Summary: A 78-year-old male with history of left middle cerebral
artery (MCA) distribution infarct now presents after a syncopal episode.
An echocardiogram (ECG) and cardiac enzymes are negative. A head computed
tomography (CT) is ordered for further evaluation.
Ruptured dermoid cyst
Axial computed tomography (CT) images through the brain demonstrate a fat fluid level
within the frontal horn of the left lateral ventricle. A tiny fat fluid level
within the frontal horn of the right lateral ventricle is not well appreciated
by CT. The fat component measures approximately -88 Hounsfield units (HU) while
the cerebrospinal fluid (CSF) measures approximately 2 HU. No intracranial
masses are present. Extensive encephalomalacia is present within the left
middle cerebral artery vascular distribution.
The presence of intraventricular
fat-fluid levels is rare and almost certainly due to rupture of an intracranial
or spinal dermoid cyst. The key to diagnosis on CT is measurement of
attenuation of the fat component, which can easily be mistaken for air on
improperly windowed images.
Dermoid cysts are benign, ectopic,
squamous epithelial cysts that occur as a developmental anomaly, in which
embryonic ectoderm is included into deeper tissues. They may contain epithelial elements, such as
sebaceous glands, sweat glands, and hair follicles. These lesions most commonly
occur near the midline, usually suprasellar or parasellar. Less commonly they
may be seen within the posterior fossa or extracranial sites, such as the spine
or orbit. The dermoid cyst in the case above occurred within the spine.
Dermoid cysts are often found incidentally, but when symptomatic present with headache, seizures, visual
symptoms if suprasellar, and less commonly cranial nerve defects, hypopituitarism,
and diabetes insipidus. Large cysts may cause obstructive hydrocephalus.
Dermoid cysts are most often diagnosed with CT where they appear as a well defined, lobulated, nonenhancing
mass of fat attenuation, with approximately 20% containing wall calcifications.
Magnetic resonance imaging (MRI) signal characteristics include hyperintensity
on T1-weighted images due to lipid components, and variable signal intensity on
T2-weighted imaging. Fat suppression sequences may be useful to confirm lipid
elements within the dermoid cyst. The most common complication of dermoid cysts
is rupture, either spontaneously or secondary to trauma. With rupture, fat
droplets will disseminate into the subarachnoid spaces and ventricles and may
be identified with CT or MRI. Rupture may also results in a chemical meningitis
with subsequent extensive leptomeningeal enhancement. The chemical meningitis
may also induce arterial vasospasm.
Treatment consists of surgical
resection with recurrence occurring rarely. Complicated cases of rupture may
require shunt placement for hydrocephalus if symptomatic.
- Liu JK, Gottried ON, Salzman, et al. Ruptured intracranial dermoid cysts: Clinical, radiographic, andsurgical features. Neurosurgery. 2008;62:377-84.
- Smirniotopoulos JG, Chiechi MV. Teratomas, dermoids, and epidermoids of the head and neck. Radiographics. 1995;15:1437-1455.
- Osborn AG, Preece MT. Intracranial cysts: Radiologic-pathologic correlation and imaging approach. Radiology. 2006;239:650-664.