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Differential Diagnosis and Surgical Management of Cerebellopontine Angle Cystic Lesions Tobias Alécio Mattei, M.D.1 Carlos R. Goulart, B.S2 Julia Schemes de Lima, B.S.3 Ricardo Ramina, M.D, PhD.4

SUMÁRIO ABSTRACT

A maioria dos tumores de ângulo ponto-cerebelar em adultos Cerebellopontine angle (CPA) tumors in adults are mainly são benignos e extra-axiais. A lesão mais comum do ângulo benign and extra-axial. Although the most common CPA lesion ponto-cerebelar ( vestibular) é familiar à maioria (vestibular schwannoma) is familiar to most neurosurgeons, dos neurocirurgiões. Entretanto lesões císticas do ângulo cystic lesions of the CPA do pose an important diagnostic ponto-cerebelar merecem uma análise cuidadosa, levando-se challenge demanding a careful consideration of a wide em consideração uma ampla gama de diagnósticos diferenciais, range of differential diagnosis including: epidermoid cysts, dentre os quais: cistos epidermóides, cistos aracnóides, arachnoid cysts, cystic , cystic neurinomas císticos, meningiomas císticos, bem como outras as well as other rare entities such as vascular and malignant entidades mais raras como lesões vasculares e tumorais tumoral lesions. The authors present a critical review of malignas. Os autores apresentam uma revisão critica da the current literature on cystic CPA lesions, providing an literatura, proporcionando ao leitor uma visão geral sobre os overview about possible differentials as well as guidelines for possíveis diagnósticos diferenciais bem como atuais diretrizes preoperative imaging evaluation of a cystic CPA lesion. para a avaliação imagenológica de lesões císticas no ângulo Keywords: Cerebello-pontine angle, epidermoid cysts, ponto-cerebelar. arachnoid cysts, cystic schwannomas, cystic meningiomas, diferencial diagnosis, surgical management. Palavras-chave: ângulo ponto-cerebelar, cisto epidermóide, cisto aracnóide, neurinoma do acústico, schwannoma vestibular, diagnóstico diferencial, tratamento cirúrgico.

1. Neurosurgery Department – ‘University of Illinois at Peoria’ – IL/USA 2. President of League of Neurosurgery of “Instituto de Neurologia de Curitiba” – Brazil 3. Medical Illustrator - League of Neurosurgery “Instituto de Neurologia de Curitiba” – Brazil 4. Chief of Neurosurgery Department of “Instituto de Neurologia de Curitiba” – Brazil

Recebido em 1º de junho de 2011, aceito em 29 de julho de 2011 Mattei TA, Goulart CR, Lima JS, Ramina R - Differential Diagnosis and Surgical Management of Cerebellopontine Angle Cystic Lesions J Bras Neurocirurg 22 (3): 66-71, 2011 67

Revisão

However, the most striking characteristic, which is very sug- Introduction gestive of epidermoid tumors, is the marked restriction (pre- senting a bright appearance) at Diffusion-weighted imaging Cerebellopontine angle tumors in adults are mainly benign (DWI). The apparent diffusion coefficient (ADC) values of and extra-axial. Cystic lesions of the CPA often pose as an im- epidermoid tumors are significantly lower than that of CSF, portant challenge to neurosurgeons, demanding a careful pre- and higher than that of deep .9 There are, however operative evaluation about a wide range of possible differential reports of unusual image findings in epidermoid tumors such diagnosis, as well as a tailored surgical technique according to as hyperdensity in computed tomography (CT) and on T1- and each particular lesion. T2-weighted MRI. These late imaging characteristics are thou- The possible histopathological diagnosis for a cystic lesion in ght to be caused by a high protein concentration within the the CPA is, in order of frequency: epidermoid cyst, arachnoid content of the cyst.26 cyst, cystic schwannoma, cystic and other rare en- tities, described in few case reports, such as neurocysticercosis, neurenteric cyst, cavernous malformations as well as malig- nant tumoral lesions, which may present as cystic heteroge- neous masses due to intra-tumoral necrosis.

