Clinical features

•Tender or painful, sharply delineated typically blue 1-3 cm dermal nodule nodule

•Ventral skin, most on the upper half of the integument (head, neck & trunk)

•Rarely multiple lesions

2nd-4th decade

•Giant variant

•Linear, Blaschkoid, variants

•Autosomal dominant familial variant

•May occur as part of the Brooke-Spiegler syndrome

Histological features

•Nodule/multiple blue encapsulated nodules in the dermis +/- subcutaneous fat

•Common association with an adjacent nerve & exceptional intraneural component

•Outer layer of small intensely basophilic cells surrounding larger pale staining or eosinophilic cells with vesicular nuclei & small nucleoli

•Intra-tumoral lymphocytes

•Ductal & exceptionally, glandular differentiation

•Cystic variant

•Exceptionally, adenoid cystic carcinoma-like features

•No pleomorphism & only sparse mitoses or no mitoses

•Basement membrane thickening & intralobular eosinophilic globules

•Exceptionally sebaceous differentiation

•Marked lymphedema sometimes present- lymphangiectatic variant

•Spiradenocylindroma

•Telangiectatic variant

•Association with trichoepithelioma & trichoblastoma

•The tumor is so distinctive that IHC is rarely necessary- EMA & CEA highlight ductal/glandular differentiation, CK7 & β catenin +ve, myoepithelial cells- SMA & S100 +ve