Posterior Fossa Abscess with Obstructive Hydrocephalus in a Child with Occipital Dermal Sinus with Dermoid Cyst Manifestation –  a Case Report

Overview

Posterior fossa dermoid cysts with dermal sinuses are rare cerebral tumours. Authors recently treated a 7- month‑ old girl who suffered from a posterior fossa dermoid cyst with dermal sinus. In addition, cerebellar abscess in the left cerebellar hemisphere was detected by CT and MRI. Surgery was performed the day after external ventricular drainage insertion, and the dermoid cyst and cerebellar abscess were fully excised. Early detection and adequate management of these benign tumours can prevent serious complications, as argued within the discussion section.

Key words:
dermoid cyst – mature teratoma – dermal sinus – cerebellar abscess

Introduction

Dermoid cysts are among the rarest of intracranial tumours, representing 0.3% of intracranial tumours [1]. They tend to manifest at an early age, during childhood and adolescence, due to large production of oil within the lesion, resulting in a large mass lesion. These tumours are known to develop during early embryonic development of the neural tube (3^rd and 5^th week of gestation), at which time cutaneous tissue cells are sequestered within the neural tube to form an intradural dermoid cyst. They tend to form lines of the neuraxis and vertebral canal in the midline along posterior closure, from displaced cellular elements with cutaneous commitments [1]. The posterior fossa is a rare but recognized site for dermoid development [2]. These posterior fossa dermoid cysts can be divided into four categories based on the following two criteria: 1. anatomical situation (intradural or extradural) 2. degree of occipital dermal sinus development (absent, partial or complete) [3]. Patients with a posterior fossa dermoid cyst and an associated dermal sinus may develop bacterial meningitis or abscess of the dermoid itself [4]. Embryogenesis explains why these tumours most commonly appear in the midline, most frequently near the fourth ventricle (one third of the lesions), spine (especially in the first year of life when they account for 17% of primary spinal tumours), third ventricle or even base of the brain. Lesions in the cauda equina and the cerebellar vermis are often associated with a dermal sinus [1]. These cranial dermal sinuses were first described by Ogle in 1865 [5].

Case report

We report a case of a paediatric patient with abscessing posterior fossa dermoid cyst with dermal sinus. A 7- month‑ old girl was admitted to our department with fever lasting three days and signs of increased intracranial pressure (vomiting with elevated anterior fontanelle). She also had a small oedema at her occipital region that occurred at three months of age, ruptured spontaneously 10 days before the admission; the rupture was followed by purulent secretion. CT scan showed decompensated obstructive hydrocephalus, lobulated, cystic space occupying a lesion in the posterior fossa midline and a midline defect at the occipital bone region (suggesting the possibility of dermal sinus). Blood analysis revealed an elevated C reactive protein level and leucocytosis. Neurological examination revealed paresis of the left abducens nerve. The patient underwent emergency surgery to manage the decompensated obstructive hydrocephalus and external ventricular drainage was inserted into the frontal horn of the right lateral ventricle. Anti­­biotic treatment with ceftriaxon (Rocephin) and amikacine (Amikin) was administered intravenously. Subsequent MRI revealed several cerebellar abscesses with a dermoid cyst and a complete dermal sinus (Fig. 1). The patient underwent definitive operative treatment for the abscessing dermoid cyst in the posterior fossa with spreading to the four ventricle and associated complete dermal sinus (Fig. 2). Postoperative MRI showed that the tumour was totally removed (Fig. 3). Histological examination of surgical specimens confirmed the dia­gnosis of mature teratoma (Fig. 4). Bacteriological cultures from specimens were positive for Staphylococcus aureus and the treatment with oxaciline (Prostaphlin) was initiated. Postoperative clinical course was very positive. Obstructive hydrocephalus regression allowed removal of the external ventricular drainage 10 days post‑surgery. The girl was discharged from the hospital seven days later. She underwent further re­habilitation and six months after the surgery her psychomotor skills were within the normal range. As the left abducent nerve paresis slightly persisted, the patient underwent another surgery one year later to correct the paresis.

