Presigmoid Transpetrosal Approach for the Treatment of a Large Trochlear Nerve Schwannoma

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1 Neurol Med Chir (Tokyo) 42, 31 35, 2002 Presigmoid Transpetrosal Approach for the Treatment of a Large Trochlear Nerve Schwannoma Case Report Toru MATSUI, EiharuMORIKAWA, Tadashi MORIMOTO, andtakaoasano Department of Neurosurgery, Saitama Medical Center/School, Kawagoe, Saitama Abstract A 61-year-old man presented with a rare, large trochlear nerve schwannoma manifesting as left-sided weakness and hypesthesia, bilateral bulbar pareses, and trochlear nerve paresis persisting for 3 months. T 1 -weighted magnetic resonance imaging with gadolinium revealed an intensely enhanced, wellcircumscribed lesion with multicystic formation occupying the prepontine and interpeduncular cisterns and compressing the pons and midbrain with greater extension to the right. The mass was completely removed through the presigmoid transpetrosal approach with preservation of the posterior cerebral, superior cerebellar, and basilar arteries and their branches. Neuroradiological examination after 3 years demonstrated no recurrence. Enlargement of a tumor in the cisternal portion is inclined to involveand/orencasetheadjacentmajorarteriesandtheirbranches.thepresigmoidtranspetrosal approach is one of the best surgical routes to remove a large trochlear nerve schwannoma safely and completely. Key words: trochlear nerve schwannoma, presigmoid transpetrosal approach Introduction Trochlear nerve sheath tumors are uncommon, with only 15 cases reported. 1,3,5 7,11,12,14 17,19,20) Intracranial schwannomas occur in a number of mixed and purely motor cranial nerves, especially in association with neurofibromatosis type 2. 4,8,11,16) Total removal of a large tumor in the region associated with the trochlear nerve requires retraction of the temporal lobe to obtain an adequate operative field. Therefore, the use of a modern cranial base approach is thought to be preferable to a simple subtemporal approach. 18) Previous cases involved a relatively midsized tumor, so the subtemporal approach was used to obtain total or subtotal removal. However, removal of a large tumor sometimes leads to unexpected postoperative neurological deficits, possibly due to the intraoperative compression of the temporal lobe. 13) Here, we present an extremely rare case of a large trochlear nerve schwannoma without neurofibromatosis treated by the presigmoid transpetrosal approach, which allowed complete removal. Received June 25, 2001; Accepted October 11, 2001 Case Report A 61-year-old man presented in December 1997 with left-sided weakness and hypesthesia, bilateral bulbar pareses, and trochlear nerve paresis which had persisted since September During the 4 weeks before his admission, he had had difficulty in swallowing with intake of liquid and needed support because of cerebellar ataxia. He had no family history of neurofibromatosis. Examination found no cutaneous stigmata of neurofibromatosis. His visual fields were full. The pupils were equal and reacted directly and indirectly to light. He had diplopia on downward gaze to the right, suggesting right trochlear nerve paresis. Corneal reflexes were brisk bilaterally, and facial sensation was normal. The functions of the VIIth to XIIth cranial nerves were intact. He demonstrated mild left-sided weakness of the upper motor neuron type, with hyperreactive reflexes. There was no convincing sensory loss. T 1 -weighted magnetic resonance (MR) imaging with gadolinium revealed an intensely enhanced, well-circumscribed lesion with multicystic formation occupying the prepontine and interpeduncular cisterns. The midbrain and upper pons were compressed and shifted to the left by the 31

2 32 T. Matsui et al. large extension of the tumor, and the tumor was attached to the upper third clivus and petrous bone (Fig. 1). T 2 -weighted MR imaging clearly demonstrated involvement of the basilar artery (BA) and the neighboring major arteries and their branches (Fig. 1). Cerebral angiography demonstrated no tumor blush. The preoperative diagnosis was trigeminal neurinoma rather than petroclival meningioma. Therefore, we decided to approach this lesion via the presigmoid transpetrosal approach with the goal of removing bone to preserve the brain. 