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Case Reports

Abstract

34-year-old woman presented with a 2.5 x 2.0 cm pink, domed, and hairless plaque at the vertex scalp. This lesion had been present her whole life and often bled and became irritated. Reportedly, prior biopsy at an outside institution was called hemangioma. However, ultrasound to evaluate for vascularity was inconclusive. The lesion underwent a shave biopsy and excision, both demonstrating an exophytic papillary structure lined by a bilayered cuboidal and columnar epithelium with plasma cell-rich stroma, consistent with syringocystadenoma papilliferum (SCAP). No hair follicles or sebaceous glands were present in the shave biopsy. However, the subsequent excision demonstrated a subjacent dermal proliferation of hyperplastic apocrine glands, consistent with apocrine hamartomatous nevus (AN). Notably, a clear transition from the AN to the bilayered SCAP epithelium was seen. The final diagnosis was SCAP arising from a subjacent AN. SCAP and AN are both rare benign appendageal tumors that commonly present on the head and neck. SCAPs are known to occur alone or with a variety of other lesions, most often nevus sebaceus. However, association with AN has only been reported once before. Our case is unique because it shows a clear transition from AN to SCAP, suggesting that the SCAP developed from the underlying apocrine lesion. The histogenesis of SCAP, whether it is of apocrine or eccrine origin, is unclear, with research yielding conflicting histologic and ultrastructural findings. This present case reveals SCAP with distinct apocrine origin.