Neurosurg. R e v .
N o n - a c o u s t i c tumors o f the cerebellopontine angle
15 (1992) 117-123
Ismail H. Tekk6k, Tuncer Siizer, and Aykut Erbengi Dept. of Neurosurgery, Hacettepe University School of Medicine, Ankara, Turkey
Abstract
2 Materials and methods
52 patients with non-acoustic neurinoma tumors of the cerebellopontine angle undergoing surgery over a 16 year period (1974-1989) are analyzed with regard to epidemiologic factors, presenting symptoms, neurological findings, diagnostic procedures, surgical approaches, recurrences, and longterm survival rates. Meningiomas (20 cases) and epiderrnoid tumors (16 cases) outnumber the rare tumors which exhibit wide histological variation. Trigeminal neuralgia was found as a significantly frequent sign of epidermoids. Total removal was possible in nine meningiomas (45 %), fourteen epidermoid tumors (87.5%) and 11 (69%) mostly malignant rare tumors. There were many longterm survivors in meningioma and epidermoid groups with a median follow-up period of 4.1 years. The results are compared to those reported in the literature and a brief review of reported rare tumors of the angle is presented.
From January 1974 to December 1989, 193 patients underwent surgery for CPA pathologies at Hacettepe University Hospital, Department of Neurosurgery. 52 of these patients (26.9%) had tumors other than acoustic neurinoma. Half of these non-acoustic tumor patients (n = 26) were operated during the last four years. The histories, x-rays, audiovestibutar test results, operation notes, and when necessary histo-pathological slides were reviewed. All histopathological studies were carried out at the Pathology Department of Hacettepe University School of Medicine. In a few cases follow-up was obtained by correspondence.
Keywords: Brain tumor, cerebellopontine angle, CT, epi-
Twenty eight of the 52 cases were female. The youngest patient was 14 and the oldest 65. There was a definite female bias among the 20 patients with meningiomas (70%). The female : ratio was 1 : 1 for epidermoid tumor cases (Table I).
dermoid, malignant teratoma, meningioma.
1 Introduction 8-:10% of all intracranial tumors are located at the cerebellopontine angle (CPA) [6, 27, 28]. While the most common tumors of the CPA are acoustic neurinomas ( 7 9 - 9 1 % ) [9, 12, 16, 24, 27], nonacoustic neurinoma tumors (NANT), especially meningiomas and epidermoids also occur at reported rates of 3 . 6 - 1 4 . 5 % and 1 . 2 - 8 . 3 % , respectively [12, 13, 16, 24]. In addition to these, rare tumors of a wide histological variety are also significant (6.9-14.5%) [9, 12, 24]. Although there have been reports of no operative mortality and 6 4 - 1 0 0 % [22, 27] total removal, CPA meningiomas still remain a challenge for both the neurosurgeon and the patient. Epidermoids present less risk. The purpose of this paper is to review 52 cases with N A N T of the CPA operated on at our institution between 1974 and 1989 and to compare the results with that of update literature. 9 1992by Walter de Gruyter& Co. Berlin. New York
3 Results
Table I. Age and sex distribution
All (n =
Male/ Female
Mean age
14-65
24/28
39.5
21-61
6/14
47
2 0 - 63
8/8
39
52)
Meningioma (n =
Age range
20)
Epidermoid (n = 16)
3.1 Symptoms and signs Average elapsed time between the onset of symptoms and the diagnosis was 3.2 years for meningiomas and 3.4 years for epidermoid tumors.
118
Tekk6k et al., Non-acoustic tumors of the cerebellopontine angle
Table H. Presenting symptoms Meningioma Epidermoid n=20 n=16 % Headache Hearing loss Unsteady gait Dizziness Nausea & vomiting Numbness on one side of the face Tinnitus Double vision Facial pain Facial twitching Facial weakness Hoarseness Difficulty in swallowing Weakness on one side Speech difficulty
%
11 10 9 8 5 3
55 50 45 40 25 15
7 4 4 2 2 5
44 25 25 12.5 12.5 31
3 1 1 1
15 5 5 5
12.5
1 1
5 5
2 -8 -1 1 2
1 1
5 5
1 1
-
The various neurological signs observed are summarized in table III. Two-thirds o f patients with m e n i n g i o m a were ataxic, but only one-third o f epidermoid t u m o r patients showed this symptoms. Of m e n i n g i o m a patients, ten (50%) h a d hearing loss and eight (40%) had mild facial weakness, whereas involvement o f trigeminal nerve occurred in seven (35%) cases. Ten patients with epidermoids (63%) showed Vth nerve involvement either as trigeminal neuralgia or facial hypoesthesia. F a cial nerve involvement was observed in eight (50%) a n d hearing loss in five (31%).
50
6 6 12.5 6 6
Papilledema was present in a p p r o x i m a t e l y 30% o f each group.
Table IIL Neurological findings Meningioma Epidermoid n = 20 n = 16 % Ataxia Nystagmus VlIIth nerve VIIth nerve Vth nerve Papilledema IX-- Xth nerves I X - X - X I - X I I t h nerves VIth nerve Pyramidal tract signs
13. 12 10 8 7 6 2 1 1 1
Presenting s y m p t o m s are given in table II. H e a d ache was present in a p p r o x i m a t e l y half o f the patients in the m e n i n g i o m a and epidermoid subgroups. H e a r i n g loss was present in 50% of m e n i n g i o m a patients but only 25% o f the epiderm o i d t u m o r patients. Dysequilibrium was a m o r e p r o m i n e n t feature in m e n i n g i o m a patients. Facial p a i n and numbness were most c o m m o n in patients with epidermoids.