Epidermoid Cysts

Typically epidermoid cists are extra-axial lesions with the ima- ging signal similar to the . These tumors usually show ondulating margins, modeling their shape to ma- tch with the CPA and insinuating themselves around the ner- ves and blood vessels in the CPA. A lamellated or onion-skin appearance and small peripheral rim of calcification may be seen in few cases.11 Magnetic resonance imaging (MRI) usually show no enhance- ment with gadolinium: they are of hipo or iso-intense sign in T1 weighted (T1W) images with iso or high signal intensity on T2W images and FLAIR (Fig. 1).33,34

Figure 1. In epidermoid cysts, although MRI sequences may demonstrate an ex- Figure 2. Surgical illustration of a right retrosigmoid approach and intraoperati- pansive lesion with compression of the cerebellar parenchyma (Patient 1 -A, B and ve images demonstrating surgical ressection of a cystic lesion of the CPA . Note C), the lesion usually spread diffusely through the cisternal spaces. (Patient 2 - D, E and F). These lesions usually are non-enhancing (A and B) and present hype or the white (pearl-like) and non-vascular appearance of the lesion, typical of epider- isointense signal in T2 (C) and FLAIR (D) and a typical pattern of marked restriction moidcysts. (Cr: cranial; Ca: Caudal; Lat: lateral; Med: medial). in diffusion-weighted sequences (E) with typical low apparent diffusion coefficient (ADC) values (F).

Mattei TA, Goulart CR, Lima JS, Ramina R - Differential Diagnosis and Surgical Management of Cerebellopontine Angle Cystic Lesions J Bras Neurocirurg 22 (3): 66-71, 2011 68

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Surgery is the only definitive treatment for epidermoid cysts. Hemosiderin deposits and hemosiderin-containing phagocytes However, the decision to operate should be carefully discussed are also found near these vessels. Myxoid degeneration and ne- for each patient, particularly if the patient is asymptomatic.31 crosis are evident in vast areas. In fact, such degenerative chan- The extent of the lesion at the anterior aspect of the , ges appear to be the main cause of formation of the large cysts. and sometimes above the tentorium, the fragile cortex and ves- As some series suggest, the surgical outcome of cystic vestibu- sels, and the hazards of postoperative chemical meningitis often lar schwannomas tends to be poorer compared with non-cystic make such surgery more challenging. Therefore, in many cases, vestibular schwannomas of matching size.6,20 There is also evi- radical total resection should not be attempted, because the cyst dence that schwannomas may suffer cystic enlargement after membrane may be very adherent to local structures such as cra- undergoing radiosurgery, specially in already large tumors.14 nial nerves and surrounding skull base vessels (Fig. 2). In cystic tumors, rapid clinical worsening is common due to sudden expansion of cystic elements. Tighter adherences are found between cystic tumors and surrounding nervous ele- Cystic Schwannomas ments (particularly brainstem and possibly ) when compared to solid lesions. Therefore, a ‘wait-and-see policy’ is usually not recommended to patients with cystic vestibular Cystic schwannomas are usually larger and present a shorter schwannomas. In relation to the surgical technique, careful time to diagnosis as well as when compared with solid schwan- sharp dissection to divide the tumor adherences from the ner- nomas. CT scan usually shows a thin rim-enhancement of the vous tissue must be employed. However, severe complications cyst wall. Cystic schwannomas tend to have a funnel-shaped may be caused by excessive efforts to dissect the tumor from appearance in the axial MRI and short-club-shaped configu- brainstem adherences.4 ration on the coronal images.22 There is strong homogeneous contrast enhancement of the solid components in approximate- ly half of the tumors.16,18 Cystic schwannomas can be classified into three groups: type A - large single cysts with a thin tumor Arachnoid Cysts wall (the most common presentation); type B - single cysts with a thick tumor wall; type C – multi-cystic tumors (Fig. 3).17 Although CPA arachnoid cysts represent a small number of to- tal arachnoid cysts, the CPA is the second most common loca- tion for arachnoid cysts to occur, secondary only to the sylvian fissure. These congenital lesions are usually found in children who are either asymptomatic or present with subtle signs or symptoms related to compression of adjacent cerebral and neu- rovascular structures.34

