Track

Case Reports

Abstract

A 17-year-old male presented with a two-centimeter firm to spongy nodule with overlying focal decreased hair shaft density on the right frontal scalp. Clinically this was suggestive of pilar cyst, and he was referred for excision. Histological examination of the excision specimen revealed a cyst composed of squamous epithelium lacking a granular layer with diffuse eccrine ductal differentiation within the cyst wall highlighted by epithelial membrane antigen (EMA) staining. Thus far, very few instances of this phenomenon have been reported in the literature; only six cases of pilar cysts with eccrine ductal structures have been described. The presence of ductal differentiation in pilar cysts may thus be an underrecognized feature. While the vast majority of adnexal neoplasms differentiate toward a single appendage type, it has been hypothesized that pluripotent germinal cells within the dermis have the potential to participate in multidirectional differentiation. This can subsequently generate features such as apocrine, eccrine, or sebaceous structures. Why this occurs in some scenarios and not others remains unclear; additional studies are necessary to elucidate possible triggers for divergent differentiation. Ultimately, however, the presence of such ductal structures does not appear to significantly alter prognosis, as our case and those previously detailed report no recurrences. Our case supplements those present in the literature and highlights this rare finding.