Child's Nerv Syst (1996) 12:318-322 9 Springer-Verlag 1996

Ismail H. Tekk6k Saleh S. Baeesa Michael J. Higgins Enrique C. G. Ventureyra

Received: 30 November 1995

I. H. Tekk6k 9M. J. Higgins E. C. G. Ventureyra ([]) Division of Neurosurgery, Children's Hospital of Eastern Ontario, 401 Smyth Road, Ottawa, Ontario K1H 8L1, Canada Tel.: (613) 737-2316 Fax: (613) 738-4228 S. S. Baeesa 9E. C. G. Ventureyra Division of Neurosurgery, University of Ottawa School of Medicine, Ottawa, Ontario, Canada

Abscedation of posterior fossa dermoid cysts

Abstract Dermoid cysts of the posterior fossa are uncommon. When associated with a dermal sinus, these cysts are often diagnosed during early childhood. The main risk of such an association is contamination of the cyst leading to abscedation of the dermoid itself or formation of daughter abscesses within the cerebellar hemisphere. We recently treated a 20-month-old girl who had a congenital dermal sinus leading to an intradural dermoid cyst. In addition to the midline dermoid cyst, computerized tomography revealed an enhancing lesion extending into the adjacent left cerebellar hemisphere. Suboccipital craniectomy was undertaken after 2 days of external ventricular drainage, and the infected dermoid and adjacent cerebellar abscess were excised. Cultures of the operative specimen revealed Corynobacterium aquaticum, Enterobacter sakazakii and Enterobacter cloacae, requiring 6 weeks of intra-

Introduction Dermoid cysts account for 0.1-0.7% of all intracranial space-occupying lesions [6, 10, 17, 23]. Dermoids usually become symptomatic during childhood or early adulthood [10]. These cysts originate from misplaced ectoderm during the 3rd-4th week of intrauterine life [6, 9]. In contrast to epidermoid cysts, which contain only keratinized epithelium and tend to occur paraxially, dermoid cysts contain dermal appendages, hair follicles and apocrine glands and tend to occur in the midline [6, 24]. Their most corn-

venous antibiotic therapy consisting of ceftriaxone, penicillin and gentamicin. A diligent literature search revealed only 24 sporadic cases reported over a period of 56 years. All 24 cases were in children (mean age 17 months), and one-third were in infants under the age of 1 year. All but 1 of these patients underwent posterior fossa surgery, with mortality and morbidity rates of 13% and 10%, respectively. Eleven (40%) children had suppuration within the cerebellar parenchyma, while the rest had abscedation of the dermoid cyst alone. Among the cases reviewed S. aureus was the most common agent, occurring with a probability of 64%. Key issues for appropriate management of these benign lesions are discussed. Key words Brain abscess 9 Cerebellar abscess 9Dermoid cyst 9 Dermal sinus 9 Enterobacter cloacae. Staphylococcus aureus

mon locus is the posterior fossa, usually at the vermis, and occasionally within the IV ventricle [6, 9, 23]. Rarely, the maldevelopment generating the formation of the dermoid cyst may extend to the level of skin producing a coexisting dermal sinus. This tube, usually lined with epithelium, therefore contains the glandular architecture of skin, favouring colonization by microorganisms. Through this communication, microorganisms may travel into the cyst with potential risk of central nervous system suppuration. Mount was the first to describe abscedation of an intracranial dermoid cyst in a 1-year-old female infant who had presented previously with signs and symptoms suggestive

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of m e n i n g i t i s but was repeatedly treated for otitis or b r o n chitis or tonsillitis. Finally, neurologic deterioration suggested a cerebellar abscess. Posterior fossa exploration revealed an infected dermoid cyst; unfortunately the patient died on the 3rd postoperative day [14]. The c o m b i n a t i o n of a posterior fossa dermoid, dermal sinus and subsequent abscess formation is so rare that m a n y large cerebral and/or cerebellar abscess series do not include a single case [7, 15, 19, 22]. A literature search revealed 24 previously reported cases, mostly in the form of case reports or occasionally as small clinical series [1, 2, 4, 5, 8 - 1 2 , 14, 17, 18, 20, 21, 24]. Our experience with such a case prompted us to review and analyze p r e v i o u s l y reported cases with special emphasis on the surgical treatment, microbiological agents and outcome.

