OPERATIVE TECHNIQUES
POSTERIOR TRANSPETROSAL APPROACH: LESS IS MORE Eric H. Sincoff, M.D. Departments of Neurological Surgery Oregon Health and Science University, Portland, Oregon.
Sean O. McMenomey, M.D. Departments of Neurological Surgery Oregon Health and Science University, Portland, Oregon.
Johnny B. Delashaw, Jr., M.D. Departments of Neurological Surgery Oregon Health and Science University, Portland, Oregon. Reprint requests: Johnny B. Delashaw, Jr., M.D., Department of Neurological Surgery, CH8N, Oregon Health and Science University, 3303 SW Bond Ave., Portland, OR 97239. Email:
[email protected] Received, March 15, 2006. Accepted, June 6, 2006.
OBJECTIVE: We describe our surgical posterior transpetrosal technique, particularly the transcrusal variant for lesions involving the upper and middle clivus, petroclival regions, and lesions that involve both the posterior and middle fossae. METHODS: An outline of the posterior transpetrosal technique involved, particularly the transcrusal variant, is described. Important superficial landmarks are identified, and a radical mastoidectomy is performed. The antrum is identified and entered, and, upon completion of the mastoidectomy and when Trautman’s triangle is defined, the temporal and suboccipital craniotomies are completed. After bone flap elevation, dura opening, and incision along the middle fossa dura, the superior petrosal sinus is ligated and cut. Tentorium cut completion is at the incisura posterior to the trochlear nerve. Watertight dural closure and standard flap replacement and skin closure complete the technique. RESULTS: Clival exposure and the degree of temporal bone resection increase. Operative freedom also increases with increased temporal bone resection, especially when going from the retrolabyrinthine to transcrusal variants. Little is gained in terms of operative freedom and exposure of the clivus with resection of additional temporal bone beyond that of the transcrusal variant, and resection carries the cost of increasing morbidity, especially with respect to VIIth and VIIIth nerve function. CONCLUSION: The posterior transpetrosal approach and the transcrusal variant provide a lateral operative corridor to lesions of the upper and middle clivus. The transcrusal variant provides increased exposure and operative freedom similar to that provided by the transcochlear approach while minimizing cranial nerve morbidity. KEY WORDS: Clival, Petroclival, Posterior transpetrosal approach, Transcrusal Neurosurgery 60[ONS Suppl 1]:ONS-53–ONS-59, 2007
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esions of the petroclival and clival regions most commonly include meningiomas, epidermoids, chordomas, chondrosarcomas, trigeminal neurinomas, and vertebrobasilar and mid-basilar aneurysms. For the cranial base surgeon, small operative corridors and proximity to neurovascular structures can make the petroclival region one of the most difficult areas to access (1, 3–6, 10, 14). Cranial base approaches to this area include anterior transpetrosal, posterior transpetrosal, retrosigmoid, and combined approaches (Table 1) (10). The choice of approach is dictated by the presumed pathology of the lesion as well as lesion location relative to the dorsum sellae, internal auditory canal (IAC), and jugular foramen. Extradural lesions arising high on the clivus and petroclival areas between the dorsum sellae and upper IAC are often approached via an anterior transpetrosal approach, essentially an extended middle fossa approach with an ante-
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DOI: 10.1227/01.NEU.0000249232.12860.A5
rior petrosectomy (1, 2). Lesions that involve the upper and middle clivus and petroclival areas and lesions that extend from the posterior to middle fossae are often approached via a posterior transpetrosal approach (1, 2, 8). In the case of some lesions involving the posterior fossa with limited extension into the middle fossa, a retrosigmoid approach with resection of the suprameatal tubercle above the IAC can provide sufficient exposure (11, 13). Lesions that lie from below the jugular tubercle to the lower clivus are essentially foramen magnum lesions and can be approached via a lateral or transcondylar approach (1). Abdel Aziz et al. (1) have described a convenient method to view this area, with three zones defined: Zone I extends from the level of the dorsum sellae to the level of the upper border of the IAC, Zone II extends from the upper border of the IAC and the upper border of the jugular tubercle, and Zone III extends from the upper border of