65
60 50 40 35 30 10 5 5 5
3.2 Diagnostic studies
All patients h a d routine plain skull X-rays. Only in one patient with a calcifying m e n i n g i o m a with extracranial extension, did plain X-rays prove helpful. Diagnostic procedures are t a b u l a t e d in table IV. In nine patients presenting before the installation o f CT at our institution in late 1975, the diagnosis was reached by techniques like ventriculography, C P A myelography, and angiog r a p h y plus a n u m b e r o f combinations o f these. The remaining 43 patients h a d CT scans a n d 18 o f these additional angiograms. Two patients with hypodense C P A lesions suggesting either an epi-
% 6 7 5 8 10 5 1 1 4
37.5 44 31 50 63 31 6 5 25
Table IV. Diagnostic procedures Meningioma n = 20 Angiography alone Angio + ventriculography Angio + CPA myelography CT alone CT § angiography CT + cisternography Audiovestibular tests (A/T) Radionuclide scintigraphy (A/T)
Epidermoid n = 16
1
2 10 6
3
1
6 7
1 9 5
-
-
2
10/12
7/12
4/4
Miscellaneous n = 16
-
4/6 1/1
CT = computerized tomography, A/T = abnormal to total ratio Neurosurg. Rev. 15 (1992)
Tekk6k et al., Non-acoustic tumors of the cerebellopontine angle dermoid or an arachnoid cyst on plain CT scans had iohexol cisternography to delineate the t u m o r borders, and hence differential diagnosis. O n CT, tumors originating from vessels (angioblastoma or vascular h a m a r t o m a ) or rich in vessels (choroid plexus papilloma) as well as meningiomas appeared hyperdense showing marked contrast enhancement. All epidermoids appeared as irregular n o n - e n h a n c i n g hypodense masses. Two of these also had an extension to the middle fossa. N o patient in this series was examined by magnetic resonance (MR), since it became operational in A n k a r a in December 1990. Of the m e n i n g i o m a cases undergoing angiography (n = 10), 60% showed t u m o r blush. The angiograms showed displacement of major arteries in all but one. Only three epidermoid t u m o r patients showed basilar artery shifts.
119
Thirty patients had audiovestibular tests. These proved especially useful in meningiomas (abnormal to total ratio = 82.5%). F o u r patients with meningiomas had had a radionuclide scintigraphy and all showed pathological radioactivity in the CPA. Brain stem auditory evoked responses were studied in last four patients (2 meningioma, 2 epidermoid), all of w h o m showed lengthened, a b n o r m a l responses. 3.3 Tumor location
Meningiomas usually occurred on left side (65%), and epidermoids on the right (62.5%). 3.4 Treatment and outcome
All patients were treated surgically. Total removal was possible in 9 (45%) of patients with m e n i n -
Table V.
% in CPA total (n = 193)
a - Meningiomas & epidermoids: Histopathological variation -
-
-
20 fibroblastic (f) meningothelial (n) mixed (f + m) angiomatous + m calcifying
Epidermoid tumor
10.4
6 6 5 2 1 16
8.3
b - Rare tumors: Histopathological variation, treatment and follow-up Age/sex
Main surgery
Araclanoid cyst 1
18/F
2
29/F
1
56/M
Drainage into the cisterns Drainage into the cisterns Total removal
Astroeytoma
2 Angioblastoma I 2 Arachnoiditis Cavernous hemangioma Ch. plex. papilloma Cyst hydatid Malignant melanoma Malignant teratoma Medulloblastoma Metastatic adenocarcinoma Mucoid carcinoma Vascular hamartoma
22/M 30/F 52/M 44/M 30/F 35/F
16IF 34/F 25/M 14/M 65/M 35/M 24/M
Subtotal removal Total removal Subtotal removal Biopsy Total removal Total removal Total removal Total removal Total removal Subtotal removal Subtotal removal Total removal Total removal
RT
Follow-up Alive 2 Y Alive 5 m
[surgical mortality] + --
+ -
+
-
+
+
+ + -
+
AT = radiotherapy, ChT = chemotherapy, Y = year(s), m = month(s) Neurosurg. Rev. 15 (1992)
ChT
+ -
Died at t.8 Y Alive 3.2 Y Died at 3.8 Y Lost after 1 Y Lost after 6 Y Died at 4 Y Died at 1.5 m Alive at 10 Y Died at 2.5 m Alive at 2.5 Y Lost after 3 m Died at 1 Y Alive at 7.5 Y
120
Tekk6k et al., Non-acoustic tumors of the cerebellopontine angle
giomas, in 14 (87.5%) of patients with epidermoid tumors, and 11 (69%) patients with rare tumors. Cerebellar resection was necessary in 6 meningioma, 2 epidermoid tumors, and 5 rare tumor patients. Histopathological variation of the tumors is given in table V.
Table VI. Reoperations for recurrences
Pathology
N
Interval
Surgical mortality
Meningioma Epidermoid Angioblastoma Astrocytoma Ch. plexus pap. Malignant teratoma
1 2 t t t t
2.2 Y 4 and 8 m 4Y 1.8 Y 4Y 2 all
+ + + -[-
Overall surgical mortality (patients undergoing operation and surviving less than a month) during the 16 year-period was 13.4% (7/52). Of four patients with subtotally removed meningioma expiring during the postoperative period, 2 had tumors with an angiomatous component and two had presented with hemiparesis. Surgical mortality of patients with total meningioma removal was 0%, and and of patients with subtotal removal 36% (overall for meningioma = 20%). Two of 16 patients with epidermoids died postoperatively (14%); both had been operated on before CT was available.
table VI. One patient with subtotally removed meningioma was found to have the tumor growing upwards through tentorial incisura; this was again subtotally removed. In two epidermoid patients, 10% of the tumor with its capsule being adherent to the brain stem had to be left during primary surgery; both recurred.
In the last four years (n = 26), we had no operative mortality.
The patients with recurrent malignant rare tumors died soon after their second operations.
3.5 Complications
3.7 Survival
One meningioma patient developed wound infection and subsequent osteomyelitis of the craniotomy flap which necessitated bone flap removal. A patient with epidermoid tumor developed aseptic meningitis which subsided with antibiotic and steroid cover. A patient with angioblastoma who had a persistent hydrocephalus needed a lumboperitoneal shunt 25 days postoperatively and another patient with meningioma received a V-P shunt a year later.
Sixteen meningioma patients were discharged. One died at home three months later. Thirteen (87.5%) were available for follow-up during a period ranging between 13 months and 16 years (median 4, average 4.1 years). Three died at home after 2, 5, and 14 years. The cause of death was not obtained.
As of operative complications related to cranial nerves, a total of 13 patients had postoperative facial paralysis but 7 recovered without further surgery by the end of first year, four patients needed tarsorrhaphy, and two accessory-facial nerve anastomosis. Permanent paralysis of VIIIth nerve occurred in only two patients with meningiomas and one with an epidermoid. The recurring meningioma patient with unilateral VIth nerve palsy underwent lateral rectus muscle recession performed by ophthalmologists. 3.6 Recurrences
Seven patients needed a second operation on their tumors. The histological types and the time intervals between two operations are summarized in
Y = year(s), m = months
All epidermoid tumor patients discharged (n = 14) were available for follow-up during a period between 8 months and 15.5 years (median 3, average 4.1 years), and all are alive. Follow-up for rare tumors of the angle is given in table V. 4 Discussion
Differential diagnosis of space-occupying lesions in CPA shows that acoustic neurinomas and meningiomas are of overwhelming majority. Other lesions found are epidermoid tumor, neurinomas of the cranial nerves V, VII, IX, X, XI, and other rare tumors such as arachnoid cysts [9, 12, 16, 24], aneurysm [9, 12, 27], astrocytoma [27], chondromyxoma [27], chondrosarcoma, chordoma [12, 24, 27], choroid plexus papilloma [12, 15], craniopharyngioma [2], cysticercosis [12], dermoid [27], ependymoma [9, 24], ependymoblastoma [24], glomus jugulare tumor [16, 27], granuloma (tuberculoma, gumma, fungus) [27], hemangioma, heNeurosurg. Rev. 15 (1992)
Tekk6k et al., Non-acoustic tumors of the cerebellopontine angle mangioblastoma [12], hemangiosarcoma [9], hydatid cyst [12], lipoma, lymphoma, medulloblastoma, osteoma, teratoma [28], reticulosarcoma [7, 24] and metastases.
