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.1

a. Intradural extramedullary space-occupying lesion at the level anterior to the conus medullaris, inhomogeneously hyperintense in T2-weighted image (arrowheads). b. In a T1-weighted image the lesion is inhomogeneously hyperintense, without enhancement. c, d. MR of the head, T1-weighted images; multiple punctate foci of hyperintensity are seen within the ventricles and in the subarachnoid spaces. They represent droplets of fat escaped from the ruptured capsule of the tumour.The patient had suffered two episodes of aseptic meningitis. e. MR, T2-weighted image. The droplets of fat are hypointense.
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)