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There are four basic variations of the posterior transpetrosal approach: retrolabyrinthine, transcrusal (partial labyrinthectomy), transotic, and transcochlear (Table 1). Each differs in the amount of temporal bone resected, with increased temporal bone resection providing greater operative exposure and increased surgical freedom. The increase in exposure and surgical freedom comes at the expense of increased surgical morbidity in the form of increased risk of cranial nerve deficits, particularly the VIIth and VIIIth cranial nerves. The transotic and transcochlear approaches sacrifice hearing and place the facial nerve and its function at increased risk (2, 7–10, 12, 15). The transcrusal variant of the posterior transpetrosal approach allows sacrifice of the superior and posterior semicircular canals, in essence a partial labyrinthectomy, and provides 89% of the clival exposure of the more aggressive transotic and transcochlear variants with much less risk to hearing and facial nerve function (4, 8, 9, 12). Patient preoperative preparations for the posterior transpetrosal approach are similar to those of any large cranial base procedure and include evaluation and medical clearance. Evaluation includes assessment of cardiac and pulmonary function and, if indicated, echocardiography and pulmonary function testing. Optimization of patient cardiac and pulmonary function, by the medical team, should be undertaken preoperatively as needed and when indicated. Patients should also have a preoperative audiometric evaluation and a formal swallow evaluation where indicated. Radiographic studies should include computed tomographic scanning with special attention to creating bone windows, magnetic resonance imaging with sequences that best demonstrate the pathology to be resected, and magnetic resonance venography. Angiography should possibly be considered to fully evaluate the patency and dominance of the sigmoid sinuses (especially if sigmoid sinus sacrifice is being contemplated) and the course of the vein of Labbé. The procedure is performed with standard neuroanesthesia and to facilitate monitoring of facial nerve function without neuromuscular blockade. In general, brainstem auditory evoked response testing and electroencephalography (EEG) are
not used at our institution. Standard antibiotic prophylaxis is a first generation cephalosporin or equivalent. Before final positioning, a lumbar drain is placed in the standard manner to facilitate brain relaxation and to provide for temporary postoperative cerebrospinal fluid (CSF) diversion. After the lumbar drain is placed, the patient is positioned supine with the head rotated and tilted toward the contralateral shoulder, aided by a shoulder roll to provide exposure of the mastoid (Fig. 1A). Care should be taken not to rotate or tilt the head too much, as this can potentially compress the contralateral jugular vein or aggravate existing cervical stenosis. An incision is made in a retroauricular fashion extending from 1 cm in front of the tragus, curving above the ear, and ending approximately 1 cm inferior to the mastoid tip. The incision can be modified as needed if the approach is to be combined with another approach, such as a retrosigmoid, middle fossa, or frontotemporal exposure (Fig. 1B). Careful planning is essential with combined incisions to ensure that blood supply from the posterior branch of the superficial temporal artery and the occipital artery is not compromised. The skin is elevated with the pericranium until the posterior aspect of the external ear canal can be identified. To provide important superficial landmarks for the initial bone work, the asterion, posterior root of zygoma, mastoid tip, spine of Henle, and temporal line are identified (Fig. 1C). A radical mastoidectomy is then performed and is required for all four variations of the posterior transpetrosal approach. The mastoidectomy starts by using an aggressive ball or acorn burr to resect the outer cortex of the mastoid triangle. A suction-irrigator should be used for temporal bone work to keep the field free of bone dust and the underlying structures cool. The mastoid triangle is bounded superiorly by the inferior temporal line, anteriorly by the posterior ear canal, and posteriorly by the occipital bone (Fig. 1D). The mastoid air cells are entered. The mastoid air cells are then drilled down, and the sigmoid is delineated at the posterior extent of the mastoid triangle; a thin shell of bone can be left on the sigmoid and can later be elevated with a Freer elevator. Once the sigmoid is delineated, the tegmen, the middle fossa plate, and the posterior fossa plate are identified and a thin shell of bone is left on each. This shell of bone can be later elevated with a Freer elevator. When the neurosurgeon or the neuro-otologist performs the mastoidectomy, it should be wide, fully defining the sigmoid and transverse sinuses. Additionally, it is important to fully delineate the sinodural angle, the angle defined by the sigmoid sinus with the middle and presigmoid posterior fossa dura. Once air cells have been drilled away, the antrum is identified lying posterior to the posterior ear canal, deep within Macewen’s triangle, and posterior to the spine of Henle. The antrum is a large air cell that lies superficial to the bony labyrinth and leads into the middle ear. The incus, the first middle ear structure encountered, can be observed deep and anterior to the antrum. At this point, a diamond burr should be used for the more precise dissection to follow. The antrum is entered by drilling through the remaining superior mastoid air cells. Once the antrum is entered, the lat-
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TABLE 1. Cranial base approaches for petroclival and clival area lesions Anterior transpetrosal Posterior transpetrosal Retrolabyrinthine Transcrusal (partial labyrinthectomy) Transotic Transcochlear Retrosigmoid Combined
the jugular tubercle to the lower edge of the clivus. Lesions arising in Zone II can use the posterior transpetrosal approach with its four variations.