4.1 Meningiomas 8-~L2% of all intracranial meningiomas are located within the posterior fossa [6, 20]. 42% of all posterior fossa meningiomas originate from the posterior surface of the petrous bone and 3 0 53% are in the CP angle [6]. Meningiomas of the angle can grow to a remarkable size without any clinical signs, thus prolonging the interval between tumoral transformation and the initial symptoms and hence the diagnosis. Time between the first symptoms and the diagnosis was 3 years for women and 7 years for men in YASARGIL'S series [27] which is in contrast to ours with 4 and 1 years, respectively. This interval has probably shortened with increased use of CT. There is a definite female preponderance, with most patients presenting in late fifth and sixth decade as also observed by others [6, 22]. We were able to find only one other report of a preponderance of lesions on the left side [13]. Meningiomas are known to cause hearing loss less often than acoustic neurinomas [13, 16, 24]. Symptoms involving the facial nerve start earlier in meningiomas than in acoustic tumors, while the VIIIth nerve is almost invariably involved earlier in acoustic neurinoma cases. The effect of meningiomas on facial and hearing functions is opposite to that of neurinomas. Amongst 20 meningioma patients in this series, only 1 had symptomatic trigeminal neuralgia. Lower cranial nerve involvement (5%) was less in our series than has been reported in the literature (15%) [13, 27]. On CT scans meningiomas appear to be well defined, usually enhancing hyperdense lesions which are based broadly on the petrous bone. They are not centered over the porus, and do not have a defined neck [13, 14, 27]. Lack of a widening of the internal acoustic canal and calcification with hyperosteosis of the bone are other differential hallmarks of CP angle meningiomas. Angiography is helpful not only for differentiating between a calcified aneurysm and other vascular tumors, but also for planning therapeutical strategies, including preoperative embolization [17]. One patient with an initial CT diagnosis of a meningioma was found to harbor an angioblastoma. Neurosurg. Rev. 15 (1992)
121
Several surgical approaches for CPA meningiomas are discussed in detail by YASARGIL [27] and SEKHAR [22]. Both discuss subtemporal, translabyrintine, and transmeatal retromastoid suboccipital approaches and both advocate the transmeatal approach as the most efficacious, citing many benefits as well as 0% mortality. All meningiomas in this series were operated similarly. Unfortunately, all 20 patients had meningiomas larger than 3 cm. This was most possibly due to educational level or the referral pattern. GIANNOTTA suggests translabyrintine removal as a serious alternative for the removal of meningiomas as big as 4 cm, but we find the sacrifice of hearing unnecessary since it may well be preserved by transmeatal approach [5]. One important point is that cerebellar resection must be avoided, since it increases perioperative morbidity and mortality. Laser and ultrasonic aspirator (CUSA) have been used at our institution since January, 1988, and have proven most useful for large meningiomas, which are alternately shrunk and aspirated several times. In this way cerebellar resection can be avoided even for huge tumors. We underline the fact that operative mortality decreases with total removal and that it is lower for meningiomas other than the angioblastic subtype. 4.2 Epidermoid tumors These arise from the displaced epithelial tissue during the closure of the neural tube between the 3rd and 5th weeks of gestation [3]. Epithelial remains are possibly carried into the angle with the developing otic vesicles. Epidermoids in general constitute 0 . 2 - 1 . 8 % of all intracranial tumors [3, 7] and occur almost equally in both sexes. The most frequent site is CPA and the parasellar region [7, 18, 25, 26]. These tumors grow slowly through gradual accumulation of normally dividing cells with a linear growth rate resembling the growth of human epidermis [3]. They spread along the cisterns and may extend into the middle fossa through tentorial incisura as occurred in our two patients with recurrences. Mean duration of symptoms in our series agreed with recent reviews discussing posterior fossa epidermoids in general (4.2-4.3 years) [3, 21]. Epidermoids cause a combination of cerebellopontine angle and jugular foramen syndromes, but, most notably, they cause trigeminal neuralgia and less commonly hemifacial spasm and glossopharyngeal neuralgia. According to JANETTAa tu-
122
Tekk6k et al., Non-acoustic tumors of the cerebellopontine angle
mor causing trigeminal pain does so by pushing the trigeminal nerve against the blood vessel [11]. The occurence of trigeminal pain in 50% of our cases is in accord with experience of BERGER [3], GUIDETTI [7], SABIN [21] and THOMSEN [24]. Pain subsided in all eight cases immediately after operation. As a rule epidermoids show distortion of adjacent vessels on angiograms, so that an avascular area can be outlined. CT almost always demonstrates a low attenuation due to saponification of keratinized debris [3] and occasional peripheral calcifications in a non-enhancing lesion. Enhancement of an epidermoid is very rare and may suggest a malignant epithelial component [4]. Hyperdense epidermoids do occur and may result in an erroneous preoperative diagnosis of meningioma, but this is exceptionally rare in the CPA [23] (4 reported cases). CT cisternography may be essential in lesions appearing as a low density equivalent to that of CSF, but without familiar irregular borders, in order to demonstrate the nature and extension of the lesion [8]. With increasing use of M R even this becomes unnecessary because signals from the CSF and epidermoid tumors differ on M R scans. In all but two patients a total excision was possible. It is obvious that in two patients having recurrences in less than a year, tumor regrowth originated from the part of the capsule not removed for fear of increasing neurological deficit. Why enormous recurrences occurred in such a short time is uncertain. According to Collins' rule the tumor should normally grow to its preoperative size in a period equal to patients age plus nine months. Extensive histopathological studies of the specimens from the second operations were carried out to rule out any carcinomatous degeneration and proved negative. The recurrence rate of 12.5 % is parallel to those found in the literature. We would like to stress the fact that all our epidermoid patients are now alive with tumor-free survivals up to 16 years. As for rare tumors of the angle, we would like to discuss only the ones of interest: Approximately 10% of all intracranial araehnoid cysts occur within the CPA. In a review of literature from 1831 through 1980, RENGACHARY and WATANAB~ were able to find 22 cases of CPA arachnoid cysts [19]. The cases reported here were successfully treated by partial excision of the cyst wall to allow free communication of the cyst with the subarachnoid cisterns.