Fig. l Non-enhanced CT images of the posterior fossa depicting a a round hypodense dermoid cyst penetrating through midline occipital bone and b the lowermost portion of the midline mass (a lower slice); at this level, anatomical details of the left cerebellar hemisphere are ill-defined

Case history A 20-month-old girl presented to a local hospital with a 3- to 4-day history of imbalance, soon followed by the onset of nausea, vomiting, and irritability. She was admitted for observation and given intravenous fluids, and antibiotic treatment was initiated for "pneumonia", after which she was discharged the following day. Twenty-four hours later, she and her brother collided, both children striking their foreheads. She remained unresponsive for several minutes after impact and then recovered. According to her mother, she had been "wobbly" prior to striking her head. The girl was readmitted in a lethargic state, with recurrent nausea and complaints of headache. She then became less responsive, with bradycardia and intermittent hypertension, prompting emergency transfer to our institution. Upon arrival, she was awake, presenting a variable level of consciousness. Bradycardia and hypertension recurred, and she was intubated and sedated prior to neurosurgical assessment. Fnndoscopic examination was benign, and motor power, tone and sensation were symmetric and normal. No cerebellar signs were noted. Laboratory workup revealed a WBC of 17 600/ram 3 and an ESR of 39 mm/h. Computerized tomography (CT) scans showed a lobulated, cystic space-occupying lesion in the posterior fossa midline and to the left. Overall the mass measured 4 x 3 cm. The midline portion of this lobulated mass was hypodense (Fig. 1). The IV ventricle was displaced anteriorly and to the right. Moderate dilatation of the III and the IV ventricles was compatible with secondary obstructive hydrocephalus. After contrast injection, there was faint enhancement of the midline cyst wall, but the ovoid lesion extending into the left cerebellar hemisphere enhanced markedly (Fig. 2). The peculiar configuration of the occipital bone suggested a possible dermal sinus tract. She quickly responded to external ventricular drainage (EVD) via right frontal ventriculostomy, remaining awake, responsive, and hemodynamically stable without focal neurologic signs. Forty-eight hours later, she underwent definitive operative treatment. After shaving of the operation site, a small subcutaneous nodule measuring 7 m m x 7 mm was palpated exactly over the external occipital protuberance. There was no obvious sinus, ostium, or skin discoloration. Through a midline vertical incision, however, a stalk originating from this small subcutaneous nodule was found penetrating bone and extending through the midline dura (Fig. 3). After suboccipital craniectomy, the dura was opened and the midline cyst proved to be a dermoid. The extension of the mass into the left hemisphere was in fact an abscess cavity. The mass and the abscess capsule were removed with no complications, after which the girl became neurologically normal. Cultures of the pus from the left hemispheric abscess revealed Cot~nobacterium aquaticum, Enterobacter sakazakii and Entero-

Fig. 2a, b Contrast enhanced CT images through the same levels as in Fig. 1. a The enhancement of the dermoid cyst wall is faint overall, but appears marked adjacent to the cerebellar abscess, b The ill-defined image in Fig. lb is now clearly seen to be an avoid lesion in the left cerebellar hemisphere, with a markedly enhancing capsule and iso- to slightly hypodense contents. This lesion is the abscess bacter cloacae. Postoperatively the patient received 6 weeks' intravenous treatment with ceftriaxone (800 rag/day), penicillin G (2400000 U/day) and gentamicin (75 rag/day). Ceftriaxone and gentamicin treated the Enterobacter species and penicillin G and gentamicin treated the diphtheroids. The WBC count became normal by the 3rd postoperative day, but the ESR stayed high throughout the entire course of i.v. antibiotic treatment. At 2.5 years postoperatively, the girl is neurologically intact and developing well.

