:Acta . Ndi/rochlrurgica
Acta Neurochir (Wien) (1987) 85:34-39
9 by Springer-Verlag1987
Posterior Fossa Epidermoid Cysts * J. Salazar, J. Vaquero, G. Saucedo, and G. Bravo Puerta de Hierro Clinic, Departments of Neurosurgery and Neuroradiology, Autonomous University, Madrid, Spain
Summary The authors present their clinical and surgical experiencewith 18 posterior fossa cholesteatomas, including three cases with atypical CT scan appearances that corresponded to calcification, haemorrhage or malignant change into an epidermoid carcinoma, respectively.
Keywords:Epidermoid cyst; posterior fossa cholesteatoma; computerized tomography; epidermoid carcinoma.
Clinical Material From 1971 to 1985, 18 patients with posterior fossa epidermoid cysts have been treated in our Clinic. The clinical features of these cases are summarizedon Table 1.12 caseswere evaluated by CT scan examinations and their main characteristics are recorded in Table 2.
Results A m o n g the patients in this group there were 10 males and 8 females (male/female: 1.25). Their ages ranged from 15 to 60 years. The symptoms started one m o n t h to 10 years prior to the diagnosis (mean interval of 3.8 years). H a l f of the patients showed evidence of cranial nerve involvement. 45% had pyramidal and long tract signs due to brainstem damage. Cerebellar signs were present in 39% of the cases and hydrocephalus in 30%. 6 patients were evaluated before the advent of CT scan, their clinical study included the following examinations: a) Electroencephalography which showed abnormal uncharacteristic patterns in 5 cases (28%). * This paper was presented at the 38th Congress of the SpanishPortuguese Society of Neurosurgery, held in Coimbra, Portugal, on May 7, 1986.
b) Pneumoencephalography, demonstrated signs of mass effect in 5 cases, two of them had a typical mottled distribution of air around the tumour. c) Serial brain seintigraphy evidenced perfusion defects in 2 cases, one showing radionuclide uptake on the right cerebello-pontine angle (case 4). d) Planar tomography depicted bone destruction of the petrous apex and erosion of the internal auditory meatus in 4 cases (22%). e) Cerebrospinalfluid analysis showed findings compatible with aseptic menirrgitis in one case (case 5), and in other one (case 13) it showed increased levels of gammaglobulin, compatible with a diagnosis of multiple sclerosis. f) Cerebral angiography showed only displacement of normal vessels by the tumour in 5 cases.
CT Scan Examination Computerized t o m o g r a p h y was performed in 12 cases (Table 2). In 9 cases (75%) there were typical images which corresponded to hypodense lesions with attenuation values close to those of the CSF (Fig. 1). On the other hand, atypical CT scan appearances were observed in 3 cases (25%) which included a hyperdense area within or around the hypodense tumour. Surgical exploration of the latter cases confirmed areas of calcification in case no. 6, intratumoural haemorrhage in case no. 11 (Fig. 2), and malignant degeneration of the epidermoid cyst into an epidermoid carcinoma was found in case 15 (Figs. 2 and 3). The last two cases showed evidence of contrast enhancement. Most of the epidermoids were located within the cerebello-pontine angle and basal parapontine cisterns. 12 were on the right side and there was bilateral involvement in 4 cases. Upward extension of the epidermoid through the
J. Salazar etal.: Posterior Fossa Epidermoid Cysts
35
Fig. 1. Typical CT scan image of posterior fossa epidermoid cyst. Case no. 7. CT scan image shows a hypodense lesion in the right cerebello-pontine angle, without contrast uptake and moderate displacement of the fourth ventricle
Table l. Clinical Manifestations of Posterior Fossa Epidermoids Signs
Cranial nerve involvement VIII: hypoacusia nystagmus vertigo dizziness tinnitus V: corneal hypoaesthesia trigeminal neuralgia IX, X, XI, XII: dysarthria, dysphagia tongue deviation Ill, IV, VI: diplopia, ptosis strabismus
Number of cases
%
8 9 4 2 2 8 3
44 50 22 11 I1 44 17
7
39
6
33
Brain-stem involvement Hemiparesis Hyperreflexia Babinski sign
8 6 4
44 33 22
Cerebellar involvement Gait ataxia Limb ataxia Cerebellar tremor
10 6 3
56 33 I7
Intracranial hypertension Headache Papilloedema Nausea and vomiting Altered level of consciousness Temporal lobe seizures
9 3 4 5 2
50 17 22 28 i1
Meningeal irritation Aseptic meningitis
i
6
Fig. 2. Atypical CT scan image of posterior fossa epidermoid cyst. Case no. I1. CT scans showing a right cerebello-pontine angle epidermoid cyst with a peripheric hyperdensering that corresponded to an area of intratumoural haemorrhage
tentorial hiatus into the h i p p o c a m p a l region was observed in 3 cases (17%). I n 6 cases (33%) the t u m o u r eroded the petrous apex a n d extended into the middle fossa. One case (5.5%) was confined to the cerebellar vermis a n d fourth ventricle, a n d initially it was diagnosed as a cerebellar a s t r o c y t o m a prior to surgery. O n e case (no. 15) occupied the basal cisterns of the right cerebello-pontine angle a n d also showed i n v a s i o n of the pons after m a l i g n a n t degeneration. Five cases (28%) had evidence of ventricular d i l a t a t i o n a n d compression of the fourth ventricle.