Arachnoiditis, although very rare, may mimic an angle mass as suggested by ADELO~q~ [1]. Ethiopathogenesis is best explained by a previous ear disease or vascular bleeding subsequently leading to the formation of meningeal adhesions. Our only case presented before CT was available to us and was operated due to a filling defect on CPA myelogram. Cavernous hemangioma was described and discussed in detail in a previous paper as the first cystic cavernous hemangioma of the angle in the literature [10].
Choroid plexus papillomas usually occur during the first two decades and have a male preponderance. Our patient was female and 35 years of age. Although these papillomas are known to be insensitive to radiation therapy [15], total removal complemented with radiotherapy gave to our patient years of useful life before microscopic disease caused death. CPA is a very rare site for hydatid cyst, especially if it is primary. Our patient had had surgery for a cyst in the corpus callosum a year before she presented with dysphagia, dysphonia, and ataxia so that the cyst in the angle is more likely to have been due to previous spillage. This patient died at home 45 days later. Our malignant melanoma patient benefited from total excision followed by radio- and chemotherapy. She is alive after 10 years. The chemotherapy regimen consisted of D T I C and mCCNU, and the radiotherapy dose was 60 Gy. Our malignant teratoma patient was atypical. First, 50% of teratomas are detected in newborns, and he was 25; secondly, teratomas are most commonly found in midline locations and his tumor was exclusively in the CPA; and, finally, to our knowledge he is the first case of malignant teratoma tumor in the angle. In conclusion, although there are many surgeons who believe that preoperative differential diagnosis of CPA tumors is of no great practical value from a surgical standpoint, we think that CPA tumors can be histologically classified preoperatively when all the variables discussed in this paper are considered. This knowledge will then help us to define the therapeutical approach, to define the existing risks, and even to predict approximate life expectancy. Mortality and morbidity increases with the size of the tumor, but with modern neurosurgical tools the prospects of patients undergoing angle surgery seem very good. Neurosurg. Rev. 15 (1992)
Tekk6k et al., Non-acoustic tumors of the cerebellopontine angle
123
References [1] ADELOYEA, O OGAN,AA OLUMIDE:Arachnoiditis presenting as a cerebello-pontine angle tumour. J Laryngol Otol 92 (1978) 9 1 1 - 9 1 3 [2] ALTINORSN, E SENVELI,A ERDOGAN,N ARDA, I PAK: Craniopharyngioma of the cerebellopontine angle. Case report. J Neurosurg 60 (1984) 842844 [3] BERGERMS, CB WILSON; Epidermoid cysts of the posterior fossa. J Neurosurg 62 (1985) 214--219 [4] GARCIACA, PALMCGARRY,F RO3RIGUEZ:Primary intracranial squamous cell carcinoma of the cerebellopontine angle. J Neurosurg 54 (1981) 824-828 [5] GIONNOTTASL, JL PULEC, R GOODKIN: Translabyrintine removal of cerebellopontine angle meningiomas. Neurosurgery 17 (1985) 620-625 [6] GRANICKMS, RL MARTUZA,SW PARKER,RG OJEMANN, WW MONTGOMERY:Cerebellopontine angle meningiomas: clinical manifestations and diagnosis. Ann Otol Rhinol Laryngol 94 (1985) 2 3 - 3 8 [7] GUIDETTIB, FM GAGLIARDI:Epidermoid and dermoid cysts. Clinical evaluation and late surgical results. J Neurosurg 47 (1977) 12-18 [8] HIRATSUKAH, K OKADA,M MATSUNAGA,K TANAKA, N FUKAI, Y INABA:Diagnosis of epidermoid cysts by metrizamide CT cisternography. Neuroradiology 26 (1984) 153-155 [9] HITSELBERGERWE, G GARDNER:Other tumors of the cerebellopontine angle. Arch Otolaryngol 88 (1968) 164-166 [10] IPLIKCIOGLUAC, K BENLI, V BERTAN, S RUACAN: Cystic cavernous hemangioma of the cerebelloponfine angle: case report. Neurosurgery 19 (1986) 641 - 642. [11] JANETTAPJ: Treatment of trigeminal neuralgia by suboccipital and transtentorial cranial operations. Clin Neurosurg 24 (1977) 538-549 [12] KENDALL B, L SYMON: Investigation of patients presenting with cerebellopontine angle syndromes. Neuroradiology 13 (1977) 6 5 - 8 4 [13] LAIRD FJ, SG HARNER, E LAWS JR, DF REESE: Meningiomas of the cerebellopontine angle. Otolaryngol Head Neck Surg 93 (1985) 163-167 [14] M6LLER A, A HATAM,H OUVECRONA:The differential diagnosis of pontine angle meningioma and acoustic neuroma with computed tomography. Neuroradiology 17 (1978) 2 1 - 2 3 [15] NAGUIBMG, SN CHOU,A MASTRI:Radiation therapy of a choroid plexus papilloma of the cerebellopontine angle with bone involvement. J Neurosurg 54 (1981) 245-247
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[16] NE3ZELSKIJ, C TATOR:Other cerebellopontine angle (non-acoustic neuroma) tumors. J Otolaryngol 11 (1982) 248--252 [17] NUMAGUCHI5(, T KISHIKAWA,J IKEDA,Y TSUKAMOTO, M FUKUI, K KITAMURA,K MATSUURA:Angiographic diagnosis of acoustic neurinomas and meningiomas in the cerebellopontine angle - A reappraisal. Neuroradiology 19 (1980) 7 3 - 8 0 [18] OZGEN T, HK OGE, A ERBENGI,V BERTAN:Cranial dermoid and epidermoid cysts. Neurochirurgia 33 (1990) 16--19 [19] REN~ACHARYSS, I WATANABE:Ultrastructure and pathogenesis of intracranial arachnoid cysts. J Neuropathol Exp Neurol 40 (1981) 62--83 [20] RUSSELLJR, PC BucY: Meningiomas of the posterior fossa. Surg Gynecol Obstet 96 (1953) 183-192 [21] SABINHI, LT BORDI, L SYMON: Epidermoid cysts and cholesterol granulomas centered on the posterior fossa: twenty years of diagnosis and management. Neurosurgery 21 (1987) 7 9 8 - 805 [22] SEKHAR LN, PJ JANETTA: Cerebellopontine angle meningiomas. Microsurgical excision and followup results. J Neurosurg 60 (1984) 