Discussion D e r m o i d cysts are b e n i g n masses k n o w n to enlarge slowly as a result of the secretion of the sebaceous material and d e s q u a m a t i o n of the epithelium enclosed within them [9]. They can be extradural or intradural, although the latter is more c o m m o n in the posterior fossa [9, 21]. A l t h o u g h asymmetric growth over one cerebellar hemisphere is pos-

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Fig. 3 Operative photograph showing the congenital dermal sinus tract (arrow), which pierced the occipital bone terminating as an intradural dermoid cyst sible, the main bulk of the lesion almost always overlies the vermis. When the misplaced ectoderm destined to form the dermoid cyst fails to separate from the main cutaneous epithelial ectoderm embryologically, an attachment to the skin surface develops and passes through a defect in the underlying bone. Such a connection will not only permit extrusion of the content of the dermoid cyst to the exterior but, more importantly, will provide direct access for migration of microorganisms into the cyst cavity. This type of attachment, first classified by Logue and Till [9], is called a "complete congenital dermal sinus". By definition, this sinus becomes microbiologically contaminated immediately after birth. Alternatively, the embryonic communication between the cyst and the skin surface is lost, and the tract ends as a blind sac. The latter is termed an "congenital dermal sinus", and as a rule it does not penetrate bone. In the case of an intradural dermoid associated with an incomplete dermal sinus, or an extradural dermoid with any sinus, the potential for central nervous system contamination is virtually nil. Congenital dermal sinuses may or may not command attention by the presence of a visible dimple or skin discoloration; it is the sinus discharge onto the skin or hair that often attracts the attention of parents. Sometimes subcutaneous swellings form when the sinus ostium is blocked [16, 17]. At this stage, cosmetic benefit from a minor surgical procedure may be sought. If the swelling is simply excised by an inexperienced practitioner, the importance of its connection to a stalk that may pass through bone may go unrecognized and diagnosis of the intracranial lesion be missed. The histopathological diagnosis may also be quite misleading: "scalp dermoid" [12], "sebaceous cyst" [9], "fibroma" [17] or "granuloma" [4]. The microorganisms that have already colonized the cyst may remain inactive for a considerable period, but sooner or later they produce abscedation of the choleste-

rol-rich cyst contents [9]. During this process, the only barriers between the multiplying organisms and the cerebrospinal fluid (CSF) spaces are the cyst wall and the piaarachnoid. Once the cyst is full of pus, distention of the wall may cause microscopic disruptions, allowing spread of the microorganisms to the leptomeninges, precipitating meningitis. Though this has not been emphasized in the literature, microorganisms may alternatively escape into the cerebellar substance to form a true cerebellar abscess. In this latter instance, the cyst itself often remains small. Meningitis is the more common presentation [ 12]. When meningitis is diagnosed, a thorough evaluation of the skin over the craniospinal axis must be pursued. Even if not undertaken initially, such a search should be completed once an uncommon organism such as S. a u r e u s is identified as the cause of meningitis. Shaving may be necessary, but will remove the characteristic hair(s) protruding from the sinus [ 17, 20]. When found, the dimple or ostium should be gently moved sideways over the occipital bone. Complete sinuses have a characteristic retraction due to their connection through the bone. Occasionally, a sinus may be found within the confines of a port wine stain [12, 20]. Diagnosis of an intracranial dermoid cyst is now commonly made by CT or MR imagery. Nonetheless, plain skull radiographs should be obtained, as these films will often demonstrate an oval or circular defect with sclerotic margins situated along the midline just below the inion. These bony channels are usually oblique and when very small may not be visible on plain films exposed with standard projections. If there is no defect as high as the inion, there may be a groove just at the rim of the foramen magnum. Plain spine radiographs may reveal unsuspected vertebral deformities such as hemivertebrae, spina bifida or even Klippel-Feil deformity [17, 20]. Though insufficient to confirm an intracranial dermoid cyst, these radiographs supplement CT or MR images obtained to evaluate clinical signs of increased intracranial pressure or focal neurologic findings. Our literature search and analysis are limited to posterior fossa dermoid cysts with clear descriptions of pus, pus leak, suppuration, abscess formation and/or radiologic images compatible with abscedation. Dermoid cysts with meningitis but no definite abscedation were excluded. Of the 24 posterior fossa dermoid cysts associated with suppuration, 13 occurred in males and 11 in females, with no definite sex predominance. All patients presented during childhood, the mean age at presentation being 17 months (range 6 months to 16 years). Eight (33%) were infants under 1 year old. Of the 24 children with abscedation, 17 (71%) had a history of at least one episode of meningitis prior to diagnosis of intracranial dermoid cyst with dermal sinus. Three had had two meningitic episodes. A skin lesion was present in all but 3 children. There were 11 children who had swelling of the occipital scalp [5, 9, 12, 14, 18, 20, 24], 5 of whom had undergone a local surgical procedure. Local excision of the swelling was performed in 3,

