endoscopic procedure, even if the exoscope was preferred for the image acquisition, in a special way because it was fixed far enough from the operative field to not interfere with the surgical maneuvers. For the illumination, we used a 300-W xenon fiber optic light source (Xenon Nova300, Karl Storz Endoscopy, Tuttlingen, Germany). A digital high-definition (HD) video camera with a camera control unit was used to visualize the images on an HD wide flat screen (two million pixels). The AIDA compact HD System (Karl Storz, Tuttlingen, Germany) was used to record the images and video sequences.
Methods The heads were positioned to achieve a surgical suboccipital approach. Under microscopic or exoscopic magnification, a 3-cm midline skin incision was made above the craniocervical junction. The dissection was performed by splitting the muscles mediolaterally in order to access and expose the
Fig. 1 Exo-endoscopic approach to the fourth ventricle. a Exoscopic suboccipital approach to the median craniocervical junction, with exposure of the occipital bone, the posterior arch of the atlas, and the atlantooccipital membrane. The dotted circular lines show the site of the craniotomy. b Opening the dura mater in the C0-C1 region and the arachnoid of the cerebellomedullary cistern (cisterna magna). Lateral reflection of the meningeal layers and exposure of the medulla and cerebellar tonsils is also demonstrated. c Introduction of the endoscope onto the field. d The endoscopic procedure can be exoscope assisted,
Neurosurg Rev (2012) 35:341–349
inferior portion of the occipital squama, the inferior edge of the foramen magnum, the craniocervical junction, the atlantooccipital membrane, and the posterior arch of the atlas (Fig. 1a). Inserting the craniotome into the inferior edge of the foramen magnum, a 2-cm occipital craniotomy was performed (Fig. 1a). Removing the posterior arch of the atlas was never considered necessary. After opening and removing the atlantooccipital membrane, the dura mater overlying the craniocervical junction was exposed and incised longitudinally for approximately 2 cm (Fig. 1b), also to create the space to insert the spatulas for the eventual retraction of the cerebellar tonsils. Through the durotomy it was possible to insert various angled endoscopes (0°, 30°, 45°, and 70°) into the cisterna magna (Figs. 1c, d and 2e). The endoscopic approach to the cisterna cerebellomedullaris (cisterna magna) and the fourth ventricle was microscope or exoscope assisted. The exoscope was often used for the acquisition of the video images of the endoscopic procedure (Fig. 1d). After inspection of the cisterna magna, the arachnoid was removed to approach the fourth ventricle via a medial transcysternal route [30, 33] (Fig. 1e, f). To visualize
as shown in the picture. Introduction of the tip of the endoscope into the foramen of Magendie by the transforaminal median route. e The introduction in the foramen of Magendie of an endoscope with a 70°angled optic oriented towards the roof of the fourth ventricle allows visualization of the ventricular surface of the tela choroidea with the related choroidal plexi and choroidal arteries. f The transforaminal approach allows the visualization of the rhomboid fossa and the floor of the fourth ventricle
Neurosurg Rev (2012) 35:341–349
343
Fig. 2 The cerebellomedullary fissure, the fourth ventricle and the synthopy of the telovelum, demonstrated via exoscopic anatomical dissection. a The elevation of the tonsil reveals the attachments of the tela choroidea (arrows), which borders the medial sides of the fourth ventricle and continues superiorly in the arachnoid covering the mesial surfaces of the cerebellar tonsils. b The vallecula can be split to allow access to the inferior vermis. Here the superior part of the arachnoid that form the tela choroidea, like a tent (showed by the arrows), is visible covering the mesial surfaces of the tonsils. c The partial resection of the right tonsil reveals its relationships with the cerebellar biventral lobe and with the telovelum, allowing visualization of its anatomical affiliations (nidus avis, marked with an asterisk). d The complete resection of the tonsil allows visualization of the retroand sovratonsillar segments of the PICA. e The introduction of the endoscope in the fourth ventricle allows, by means of transillumination, the visualization of the attachments of the tela choroidea inferiorly
and superiorly to the telovelar junction. f The removal of both tonsils and the complete resection of the telovelum allow inspection of the fourth ventricle structures. The four corners of the rhomboid fossa are visible (obex/foramen of Magendie, opening of the aqueduct of Sylvius, and the two lateral recesses with the foramen of Luschka). The striae medullares divide the floor in a superior pontine triangle and an inferior medullary triangle, which ends in the calamus scriptorius. g The inferior triangle's base is on the striae medullares and the vertex is on the obex. In this location, one can visualize the funiculus separans, a thickening of the ependyma bordering the area postrema, and the ligula, which is the medullary insertion of the membrana tectoria. ct cuneate tubercle; Fac. Col. facial collicus; Fovea inf. fovea inferior with the vagal trigone overlying the dorsal motor nucleus of the vagus and the nucleus of the solitary tract; gt gracile tubercle (clava); Med. vestib. area medullary vestibular area; St. med. striae medullares; Trig. Hypog trigonum of the hypoglossal nerve
the roof of the fourth ventricle and the telovelum, the following methods were used: (a) mediolateral displacement of
the cerebellar tonsils using spatulas and (b) tonsillar resections, even if the latter was used only to show the anatomic
344
relationships but not considered strictly necessary for the endoscopic telovelar approach.