500--505 [23] TEKK6KIH, O CATALTEPE,S SAGLAM:Dense epidermoid cyst of the cerebellopontine angle. Case report. Neuroradiology 33 (1991) 255-257 [24] THOMSENJ: Cerebellopontine angle tumors, other than acoustic neuromas. A report on 34 cases. Acta Otolaryngol 82 (1976) 106-111 [25] YAMAKAWAK, N SHITARA, S GENKA, S MANAKA, K TAKAKURA:Clinical course and surgical prognosis of 33 cases of intracranial epidermoid tumors. Neurosurgery 24 (1989) 568-573 [26] YASARGILMG, CD ABERNATHEY,AC SARIOGLU: Microneurosurgical treatment of intracranial dermold and epidermoid tumors. Neurosurgery 24 (1989) 561 -- 567 [27] YASARGILMG, RW MORTAR& M Clmclc: Meningiomas of the basal posterior cranial fossa. In: KRAYENBUHL H (ed): Advances and Technical Standards in Neurosurgery, Vol 7, Springer-Verlag, Wien 1980 [28] ZLILCH KJ: Brain tumors. Their biology and pathology. Springer-Verlag, New York 1965, ed 2 Submitted June 6, 1990. Accepted September 27, 1990. Ismail H. Tekk6k, M.D. 2 nci Cadde No 1 - 6 Kivanc Apt Bahcelievler Ankara 06500 Turkey
N o n - a c o u s t i c tumors o f the cerebellopontine angle
15 (1992) 117-123
Ismail H. Tekk6k, Tuncer Siizer, and Aykut Erbengi Dept. of Neurosurgery, Hacettepe University School of Medicine, Ankara, Turkey
Abstract
2 Materials and methods
52 patients with non-acoustic neurinoma tumors of the cerebellopontine angle undergoing surgery over a 16 year period (1974-1989) are analyzed with regard to epidemiologic factors, presenting symptoms, neurological findings, diagnostic procedures, surgical approaches, recurrences, and longterm survival rates. Meningiomas (20 cases) and epiderrnoid tumors (16 cases) outnumber the rare tumors which exhibit wide histological variation. Trigeminal neuralgia was found as a significantly frequent sign of epidermoids. Total removal was possible in nine meningiomas (45 %), fourteen epidermoid tumors (87.5%) and 11 (69%) mostly malignant rare tumors. There were many longterm survivors in meningioma and epidermoid groups with a median follow-up period of 4.1 years. The results are compared to those reported in the literature and a brief review of reported rare tumors of the angle is presented.
From January 1974 to December 1989, 193 patients underwent surgery for CPA pathologies at Hacettepe University Hospital, Department of Neurosurgery. 52 of these patients (26.9%) had tumors other than acoustic neurinoma. Half of these non-acoustic tumor patients (n = 26) were operated during the last four years. The histories, x-rays, audiovestibutar test results, operation notes, and when necessary histo-pathological slides were reviewed. All histopathological studies were carried out at the Pathology Department of Hacettepe University School of Medicine. In a few cases follow-up was obtained by correspondence.
Keywords: Brain tumor, cerebellopontine angle, CT, epi-
Twenty eight of the 52 cases were female. The youngest patient was 14 and the oldest 65. There was a definite female bias among the 20 patients with meningiomas (70%). The female : ratio was 1 : 1 for epidermoid tumor cases (Table I).
dermoid, malignant teratoma, meningioma.
1 Introduction 8-:10% of all intracranial tumors are located at the cerebellopontine angle (CPA) [6, 27, 28]. While the most common tumors of the CPA are acoustic neurinomas ( 7 9 - 9 1 % ) [9, 12, 16, 24, 27], nonacoustic neurinoma tumors (NANT), especially meningiomas and epidermoids also occur at reported rates of 3 . 6 - 1 4 . 5 % and 1 . 2 - 8 . 3 % , respectively [12, 13, 16, 24]. In addition to these, rare tumors of a wide histological variety are also significant (6.9-14.5%) [9, 12, 24]. Although there have been reports of no operative mortality and 6 4 - 1 0 0 % [22, 27] total removal, CPA meningiomas still remain a challenge for both the neurosurgeon and the patient. Epidermoids present less risk. The purpose of this paper is to review 52 cases with N A N T of the CPA operated on at our institution between 1974 and 1989 and to compare the results with that of update literature. 9 1992by Walter de Gruyter& Co. Berlin. New York
3 Results
Table I. Age and sex distribution
All (n =
Male/ Female
Mean age
14-65
24/28
39.5
21-61
6/14
47
2 0 - 63
8/8
39
52)
Meningioma (n =
Age range
20)
Epidermoid (n = 16)
3.1 Symptoms and signs Average elapsed time between the onset of symptoms and the diagnosis was 3.2 years for meningiomas and 3.4 years for epidermoid tumors.
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Tekk6k et al., Non-acoustic tumors of the cerebellopontine angle
Table H. Presenting symptoms Meningioma Epidermoid n=20 n=16 % Headache Hearing loss Unsteady gait Dizziness Nausea & vomiting Numbness on one side of the face Tinnitus Double vision Facial pain Facial twitching Facial weakness Hoarseness Difficulty in swallowing Weakness on one side Speech difficulty
%
11 10 9 8 5 3
55 50 45 40 25 15
7 4 4 2 2 5
44 25 25 12.5 12.5 31
3 1 1 1
15 5 5 5
12.5
1 1
5 5
2 -8 -1 1 2
1 1
5 5
1 1
-
The various neurological signs observed are summarized in table III. Two-thirds o f patients with m e n i n g i o m a were ataxic, but only one-third o f epidermoid t u m o r patients showed this symptoms. Of m e n i n g i o m a patients, ten (50%) h a d hearing loss and eight (40%) had mild facial weakness, whereas involvement o f trigeminal nerve occurred in seven (35%) cases. Ten patients with epidermoids (63%) showed Vth nerve involvement either as trigeminal neuralgia or facial hypoesthesia. F a cial nerve involvement was observed in eight (50%) a n d hearing loss in five (31%).
50
6 6 12.5 6 6
Papilledema was present in a p p r o x i m a t e l y 30% o f each group.
