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Melanocytoma

Case contributed by: Dr Frank Gaillard

Presentation:

Progressive minor weakness, particularly in the right arm.

Patient Data:

Age: 50 years
Gender: Male
Race: Indian/Pakistani
Modality: CT

Non-contrast CT brain demonstrates a lesion within the medulla.  The solid component more anteroinferiorly measures 14 x 14 x 16 millimetres in orthogonal planes and is densely hyperdense.  There is a cystic component posterosuperior to this. There are no fatty elements identified within the lesion.There is ossification of the apical ligament superior to the dens.  No midline defects identified.

The patient was observed over a number of years, with minor but progressive symptoms. The provisional diagnosis had been of an atypical cavernous malformation, or of an unusual intramedullary tumour. Eventually the decision was made to remove the lesion as slow growth was confirmed. 

MRI brain

Modality: MRI

A heterogeneous inferior medullary mass is noted measuring up to 15-16 mm in diameter. It is strikingly T1 hyperintense and mostly T2 hypointense with moderate magnetic susceptibility, in keeping with calcification and/or haemosiderin staining, with no convincing enhancement or diffusion restriction.  Of note, the eccentric medullary cyst, centred eccentrically over the right posterosuperior margin of the mass, has decreased in size, currently measuring up to 10 x 5 mm diameter, with minor adjacent marginal parenchymal T2 hyperintense signal abnormality. 

Histology

Modality: Histology

MICROSCOPIC DESCRIPTION: The sections show a moderately hypercellular tumour. This consists of epithelioid and spindle cells which are heavily laden with globular brown pigment and show strong immunostaining for the melanocyte markers, tyrosinase and melan A. Tumour cells show moderate nuclear pleomophism with vesicular nuclei containing conspicuous nucleoli. No mitotic figures are identified and the topoisomerase index is <1%. A small focus of coagulative necrosis is also noted. Focal dural attachment is identified in one tumour fragment. 

DIAGNOSIS: Melanocytic tumour with features favouring meningeal melanocytoma.

Case Discussion:

Meningeal melanocytomas are rare tumours, with can be seen anywhere along the neuraxis. The intense T1 hyperintensity and slow progression (compared to melanoma metastasis) are typical. 

Histology courtesy of Dr M Gonzales, Royal Melbourne Hospital, Australia 

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