Results The introduction of the endoscope into the cisterna magna offers a panoramic view of the inferomedial part of the cerebellar hemispheres, the inferior portion of the vermis, the branches of the posterior inferior cerebellar artery (PICA), the posterior cerebellar and medullary veins, the cerebellomedullary fissure, and the foramen of Magendie (Figs. 1c and 2b–d). A preliminary inspection of the fourth ventricle can be performed by means of the classic medial transcysternal route [30, 33]; the introduction of the endoscope into the foramen of Magendie gives a wide panoramic view of the fourth ventricle (Fig. 1e, f). The endoscope is introduced into the foramen of Magendie, obtaining a wide panoramic view of the floor of the rhomboid fossa, the superior velum, the superior and middle cerebellar peduncles, the opening of the aqueduct in the fourth ventricle, and the interior aspect of the telovelum with the related choroid plexus. The insertion of the angled endoscope (particularly 45° and 70°) into the foramen of Magendie allows visualization of the ventral (ventricular) surface of the tela choroidea where it is possible to identify the choroid plexus and its related vessels (Fig. 1e). A broad panoramic view of the fields can be obtained by rotating the scope on its axis. The lateral displacement of the tonsils (unilaterally or bilaterally) allows for endoscopic navigation of the cerebellomedullary fissure (Fig. 2b). The distance of the displacement ranged from 0 to 10 mm, depending on the anatomical conditions (e.g., the size of the tonsils and the intertonsillar distance). In six cases (30%), in fact, the intertonsillar distance was inferior to 5 mm, and it was necessary to displace the tonsils 1 cm laterally, in order to achieve the cerebellomedullary fissure. In ten cases (50%), the required displacement was less than 5 mm, while in four cases (20%) the intertonsillar distance was quite wide (10 mm), requiring no lateralization. The introduction of the endoscope in the medullotonsillar space allowed the exploration of the cerebellomedullary fissure and tela choroidea. The tela choroidea was cut unilaterally or bilaterally by starting the incision at the level of the foramen of Magendie and following it laterally to the foramen of Luschka. The inferior margin of the tela choroidea was found at a distance from the obex ranging 2–12 mm, forming in the middle the foramen of Magendie (average diameter, 5 mm). Opening the telovelum bilaterally provided complete access to the floor and body of the fourth ventricle, from the aqueduct to the obex, rostrocaudally, reaching the lateral recesses mediolaterally (Fig. 2f). Opening the telovelum unilaterally allowed the introduction of the endoscope and the opportunity to
Neurosurg Rev (2012) 35:341–349
visualize, by means of the 30°, 45°, and 70° angled scopes, the contralateral structures (Fig. 3f). To achieve good visualization of the complete intraventricular structures, it was deemed unnecessary to cut the telovelar junction, limiting the resection to the lateral attachments of the tela choroidea. Moreover, a partial opening of the tela choroidea was considered sufficient to introduce and move the endoscope and any surgical tools within the fourth ventricle (Fig. 3). The endoscopic panoramic view of the cerebellomedullary fissure makes it possible to observe the branches of the posterior cerebellar arteries, the foramen of Magendie, the obex, and the tela choroidea (Figs. 1b, c and 2a–d). The medial anatomic landmarks are the pyramid and the uvula (inferior portion of the vermis) in the posterior cerebellar incisura (Fig. 1d). The nodule of the vermis faces the lower half of the roof of the fourth ventricle. The vallecula is the inferior continuation of the posterior cerebella fissure, separating the two tonsils. The depth of the vallecula depends on the anatomical conformation of the tonsils—virtual in some cases (very “tied” tonsils) or very wide—when the mesial tonsillar portions face each other at a distance of about 1 cm. The resection of the tonsils reveals the socalled nidus avis (bird's nest) [35] and the relationships between the tonsillar faces and the inferior medullary velum, tela choroidea, uvula and biventral lobules, in the space called the telovelotonsillar cleft, where the portions of the PICA (retrotonsillar and subtonsillar portions of the telovelotonsillar segment of the PICA) run (Fig. 2c, d, f). Starting at the foramen of Magendie, the taenia along the inferior cerebellar peduncles can be cut to reach the lateral recess, on a single side or bilaterally (Fig. 2f). The tela choroidea can be elevated rostrally (unilaterally