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and drainage of a soft-tissue occipital abscess in 2 children. Of the remaining 10 children with only a dermal sinus, intermittent pus drainage was noted in 5. Radiographic details or direct observations confirming the presence or absence of occipital bone defects were available for 22 children. All but 1 had occipital defects varying between 2 mm and 20 mm in diameter. Seventeen cases were reported or managed in the pre-CT era [1, 8-10, 12, 14, 17, 20, 24]. Ventriculography was then the basic diagnostic procedure used to localize the cyst by secondary distortion of the IV ventricle. Not surprisingly, in 14 patients the coexisting abscess was an unexpected finding. Despite this, ventricuIography was still beneficial since it allowed the surgeons to alleviate elevated intracranial pressure by draining CSF while simultaneously obtaining CSF for microbiological analysis. Seven patients were diagnosed by CT [2, 4, 5, 10, 11, 18, 21]. On CT, dermoid cysts classically appear as hypodense or, rarely, isodense lesions that do not prominently enhance following contrast administration [10]. Although the contents of infected dermoids still appear hypodense, moderate to marked enhancement of the capsule occurs when suppuration is present. Cerebellar abscesses are more dense (less hypodense or isodense) than the associated dermoid cysts and, as a rule, present marked capsular enhancement. CT also demonstrated that 6 of these 7 children were hydrocephalic at presentation; the 7th became hydrocephalic after posterior fossa surgery. Contrast administration must be included in the CT examination for abscessed dermoids, and the images should also be viewed with bone windows. In two cases from the CT era, an immediate diagnosis could not be established because contrast injection was not done [2, 4]. Even with bone windows, it is still necessary to be cautious, since CT may not reveal an existing bony defect if the axial slices do not intersect it. MRI has the unique advantage of multiplanar imaging, and especially with sagittal images, a diligent search will demonstrate the typically oblique stalk or tract that links cyst and skin [10]. Only two posterior fossa dermoids with abscedation have been reported with reference to MR images, and how MRI contributed to the diagnosis or management of either infected dermoid cyst is unclear [2, 4]. What Erdem et al. called "very unusual" images for intracranial dermoid cysts, i.e. images showing the presence of ring enhancement, daughter cyst and surrounding edema in cerebellar white matter [2], were in fact evidence of abscedation. Although still advocated by some authors [4], sinography or fistulography should be avoided because of the prohibitive risks of introducing additional microorganisms intracranially and iatrogenic distention or rupture of the infected cyst. Thirteen children (54%) had pus formation within their dermoid cyst [1, 4, 9, 10, 12, 14, 17, 20, 24] while a distinct cerebellar abscess formed in 11 children. In 7 of the latter, extension of the infectious process caused hemispheric cerebellar abscesses [5, 8, 11, 18, 20, 24]. The number of hemispheric abscesses present varied between 1 and

