Intradermal Syringocystadenoma Papilliferum on the Popliteal Fossa: A Rare Dermal Variant in an Atypical Location

Syringocystadenoma papilliferum (SCAP) is a benign adnexal tumor commonly found on the scalp and face, and often associated with nevus sebaceous, with about half of cases appearing in early childhood. SCAP exhibits cystic invaginations with papillary structures and a double-layered glandular epithelium linked to the epidermal surface and stromal plasma cells. We are reporting a rare instance of intradermal SCAP in a 55-year-old male. He sought evaluation for a long-standing asymptomatic dark-pink papule in his left popliteal fossa, measuring 0.7 x 0.5 x 0.4 cm. A shave biopsy revealed papillary dermal fibrosis, glandular epithelium with apocrine secretion, and papillary projections without an epidermal connection. Infundibulofollicular keratinization was observed, along with stromal plasma cells. The patient chose local excision as the treatment option. This case highlights the rarity of intradermal SCAP, especially in the left popliteal fossa, with only one other reported case in the literature.