or bilaterally) in order to obtain access to the fourth ventricle; the arachnoid of the vermian cistern can be dissected, splitting the uvulotonsillar cleft. The telovelum is formed by two thin, membranous layers: the tela choroidea and the inferior medullary velum [17, 20, 31, 32]. The site where the two membranes attach to each other is the telovelar junction (Fig. 2e). The cranial extension of the tela choroidea is the uvulotonsillar space; according to Matsushima's definition [27], this space is a tent formed by two layers of arachnoid, which cover the mesial and posterior faces of the tonsils. In some cases, when the tonsil was tied tightly, the vallecula became a virtual space and these two arachonidal layers seemed to be fused in a kind of “tonsillar falx”. However, careful dissection always revealed the existence of the two separated layers, covering the mesial tonsillar surfaces, reaching rostrally to the uvula and continuing into the arachnoid covering the pyramid (Fig. 2a, b). On the ventricular surface of the tela choroidea, one can recognize the choroid plexus with its associated choroidal arteries, which originate from the supratonsillar segment of the PICA (Fig. 1e) [11]. Some
Neurosurg Rev (2012) 35:341–349
345
Fig. 3 Endoscopic telovelar approach. By using an appropriate insertion point for the endoscope, angle of visualization and angled lens, it is possible to visualize the anatomical structures within the fourth ventricle. AS Opening of the aqueduct of Sylvius; ChPl choroid plexus; FColl facial colliculus; inf CP inferior cerebellar peduncle; infFov inferior fovea; LR lateral recess; me medial eminence; mVA medullary vestibular area; ms median sulcus; pSL paramedian sulcus limitans; pVA pontine vestibular area; SMV superior medullary velum; sup CP superior cerebellar peduncle; supFov superior fovea
veins originate from the lateral edge of the nodule and uvula, crossing the telovelar junction and taking some outflows from the telovelum [28]. The entire floor of the fourth ventricle is visible in its typical rhomboid shape. The four corners of the rhombus, formed by the opening of the aqueduct proximally, the foramen of Magendie caudally and medially, and the two foramina of Luschka laterally are endoscopically visible (Fig. 3). The median sulcus divides the floor into two symmetrical halves; this sulcus serves as a good “corridor” to follow when advancing the endoscope along the floor of the fourth ventricle. It is also a very visible and constant landmark to be used to avoid losing orientation intraventricullary, especially when the angled optics are used (Figs. 2f, g and 3a–e). The striae medullares (the dorsal pontocerebellar fibers and parts of the dorsal acoustic striae) [32] are very well visualized in their mediolateral variable course; in our specimens we found an average of 5±2 striae on each side, in accordance with some previously published data (Fig. 2f) [45]. The striae divide the floor into a superior pontine triangle and an inferior medullary triangle, which ends in the calamus scriptorius. The striae medullares are the inferior triangle's base while the obex is the vertex of the
inferior triangle; here the funiculus separans, a thickening of the ependyma bordering the area postrema, is visible (Fig. 2g). The median sulcus is easily visible crossing medially in the triangle, bordered paramedially by the two paired sulci limitantes (Figs. 2g and 3e). The sulcus limitans is discontinuous; it is more prominent in the pontine and medullary portions of the floor. The points in which the sulcus limitans deepens correspond to two endoscopically visible depressions: the superior and the inferior fovea (Fig. 3b, e) [31]. Lateral to the sulci limitans, the endoscope demonstrates the vagal trigone (corresponding to the dorsal motor nucleus of the vagus and the nucleus of the solitary tract) and its lateral depression, the fovea inferior, in the inferior portion (Figs. 2g and 3e). More laterally, the vestibular area is visualized, corresponding to the vestibular nuclei (Fig. 3c, f). The visible prominence in this area is the auditory tubercle, which overlies the dorsal cochlear nucleus and the cochlear part of the vestibulocochlear nerve. The dark, triangular field between the trigonum hypoglossi and the lower part of the area acoustica is the ala cinerea, corresponding to the sensory nucleus of the vagus and glossopharyngeal nerves. At the lower end of the ala cinera, the funiculus separans is visible as a narrow, translucent
346
