Neuroradiology

Dermoid tumour

congenital ectodermal inclusion cysts and the term includes epidermoid tumour and dermoid cysts. All elements of which those tumours are composed originate from the embryonic ectoderm.

They are rare tumours, accounting for less than 0.5% of all intracranial tumours; epidermoids are at least five times more common than dermoid cysts.

Dermoid cysts may be found intracranially or in the spinal canal, mainly in or near the midline; some typical locations are frontobasal, parasellar or in the posterior fossa. They are cystic masses, with a fibrous capsule lined with squamous epithelium and containing a thick fluid composed of cholesterol, keratin and lipid metabolites, derived from decomposed epithelial cells. The cyst may rupture and fatty components of its content may spread into the subarachnoid spaces and within the ventricles (Fig.1).

Dermoid cyst may be an occasional finding or may present clinically with seizures and headache; chemical meningitis may occur in cases of rupture.

CT shows a well delineated, hypodense, nonenhancing mass, with a density close to that of fat. Calcification of the capsule may be found. Hyperdense dermoids have been described but are unusual.

MR demonstrates a T1 hyperintense mass, with inhomogeneous T2 signal ranging from hypointense to hyperintense (Fig.2).

GS

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Fig.2

a, b. MR, midline sagittal images of the cervical spine, T1-weighted (a) and T2-weighted (b) images. An intramedullary space-occupying lesion is seen, from C7 to T1; the signal is inhomogeneous, partly hyperintense in T1 and T2 and partly isointense. At operation, a "threephillic" dermoid was found, containing cells of the three cutaneous ectodermal layers.
Dermoid tumour, Fig.1 (a)
Dermoid tumour, Fig.1 (b)
Dermoid tumour, Fig.1 (c)
Dermoid tumour, Fig.1 (d)
Dermoid tumour, Fig.1 (e)
Dermoid tumour, Fig.2 (a)
Dermoid tumour, Fig.2 (b)