Table IIL Neurological findings Meningioma Epidermoid n = 20 n = 16 % Ataxia Nystagmus VlIIth nerve VIIth nerve Vth nerve Papilledema IX-- Xth nerves I X - X - X I - X I I t h nerves VIth nerve Pyramidal tract signs
13. 12 10 8 7 6 2 1 1 1
Presenting s y m p t o m s are given in table II. H e a d ache was present in a p p r o x i m a t e l y half o f the patients in the m e n i n g i o m a and epidermoid subgroups. H e a r i n g loss was present in 50% of m e n i n g i o m a patients but only 25% o f the epiderm o i d t u m o r patients. Dysequilibrium was a m o r e p r o m i n e n t feature in m e n i n g i o m a patients. Facial p a i n and numbness were most c o m m o n in patients with epidermoids.
65
60 50 40 35 30 10 5 5 5
3.2 Diagnostic studies
All patients h a d routine plain skull X-rays. Only in one patient with a calcifying m e n i n g i o m a with extracranial extension, did plain X-rays prove helpful. Diagnostic procedures are t a b u l a t e d in table IV. In nine patients presenting before the installation o f CT at our institution in late 1975, the diagnosis was reached by techniques like ventriculography, C P A myelography, and angiog r a p h y plus a n u m b e r o f combinations o f these. The remaining 43 patients h a d CT scans a n d 18 o f these additional angiograms. Two patients with hypodense C P A lesions suggesting either an epi-
% 6 7 5 8 10 5 1 1 4
37.5 44 31 50 63 31 6 5 25
Table IV. Diagnostic procedures Meningioma n = 20 Angiography alone Angio + ventriculography Angio + CPA myelography CT alone CT § angiography CT + cisternography Audiovestibular tests (A/T) Radionuclide scintigraphy (A/T)
Epidermoid n = 16
1
2 10 6
3
1
6 7
1 9 5
-
-
2
10/12
7/12
4/4
Miscellaneous n = 16
-
4/6 1/1
CT = computerized tomography, A/T = abnormal to total ratio Neurosurg. Rev. 15 (1992)
Tekk6k et al., Non-acoustic tumors of the cerebellopontine angle dermoid or an arachnoid cyst on plain CT scans had iohexol cisternography to delineate the t u m o r borders, and hence differential diagnosis. O n CT, tumors originating from vessels (angioblastoma or vascular h a m a r t o m a ) or rich in vessels (choroid plexus papilloma) as well as meningiomas appeared hyperdense showing marked contrast enhancement. All epidermoids appeared as irregular n o n - e n h a n c i n g hypodense masses. Two of these also had an extension to the middle fossa. N o patient in this series was examined by magnetic resonance (MR), since it became operational in A n k a r a in December 1990. Of the m e n i n g i o m a cases undergoing angiography (n = 10), 60% showed t u m o r blush. The angiograms showed displacement of major arteries in all but one. Only three epidermoid t u m o r patients showed basilar artery shifts.
119
Thirty patients had audiovestibular tests. These proved especially useful in meningiomas (abnormal to total ratio = 82.5%). F o u r patients with meningiomas had had a radionuclide scintigraphy and all showed pathological radioactivity in the CPA. Brain stem auditory evoked responses were studied in last four patients (2 meningioma, 2 epidermoid), all of w h o m showed lengthened, a b n o r m a l responses. 3.3 Tumor location
Meningiomas usually occurred on left side (65%), and epidermoids on the right (62.5%). 3.4 Treatment and outcome
All patients were treated surgically. Total removal was possible in 9 (45%) of patients with m e n i n -
Table V.
% in CPA total (n = 193)
a - Meningiomas & epidermoids: Histopathological variation -
-
-
20 fibroblastic (f) meningothelial (n) mixed (f + m) angiomatous + m calcifying
Epidermoid tumor
10.4
6 6 5 2 1 16
8.3
b - Rare tumors: Histopathological variation, treatment and follow-up Age/sex
Main surgery
Araclanoid cyst 1
18/F
2
29/F
1
56/M
Drainage into the cisterns Drainage into the cisterns Total removal
Astroeytoma
2 Angioblastoma I 2 Arachnoiditis Cavernous hemangioma Ch. plex. papilloma Cyst hydatid Malignant melanoma Malignant teratoma Medulloblastoma Metastatic adenocarcinoma Mucoid carcinoma Vascular hamartoma
22/M 30/F 52/M 44/M 30/F 35/F
16IF 34/F 25/M 14/M 65/M 35/M 24/M
Subtotal removal Total removal Subtotal removal Biopsy Total removal Total removal Total removal Total removal Total removal Subtotal removal Subtotal removal Total removal Total removal
RT
Follow-up Alive 2 Y Alive 5 m
[surgical mortality] + --
+ -
+
-
+
+
+ + -
+
AT = radiotherapy, ChT = chemotherapy, Y = year(s), m = month(s) Neurosurg. Rev. 15 (1992)
ChT
+ -
Died at t.8 Y Alive 3.2 Y Died at 3.8 Y Lost after 1 Y Lost after 6 Y Died at 4 Y Died at 1.5 m Alive at 10 Y Died at 2.5 m Alive at 2.5 Y Lost after 3 m Died at 1 Y Alive at 7.5 Y
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Tekk6k et al., Non-acoustic tumors of the cerebellopontine angle
giomas, in 14 (87.5%) of patients with epidermoid tumors, and 11 (69%) patients with rare tumors. Cerebellar resection was necessary in 6 meningioma, 2 epidermoid tumors, and 5 rare tumor patients. Histopathological variation of the tumors is given in table V.
Table VI. Reoperations for recurrences
Pathology
N
Interval
Surgical mortality
Meningioma Epidermoid Angioblastoma Astrocytoma Ch. plexus pap. Malignant teratoma
1 2 t t t t
2.2 Y 4 and 8 m 4Y 1.8 Y 4Y 2 all
+ + + -[-
Overall surgical mortality (patients undergoing operation and surviving less than a month) during the 16 year-period was 13.4% (7/52). Of four patients with subtotally removed meningioma expiring during the postoperative period, 2 had tumors with an angiomatous component and two had presented with hemiparesis. Surgical mortality of patients with total meningioma removal was 0%, and and of patients with subtotal removal 36% (overall for meningioma = 20%). Two of 16 patients with epidermoids died postoperatively (14%); both had been operated on before CT was available.
table VI. One patient with subtotally removed meningioma was found to have the tumor growing upwards through tentorial incisura; this was again subtotally removed. In two epidermoid patients, 10% of the tumor with its capsule being adherent to the brain stem had to be left during primary surgery; both recurred.
In the last four years (n = 26), we had no operative mortality.
The patients with recurrent malignant rare tumors died soon after their second operations.
3.5 Complications
3.7 Survival
One meningioma patient developed wound infection and subsequent osteomyelitis of the craniotomy flap which necessitated bone flap removal. A patient with epidermoid tumor developed aseptic meningitis which subsided with antibiotic and steroid cover. A patient with angioblastoma who had a persistent hydrocephalus needed a lumboperitoneal shunt 25 days postoperatively and another patient with meningioma received a V-P shunt a year later.