ridge; more inferiorly, closely related to the clava, there is the area postrema. The sulcus medianus continues in the superior triangle, ending at the superior angle of the rhomboid fossa where the opening of the aqueduct is visible (Fig. 3). The sulcus limitans divides the superior triangle in a similar fashion with a mediana area, where the median eminence (containing the facial colliculus) and a lateral pontine vestibular area. A good landmark for endoscopic navigation through the lateral recesses is the superior fovea (fovea trigemini), which corresponds to the motor trigeminal nucleus (Fig. 3b). More superiorly, at the upper end of the sulcus limitans, lies the locus coeruleus although it is not endoscopically (or even by the operating microscope) identifiable. On the roof of the fourth ventricle lies the superior medullar velum medially and the cerebellar peduncles more laterally, each one separated by a very welldefined sulcus: the superior cerebellar peduncle medially and the inferior cerebellar peduncle laterally (Fig. 3). The dentate tubercle, formed in the fourth ventricle by the impression of the overlying dentate nucleus, is visible in the superolateral portion of the roof (Fig. 3e). The lateral portions of the cerebellar peduncles are very well visualized using the angled endoscopes. The angled lenses, especially the 45° and 70° lenses, permit visualization of the lateral recesses to the foramina of Luschka, which open in the inferior cerebellopontine cisterns. If the tela choroidea is opened only on one side, the introduction of the endoscope with the angled lens allows for visualization of the contralateral recesses (Fig. 3f).
Discussion It is known that the cerebellomedullary fissure is a useful route by which to approach the fourth ventricle and avoid splitting the vermis [6, 16, 18, 19, 26, 27, 31, 43, 44, 46]. The opening of the tela choroidea and eventually the inferior medullary velum (telovelar approach) allows for complete visualization of the fourth ventricle also including the most proximal and lateral portions, from the aqueduct to the lateral regions around the lateral recesses. This has been demonstrated in several previous surgical reports and in qualitative and quantitative anatomic studies [8, 19, 26, 27, 31, 36, 37, 40]. The fourth ventricle can also be approached endoscopically. The paradigm of modern neurosurgery, to offer therapies by means of minimal surgery and less traumatic approaches, has developed into the philosophy of minimally invasive neurosurgery [9, 33, 34] or, more appropriately, minimally traumatizing neurosurgery [42]. It should be emphasized that endoscope is an additional tool which can be used in neurosurgical procedures as well in anatomical
Neurosurg Rev (2012) 35:341–349
studies, even if no randomized controlled studies have never been performed to prove its clinical advantages when compared to the operations performed by means of microscope. In the 1990s, the first reports detailing endoscopic caudal exploration of the fourth ventricle and the aqueduct were published [3, 15, 30, 33, 39]. Subsequently, other surgical or anatomical reports were published detailing the anatomy of the fourth ventricle as visualized by the endoscope using a transaqueductal approach [10, 13, 22, 23, 38, 41]. From the first anatomic reports that the fourth ventricle and aqueduct could be approached endoscopically, not only from the third ventricle but also through a tailored craniocervical approach [30, 33], other applications of this surgical approach were investigated. In some selected cases, this endoscopic approach has been used in the management of obstructive hydrocephalus due to aqueduct obstruction, reestablishing the free communication between the third and fourth ventricle [4, 14, 41]. However, this approach via the foramen of Magendie limits the introduction and manipulation of other surgical tools within the lateral recesses of the fourth ventricle; these limits are overcome with the telovelar approach. Matsushima et al., who pioneered the technique of the telovelar approach, emphasized that a detailed understanding of the anatomy of the fissure and its surroundings is required to perform this kind of approach [26, 27]. The microsurgical exploration of the fourth ventricle by means of the telovelar approach can also be performed endoscopically. We chose to demonstrate this for two reasons: (a) to show the feasibility of the technique and (b) to offer a different perspective on the same anatomical structures, improving the anatomical orientation of the surgeons who perform this type of surgery in this very complex region. It is important to emphasize that this manuscript does not advocate for the superiority of the endoscopic approach over the microsurgical method. In the best