Discussion

Dermoid cysts are true ectodermal inclusion lesions lined with epithelium, composed of various amounts of well‑differentiated ectodermal and mesodermal elements (endodermal elements are usually not observed, these are more suggestive of a germ cell tumour). Some of these ectodermal inclusions may be hair follicles, sebaceous glands or even sweat glands. The majority of congenital dermoid tumours probably develop during the early stages of development, between the 3^rd to 5^th week of gestation. The presence of another associated congenital anomaly in 50% of patients with dermoid cysts is suggestive of a midline fusion defect. According to the available literature, dermoid cysts are not only congenital but also iatrogenic (e. g. due to lumbar puncture performed with an open needle) or traumatic (e. g. due to a stab or puncture wound), occurring as a consequence of an implantation of skin elements from the surface into underlying tissues. This type of a cyst may occur at any age but much less commonly than the congenital one [6]. At present, CT and MRI scans are both used for the dia­gnosis of this tumour. CT images the dermoid cyst as a hypodense lesion, not enhancing after a contrast agent administration, unlike abscesses that, if present, are more dense and their capsule is markedly enhanced by a contrast agent. CT bone window is used for bone defects detection. Defects not dia­gnosed with CT (axial slices may miss it) can be identified with MRI, especially with sagittal plane sections that show the typically oblique stalk that links the cyst with the skin [7]. Dermoid cysts tend to show an increased signal intensity on both T1 and T2- weighted MRI images and a low signal intensity on STIR images [8], although a ruptured cyst may be hypointense on T1- weighted images and hyperintense on T2 [8]. Posterior fossa dermoid cysts may be divided into four types: extradural dermoid cysts with a complete dermal sinus, intradural dermoid cysts without a dermal sinus, intradural dermoid cysts with an incomplete dermal sinus and, as in our case, intradural dermoid cyst with a complete dermal sinus [3]. Intradural dermoid cysts with a complete dermal sinus are difficult to manage since they communicate with the skin and this promotes microbial colonization [9]; this introduces a risk of deeper suppuration [5] and abscess formation. Mortality and morbidity increases significantly in patients with bacterial or chemical meningitis [10]. Total microsurgical excision is the only treatment known to be effective in patients with dermoid cysts. The surgery has to be performed so that it avoids cerebrospinal fluid (CSF) contamination or rupture of the cyst into the ventricles [11]. Maximal but incomplete resection of the dermoid cyst wall is preferred in case of close approximation to adjacent nerves and vessels. Benign course of these tumours and the slow regrowing rate of remaining dermal cells most commonly will not lead to a clinically symp­tomatic recurrence. Since these methods have been adopted, the risk of mortality decreased from 70% in the 30s (Bailey 1920; Sweet 1940) to around 5% [1]. When a dermal sinus penetrates the occipital region, peroperative care must be taken to avoid a rapid and fatal exsanguination due to a possible connection with the cranial venous confluence [9]. If cerebellar abscesses are present, aspiration should not be performed since it might cause dissemination of an encapsulated lesion through the puncture site and may even produce haemorrhage with compression or shift of adjacent brainstem structures [12]. Since postoperative meningitis is one of the most common complications of this neurosurgery excision, broad‑ spectrum intravenous antibio­tics should be admin­­istered until the specific pathogen is cul­tured and corresponding antibio­tic sensitivity is identified. In our case, since the child presented with the signs of decompen­-sated hydrocephalus (vomitus, elevated anterior fontanel, CT finding), external ventricular drainage was inserted to alle­viate the elevated intracranial pressure and to promote more favourable surgery conditions (and perhaps to decrease the need for permanent CSF derivation). Hydrocephalus is the second most common presentation of dermoid cysts after infection and may be present due to the CSF circulation obstruction or secondarily due to an infection [11,13].

Conclusion

When a depression, subcutaneous swelling or skin or hair exudate occurs in the occipital region, an experienced practitioner should be sought in order to avoid misdia­gnosis and potential complications of the dermoid cysts (such as meningitis, cerebellar abscesses, obstructive hydrocephalus or adhesions to adjacent brain structures). MRI scans are very helpful for the dia­gnosis of these lesions and to plan surgery. Neurosurgical microexcision is the only effective treatment for dermoid cysts with dermal sinuses. Postoperative meningitis can be prevented with intra­venous administration of antibio­tics.

The informed parental consent for publication of this case report was obtained

The authors declare they have no potential conflicts of interest concerning drugs, products, or services used in the study.

The Editorial Board declares that the manu­script met the ICMJE “uniform requirements” for biomedical papers.

Accepted for review: 21. 10. 2014

Accepted for print: 26. 2. 2015

Brichtova Eva, M.D., Ph.D., Assoc. Prof.

Department of Neurosurgery

Masaryk University Medical School

St. Anne University Hospital in Brno

Pekarska 664/53

656 91 Brno

e-mail: brichtovae@seznam.cz