18) The patient was positioned for the right presigmoid transpetrosal approach. A U-shaped skin incision starting two fingerbreadths anterior to the external auditory canal (EAC) was carried out superiorly and then curved posteriorly three fingerbreadths superior to the EAC and curved again downward to the suboccipital area, two fingerbreadths posterior to the mastoid process. A temporo-occipito-suboccipital craniotomy with mastoidectomy was then performed. The mastoidectomy was designed preoperatively to preserve the vestibulocochlear apparatus, based on computed tomography (CT) (Fig. 2). Postoperative hearing loss should thus be avoided through rongeuring off the mastoid bone. Following the craniotomy, the presigmoid and temporal dura was incised, and then the superior petrosal sinus and tentorium cerebelli were coagulated and cut. Evacuation of cerebrospinal fluid from the ambient cistern was helpful to obtain a large space for surgery by mild retraction of the temporal lobe and cerebellum (Fig. 3). First of all, the arachnoid membrane surrounding the petrosal vein was incised to expose the trigeminal nerve. The trigeminal, facial, and acoustic nerves were easily identified and dissected from the tumor, but the branches of the superior cerebellar artery (SCA) were overlying the tumor. The distal portion of the trochlear nerve was identified on the inner aspect of the tumor. A large mass was located at the ambient portion of the trochlear nerve. Yellowish-green fluid was evacuated from the tumor but the lumen was multilobulated. Unexpectedly, the tumor was composed of parenchymatous as well as cystic components. The tumor was removed by piecemeal resection to preserve the small branches from the major arteries such as the BA, posterior cerebral artery (PCA), and SCA. A large tumor located in the cisternal region is likely to involve and/or encase vascular components, so careful attention was paid to preserving any vessels. Finally, complete excision of the tumor including part of the trochlear nerve was obtained. Subsequently, the oculomotor nerve and the abducens nerve were identified in the ventral Fig. 1 Preoperative T 1 -weighted magnetic resonance images with gadolinium revealing an intensely enhanced, well-circumscribed lesion with multicystic formation occupying the prepontine, ambient, and interpeduncular cisterns. The pons and midbrain are extremely compressed with greater extension to the right, and an attachment to the upper third clivus and petrous bone. The medial portion of the tumor is attached to the basilar artery, suggesting involvement of its perforators. Fig. 2 Postoperative bone window computed tomography scan clearly showing preservation of the vestibulocochlear apparatus. region of the BA-PCA junction and in the ventral site of the SCA and the trigeminal root, respectively. These observations suggested that the tumor origi- Neurol Med Chir (Tokyo) 42,January,2002

3 Large Trochlear Nerve Schwannoma 33 Fig. 4 Postoperative T 1 -weighted magnetic resonance images with gadolinium (left) within a month after surgery revealing complete resection, and (right) at3yearsafter surgery showing no recurrence of the tumor. The brainstem dislocated by the large mass has normalized within 3 years. nated from the trochlear nerve. Histological examination of the tumor specimen showed compact areas of spindle cells arrayed in bundles (Antoni A type), alternating with areas of loosely structured tissue (Antoni B type). The histological diagnosis was neurinoma. Immediately after the surgery, left hemiparesis and dysphagia disappeared. Diplopia due to right trochlear nerve paresis also disappeared with visual correction by control of the head position during the first year after surgery. Postoperative MR imaging demonstrated complete removal of the tumor, and almost 3 years later there was no evidence of recurrence (Fig. 4). Discussion Fig. 3 Intraoperative photograph and sketch showing that minimal retraction of temporal lobe (Temp) and cerebellum (cerebelli) allowed exposure of the important anatomical details of the cerebellopontine angle such as the trochlear nerve (Tro), tumor (Tum), branches of the superior cerebellar artery (SCAb), petrosal vein (Pv), and the trigeminal nerve (Tri). The tumor clearly originated from the trochlear nerve. P: rongeured petrous bone covered with cotton plugs, R1 and R2: Sugita retractors, S: sucker. Preoperative localization of intraaxial or extraaxial lesions located in the parapeduncular region was very difficult before the development of highresolution CT and/or MR imaging, but now only small iso-intense lesions present problems. 8) The present tumor appeared with the following characteristics of meningioma and neurinoma. The mass was iso-intense on T 1 -andt 2 -weighted MR images and brightly enhanced with gadolinium. 1,2,17) An extremely peculiar case of cystic trochlear nerve neurinoma mimicked a brainstem tumor. 