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POSTERIOR TRANSPETROSAL APPROACH: LESS IS MORE
A
B
C
D
eral semicircular canal is identified lying deep to the antrum. The fallopian canal, housing the facial nerve, is identified by following the short process of the incus and lying at the anterior and inferior border of the antrum. The incus and middle ear structures are deep and anterior to the antrum and must not be manipulated, or a conductive hearing loss may result (Fig. 2A). Attention is then directed toward the digastric ridge at the inferior portion of the mastoid at the mastoid tip. Anterior to the digastric ridge lies the facial nerve within the fallopian canal. To avoid damaging the facial nerve, the canal should not be skeletonized, but rather a thin layer of bone should remain protecting the nerve. The remainder of the labyrinth within the hard otic capsule can then be delineated. The posterior semicircular canal is identified at the point at which the lateral semicircular canal bisects it. The superior semicircular canal is perpendicular to the lateral semicircular canal and is exposed by drilling anteriorly from the sinodural angle along the middle fossa. Characteristically, the otic capsule bone is harder than the surrounding bone and provides an additional means of identifying the otic capsule. At this point, Trautman’s triangle can be identified and is bordered posteriorly by the sigmoid, superiorly by the superior petrosal sinus, and anteriorly by the posterior semicircular canal (Fig. 2B) (10). Upon completion of the mastoidectomy and when Trautman’s triangle is defined, the temporal and suboccipital craniotomies can be completed by drilling four burr holes on both sides of the transverse sinus, two flanking the sinus just medial to the asterion and two further medially on the subocciput. The craniotome with the footplate can then be used to complete the craniotomy with the bone cuts over the transverse sinus performed last. Special attention should be given to separating the transverse and sigmoid sinus dura from the inner table of the cranium, as they can be quite adherent (Fig. 2C). Bleeding from small holes in the sigmoid and transverse sinuses can be quite vigorous but can be controlled with Gelfoam (Upjohn Co., Kalamazoo, MI) and pressure. The bone flap is elevated and the dura opened with an incision along the middle fossa dura; care is taken to avoid the vein of Labbé as it empties into the transverse sinus. The posterior fossa dura is then opened anterior of the jugular bulb toward the superior petrosal sinus with a cut made superior to the transverse sinus towards the superior petrosal sinus. The superior petrosal sinus can then be ligated and cut (Fig. 2D). The tentorium is now exposed and can be cut, taking care to avoid the trochlear nerve. Cut completion is at the incisura posterior to the trochlear nerve. Retractors are then placed using the tentorium between the retractor blade and the temporal lobe to protect the underlying temporal lobe cortex. FIGURE 1. A, The patient is positioned supine with the head turned to expose the mastoid; a shoulder roll is used to prevent kinking of the internal jugular vein. B, illustration of the retroauricular skin. C, boney landmarks to be noted before incision include the asterion, posterior root of zygoma, superior temporal line, mastoid tip, and spine of Henle. D, beginning of mastoidectomy showing superficial air cells within the mastoid triangle that is bounded by the superior temporal line, occipital bone, and posterior ear canal.