3 (mean 2). In the remaining 4 children, the abscess formed over the cerebellar vermis, anterior to (2) or behind (2) the dermoid cyst [2, 8, 14, 21]. Detailed microbiological information was available for 14 patients [1, 2, 5, 9, 11, 12, 14, 17, 20, 24]. In those with no identified agent(s) cultured from the abscess content, the microorganism(s) isolated from CSF or discharge material was (were) considered to be the agent(s) causing intracranial suppuration. In 9 cases (64%) Staphylococcus aureus grew from CSF, discharge material, or pus from the intracranial abscess. Specimens from the other 5 revealed Gram-negative bacteria (E. coIi, 2 patients; B. fragilis, Proteus species, Klebsiella species). Our patient is the first documented with E. cloacae cultured from the operative specimen. Brain abscess due to E. cloacae is very rare [ 13]; among 130 children with brain abscesses only i was found to have E n t e r o b a c t e r species as the responsible agent [22]. The culture yield rate from cerebellar or cyst abscess due to S. aureus was 67%, while yield due to Gram-negative pus was 40%. Positive cultures were obtained from the CSF of patients with S. aureus as the contaminating agent in 22%, while Gram-negative bacteria were isolated from CSF is as many as 80%. Age at presentation was not linked with the causative agent. The mean age at presentation was 16 months for those with S. aureus and 14 months for those with Gram-negative bacteria. There were 4 infants (44%) among the 9 who harbored S. aureus, and 2 infants (40%) among the 5 Gram-negative patients. The only effective treatment for dermoid cysts associated with a dermal sinus is timely and appropriate microsurgical excision. Of the 24 cases reviewed, all but 1 underwent surgery, most commonly posterior fossa exploration and/or suboccipital craniectomy. Logue and Till's second case was the only one with an autopsy diagnosis [9]. Percutaneous aspiration of the cerebellar abscesses prior to definitive treatment has been reported in 3 patients [9, 12, 18]. In the pre-CT era, 5/17 patients needed external ventricular drainage (EVD) before definitive surgery, and fortunately only 1 needed a permanent shunt [20]. In contrast, of the 7 children managed after the advent of CT, 2 received ventriculoperitoneal shunts prior to posterior fossa surgery, while 1 child was shunted after posterior fossa exploration. Various antibiotic combinations were used postoperatively. Although we emphasize the need for sustained intravenous antibiotic treatment, an appropriate treatment regimen must rely upon thorough microbiological assessment and close consultation with experts in infectious diseases. The medical treatment in our patient was determined by the antibiotic sensitivity results. Flucloxacillin and chloramphenicol, as used by Groen and van Ouwerkerk, may prove advantageous until the culture and sensitivity results become available [5]. Of the 23 children who underwent surgery, 3 died postoperatively [2, 14, 24], giving a relatively high surgical mortality rate of 13%. Two other children had severe neurologic deficits (10% morbidity) [12, 21]. Mortality and

