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

AIMS: To describe the histopathological features of heterotopic cutaneous meningeal tissue.

METHODS AND 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.