Surgical Management Suboccipital craniectomy was performed in 15 cases (83%), followed by a s u b t e m p o r a l c r a n i o t o m y in four cases to remove considerable t e m p o r a l extension of the epidermoid. I n 2 cases the s u b t e m p o r a l a p p r o a c h was used as the p r i m a r y procedure. O n e p a t i e n t who
36
J. Salazar et al.: Posterior Fossa Epidermoid Cysts
Fig. 3. Atypical CT scan images of posterior fossa epidermoid cyst. a Case 15. CT scan demonstrates a hypodense lesion in the right cerebellopontine angle with a medial hyperdense nodule. Suboccipital craniectomy was performed removing an epide~noid cyst. b Same patient as above 3 months later with increased neurological deficit, shows a different CT scan image of a lobulated hyperdense pontine mass with marked contrast enhancement. Reoperation showed an intrapontine tumour which was removed. Histological examination demonstr~tted a malignant process which corresponded to an epidermoid carcinoma
Table 2. Clinical and C T Scan Features o f Posterior Fossa Epidermoids Case number
Age, years
Sex Duration of symptoms
2
22
M
3 months
5 6
31 33
F M
4 years 9 years
7 10
30 19
M F
9 years 6 years
11
60
M
12
15
13
Location
Densitometry Contrast enhancement
Hydrocephalus
Surgical attitude
Outcome
hypodense
no
yes
good
hypodense hyperdense areas
no no
no yes
right cpa right cpa with H and T
hypodense hypodense
no no
no no
one month
right cpa
hyperdense areas
yes
yes
F
3 years
hypodense
no
no
44
F
2 years
hypodense
no
yes
14
36
M
10 years
right cpa with T cerebellum and 4th ventricle bilateral cpa with right T
VA shunt subtemporal A suboccipital A suboccipital and subtemporal A VA shunt suboccipital A suboccipital A (R) subtemporal A VA shunt suboccipital A (R) suboccipital and subtemporal A suboccipital A
hypodense
no
yes
15
49
M
1 year
no
20
F
3 years
hyperdense nodule hypodense
yes
17
right cpa and pons right cpa
no
yes
18
36
M
2 years
right cpa
hypodense
no
no
left cpa with H and T left cpa right cpa
suboccipital and subtemporal A VA shunt suboccipital A (R) VP shunt and suboccipital A not operated 4 years of CT scan and clinical follow up
good good shunt nephritis good moderately disabled died from pulmonary infection good good good
moderately disabled good asymptomatic
F = female, M = male, cpa = cerebello-pontine angle, VA = ventriculo-atrial, VP = ventriculo-peritoneal, H = hippocampal extension, T = temporal extension, A = approach, (R) = reoperation.