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tion, the transcochlear approach only minimally increases clival access and transposition of the facial nerve in the transcochlear approach compared with the transcrusal approach which will usually result in a facial nerve paresis rarely recovering to better than House-Brackmann Grade III. As alluded to earlier in this article, the transcrusal posterior transpetrosal approach sacrifices the superior and posterior semicircular canals from their ampullae to the common crus (Fig. 3, A–D). The openings into the canals are occluded with bone dust and wax to contain the endolymph. By only removing two of the three semicircular canals, hearing can be preserved in many cases while providing 89% of the clival exposure afforded by the more a g g re s s i v e t r a n s c o c h l e a r approach (8, 9). At our institution, we use the transcrusal approach almost exclusively when performing a posterior transpetrosal approach and have had 90% hearing preservation with this approach. To avoid CSF leak, the dural c l o s u re f o r t h e p o s t e r i o r transpetrosal approach must be watertight. Fascia lata, periosteum, or other dural substitutes can be used, as the dura often shrinks with this FIGURE 2. A, mastoidectomy once the superficial air cells have been drilled showing the opening into the antrum, lateral type of approach. Tissue glue semicircular canal, fallopian canal, and incus. B, completion of the mastoidectomy shows the otic capsule revealing the semi- or similar products can also be circular canals and Trautman’s triangle bounded by the sigmoid, superior petrosal sinus, and posterior semicircular canal. used to reinforce dural closure. C, completion of the craniotomy with exposure of the transverse sinus and outline of the dural incisions. D, illustration of Abdominal fat is then used to the completed dural incisions and cutting along the tentorium with ligation of the superior petrosal sinus. pack the mastoid cavity, taking care not to pack the middle ear because doing so can create a conductive hearing loss. Small The presigmoid retrolabyrinthine posterior transpetrosal bone chips can be used to prevent fat from entering into the approach, as described above, avoids entering the labyrinth, antrum and middle ear while, at the same time, sealing off the thereby preserving hearing. The transotic posterior transpetrosal middle ear from the rest of the mastoidectomy. Some reports approach sacrifices the labyrinth at the expense of hearing funchave described packing the middle ear with oxidized cellulose tion and is an option for increased exposure when a patient presto prevent CSF leak from the eustachian tube (the oxidized celents with ineffectual hearing. The transcochlear posterior lulose is eventually resorbed and does not result in a permanent transpetrosal approach allows greater exposure of temporal bone conductive hearing deficit) (12). Bone flap replacement and skin by transposing the facial nerve from the fallopian canal and closure can then be completed in the standard fashion. The masdrilling out the cochlea. This has the undesired effect of not only toidectomy defect is repaired with thin titanium mesh and bone sacrificing hearing, but also risking facial nerve function. In addi-
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toring provides an added level of protection to the facial nerve. Additionally, as is the case for any large posterior cranial base approach, CSF leak and pseudomeningocele are potential complications that are minimized by careful attention to dural closure. Vertigo and vestibular symptoms can occur with the transcrusal approach; these symptoms are usually transient (12). Other risks are vascular in nature and involve temporal lobe drainage via the vein of Labbé; these risks can be avoided by taking care not to stretch or sacrifice this important vein. If the vein of Labbé does develop a small hole, it should be sealed with Gelfoam and never bipolared.
Illustrative Case
FIGURE 3. Illustrations of operative view directed at the petroclival area and middle of clivus through posterior transpetrosal approach with retrolabyrinthine exposure (A), transcrusal exposure with amputation of the posterior and superior semicircular canals at the common crus and packed with wax (B), translabyrinthine exposure (C), and transcochlear exposure with transposition of facial nerve from the fallopian canal (D).
cement. The titanium mesh further pushes the fat into the mastoidectomy defect, further sealing the mastoid. As an extra measure to prevent CSF leak, a lumbar drain remains in place for 48 hours. Antibiotics are continued until the drain is removed.
An example of a patient harboring a lesion for which the posterior transpetrosal approach has been employed is a 39-year-old woman who presented with right-sided facial numbness. Preoperative audiometric evaluation revealed normal hearing. The remainder of the patient’s neurological examination was unremarkable. Magnetic resonance imaging scans revealed a right-sided petroclival lesion, suggestive of a meningioma (Fig. 4A). A transcrusal posterior transpetrosal craniotomy was undertaken and a complete resection performed, as is evident by postoperative imaging (Fig. 4B). Postoperatively, the patient’s hearing was fully intact and, during the next 6 months, facial numbness completely resolved.