Arachnoid cysts are smoothly marginated, presenting CSF- like signal intensity in all MRI imaging sequences and do not enhance after contrast administration (Fig. 4). Arachnoid cysts may be much similar to epidermoid cysts in their radiological features, especially in the CPA.10 It is essential, therefore, to di- fferentiate the two lesions because they may warrant different therapeutic interventions. Both lesions are characteristically well-demarcated and have a homogeneous low-density, simi- lar to cerebrospinal fluid on CT scan, presenting no contrast Figure 3. MRI sequences and 3D-reconstruction of a large (3,6 x 2,0 x 2,3 cm) enhancement. On MRI, both epidermoids and arachnoid cysts multi-cystic CPA lesion. The pathological specimen confirmed a vestibular schwan- appear hypointense on T1-weighted images and hyperintense noma with areas of cystic degeneration and necrosis. on T2-weighted images. On FLAIR, however, an arachnoid cyst tends to follow the cerebrospinal fluid intensity, whereas The cystic components of vestibular schwannomas are well- an epidermoid tumor becomes strongly hyperintense. Howe- correlated with their histological features. Histopathological ver, a few times, an epidermoid may appear as a low-intensity analysis of the cyst wall reveals the presence of numerous ab- lesion on FLAIR. This dilemma is solved with the use of echo normal sinusoid and telangiectasia-like vessels, which may planar diffusion scanning, in which an epidermoid cyst remains occasionally reveal signs of thrombosis.25 The vessel walls bright, while arachnoid cyst not.12 display endothelial proliferation and are frequently hyalinized.

Mattei TA, Goulart CR, Lima JS, Ramina R - Differential Diagnosis and Surgical Management of Cerebellopontine Angle Cystic Lesions J Bras Neurocirurg 22 (3): 66-71, 2011 69

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of CPA lesions. However, cystic meningiomas in the CPA are much rarer. These tumors usually appear oval or hemispheric, with broad dural-based attachments to the tentorium or petrous bone dura. Commonly there is a solid component, which de- monstrates marked contrast- enhancement.12 Usually no ex- tension into the internal auditory canal is noted.15 The surgical resection of such tumors is in general easier when compared to vestibular schwannomas (unless there is a presence of hard component) and nerve function preservation rates tends to be higher.

Meningiomas of the CPA rarely extend into the internal audi- tory canal (IAC) or arise from its dural lining (approximately 1.7% of all CPA meningiomas and almost all of them non-cys- tic).30 The clinical symptoms of intracanalicular meningiomas are very similar to those of vestibular schwannomas. Most of the patients reported in the literature, at the time of diagnosis present with disturbances, such as he- aring loss, tinnitus, disequilibrium and , or facial nerve paralysis.8 These CPA meningiomas involving the IAC require special surgical management. In most of the patients whose Figure 4. MRI sequences demonstrating a large (5,5 x 4,5 x 4,0) cystic CPA le- tumor arises from the dura within the IAC, facial and cochlear sion without extension in the internal acoustic canal. The lesion does not present nerve preservation is much more difficult to be achieved, be- 16 contrast-enhancement nor displaces the VII/VIII nerves, a common finding of ara- cause of the infiltrative behavior of such lesions. chnoid cysts. Not all arachnoid cysts require surgical intervention.29 Patients with asymptomatic cysts should be followed clinically and radiologically with sequential MRI. Indications for operative Rare Lesions management include lesions that demonstrate growth, neural compression, hydrocephalus or refractory symptoms that may Neurocysticercosis be related to cysts in this location, such as auditory loss or ce- rebellar signs.2 Although the brain parenchyma is regarded as the most usual site of involvement of neurocysticercosis, certain reports claim The definitive treatment for arachnoid cysts still remains cra- that subarachnoid space is main location for such lesions. If niotomy and microsurgical resection or fenestration of the cyst the larvae lodge in the meningeal layers, the infestation may walls, usually through a retrosigmoid suboccipital approach.28 involve the subarachnoid space.5 Such subarachnoid cysts may More recently, some authors have endoscopic cisternostomy become multi-loculated, resembling a “cluster of grapes”. This through a single key-hole, as a minimally invasive approach.21 is usually referred as the ‘racemose’ form of neurocysticerco- sis. Within the subarachnoid space, the CPA and suprasellar An alternative would be the insertion of a cyst-peritoneal cisterns are the most common locations.38 On MRI, these le- shunt, but the high incidence of shunt malfunction demanding sions show the same signal intensity as the CSF on all pulse a second shunt review operation and the relatively good results sequences, with no post-contrast enhancement. using the marsupialization, make it second-line modality of treatment for arachnoid cysts, especially in the CPA.21 The diffuse infestation observed in some racemose forms can sometimes be difficult to be distinguished from the surroun- ding CSF space. The clue to the presence of such lesions is the focal widening of the CSF space or secondary inflammatory Cystic Meningiomas response in the adjacent parenchyma. Infestation of the suba- rachnoid space may also result in communicating hydrocepha- lus due to chronic meningitis. Additionally MRI may show Meningiomas are the second most common tumors of the CPA enhancement of the subarachnoid cisterns due to inflammatory after vestibular schwannomas, comprising 6 to 15% of cases response.