J. Salazar etal.: Posterior Fossa Epidermoid Cysts complained of trigeminal neuralgia had a small (case 18) cerebello-pontine angle epidermoid and surgery has not been performed, because the symptoms were controlled with carbamacepine; after 4 years of clinical and CT scan follow up examinations the patient remains asymptomatic and there are no changes in the lesion. In all the surgical procedures, using standard microsurgical techniques the lesions were resected, respecting adherent parts of the capsule which left in situ, while the cyst contents could be easily removed. Postoperative CT scan examinations showed evidence of remaining tumour capsule and small remnants in 7 cases. 4 of them remained at a mean interval of 6.8 years in asymptomatic patients, who have been closely controlled by serial clinical and CT scan examinations. Three other cases showed progressive symptoms at an interval of one month (case 15), 3 years (case 6) and 9 years (case 5), after surgical removal and were reexplored. Case no. 15 corresponds with the case of 49-year-old man who complainedof hypoacusis,paraesthesiaeand progressivelefthemiparesis, ataxia; hyperreflexia,left dysmetria and lower cranial nerve disfunction. Initial CT scans showed a hypodenselesion in the right cerebellopontine angle, with a hyperdensemedial nodule (Fig. 3 a). Suboccipital craniectomy was carried on June I2, 1985 and an apparently typical epidermoid was excised. Nevertheless, due to increasing neurologicaldeficit, and a changing CT scan showing a hyperdense lobulated pontine mass with marked contrast uptake (Fig. 3b), reoperation was carried out on September 18, 1985. Surgical reexploration revealed small epidermoid rests and a trilobulated intrapontine tumour which was resected. Histopathological examination revealed malignant change, and the diagnosis of epidermoid carcinoma was clearly established. Radiotherapy was instituted, and the patient remains alive in semidependent ambulatory care, 10 months after reoperation.
Postoperative Course Five patients required shunting procedures of the cerebrospinal fluid to control hydrocephalus. 2 shunts were implanted before the tumour was removed, and three after excision of the tumour. One case (no. 11) died due to pulmonary complications 18 days after surgery. Case no~ 6 developed shunt nephritis two years after a ventriculoatrial shunt was inserted. Removal of the shunt and systemic antibiotics resolved this complication. One case (no. 12) remains with occasional temporal lobe seizures despite medical treatment. 14 cases carry on an independent life and showed important relief of their complaints. 2 patients with lower cranial nerve involvement and spastic hemiparesis have a semidependent life.
37
Discussion Epidermoid cysts or cholesteatomas, represent 1.8 % of all intracranial tumours l, 3, 22, 29. At least 50% of them arise from the cerebello-pontine angle and basal subarachnoid cisterns of the posterior fossa and parasellar region 7, 8, 20, 22, and less frequently appear within the cerebellum 2a, fourth ventricle 23 and brain stem 19, 24. Sometimes they show extension through the tentorial hiatus into the hippocampal region 1, 3, this occured in 17% of our cases. Also they can erode the petrous apex and reach the medial aspect of the middle fossa 3, such temporal extension was appreciated in 6 of our patients (33%). The surgical exposure for the latter cases was achieved by suboccipital craniectomy followed by a subtemporal approach. Epidermoids are derived from ectodermal epithelial cell rests that are ectopically situated in the central nervous system around the 5th week of gestation 11, 2628. Multipotential embryonic cell rests have also been stated as a source of their origin 12. Histologically the cyst contents are composed of concentric layers of epidermal desquamated cells with abundant cholesterol, and surrounded by a thin white capsule of stratified squamous epithelium l, 22, 28. This structure confers a typical macroscopic appearance of a pearly tumour. Epidermoid cysts are clearly differentiated from dermoid cysts which contain elements from the ectodermal and mesodermal germ cell layers 18, 2a and from teratomas that derive from all three germinal layers 3o. Signs and symptoms are produced by a slow growing mass which displaces the nearby neural or vascular structures. In the present series the mean duration of complaints befored the diagnosis was made was 3.8 years. Signs due to involvement of cranial nerves (50%), brain stem (45%) and cerebellum (40%) were