CONCLUSION
Complications from the posterior transpetrosal approach include the already mentioned risks to the VIIth and VIIIth nerves. These complications are kept to a minimum with the retrolabyrinthine and transcrusal variants. Facial nerve moni-
The posterior transpetrosal approach is unique in that it provides a lateral operative corridor to lesions of the clival and petroclival area. The transcrusal variant of this approach provides further increased exposure and provides access to the central clival depression, an area located in the middle clivus that is bounded superiorly by the intermeatal plane and inferiorly by the jugular tubercles, as described by Abdel Aziz et al. (1). The retrolabyrinthine variant does not provide easy access to the central clival depression. The transotic and transcochlear
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B
FIGURE 4. A, magnetic resonance imaging scan with contrast of a patient presenting with facial numbness and petroclival lesion on the right side. B, postoperative magnetic resonance imaging scan showing complete resection and fat that has been packed into the mastoid air cells.
variants sacrifice hearing and place the facial nerve at risk, especially with transposition of the facial nerve when utilizing the transcochlear variant. At our institution, we use the transcrusal approach almost exclusively. The added risk and very minimal increase in exposure obtained with the transcochlear approach are neither worth the added time required for the temporal bone resection required to perform it, nor is it worth the permanent facial nerve paresis that results from translocating the facial nerve. In conclusion, the posterior transpetrosal approach and the transcrusal variant provides a lateral operative corridor to lesions of the upper and middle clivus. The transcrusal variant provides increased exposure and operative freedom similar to that provided by the transcochlear approach while minimizing cranial nerve morbidity.
Disclosure None of the authors received financial support in conjunction with the generation of this submission.
REFERENCES 1. Abdel Aziz KM, Sanan A, van Loveren HR, Tew JM Jr, Keller JT, Pensak ML: Petroclival meningiomas: Predictive parameters for transpetrosal approaches. Neurosurgery 47:139–150, 2000. 2. Blevins NH, Jackler RK, Kaplan MJ, Gutin PH: Combined transpetrosalsubtemporal craniotomy for clival tumors with extension into the posterior fossa. Laryngoscope 105:975–982, 1995. 3. Canalis RF, Black K, Martin N, Becker D: Extended retrolabyrinthine transtentorial approach to petroclival lesions. Laryngoscope 101:6–13, 1991. 4. Chanda A, Nanda A: Partial labyrinthectomy petrous apicectomy approach to the petroclival region: An anatomic and technical study. Neurosurgery 51:147–160, 2002. 5. Cho CW, Al-Mefty O: Combined petrosal approach to petroclival meningiomas. Neurosurgery 51:708–716, 2002. 6. Couldwell WT, Fukushima T, Giannotta SL, Weiss MH: Petroclival meningiomas: Surgical experience in 109 cases. J Neurosurg 84:20–28, 1996. 7. Daspit CP, Spetzler RF, Pappas CT: Combined approach for lesions involving the cerebellopontine angle and skull base: Experience with 20 casespreliminary report. Otolaryngol Head Neck Surg 105:788–796, 1991.
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8. Horgan MA, Anderson GJ, Kellogg JX, Schwartz MS, Spektor S, McMenomey SO, Delashaw JB: Classification and quantification of the petrosal approach to the petroclival region. J Neurosurg 93:108–112, 2000. 9. Horgan MA, Delashaw JB, Schwartz MS, Kellogg JX, Spektor S, McMenomey SO: Transcrusal approach to the petroclival region with hearing preservation. Technical note and illustrative cases. J Neurosurg 94:660–666, 2001. 10. Miller CG, van Loveren HR, Keller JT, Pensak M, el-Kalliny M, Tew JM Jr: Transpetrosal approach: surgical anatomy and technique. Neurosurgery 33:461–469, 1993. 11. Samii M, Tatagiba M, Carvalho GA: Retrosigmoid intradural suprameatal approach to Meckel’s cave and the middle fossa: Surgical technique and outcome. J Neurosurg 92:235–241, 2000. 12. Sekhar LN, Schessel DA, Bucur SD, Raso JL, Wright DC: Partial labyrinthectomy petrous apicectomy approach to neoplastic and vascular lesions of the petroclival area. Neurosurgery 44:537–550, 1999. 13. Seoane E, Rhoton AL Jr: Suprameatal extension of the retrosigmoid approach: microsurgical anatomy. Neurosurgery 44:553–560, 1999. 14. Slater PW, Welling DB, Goodman JH, Miner ME: Middle fossa transpetrosal approach for petroclival and brainstem tumors. Laryngoscope 108:1408–1412, 1998. 15. Spetzler RF, Daspit CP, Pappas CT: The combined supra- and infratentorial approach for lesions of the petrous and clival regions: Experience with 46 cases. J Neurosurg 76:588–599, 1992.
