The histopathological spectrum of cutaneous meningeal heterotopias: clues and pitfalls.

OBJECTIVE

To describe the histopathological features of heterotopic cutaneous meningeal tissue.

RESULTS

Nineteen cases were collected between 1993 and 2010. Immunohistochemistry for epithelial membrane antigen (EMA), neuron specific enolase (NSE), S100, glial fibrillary acid protein (GFAP), progesterone receptor (PR), CD31, glucose transporter-1 (Glut-1), podoplanin and NKI-C3 was performed. Lesions were congenital (100%) and presented as aplasia cutis with alopecia (63%) or lumps (37%), on the scalp (18 of 19) and sacral region. Resonance magnetic imaging revealed four underlying anomalies of the neuraxis. Histopathological analysis showed meningeal tissue arranged in four variably associated architectural patterns: fibrous (100%), pseudovascular (100%), cellular (68%) and pseudomyxoid (32%). Other features included collagen bodies (58%), calcifications (26%) and dermal melanocytes (32%). Heterotopic brain tissue or heterotopic ependymal cyst was associated in two cases. Arachnoidal cells expressed EMA and NSE, but not S100 protein, CD31 or GFAP. They expressed podoplanin (93%), especially in pseudovascular areas, NKI-C3 (79%), and less frequently Glut-1 (46%) and PR (30%).

CONCLUSIONS

Histopathological features of cutaneous meningeal heterotopias are various and sometimes misleading. Fibrous lesions should not be misdiagnosed as aplasia cutis. Podoplanin-positive pseudovascular spaces represent the main pitfall and should not be diagnosed as lymphangioma. Correct diagnosis is confirmed by EMA and NSE coexpression within the lesion.