scenario, endoscopic assistance in the microsurgical treatment of lesions involving the fourth ventricle could allow visualization around corners including those opposite to the microsurgical field, allowing a less invasive and traumatic surgery. The topographical relationships between the anatomic structures and landmarks are fundamental in neuroendoscopy. Working in an anatomical training lab is essential to develop a sense of spatial orientation; such a lab allows the surgeon to compare different images of the same anatomical area and to form a three-dimensional mental image of the fourth ventricle. This type of training is very helpful in understanding pathoanatomic topography. There is no “microsurgical” or “endoscopic” anatomy: the anatomy stays the same although it is visualized differently through a microscope and an endoscope. It is important to develop spatial orientation to understand surgical anatomy, bearing in mind that the apparent differences in the same structures when they are seen laterally or medially, rostrally
Neurosurg Rev (2012) 35:341–349
or caudally, or through the operative microscope or through an endoscope [42]. In our study, we found a large variability in the insertion points of the inferior limits of the tela choroidea. As demonstrated by Barr in 1948 [1], the outlets of the fourth ventricle have a highly variable shape and dimension. At the level of the foramen of Magendie, the different insertions of the caudolateral margins of the telovelum could justify this variability. Thus, even if no neurologic deficits are associated with the opening of the telovelum of the fourth ventricle, in cases in which the foramen of Magendie is very small, a wide resection of the attachment of the tela choroidea is required for the introduction and manipulation of the endoscope and any surgical tools. In cases in which the foramen is very wide, the resection of the tela can be limited. The opening of the tela choroidea on the lateral margins allows the introduction of the endoscope to visualize all of the intraventricular anatomical structures. The additional opening of the inferior medullary velum offers a more cranial visualization of the fourth ventricle, even if it is not generally required. It is interesting that the sense of three dimensionality in the two-dimensional endoscopic images can be suggested by the “shadows” and intensity of colors caused by the protuberances and depressions, as on the floor of the fourth ventricle at the level of the foveae (Fig. 3b, e). The intracranial and intraventricular endoscopic approach can be microscope or exoscope assisted. It has recently been suggested that exoscopes could be used in neurosurgical procedures, particularly in spinal operations [24, 25]. Exoscopes are telescopes that, like microscopes, are not introduced into the surgical field. They offer very high quality images with very good illumination and, as they are fixed to a holder remote from the operating field, they do not interfere with the handling of surgical instruments. However, their technical limitations include the fact that the images are focused centrally (and are therefore less focused peripherally) and, like endoscopes, they lack true stereopsis. We have recently begun using exoscopy for anatomical dissections and image acquisition [7, 42], suggesting its use especially in anatomical laboratories where the purchase of an operative microscope is limited by some economical reasons. A relative advantage of the endoscopic telovelar approach is that it requires less space than the normal microscopic approach so that the opening of telovelum, the resection of some choroidal vessels, and the lateralization of the tonsils can be limited. The latter is very important as excessive stretching of the tonsils can cause a compression on the related dentate nuclei and cerebellar peduncles. It is known that the neurologic deficits related to dentate nuclei injury are disturbances much more serious than the ones caused by vermis splitting [12, 21]. Moreover, the craniotomy performed in our study
347
was relatively small and no specimens required laminectomy of the atlas. Using the described approach, the visualization of the anatomical structures of the fourth ventricle is optimal and the space to maneuver surgical tools seems to be adequate. However, the surgeon must recall that the movements of the tip of the endoscope within the fourth ventricle should be very accurate; a “soft” pressure of the tip of the endoscope against the anatomical structures can cause injuries, particularly on the protruding structures (e.g., cerebellar peduncles, dentate tubercle, and facial collicus).