7) Generally, trochlear nerve neurinoma is preoperatively identified as trigeminal neurinoma, meningioma, or epidermoid cyst. 1,2,5,11,16,17) In almost all case, direct surgery revealed trochlear nerve neurinoma. Trochlear nerve paresis was present in eight of 16 reported cases, including this case, and five of these 16 cases manifested as involvement of other cranial nerves (Table 1). The unilateral combination of hemiparesis, cerebellar ataxia, and sensory disturbance in the presence of extraaxial mass at the tentorial notch is more strongly suggestive of trochlear nerve neurinoma. 5) However, these symptoms remain silent until the tumor size exceeds more than 3 4 cm diameter. A trochlear nerve neurinoma of 1.5 cm diameter, although extremely rare, was found at autopsy. 10) No preoperative trochlear nerve involvement was presentinatleast45%ofpreviouscases.themost frequently used surgical approach was the subtem- Neurol Med Chir (Tokyo) 42, January, 2002

4 34 T. Matsui et al. Table 1 Previous cases of trochlear nerve schwannoma Case No. Author (Year) Age/ Sex n.iv sign* Other symptoms Tumor site Surgery Follow up 1 King (1976) 12) 55/F + rt hyperesthesia, cisternal subtemporal and 18 mos 2 Boggan et al. 32/F + lt hemiparesis, cisternal frontotemporal, 8mos (1979) 3) amenorrhea, subtemporal, and 3 Leunda et al. 54/M + headache cisternal subtemporal and 1yr (1982) 14) 4 16/F + headache cisternal and subtemporal and 6mos cavernous 5 Yamamoto et al. 37/F + increased ICP, cisternal subtemporal and 5yrs (1987) 20) temporal headache 6 Garen et al. 18/F - diplopia, n.iii cisternal subtemporal and? (1987) 7) 7 Tokuriki et al. 43/M - lt numbness, cisternal subtemporal and 1mo (1988) 19) gait disturbance, 8 Mauice-Williams 56/M - rt hemiparesis, cisternal suboccipital 2 yrs (1989) 15) diplopia 9 Celli et al. 51/M + lt hemiparesis, cisternal subtemporal and 5yrs (1992) 5) lt cerebellar ataxia 10 Jackowski et al. 26/F + lt facial numbness cisternal transtemporal and 6mos (1994) 11) 11 Abe et al. 60/M - lt hemiparesis cisternal suboccipital? (1994) 1) 12 57/M - lt facial numbness cisternal subtemporal and? 13 Dolenc and Coscia (1996) 6) 68/M - lt hemiparesis, diplopia (transient) cisternal and cavernous subtemporal and suboccipital 2mos 14 Santoreneos et al. (1997) 17) 35/F - lt hemiparesis, bil bulbar pareses, emotional disorder, n.vii 15 Nadkarni and Goel cisternal subtemporal and (1999) 16) 48/F - pathological laughter cisternal subtemporal and 16 Present case 60/M + lt hemiparesis, cisternal presigmoid and diplopia, dysphagia transpetrosal 23 mos 6mos 2.5 yrs *+: present,-: none. ICP: intracranial pressure, n.iii: oculomotor nerve, n.iv: trochlear nerve, n.v: trigeminal nerve, n.vii: facial nerve. poral approach combined with tentorial incision (Table 1), and the tumor was almost totally excised. However, postoperative complications included temporary oculomotor and abducens nerve pareses, temporary hemiparesis and expressive dysphasia due to intraoperative compression of the temporal lobe and pons, and/or subsequent contusion. 13) Even if long-term follow up indicated recovery of the preoperative deficit, modern cranial base surgery is preferable to the simple subtemporal approach, 18) but the presigmoid transpetrosal approach has never been used, possibly due to the low incidence of trochlear nerve schwannoma. The preoperative diagnosis was large trigeminal nerve schwannoma, so the presigmoid transpetrosal approach was performed in the present case. At 2 weeks after surgery, dysphagia and left-sided weakness had completely disappeared. The presigmoid transpetrosal approach provides excellent exposure of the cerebellopontine angle and pons, so removal of the tumor compressing the pons is unlikely to cause neurological deterioration, if the plane between the tumor and the pons is successfully dissected. To remove bone and preserve brain function, cranial base surgery technique is essential, and the total removal of such a large trochlear nerve schwannoma located in the cisternal portion is a good indicator of the effectiveness of this approach. Oculomotor, trochlear, and abducens nerve schwannomas generally arise far from the glial Schwann sheath junction, at not more than 1 mm from the neuraxis. 5) Trochlear nerve schwannomas arise almost exclusively from the cisternal segment. Therefore, the tumor grows in the space occupied by Neurol Med Chir (Tokyo) 42,January,2002