Acknowledgments We thank Andy Rekito, M.S., for figure preparation and Shirley McCartney, Ph.D., for manuscript assistance and editing.
COMMENTS
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his is a valuable contribution in terms of outlining the details of the transcrusal variant of the transpetrosal approach. I agree with the authors that this variant is quite useful in terms of gaining nearly equivalent exposure to the transcochlear or translabyrinthine variants of the approach without the obligatory morbidity to the VIIth and VIIIth cranial nerves. When performed as outlined in this article, the risk to hearing is low. This should serve as an important guide to the proper steps and technique for those not experienced in this approach. John D. Day Englewood, Colorado
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he authors describe their surgical posterior transpetrosal technique, particularly the transcrusal variant for lesions involving the upper and middle clivus or petroclival regions and lesions that involve both the posterior and middle cranial fossae. In essence, the authors describe the advantages of the posterior transpetrosal transcrusal variant and discuss how this variant allows exposure obtained by the translabyrinthine and transcochlear approaches while, at the same time, attempting to preserve hearing and minimize the morbidity that can be associated with the translabyrinthine and transcochlear approaches. The traditional posterior cranial base approaches comprise combinations of the well-known retrosigmoid approach, the pre-sigmoid exposures, and the middle fossa approach. For pathology lateral and anterior to the brainstem, the most common approach is a combination of a presigmoid retrolabyrinthine approach and a middle fossa exposure with ligation of the superior petrosal sinus and splitting of the tentorium down to the tentorial hiatus. However, as the authors indicate, this exposure provides somewhat limited access and is less than ideal for tumors lying predominantly anterior to the upper brainstem. For these tumors, we have used the presigmoid transcochlear approach with rerouting of the facial nerve either anteriorly or posteriorly.
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Sincoff et al. contend that the transcrusal variant of the posterior transpetrosal approach provides similar access, but with sparing of hearing and less risk to facial nerve function. The transcrusal variant involves sacrifice of the superior and posterior semicircular canals, is essentially a partial labyrinthectomy, and preserves hearing that is sacrificed during the transcochlear approach. In essence, it is really a compromise between the more traditional retrolabyrinthine exposure and the transcochlear exposure. Although this does seem to be a reasonable compromise in exposure, surgery on tumors lying anterior to the upper brainstem is extremely challenging; in such cases, I personally need all the exposure I can get to minimize damage to the brainstem and vessels lying anterior to it. Robert Briggs Andrew H. Kaye Melbourne, Australia
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incoff et al. have described their approach in which partial labyrinthectomy enables resection of midclival and petroclival lesions. This article provides an excellent anatomical description with case illustrations showing a step-by-step approach for exposure. My own preference is to perform the bone flap and proceed with the mastoidectomy; we have sometimes modified this by not performing a labyrinthectomy for smaller lesions that are easily accessible using just a partial mastoidectomy. Furthermore, I prefer a retromastoid corridor in addition to the presigmoid exposure because the clival angle is more obtuse in some cases and the visualization provided by the retromastoid corridor is better. All in all, this is an excellent approach and is an essential part of the cranial base armamentarium for midclival and petroclival lesions. Anil Nanda Shreveport, Louisiana
Govard Bidloo, 1649–1713, Ontleding des Menschelyken Lichaams. Amsterdam: By de weduwe van Joannes van Someren, de erfgenaamen van Joannes van Dyk, Hendrik en de weduwe van Dirk Boom, 1690 (courtesy, of the U.S. National Library of Medicine, National Institutes of Health, Bethesda, Maryland).
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