Case 18 :  

A young male presents with convulsions.
What is the diagnosis?

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Fig 1

Fig 2

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Imaging Findings
A slightly lobulated markedly hyperintense mass is present in the right parasellar region. The lateral lobule of the mass is markedly hyperintense.  The  medial lobule demonstrates considerable heterogeneity of its intensity appearing predominently hypointense suggestive of fatty material.

Dermoid Cyst

Intracranially these are rare tumors compared to epidermoid cysts. As with epidermoid cysts, they arise from inclusion of ectodermoid elements in the neural groove at its time of closure. Not uncommonly there is a persistent defect in the overlying skin, with a sinus tract extending into the intracranial portion.

Clinically, they usually present in the third decade and are most commonly located in the posterior fossa in the midline but may occur in the cisterns about the sella turcica and elsewhere. They may also have an intraventricular location arising within the cisterns of the tela choroidea in the lateral, third, or fourth ventricular regions. Microscopically, these cysts may contain elements from all layers of the skin. Much of the wall of the cysts may be lined (as in epidermoid tumors) by stratified squamous epithelium supported by an outer collagen layer. More solid portions of the tumor may contain hair follicles along with sebaceous, sweat, and apocrine glands. Calcification may develop in the portion of the walls, and there may be bone and cartilage within some of the cysts.


Imaging Findings
Dermoid cysts typically demonstrate marked hyperintensity on short TR/TE MR images due to their fatty content, which consists of triglycerides and unsaturated fatty acids. On long TR images, the cysts usually show hypointensity, particularly on long TE images, again due to the presence of the fatty material. The hypointensity of the mass may be throughout or within one or more loculations within the lesion. Other portions of the cysts may demonstrate a pattern consisting of inhomogeneous hyperintensity, similarto epidermoid tumors. The cysts may rupture into the subarachnoid space or, for those arising in the tela choroidea, intraventricularly. Subarachnoid rupture will demonstrate droplets and streaks of high intensity within the subarachnoid cisterns about the tumor and possibly more distally in the brain. Within the ventricles a fat-fluid level will develop in the anterior superior portions. A chemical shift artifact will frequently be projected into the lesion on long TR sequences. On short TR sequences a high-intensity fluid level will be present anterior to the hypointensity of CSF, whereas on long TR sequences an intermediate and low-intensity fluid collection will be observed anterior to the high intensity of the CSF.



Dr. Ashok Raghavan, Manipal Hospital, Bangalore