5 Large Trochlear Nerve Schwannoma 35 thepca,sca,ba,andperforators.trochlearnerve schwannoma in the basal cistern is likely to form severe adherences to these anatomical structures, making total removal more difficult. We started to treat large lesions located in the petroclival region employing the presigmoid transpetrosal approach in 1988 according to Hakuba et al. 9) Acoustic neurinoma could be basically removed via a lateral suboccipital route, but such tumor with severe upward compression of the tentorium cerebelli and extension into the petroclival region was treated via the presigmoidal route. Postoperatively, MR imaging was repeated to detect recurrence of the tumor every one year, and MR angiography was performed to investigate the patency of the lateral and sigmoid sinus in the operated site after more than 3 years in 11 of a total of 30 patients. Although four of the 11 examined patients showed obstruction of the lateral and sigmoid sinuses, but did not present with any symptoms due to deterioration of venous drainage system, due to development of the compensatory venous drainage system following gradual obstruction of the sinuses. Thus, this approach is thought to be safe. The possibility of total removal depends upon the severity of adhesion of the tumor to the brainstem and/or important vessels in the deep brain region, and can be well predicted by preoperative MR imaging, as the presence of thin low-intense areas on T 1 -weighted MR imaging, suggesting cerebrospinal fluid collection, between the tumor and brainstem. Furthermore, T 2 -weighted MR imaging shows whether the tumor involves and/or encases the major arteries in the cranial base and severely compresses the upper brainstem. Such conditions require a wide working space where many important anatomical structures such as the BA, PCA, SCA, IIIrd to VIIth cranial nerves, and pons can be exposedwithminimalretractionofthebrain. The present case indicates that the presigmoid transpetrosal approach is the first choice to treat a patient with a large trochlear nerve schwannoma located in the ambient, parapeduncular, interpeduncular, or prepontine cistern. References 1) Abe T, Iwata T, Shimazu M, Iida M, Izumiyama H, Matsumoto K, Mizutani T, Tanaka H, Aruga T: [Two cases of trochlear nerve neurinoma]. No Shinkei Geka 22: , 1994 (Jpn, with Eng abstract) 2) Beppu T, Yoshida Y, Wada T, Arai H, Suzuki M, Kuroda K, Ogawa A: Trochlear and abducens nerve neurinomas accompanied by a cerebellopontine angle meningioma. Case report. Neurol Med Chir (Tokyo) 37: , ) Boggan JE, Rosenblum ML, Wilson CB: Neurilemmoma of the fourth cranial nerve. Case report. JNeurosurg 50: , ) Brodsky MC, Boop AF: Primary trochlear nerve neoplasm in a child with neurofibromatosis 1. JPediatr Ophthalmol Strabismus 33: , ) Celli P, Ferrante L, Acqui M, Mastronardi L, Fortuna A, Palma L: Neurinoma of the third, fourth, and sixth cranial nerves: a survey and report of a new fourth nerve case. Surg Neurol 38: , ) Dolenc VV, Coscia S: Cystic trochlear nerve neurinoma. Br J Neurosurg 10: , ) Garen PD, Harper CG, Teo C, Johnston IH: Cystic schwannoma of the trochlear nerve mimicking a brain-stem tumor. Case report. J Neurosurg 67: , ) Gentry LR, Mehta RC, Appen RE, Weinstein JM: MR imaging of primary trochlear nerve neoplasms. AJNR Am J Neuroradiol 12: , ) Hakuba A, Nishimura S, Jang BJ: A combined retroauricular and preauricular transpetrosal approach to clivus meningiomas. Surg Neurol 30: , ) Ho KL: Schwannoma of the trochlear nerve. Case report. Neurosurgery 55: , ) Jackowski A, Weiner G, O'Reilly G: Trochlear nerve schwannomas: a case report and literature review. Br JNeurosurg8: , ) King JS: Trochlear nerve sheath tumor. Case report. J Neurosurg 44: , ) Lanotte M, Giordana MT, Forni C, Pagni CA: Schwannoma of the cavernous sinus. Case report and review of the literature. J Neurosurg Sci 36: , ) Leunda G, Vaquero J, Cavezudo J, Gacia-Uria J, Bravo G: Schwannomas of the oculomotor nerve. Reports of four cases. J Neurosurg 57: , ) Mauice-Williams RS: Isolated schwannoma of the fourth cranial nerve. J Neurol Neurosurg Psychiatry 52: , ) Nadkarni TD, Goel A: Trochlear nerve neurinoma presenting as pathological laughter. Br J Neurosurg 13: , ) Santoreneos S, Hanieh A, Jorgensen RE: Trochlear nerve schwannomas occurring in patients without neurofibromatosis: case report and review of the literature. Neurosurgery 41: , ) Sekhar LN: Comments to Santoreneos S, et al. Neurosurgery 41: 287, ) Tokuriki Y, Yamashita J, Kikuchi H, Asato R, Handa H: Trochlear nerve neurinoma. Case report. Neurol Med Chir (Tokyo) 28: 70 73, ) Yamamoto M, Jimbo M, Ide M, Kubo O: Trochlear neurinoma. Surg Neurol 28: , 1987 Address reprint requests to: T.Matsui,M.D.,Department of Neurosurgery, Saitama Medical Center/School, 1981 Kamoda, Kawagoe, Saitama , Japan. matsui@ns2.saitama-med.ac.jp. Neurol Med Chir (Tokyo) 42, January, 2002