the most prominent. This is in accordance with previous reports 3, 9, 20, 22 Hydrocephalus results from tumoural obstruction of the fourth ventricle 3, 6 and cerebrospinal fluid pathways by rupture of the cyst spreading its contents along the subarachnoid cisterns, also producing bouts of aseptic meningitis 3, 6, 7, 1< ~6, 24, 28 Shunting procedures should be performed to control hydrocephalus whenever it is present, both before or after removal of the epidermoid 3, 7, 22. Irrigation of the operative field with hydrocortisone and the use of systemic dexamethasone have been used to treat aseptic meningitis 3,6,25. CT scan is the diagnostic procedure of choice. Typical epidermoid cysts appear as low density lesions
38 with attenuation values similar to those o f cerebrospinal fluid, ranging f r o m + 2 to + 10 Hounsfield units4 and show no evidence o f contrast enhancement 7-9, 23. O n the contrary, atypical images show high density values. Hyperdensc zones in epidermoids can be f o u n d with deposits o f calcium 5, 8, 9, 11, 21 or haemosiderin 17 and also with areas o f cyst saponification 5, 21 or haemorrhage, such an appearance m a y suggest a diagnosis o f m e n i n g i o m a 17. The C T scan differential diagnosis o f epidermoid cysts would include arachnoid cyst, solitary hydatid cyst, g u m m a , and old h a e m o r r h a g i c cavities 4. C T scan contrast uptake is an a b n o r m a l finding with epidermoids 4, 7-9. In our series two cases showed contrast enhancement. Case no. 11 corresponded to an area o f h a e m o r r h a g e in the tumour. C o n t r a s t enhancement after surgical resection, if it is associated with early progression o f symptoms, suggests process of infection or malignant degeneration 3, 13, 21, 23. The latter event was present in case no. 15 where an epidermoid carcinoma invading the brain stem developed a few m o n t h s after the initial excision o f an apparently benign epidermoid (Figs. 3 a and b). The surgical m a n a g e m e n t o f posterior fossa cholesteatomas or epidermoids requires a rather conservative attitude. The techniques o f suboccipital and subtemporal-transtentorial approaches have been described elsewhere 1, 3, 12, 20. Excision o f the t u m o u r contents and n o n a d h e r e n t portions o f the capsUle should be acomplished. Nevertheless, due to the fact that epidermoids do spread along vital neurovascular structures o f the posterior fossa, a complete removal is not justified 3, 16, 28 and carries an increased risk o f postoperative morbidity or mortality. O n the other hand, remaining fragments o f t u m o u r capsule which c a n n o t be removed, could possibly constitute a focus for cyst recurrence. Epidermoid cysts grow slowly, with a linear rate 2, therefore evidence o f recurrence is to be expected only several years after surgical removal 5, 12, 14, 28. C T scan will easily identify such t u m o u r rests and should be used to follow up closely the evolution o f these lesions. Conservative m a n a g e m e n t is recomm e n d e d in those a s y m p t o m a t i c cases with C T scan evidence o f t u m o u r rests 3. We have followed-up in this m a n n e r 4 cases over a period o f 6.8 years without evidence o f increased neurologic deficit. We feel on the other h a n d that reoperation is indicated in patients w h o show early recurrence or increased s y m p t o m a t o l o g y 3, even m o r e so if there is C T scan evidence o f t u m o u r g r o w t h or features that suggest a malignant change, as it occured
J. Salazar et al.: Posterior Fossa Epidermoid Cysts in our case no. 15. In the latter event postoperative radiotherapy is indicated 13, 15, 21, 23
Acknowledgement The authors wish to thank Dr. Hugo Liafio for refering case no. 15, to Miss Carmen Tirado and Mrs. Cristina S~nchez-Porro for their assistance with the manuscript.
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39 27. Toglia JU, Netsky MG, Alexander E Jr (1965) Epithelial (epidermoid) tumors of the cranium. J Neurosurg 23:384-393 28. Tytus JS, Pennybacker J (1956) Pearly tumors in relation to the central nervous system. J Neurol Neurosurg Psychiatry 19:241259 29. Ulrich J (1964) Intracranial epidermoids. A study on their distribution and spread. J Neurosurg 21:1050-1058 30. Willis RA (1971) Nervous tissue in teratomas. In: Minckler J (ed) Pathology of the nervous system. McGraw Hill, New York, pp 1937-1943
Authors' address: Jorge Salazar, F.M.D., Department of Neurosurgery, Puerta de Hierro Clinic, San Martin de Porres 4, E-28035 Madrid, Spain.