Sixteen meningioma patients were discharged. One died at home three months later. Thirteen (87.5%) were available for follow-up during a period ranging between 13 months and 16 years (median 4, average 4.1 years). Three died at home after 2, 5, and 14 years. The cause of death was not obtained.
As of operative complications related to cranial nerves, a total of 13 patients had postoperative facial paralysis but 7 recovered without further surgery by the end of first year, four patients needed tarsorrhaphy, and two accessory-facial nerve anastomosis. Permanent paralysis of VIIIth nerve occurred in only two patients with meningiomas and one with an epidermoid. The recurring meningioma patient with unilateral VIth nerve palsy underwent lateral rectus muscle recession performed by ophthalmologists. 3.6 Recurrences
Seven patients needed a second operation on their tumors. The histological types and the time intervals between two operations are summarized in
Y = year(s), m = months
All epidermoid tumor patients discharged (n = 14) were available for follow-up during a period between 8 months and 15.5 years (median 3, average 4.1 years), and all are alive. Follow-up for rare tumors of the angle is given in table V. 4 Discussion
Differential diagnosis of space-occupying lesions in CPA shows that acoustic neurinomas and meningiomas are of overwhelming majority. Other lesions found are epidermoid tumor, neurinomas of the cranial nerves V, VII, IX, X, XI, and other rare tumors such as arachnoid cysts [9, 12, 16, 24], aneurysm [9, 12, 27], astrocytoma [27], chondromyxoma [27], chondrosarcoma, chordoma [12, 24, 27], choroid plexus papilloma [12, 15], craniopharyngioma [2], cysticercosis [12], dermoid [27], ependymoma [9, 24], ependymoblastoma [24], glomus jugulare tumor [16, 27], granuloma (tuberculoma, gumma, fungus) [27], hemangioma, heNeurosurg. Rev. 15 (1992)
Tekk6k et al., Non-acoustic tumors of the cerebellopontine angle mangioblastoma [12], hemangiosarcoma [9], hydatid cyst [12], lipoma, lymphoma, medulloblastoma, osteoma, teratoma [28], reticulosarcoma [7, 24] and metastases.
4.1 Meningiomas 8-~L2% of all intracranial meningiomas are located within the posterior fossa [6, 20]. 42% of all posterior fossa meningiomas originate from the posterior surface of the petrous bone and 3 0 53% are in the CP angle [6]. Meningiomas of the angle can grow to a remarkable size without any clinical signs, thus prolonging the interval between tumoral transformation and the initial symptoms and hence the diagnosis. Time between the first symptoms and the diagnosis was 3 years for women and 7 years for men in YASARGIL'S series [27] which is in contrast to ours with 4 and 1 years, respectively. This interval has probably shortened with increased use of CT. There is a definite female preponderance, with most patients presenting in late fifth and sixth decade as also observed by others [6, 22]. We were able to find only one other report of a preponderance of lesions on the left side [13]. Meningiomas are known to cause hearing loss less often than acoustic neurinomas [13, 16, 24]. Symptoms involving the facial nerve start earlier in meningiomas than in acoustic tumors, while the VIIIth nerve is almost invariably involved earlier in acoustic neurinoma cases. The effect of meningiomas on facial and hearing functions is opposite to that of neurinomas. Amongst 20 meningioma patients in this series, only 1 had symptomatic trigeminal neuralgia. Lower cranial nerve involvement (5%) was less in our series than has been reported in the literature (15%) [13, 27]. On CT scans meningiomas appear to be well defined, usually enhancing hyperdense lesions which are based broadly on the petrous bone. They are not centered over the porus, and do not have a defined neck [13, 14, 27]. Lack of a widening of the internal acoustic canal and calcification with hyperosteosis of the bone are other differential hallmarks of CP angle meningiomas. Angiography is helpful not only for differentiating between a calcified aneurysm and other vascular tumors, but also for planning therapeutical strategies, including preoperative embolization [17]. One patient with an initial CT diagnosis of a meningioma was found to harbor an angioblastoma. Neurosurg. Rev. 15 (1992)
121
Several surgical approaches for CPA meningiomas are discussed in detail by YASARGIL [27] and SEKHAR [22]. Both discuss subtemporal, translabyrintine, and transmeatal retromastoid suboccipital approaches and both advocate the transmeatal approach as the most efficacious, citing many benefits as well as 0% mortality. All meningiomas in this series were operated similarly. Unfortunately, all 20 patients had meningiomas larger than 3 cm. This was most possibly due to educational level or the referral pattern. GIANNOTTA suggests translabyrintine removal as a serious alternative for the removal of meningiomas as big as 4 cm, but we find the sacrifice of hearing unnecessary since it may well be preserved by transmeatal approach [5]. One important point is that cerebellar resection must be avoided, since it increases perioperative morbidity and mortality. Laser and ultrasonic aspirator (CUSA) have been used at our institution since January, 1988, and have proven most useful for large meningiomas, which are alternately shrunk and aspirated several times. In this way cerebellar resection can be avoided even for huge tumors. We underline the fact that operative mortality decreases with total removal and that it is lower for meningiomas other than the angioblastic subtype. 4.2 Epidermoid tumors These arise from the displaced epithelial tissue during the closure of the neural tube between the 3rd and 5th weeks of gestation [3]. Epithelial remains are possibly carried into the angle with the developing otic vesicles. Epidermoids in general constitute 0 . 2 - 1 . 8 % of all intracranial tumors [3, 7] and occur almost equally in both sexes. The most frequent site is CPA and the parasellar region [7, 18, 25, 26]. These tumors grow slowly through gradual accumulation of normally dividing cells with a linear growth rate resembling the growth of human epidermis [3]. They spread along the cisterns and may extend into the middle fossa through tentorial incisura as occurred in our two patients with recurrences. Mean duration of symptoms in our series agreed with recent reviews discussing posterior fossa epidermoids in general (4.2-4.3 years) [3, 21]. Epidermoids cause a combination of cerebellopontine angle and jugular foramen syndromes, but, most notably, they cause trigeminal neuralgia and less commonly hemifacial spasm and glossopharyngeal neuralgia. According to JANETTAa tu-
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Tekk6k et al., Non-acoustic tumors of the cerebellopontine angle
mor causing trigeminal pain does so by pushing the trigeminal nerve against the blood vessel [11]. The occurence of trigeminal pain in 50% of our cases is in accord with experience of BERGER [3], GUIDETTI [7], SABIN [21] and THOMSEN [24]. Pain subsided in all eight cases immediately after operation. As a rule epidermoids show distortion of adjacent vessels on angiograms, so that an avascular area can be outlined. CT almost always demonstrates a low attenuation due to saponification of keratinized debris [3] and occasional peripheral calcifications in a non-enhancing lesion. Enhancement of an epidermoid is very rare and may suggest a malignant epithelial component [4]. Hyperdense epidermoids do occur and may result in an erroneous preoperative diagnosis of meningioma, but this is exceptionally rare in the CPA [23] (4 reported cases). CT cisternography may be essential in lesions appearing as a low density equivalent to that of CSF, but without familiar irregular borders, in order to demonstrate the nature and extension of the lesion [8]. With increasing use of M R even this becomes unnecessary because signals from the CSF and epidermoid tumors differ on M R scans. In all but two patients a total excision was possible. It is obvious that in two patients having recurrences in less than a year, tumor regrowth originated from the part of the capsule not removed for fear of increasing neurological deficit. Why enormous recurrences occurred in such a short time is uncertain. According to Collins' rule the tumor should normally grow to its preoperative size in a period equal to patients age plus nine months. Extensive histopathological studies of the specimens from the second operations were carried out to rule out any carcinomatous degeneration and proved negative. The recurrence rate of 12.5 % is parallel to those found in the literature. We would like to stress the fact that all our epidermoid patients are now alive with tumor-free survivals up to 16 years. As for rare tumors of the angle, we would like to discuss only the ones of interest: Approximately 10% of all intracranial araehnoid cysts occur within the CPA. In a review of literature from 1831 through 1980, RENGACHARY and WATANAB~ were able to find 22 cases of CPA arachnoid cysts [19]. The cases reported here were successfully treated by partial excision of the cyst wall to allow free communication of the cyst with the subarachnoid cisterns.