Mattei TA, Goulart CR, Lima JS, Ramina R - Differential Diagnosis and Surgical Management of Cerebellopontine Angle Cystic Lesions J Bras Neurocirurg 22 (3): 66-71, 2011 70

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It is important to identify cysticercotic cysts and to differentiate them from other tumoral types of CPA cystic lesion35, because Conclusions the best therapeutic option for most of the patients still remains the pharmacological treatment against the larvae. In most of Although cystic schwannomas are still the most common cys- the cases, especially in subarachnoid infestation, supplemen- tic lesions of the CPA, a careful preoperative analysis is recom- tary steroids are recommended to avoid an abrupt immune mended, when evaluating a cystic lesion in the CPA. The wide response. In selected cases, if there is evidence of CSF flow range of possible differential diagnosis includes: epidermoid obstruction, surgical removal of the cyst may be indicated. cyst, arachnoid cyst, cystic meningioma as well as other rare entities such as neurocysticercosis, neurenteric cysts, and vas- Neuroenteric Cysts cular and malignant cystic tumors. Neurenteric or enterogenous cysts are lesions lined with mu- Surgical management is the mainstay treatment for the majori- cin-secreting and/or ciliated, cuboidal or columnar epithelium, ty of such lesions, with the theoretical advantage of providing resembling that found in the respiratory and intestinal tract. histological sample for confirmation of suspected diagnosis. They result from the inappropriate partitioning of the embryo- As we have previously discussed elsewhere, although the clas- nic notochordal plate and presumptive endoderm during the sic retrosigmoid route remains the standard surgical approach third week of human development. These lesion have been to CPA lesions, the surgical technique should be tailored to described with several different terms, including endodermal, each specific case according to particularities of patient’s ana- foregut, epithelial, bronchogenic, and respiratory cysts.7 Most tomy as well as lesion appearance and nature.23 commonly, they are encountered as an intradural extramedulla- ry cyst, especially in the lower cervical and upper thoracic re- gions and are usually associated with dysraphism. References Neurenteric cysts arising intracranially are rare and to date only 53 cases have been described in the literature, 92% of which were located in the posterior fossa, most of them as solitary 1. Akaishi K, Hongo K, Ito M, Tanaka Y, Tada T, Kobayashi S. lesions. These cysts tend to present a slight male predominance Endodermal cyst in the cerebellopontine angle with immuno- histochemical reactivity for CA19-9. Clin Neuropathol 2000; (60% of the cases) as well as a wide range of age of presenta- 19(6):296-9. tion - from birth to 77 years (mean 34 years).3 Clinical symp- toms are usually non-specific and result from inflammatory 2. Becker T, Wagner M, Hofmann E, Warmuth-Metz M, Nadjmi response or local mass effect. The most frequent symptoms are M. Do arachnoid cysts grow? A retrospective volumetric study. headache and gait disturbances. Our literature search yielded Neuroradiology 1991; 33(4):341-5. only 15 cases of neurenteric cysts located in the CPA.1 Similar 3. Bejjani GK, Wright DC, Schessel D, Sekhar LN. Endodermal to other lesions at this location, the reported neurenteric cysts cysts of the posterior fossa: report of three cases and review of may also present clinically involving cranial nerve deficits. literature. J Neurosurg 1998; 89(2):326-35. 4. Benech F, Perez R, Fontanella MM, Morra B, Albera R, Ducati Surgical resection is the most indicated therapy for most of A. Cystic versus solid vestibular schwannomas: a series of 80 the lesions. Intra-operatively these tumors are usually found to grade III-IV patients. Neurosurg Rev. 2005; 28(3):209-13. have a dark-red appearance, containing muddy gelatinous fluid 5. Celis MA, Mourier KL, Polivka M, Boissonnet H, Kato T, Lot in its multi-cystic compartments. The surrounding dura may be 19 G, George B, et al. Cisternal cysticercosis of the cerebellopon- thick and yellowish because of reactive hypervascularization. tine angle. Neurochirurgie 1992; 38(2):108-12. Although very rare in this location, this benign developmen- tal lesion should also be considered as a potential differential 6. Charabi S, Tos M, Børgesen SE, Thomsen J. Cystic acoustic neuromas. Results of translabyrinthine surgery. Arch Otolaryn- diagnosis for patients presenting with cystic lesions in the CPA. gol Head Neck Surg. 1994; 120(12):1333-8. Other lesions 7. Chaynes P, Bousquet P, Sol JC, Delisle MB, Richaud J, Lagarri- gue J. Recurrent intracranial neuroenteric cysts. Acta Neurochir There have been several isolated case reports of other cystic (Wien) 1998; 140(9):905-11. lesions in the CPA, such as: cavernous malformation37,39, Ec- cordosis physaliphora lesion41 (an uncommon benign lesion 8. Dazert S, Aletsee C, Brors D, Mlynski R, Sudhoff H, Hildmann originating from embryonic notochordal remnants), as well H, et al. Rare tumors of the internal auditory canal. Eur Arch Otorhinolaryngol 2005; 262(7):550-4. as other rare malignant tumors - such as anaplastic ganglio- glioma22, primary epidermoid carcinoma13, endolymphatic sac 9. Dechambre S, Duprez T, Lecouvet F, Raftopoulos C, Gosnard tumor27, primary atypical teratoid/rhabdoid tumor42. The cystic G. Diffusion-weighted MRI postoperative assessment of an epi- appearance of the malignant lesions is thought to be origina- dermoid tumour in the cerebellopontine angle. Neuroradiology 1999; 41(11):829-31. ted from intra-tumoral necrosis leading to cystic degeneration. For most of them, surgical treatment is still the first option of 10. Dutt SN, Mirza S, Chavda SV, Irving RM. Radiologic differen- treatment, having the advantage of also providing histological tiation of intracranial epidermoids from arachnoid cysts. Otol sample for analysis. Neurotol 2002; 23(1):84-92.

