Meningeal melanocytoma

Case contributed by Dr Jose Bacalla

Presentation

Nausea and vomiting.

Patient Data

Age: 40 years
Gender: Female
CT

Hyperdense posterior fossa mass with avid contrast enhancement has close relation to the internal occipital crest suggesting to be extra-axial in nature. Exhibits mass effect over the right cerebellar hemisphere effacing the fourth ventricle with enlargement of the third and lateral ventricles, in keeping with hydrocephalus. Subaracnoid spaces are effaced accounting for increased intracranial pressure.No midline shift.

MRI

T1 hyperintense extra-axial mass in the right aspect of the posterior fossa with a close relation to the internal occipital crest. Has T2 low signal and significant blooming artifact on gradient sequence. Significant enhancement of the mass on post contrast images. No other areas of pathologic enhancement. Findings suggest an extra-axial melanotic mass.  No adjacent edema. Bilateral ventricular enlargement as well as transependymal edema, in keeping with obstructive hydrocephalus. Punctate foci of white matter signal alteration in both centrum semi-ovale, most likely represent gliosis.

MRI

3D VIBE + CONTRAST

3D-VIBE with sagittal and coronal reformats helps to confirm the mass is extra-axial in nature.

No dural tail is identified

Pathology

1. Fusocellular neoplasm with areas of pigmentation consistent with melanin. 

2. Skull bone shows areas of melanocytes.

3. S100 protein marker shows diffuse positive stain.

4. Ki-67 marker shows a few punctate isolated positive foci

Case Discussion

Meningeal melanocytoma is a rare entity. Pre-operative diagnostic is challenging given that not all tumors exhibit the classic spontaneously high signal in T1 1  The T1 and T2 shortening effects seen in melanocytic tumors is mostly due to the paramagnetic effects of free radicals found in melanin 3 but are also attributed to blood products ( methemoglobin).

The dural tail sign for extra-axial pathology such as meningioma is not identified in this cases and unlike meningiomas, this entity lacks of local bony hyperostosis. Meningeal melonocytomas are most frequently found in the upper cervical region or around de foramen magnum, given that this area has more melanocytes 2

The distinction between meningeal melanocytoma , primary malignant melanoma of the meninges or metastatic melanoma to the brain/meninges is challenging. The final diagnosis is based on pathology and Immunohistochemistry. Ki-67% markers help to differentiate benign from malignant melanoma, the later exhibiting highly positive index. In this particular case, no suspicious skin lesions were identified.

 

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Case information

rID: 80336
Published: 21st Jul 2020
Last edited: 22nd Jul 2020
Inclusion in quiz mode: Included
Institution: Hospital Nacional Edgardo Rebagliati Martins