Arachnoiditis, although very rare, may mimic an angle mass as suggested by ADELO~q~ [1]. Ethiopathogenesis is best explained by a previous ear disease or vascular bleeding subsequently leading to the formation of meningeal adhesions. Our only case presented before CT was available to us and was operated due to a filling defect on CPA myelogram. Cavernous hemangioma was described and discussed in detail in a previous paper as the first cystic cavernous hemangioma of the angle in the literature [10].
Choroid plexus papillomas usually occur during the first two decades and have a male preponderance. Our patient was female and 35 years of age. Although these papillomas are known to be insensitive to radiation therapy [15], total removal complemented with radiotherapy gave to our patient years of useful life before microscopic disease caused death. CPA is a very rare site for hydatid cyst, especially if it is primary. Our patient had had surgery for a cyst in the corpus callosum a year before she presented with dysphagia, dysphonia, and ataxia so that the cyst in the angle is more likely to have been due to previous spillage. This patient died at home 45 days later. Our malignant melanoma patient benefited from total excision followed by radio- and chemotherapy. She is alive after 10 years. The chemotherapy regimen consisted of D T I C and mCCNU, and the radiotherapy dose was 60 Gy. Our malignant teratoma patient was atypical. First, 50% of teratomas are detected in newborns, and he was 25; secondly, teratomas are most commonly found in midline locations and his tumor was exclusively in the CPA; and, finally, to our knowledge he is the first case of malignant teratoma tumor in the angle. In conclusion, although there are many surgeons who believe that preoperative differential diagnosis of CPA tumors is of no great practical value from a surgical standpoint, we think that CPA tumors can be histologically classified preoperatively when all the variables discussed in this paper are considered. This knowledge will then help us to define the therapeutical approach, to define the existing risks, and even to predict approximate life expectancy. Mortality and morbidity increases with the size of the tumor, but with modern neurosurgical tools the prospects of patients undergoing angle surgery seem very good. Neurosurg. Rev. 15 (1992)
Tekk6k et al., Non-acoustic tumors of the cerebellopontine angle
123
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[16] NE3ZELSKIJ, C TATOR:Other cerebellopontine angle (non-acoustic neuroma) tumors. J Otolaryngol 11 (1982) 248--252 [17] NUMAGUCHI5(, T KISHIKAWA,J IKEDA,Y TSUKAMOTO, M FUKUI, K KITAMURA,K MATSUURA:Angiographic diagnosis of acoustic neurinomas and meningiomas in the cerebellopontine angle - A reappraisal. Neuroradiology 19 (1980) 7 3 - 8 0 [18] OZGEN T, HK OGE, A ERBENGI,V BERTAN:Cranial dermoid and epidermoid cysts. Neurochirurgia 33 (1990) 16--19 [19] REN~ACHARYSS, I WATANABE:Ultrastructure and pathogenesis of intracranial arachnoid cysts. J Neuropathol Exp Neurol 40 (1981) 62--83 [20] RUSSELLJR, PC BucY: Meningiomas of the posterior fossa. Surg Gynecol Obstet 96 (1953) 183-192 [21] SABINHI, LT BORDI, L SYMON: Epidermoid cysts and cholesterol granulomas centered on the posterior fossa: twenty years of diagnosis and management. Neurosurgery 21 (1987) 7 9 8 - 805 [22] SEKHAR LN, PJ JANETTA: Cerebellopontine angle meningiomas. Microsurgical excision and followup results. J Neurosurg 60 (1984) 500--505 [23] TEKK6KIH, O CATALTEPE,S SAGLAM:Dense epidermoid cyst of the cerebellopontine angle. Case report. Neuroradiology 33 (1991) 255-257 [24] THOMSENJ: Cerebellopontine angle tumors, other than acoustic neuromas. A report on 34 cases. Acta Otolaryngol 82 (1976) 106-111 [25] YAMAKAWAK, N SHITARA, S GENKA, S MANAKA, K TAKAKURA:Clinical course and surgical prognosis of 33 cases of intracranial epidermoid tumors. Neurosurgery 24 (1989) 568-573 [26] YASARGILMG, CD ABERNATHEY,AC SARIOGLU: Microneurosurgical treatment of intracranial dermold and epidermoid tumors. Neurosurgery 24 (1989) 561 -- 567 [27] YASARGILMG, RW MORTAR& M Clmclc: Meningiomas of the basal posterior cranial fossa. In: KRAYENBUHL H (ed): Advances and Technical Standards in Neurosurgery, Vol 7, Springer-Verlag, Wien 1980 [28] ZLILCH KJ: Brain tumors. Their biology and pathology. Springer-Verlag, New York 1965, ed 2 Submitted June 6, 1990. Accepted September 27, 1990. Ismail H. Tekk6k, M.D. 2 nci Cadde No 1 - 6 Kivanc Apt Bahcelievler Ankara 06500 Turkey