Conclusion The natural cleft of the cerebellomedullary fissure, between the vermis, the tonsils, and the medulla, can be the corridor for the introduction of the endoscope into the fourth ventricle by means of the telovelar approach, allowing complete visualization of the ventricular cavity without splitting the vermis. Considering that the telovelar approach is recommended for the treatment of lesions occupying the cerebellomedullary fissure and the fourth ventricle, especially its lateral recesses, the endoscope can be a valid tool for gaining a better anatomic understanding of this complicated neuroanatomic region; it may also be a potential tool to be used for microsurgical endoscope-assisted operations. Acknowledgments The authors wish to thank the FMEA (Society for the Promotion of Research in Microsurgical and Endoscopic Anatomy) for paying the costs related to this research. Disclosure The authors have no personal financial or institutional interest in the devices described in this article.
References 1. Barr ML (1948) Observations on the foramen of Magendie in a series of human brains. Brain 1:281–289 2. Bastian AJ, Mink JW, Kaufman BA, Thach WT (1998) Posterior vermal split syndrome. Ann Neurol 44:601–610 3. Bergsneider M (1999) Endoscopic removal of cysticercal cysts within the fourth ventricle. Technical note. J Neurosurg 91:340– 345 4. Cinalli G, Spennato P, Savarese L, Ruggiero C, Aliberti F, Cuomo L, Cianciulli E, Maggi G (2006) Endoscopic aqueductoplasty and placement of a stent in the cerebral aqueduct in the management of isolated fourth ventricle in children. J Neurosurg 104:21–27 5. Dailey AT, McKhann GM II, Berger MS (1995) The pathophysiology of oral pharyngeal apraxia and mutism following posterior fossa tumor resection in children. J Neurosurg 83:467–475 6. Deshmukh VR, Figueiredo EG, Deshmukh P, Crawford NR, Preul MC, Spetzler RF (2006) Quantification and comparison of telovelar and transvermian approaches to the fourth ventricle. Neurosurgery 58 (suppl 2):202–207
348 7. Di Ieva A, Tschabitscher M, Galzio RJ et al (2011) The veins of the nucleus dentatus: anatomical and radiological findings. NeuroImage 54:74–79 8. El-Bahy K (2005) Telovelar approach to the fourth ventricle: operative findings and results in 16 cases. Acta Neurochir (Wien) 147:137–142 9. Fries G, Perneczky A (1998) Endoscope-assisted brain surgery: part 2—analysis of 380 procedures. Neurosurgery 42:226–231 10. Fritsch MJ, Kienke S, Manwaring KH, Mehdorn HM (2004) Endoscopic aqueductoplasty and interventriculostomy for the treatment of isolated fourth ventricle in children. Neurosurgery 55:377–379 11. Fujii K, Lenkey C, Rhoton AL Jr (1980) Microsurgical anatomy of the choroidal arteries. Fourth ventricle and cerebellopontine angles. J Neurosurg 52:504–524 12. Fulton JF, Dow RS (1937) The cerebellum: a summary of functional localization. Yale J Biol Med 10:89–119 13. Galzio RJ, Tschabitscher M (2010) Endoscope-assisted microneurosurgery. Principles, methodology and applications. Verlag Endo, Tuttlingen 14. Gawish I, Reisch R, Perneczky A (2005) Endoscopic aqueductoplasty through a tailored craniocervical approach. J Neurosurg 103:778–782 15. Hamada H, Hayashi N, Endo S, Kurimoto M, Hirashima Y, Takaku A (1999) Endoscopic aqueductal plasty via the fourth ventricle through the cerebellar hemisphere under navigating system guidance—technical note. Neurol Med Chir (Tokyo) 39:950–954 16. Jittapiromsak P, Sabuncuoglu H, Deshmukh P, Spetzler RF, Preul MC (2010) Accessing the recesses of the fourth ventricle: comparison of tonsillar retraction and resection in the telovelar approach. Neurosurgery 66(Suppl):30–40 17. Johnston TB (1934) A note on the peduncle of the flocculus and the posterior medullary velum. J Anat 68:471–479 18. Kawashima M, Matsushima T, Nakahara Y, Takase Y, Masuoka J, Ohata K (2009) Trans-cerebellomedullary fissure approach with special reference to lateral route. Neurosurg Rev 32:457– 464 19. Kellogg JX, Piatt JH Jr (1997) Resection of fourth ventricle tumors without splitting the vermis: the cerebellomedullary fissure approach. Pediatr Neurosurg 27:28–33 20. Lang J (1991) Clinical anatomy of the posterior cranial fossa and