Ruptured intracranial dermoid cyst.

A 30-year-old female was referred for symptoms of severe headache for the past 4 days. She had no significant medical history. On examination, she was conscious and oriented, afebrile and her vital signs were within normal limits.

Dermoid cysts are ectodermal inclusion cysts. These lesions have a thick viscous fluid that contains fat and cholesterol. Intracranial dermoid cysts are rare lesions accounting for approximately 0.04–0.6% of all primary intracranial neoplasms.1 They are slow growing, benign, congenital neoplasms that are commonly seen in the midline, along the parasellar cisterns, and in the fronto-basal and posterior fossa locations. They usually become symptomatic in the third decade. Seizures and headache are the most common symptoms. There is a mild male predominance.1

Rupture of an intracranial dermoid cyst is rare and mostly spontaneous, or may occur iatrogenically during surgery or following head trauma.2 The contents of the ruptured cyst spread into the ventricles and along the subarachnoid spaces inciting severe meningeal inflammation. This results in chemical meningitis, seizures, vasospasm with infarction and death.1 The incidence of chemical meningitis in ruptured dermoid cysts has been reported to be 7%.2

On imaging, ruptured dermoid cysts have a dramatic CT and MR appearance. Plain CT show low-density fat droplets in the subarachnoid spaces or in the ventricles with intraventricular fat-CSF levels. There is no enhancement on post-contrast studies. In our patient on MRI, ruptured dermoid cysts showed high-signal fat droplets in the subarachnoid spaces and intraventricular fat-CSF levels on both T1 and T2-weighted images (Figure 1, 2).

Figure 1

Axial T1 weighted MR image shows a heterogeneously hyperintense mass in the midline/right suprasellar location, compressing the right cerebral peduncle with multiple small hyperintense foci seen scattered in the subarachnoid spaces.

Figure 2

Sagittal T1 weighted MR image shows a heterogeneously hyperintense mass in the midline with multiple hyperintense foci scattered in the subarachnoid spaces and along the corpus callosum.