Occipital Dermoid Cyst Associated with Dermal Sinus and Cerebellar Abscesses

Extradural dermoid cyst with an intact occipital dermoid sinus is a rare entity, with fewer than 20 cases reported in the literature 1 .We describe the unique computed tomogram (CT) and magnetic resonance (MR) imaging findings of an infant presenting with cerebellar abscesses and secondary obstructive hydrocephalus resulting from an occipital dermoid cyst with a complete dermal sinus, confirmed at operation.Early neurosurgical intervention is advocated to prevent the ongoing risk of significant complications, including cerebellar abscess formation, hydrocephalus and bacterial meningitis.The importance of cross sectional imaging in the assessment of dural venous sinus anatomy in relation to the pre-operative planning of posterior fossa dermoid cysts is discussed. CASE HISTORYA previously healthy 20-month-old female initially presented with two short and self-limited episodes of low grade fever and vomiting associated with non-specific pain and irritability.She presented two weeks later to an outside institution with lethargy and low-grade fever, for which oral amoxicillin was prescribed.Four days later, she became more lethargic, refusing to walk or feed, and began to drool, with increasing irritability and intermittent non-bilious vomiting.She was re-admitted and noted to have a white blood count of 12.5 and elevated Erythrocyte Sedimentation Rate of 85 with no obvious cause identified.She initially improved but rapidly deteriorated, with obvious head tilt, lethargy, vomiting and ataxia.No focal neurological deficit was elicited.Cranial CT examination was performed (Figure 1) showing a well defined, midline occipital serpentine bony tract directly communicating with a right cerebellar hemispheric mass lesion.Following intravenous contrast, the mass lesion showed several thick walled ring enhancing cysts and effacement of the fourth ventricle with accompanying non-communicating hydrocephalus, trans-ependymal flow and transtentorial herniation.Cranial CT venography confirmed the bony defect coursed directly underneath and through the inferior margin of the torcular Herophili and could not be clearly separated from the adjacent dural venous sinuses.A cranial MRI examination was performed under sedation to better delineate the lesion and the surrounding venous anatomy (Figure 2).Unfortunately the patient's clinical condition rapidly deteriorated during scanning, necessitating immediate neurosurgical intervention prior to performing dedicated MR venography.Cranial MRI confirmed the CT findings.Several ring enhancing cysts were identified in the posterior fossa showing

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