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m o r b i d i t y risks i n c r e a s e d r a m a t i c a l l y once the d e r m o i d cyst or c e r e b e l l a r tissue b e c o m e s infected. A l l 3 fatal cases had c e r e b e l l a r abscesses. In 2, culture r e v e a l e d E n t e r o b a c teriaceae (1 E. coli and 1 Klebsiella), while the 3rd g r e w S. aureus. Two o f the fatal cases were in infants. A l t h o u g h the n u m b e r s are small, when c a l c u l a t e d a c c o r d i n g to age, the m o r t a l i t y rate for infants was 25% (2/8), d e c r e a s i n g to 6.6% (1/15) for patients o v e r 1 y e a r o f age. A n o t h e r factor c o n t r i b u t i n g to i n c r e a s e d m o r t a l i t y and m o r b i d i t y is the i n f l a m m a t o r y r e a c t i o n within the cyst capsulb f o l l o w i n g a b s c e d a t i o n . This r e a c t i o n p r o m o t e s adhesions to a d j a c e n t structures, r e n d e r i n g "en b l o c " r e m o v a l o f the cyst difficult and s i m u l t a n e o u s l y i n c r e a s i n g the risks o f i n t r a o p e r a t i v e rupture or s p i l l a g e [12, 20]. P o s t o p e r a tive m e n i n g i t i s is also a significant factor c o n t r i b u t i n g to m o r t a l i t y and m o r b i d i t y [3, 11, 21 ]. The child r e p o r t e d b y E r d e m et al. s u c c u m b e d after d e v e l o p i n g p o s t o p e r a t i v e Klebsiella m e n i n g i t i s [2]. Safe, c o m p l e t e m i c r o s u r g i c a l e x c i s i o n o f these lesions requires accurate p r e o p e r a t i v e diagnosis. O n c e the true nature and c o m p l e x i t y o f a given lesion is r e c o g n i z e d , the

surgeon should aim at en b l o c m i c r o s u r g i c a l r e m o v a l . One should anticipate the d e v e l o p m e n t o f p o s t o p e r a t i v e m e n ingitis and p r e s c r i b e b r o a d - s p e c t r u m intravenous antibiotic c o v e r a g e until one or m o r e specific c a u s a t i v e organisms are cultured and the c o r r e s p o n d i n g antibiotic sensitivities are identified. W e do not a d v o c a t e initial aspiration and treatment o f the c e r e b e l l a r abscess(es) p r i o r to definitive e x c i s i o n o f the d e r m o i d at a s e c o n d stage, though this course has been r e p o r t e d [18]. A s p i r a t i o n itself will p r o m o t e d i s s e m i n a t i o n o f an a l r e a d y e n c a p s u l a t e d infective p r o c e s s by l e a k a g e through the p u n c t u r e site, and m a y p r o duce h e m o r r h a g e with attendant c o m p r e s s i o n or shift o f a d j a c e n t brain stem structures. W h e n a c c o m p a n y i n g h y d r o c e p h a l u s is present, an E V D will a l l e v i a t e e l e v a t e d C S F pressure, p r o m o t e m o r e f a v o r a b l e o p e r a t i v e conditions, and p e r h a p s d e c r e a s e the l i k e l i h o o d o f p e r m a n e n t C S F diversion.

Acknowledgements We wish to thank Drs. N. MacDonald and F. Diaz-Mitoma, consultants during the care of our young patient, and Pat Johnson, Rose-Marie Mongeon, and Pare LeMoine, medical librarians, who kindly facilitated our literature search.

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17. Roberts AP (1958) A case of intracranial dermoid cyst associated with the Klippel-Feil deformity and recurrent meningitis. Arch Dis Child 33:222225 18. Schijman E, Monges J, Cragnaz R (1986) Congenital dermal sinuses, dermoid and epidermoid cysts of the posterior fossa. Child's Nerv Syst 2:83-89 19. Shaw MDM, Russell JA (1975) Cerebellar abscess. A review of 47 cases. J Neurol Neurosurg Psychiatry 38:429-435 20. Smith GF, Altman DH (1959) Occipital dermal sinus. Am J Dis Child 98:713-719 21. Starinsky R, Wald U, Michowitz SD, Lahat E, Schiffer J (1988) Dermoids of the posterior fossa. Case reports and review. Clin Pediatr 27:579-582 22. Tekk6k IH, Erbengi A (1992) Management of brain abscess in children review of 130 cases over a period of 21 years. Child's Nerv Syst 8:411-416 23. Tekk6k IH, Ayberk G, Kansu T, Saglam S (1989) Bilateral internuclear ophthalmoplegia associated with fourth ventricular dermoid tumor. J Clin Neuroophthalmol 9:254-257 24. Tytus JS, Pennybacker J (1956) Pearly tumors in relation to the central nervous system. J Neurol Neurosurg Psychiatry 19:241-259