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Ruptured dermoid with aseptic meningitis

Case contributed by Yves Leonard Voss
Diagnosis certain


Presents to the emergency department with a severe headache, neck stiffness, nausea and sleepiness.

Patient Data

Age: 40 years
Gender: Male

There is a well defined cystic mass at the right cerebral peduncle showing sedimentation and a fluid level with quite a lot low density (-120 HU) content.

There are bubbles of low density (-100) spread throughout the subarachnoid space, i.e. Sylvian fissures and sulci bilaterally.

There is dilatation of the ventricles, which show inhomogeneous density and a fluid-Level rostrally.

Case Discussion

The mass at the right cerebral peduncle is well defined and shows fat density (around -100 HU) content and a fat-debris-level. While at first - in the clinical suspicion of severe meningitis - one might consider signs of ventriculitis and a cerebral abscess, the density of around -100 HU is proof of fatty content (air would show around -1000 HU density), which means we don't have gas-fluid levels but fluid-fat-levels. The bone window shows the difference in density between the fat and the air (i.e. in the paranasal sinuses, surrounding the patients head).

The diffusely spread fat locules are proof of rupture.

Based on imaging we concluded the diagnosis of a ruptured dermoid cyst.

Dermoid rupture typically leads to chemically induced aseptic meningitis due to meningeal irritation by cholesterol debris. This explains the patient's symptoms, it further is a bad prognostic marker because there is a risk of vasospasm and subsequent cerebral ischemia.

The patient went on to have a resection, and the diagnosis was confirmed by histology (which showed stratified squamous epithelium (CK-plus, CK5/6) without cellular or nuclear atypia). Later on, the patient needed ventricular drainage and was finally provided with lumbar cerebrospinal fluid drainage.

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