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11. Gao PY, Osborn AG, Smirniotopoulos JG, Harris CP. Radiolog- 28. Pradilla G, Jallo G.. Arachnoid cysts: case series and review of ic-pathologic correlation. Epidermoid tumor of the cerebello- the literature. Neurosurg Focus 2007; 22(2):E7. pontine angle. AJNR Am J Neuroradiol 1992; 13(3):863-72. 29. Punzo A, Conforti R, Martiniello D, Scuotto A, Bernini FP, Ci- 12. Hakyemez B, Yildiz H, Ergin N, Uysal S, Parlak M. Flair and offi FA. Surgical indications for intracranial arachnoid cysts. diffusion weighted MR imaging in differentiating epidermoid Neurochirurgia (Stuttg) 1992; 35(2):35-42. cysts from arachnoid cysts. Tani Girisim Radyol 2003; 9(4):418- 30. Roser F, Nakamura M, Dormiani M, Matthies C, Vorkapic P, 26. Samii M. Meningiomas of the cerebellopontine angle with 13. Ishikawa S, Yamazaki M, Nakamura A, Hanyu N. An autopsy extension into the internal auditory canal. J Neurosurg 2005; case of primary cerebellar-pontine angle epidermoid carcinoma. 102(1):17-23. Rinsho Shinkeigaku 2000; 40(3):243-8. 31. Safavi-Abbasi S, Di Rocco F, Bambakidis N, Talley MC, Ghar- 14. Iwai Y, Yamanaka K, Yamagata K, Yasui T. Surgery after radio- abaghi A, Luedemann W, et al. Has management of epidermoid surgery for acoustic neuromas: surgical strategy and histological tumors of the cerebellopontine angle improved? A surgical syn- findings. Neurosurgery 2007; 60(2 Suppl 1):ONS75-82; discus- opsis of the past and present. Skull Base 2008; 18(2):85-98. sion ONS82. 32. Sarrazin J, Hélie O, Cordoliani Y. Cerebellopontine angle tu- 15. Jallo GI, Woo HH, Meshki C, Epstein FJ, Wisoff JH. Arachnoid mors in adults. J Radiol. 2000; 81(6 Suppl):675-90. cysts of the cerebellopontine angle: diagnosis and surgery. Neu- 33. Savader SJ, Murtagh FR, Savader BL, Martinez CR. Magnetic rosurgery 1997; 40(1):31-7; discussion 37-8. resonance imaging of the intracranial epidermoid tumors. Clin 16. Jeng CM, Huang JS, Lee WY, Wang YC, Kung CH, Lau MK. Radiol 1989; 40(3):282-5. Magnetic resonance imaging of acoustic schwannomas. J For- 34. Shenouda EF, Moss TH, Coakham HB. Cryptic cerebellopon- mos Med Assoc 1995; 94(8):487-93. tine angle neuroglial cyst presenting with hemifacial spasm. 17. Kameyama S, Tanaka R, Kawaguchi T, Fukuda M, Oyanagi K. Acta Neurochir (Wien) 2005; 147(7):787-9; discussion 789. Cystic acoustic neurinomas: studies of 14 cases. Acta Neurochir 35. Singh S GS, Bannur U, Chacko G, Korah IP, Rajshekhar V. Cys- (Wien) 1996; 138(6):695-9. ticercosis of the cerebellopontine angle cistern mimicking epi- dermoid inclusion cyst. Acta Neurol Scand 1999; 99(4):260-3. 18. Kawamura Y, Sze G. Totally cystic schwannoma of tenth cranial nerve mimicking an epidermoid. AJNR Am J Neuroradiol 1992; 36. Steffey DJ, De Filipp GJ, Spera T, Gabrielsen TO. MR imaging 13(5):1333-4. of primary epidermoid tumors. J Comput Assist Tomogr. 