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A man in his late 60s presented with a sudden-onset headache, left-sided weakness and seizures. An unenhanced CT of the head showed a large low-attenuation lesion in his right frontal lobe with calcified borders, consistent with an intracranial dermoid cyst (figure 1). This cyst showed evidence of having ruptured, manifested by an adjacent collection containing a fat-fluid level and additional low-attenuation droplets in the subarachnoid space layering in the basal cisterns and cerebellar sulci. MR scan of the brain further supported this diagnosis (figure 1), with T1-weighted images showing the lesion and the subarachnoid space droplets to be hyperintense (secondary to fat). Surgical excision confirmed that this was a ruptured intracranial dermoid cyst.
Intracranial dermoid cysts are rare, benign lesions comprising <1% of all intracranial tumours.1 They are congenital hamartomatous tumours of ectodermal origin, with a dermis-like capsule containing squamous epithelium and adnexal structures (eg, hair follicles; sebaceous, apocrine and sweat glands). Cysts develop gradually, with the accumulation of glandular secretions and epithelial desquamation.2 They tend to occur close to the midline in the supratentorial compartment, usually in the sellar/parasellar, frontonasal regions or pineal fossa, or more rarely, in the posterior fossa.1 ,2 Symptoms are non-specific, and include headache, seizures, cranial nerve compression and hydrocephalus.1 ,2 Rupture is rare and usually spontaneous; aseptic chemical meningitis may result, producing headache and/or seizures, and possibly even death from infarction secondary to vasospasm.1 Rupture may not be clinically apparent acutely, as the inflammatory effects of the lipid contents circulating in the cerebrospinal fluid develop insidiously, potentially manifesting after months or years.1 Definitive treatment is surgical, with most patients having an uncomplicated postoperative course and low rates of recurrence.1
Contributors Both authors contributed equally to the manuscript.
Competing interests None declared.
Provenance and peer review Not commissioned; externally peer reviewed. This paper was reviewed by Mark Manford, Cambridge, UK.
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