its foramina. Georg Thieme Verlag Stuttgart, New York 21. Larsell O (1937) The cerebellum. A review and interpretation. Arch Neurol Psychiatry 38:580–607 22. Longatti P, Fiorindi A, Feletti A, D’Avella D, Martinuzzi A (2008) Endoscopic anatomy of the fourth ventricle. Laboratory investigation. J Neurosurg 109:530–535 23. Longatti P, Fiorindi A, Martinuzzi A, Feletti A (2009) Primary obstruction of the fourth ventricle outlets: neuroendoscopic approach and anatomic description. Neurosurgery 65:1078–1085 24. Mamelak AN, Danielpour M, Black KL, Hagike M, Berci G (2008) A high-definition exoscope system for neurosurgery and other microsurgical disciplines: preliminary report. Surg Innov 15:38–46 25. Mamelak AN, Nobuto T, Berci G (2010) Initial clinical experience with a high-definition exoscope system for microneurosurgery. Neurosurgery 67:476–483 26. Matsushima T, Fukui M, Inoue T, Natori Y, Baba T, Fujii K (1992) Microsurgical and magnetic resonance imaging anatomy of the cerebello-medullary fissure and its application during fourth ventricle surgery. Neurosurgery 30:325–330 27. Matsushima T, Inoue T, Inamura T, Natori Y, Ikezaki K, Fukui M (2001) Transcerebellomedullary fissure approach with special reference to methods of dissecting the fissure. J Neurosurg 94:257– 264
Neurosurg Rev (2012) 35:341–349 28. Matsushima T, Rhoton AL Jr, de Oliveira E, Peace D (1983) Microsurgical anatomy of the veins of the posterior fossa. J Neurosurg 59:63–105 29. Matsushima T, Rhoton AL Jr, Lenkey C (1982) Microsurgery of the fourth ventricle. Part 1: microsurgical anatomy. Neurosurgery 11:631–667 30. Matula C, Reinprecht A, Roessler K, Tschabitscher M, Koos WT (1996) Endoscopic exploration of the IVth ventricle. Minim Invasive Neurosurg 39:86–92 31. Mussi ACM, Rhoton AL Jr (2000) Telovelar approach to the fourth ventricle: microsurgical anatomy. J Neurosurg 92:812–823 32. Naidich TP, Duvernoy HM, Delman BN, Sorenson AG, Kollias SS, Haacke M (2009) Duvernoy's atlas of the human brain stem and cerebellum. Springer Wien, New York 33. Perneckzy A, Tschabitscher M, Resch KDM (1993) Endoscopic anatomy for neurosurgery. Georg Thieme Verlag, Stuttgart 34. Perneczky A, Fries G (1998) Endoscope-assisted brain surgery: part 1—evolution, basic concept, and current technique. Neurosurgery 42:219–224 35. Pernkopf E (1960) [Human topographic anatomy. Vol. IV: topographic and stratigraphic anatomy of the head]. Urban & Schwarzenberg (Ger), Munich 36. Rajesh BJ, Rao BRM, Menon G, Abraham M (2007) Telovelar approach: technical issues for large fourth ventricle tumors. Childs Nerv Syst 23:555–558 37. Rhoton AL Jr (2000) Cerebellum and fourth ventricle. Neurosurgery 47(Suppl):7–27 38. Sansone JM, Iskandar BJ (2005) Endoscopic cerebral aqueductoplasty: a trans-fourth ventricle approach. J Neurosurg 103:388–392 39. Stefanov I, Stefanov A, Westman J (1996) A new method for transcutaneous coaxial neuroendoscopy. Anat Embryol (Berl) 194:319–326 40. Tanriover N, Ulm AJ, Rhoton AL Jr, Yasuda A (2004) Comparison of transvermian and telovelar approach to the fourth ventricle. J Neurosurg 101:484–498 41. Toyota S, Taki T, Oshino S, Hashiba T, Oku Y, Hayakawa T, Yoshimine T (2004) A neuroendoscopic approach to the aqueduct via the fourth ventricle combined with suboccipital craniectomy. Minim Invasive Neurosurg 47:312–315 42. Tschabitscher M, Di Ieva A (2011) Practical guidelines for setting up and endoscopic/skull base cadaver lab. World Neurosurg. doi:10.1016/j.wneu.2011.02.045 43. Yasargil MG (1996) Microneurosurgery, vol 4B. Thieme, New York 44. Yasargil MG (1988) Microneurosurgery, vol 3B. Georg Thieme Verlag, Stuttgart 45. Ziehen T (1903) Macroscopic and microscopic anatomy of the brain. In: von Bardeleben K (ed) Handbook of human anatomy. Fischer (Ger), Jena 46. Ziyal IM, Sekhar LN, Salas E (1999) Subtonsillar–transcerebellomedullary approach to the lesions involving the fourth ventricle, the cerebellomedullary fissure and lateral brainstem. Br J Neurosurg 13:276–284