1988; 12(3):438-40. 19. Kumar R, Nayak SR. Unusual neuroenteric cysts: diagnosis and management. Pediatr Neurosurg 2002; 37(6):321-30. 37. Stevenson CB, Johnson MD, Thompson RC. Cystic cavernous malformation of the cerebellopontine angle. Case illustration. J 20. Kwon Y, Khang SK, Kim CJ, Lee DJ, Lee JK, Kwun BD. Ra- Neurosurg. 2005; 103(5):931. diologic and hispopathologic changes after gamma knife radio- surgery for acoustic schwannoma. Stereotact Funct Neurosurg 38. Takayanagui OM, Odashima NS. Clinical aspects of neurocysti- 1999; 72 Suppl 1:2-10. cercosis. Parasitol. Int 2006; 55(suppl):111-115. 21. Marin-Sanabria EA, Yamamoto H, Nagashima T, Kohmura E. 39. Vajramani GV, Devi BI, Hegde T, Srikanth SG, Shankar SK. Evaluation of the management of arachnoid cyst of the posterior Cystic cavernous malformation of the cerebellopontine angle. fossa in pediatric population: experience over 27 years. Childs Clin Neurol Neurosurg. 1998; 100(2):133-7. Nerv Syst. 2007; 23(5): 535-42. 40. Vinchon M, Pertuzon B, Lejeune JP, Assaker R, Pruvo JP, Chris- 22. Matsuzaki K, Uno M, Kageji T, Hirose T, Nagahiro S. Anaplas- tiaens JL. Intradural epidermoid cysts of the cerebellopontine tic ganglioglioma of the cerebellopontine angle. Case report. angle: diagnosis and surgery. Neurosurgery 1995; 36(1):52-6; Neurol Med Chir (Tokyo) 2005; 45(11):591-5. discussion 56-7. 23. Mattei TA, Ramina R. Critical remarks on the proposed “extend- 41. Watanabe A, Yanagita M, Ishii R, Shirabe T. Magnetic reso- ed retrosigmoid approach”. Neurosurg Rev. 2011; 34(4):527-30. nance imaging of ecchordosis physaliphora--case report. Neurol Med Chir (Tokyo) 1994; 34(7):448-50. 24. Miyagi A, Maeda K, Sugawara T. Large cystic neurinoma: a case report. No Shinkei Geka 1997; 25(7):647-54. 42. Weyers SP, Khademian ZP, Biegel JA, Chuang SH, Korones DN, Zimmerman RA. Primary intracranial atypical teratoid/rhabdoid 25. Nakamura M, Roser F, Mirzai S, Matthies C, Vorkapic P, Samii tumors of infancy and childhood: MRI features and patient out- M. Meningiomas of the internal auditory canal. Neurosurgery comes. AJNR Am J Neuroradiol 2006; 27(5):962-71. 2004; 55(1):119-27; discussion 127-8. 26. Ochi M, Hayashi K, Hayashi T, Morikawa M, Ogino A, Hash- mi R, et al. Unusual CT and MR appearance of an epidermoid tumor of the cerebellopontine angle. AJNR Am J Neuroradiol Corresponding Author 1998; 19(6):1113-5. 27. Ouallet JC, Marsot-Dupuch K, Van Effenterre R, Kujas M, Tu- Tobias Alecio Mattei, M.D – 828 biana JM. Papillary adenoma of endolymphatic sac origin: a Northeast Glen Oak Ave ap. 304 temporal bone tumor in von Hippel-Lindau disease. Case report. ZIP 61603-3285Peoria/IL J Neurosurg 1997; 87(3):445-9. e-mail: [email protected]

Mattei TA, Goulart CR, Lima JS, Ramina R - Differential Diagnosis and Surgical Management of Cerebellopontine Angle Cystic Lesions J Bras Neurocirurg 22 (3): 66-71, 2011