Comments Toshio Matsushima, Saga, Japan The authors studied the surgical anatomy of the fourth ventricle through the telovelar approach using endoscopy. We call this approach transcerebellomedullary fissure approach. However, surgical indications using this method will be limited. It seems difficult to remove large fourth ventricular tumors such as medulloblastomas or ependymomas by this method. This endoscopic
Neurosurg Rev (2012) 35:341–349 less invasive surgery seems good for small tumors or biopsy, especially lesions around the fastigium and lateral recess, which are difficult regions for observation in the microsurgery. As the authors mention, this endoscopic surgery had better be performed with microsurgery. The authors point out that excessive stretching of the tonsils can cause a compression on the related dentate nuclei and cerebellar peduncles. However, in our experiences of microsurgery the retraction of the tonsils did not cause any neurological deficits when the cerebellomedullary fissure is sufficiently opened. This is a well-written paper on endoscopic study with detailed description and will highly contribute to the surgical treatment of the fourth ventricular lesions in the future. Dattatraya Muzumdar, Mumbai, India Di Ieva et al. report a cadaveric study in 20 fresh and fixed injected anatomical specimens exploring the endoscopic anatomy of the fourth ventricle through a telovelar approach. They conclude that the endoscope can be a valid tool for gaining a better anatomic understanding of this complicated neuroanatomic region; it may also be a potential tool to be used for surgical endoscope–exoscope-assisted operations. The manuscript is well written, elaborate, and informative. The dissections are noteworthy and reveal the finer aspects of the anatomy. Microsurgical anatomy of the fourth ventricle is described in the literature but there are no elaborate articles about the use of endoscope in this area. They discuss the limitations of the study was well. Fourth ventricle is a limited space harboring critical neurovascular structures as well as the brain stem. The anatomy is complex and the lesions occurring in this limited space are formidable. Exploration of the fourth ventricle through the telovelar approach using the endoscope can be an aid or adjunct to the resection of the complex tumors in this region. The telovelar approach allows reliable access to the fourth
349 ventricle. It avoids the splitting of the vermis which is usually associated with cerebellar mutism. Endoscopic telovelar approach is truly a mimimally invasive surgery since it requires less space than the normal microscopic approach and limits the opening of telovelum. A digital HD video camera provides a panoramic view of the fields allowing for complete visualization of the fourth ventricle including the most proximal and lateral portions, from the aqueduct to the lateral regions around the lateral recesses. Anatomical laboratory training in endoscopy is indispensable and paramount to develop a sense of spatial orientation. The laboratory allows the surgeon to compare different images of the same anatomical area allowing formation of a three-dimensional mental image of the fourth ventricle. It is very helpful in understanding pathoanatomic topography. As a futuristic procedure of minimal access surgery and less traumatic approaches, it can be correctly termed as minimally invasive neurosurgery or minimally traumatizing neurosurgery. Richard Lochhead, Robert F. Spetzler, Phoenix, USA Di Ieva et al. present a cadaveric anatomical study entitled “Endoscopic Telovelar Approach to the Fourth Ventricle: Anatomical Study.” The authors use a rigid endoscope with different lenses to describe the fourth ventricular anatomy via the telovelar approach. They discuss various endoscopic approaches to the fourth ventricle with endoscopic photographs to demonstrate the fourth ventricular anatomy that can be visualized with minimal dissection and no brain retraction. This article addresses a need for increased understanding of fourth ventricular anatomy through minimally invasive techniques, and the authors are to be commended. Further work in this field may include quantification of the endoscopic access through the different approaches to improve understanding of the anatomical landmarks that can be visualized in each approach without tissue retraction.
