A 65-year-old male patient presented with a 3-mm dome-shaped cribriform pinkish nodule on the back side of his right leg ( Figure 1A ). Dermoscopy revealed thin hairpin-like vessels on the periphery, polymorphous vessels including linear curved, coiled, and hairpin vessels, and a few white clods at the center on a pinkish background ( Figure 1B/C ). Differential diagnosis included squamous cell carcinoma, inverted follicular keratosis and melanoma. The lesion was excised and histopathological examination revealed pilar sheath acanthoma.
Pilar sheath acanthoma (PSA) is a rare benign follicular neoplasm presented as a solitary, small, skin-colored, asymptomatic benign nodule with a central pore-like opening plugged with keratin, mostly seen in middle-aged individuals on the upper lip (1). Its non-specific clinical appearance may resemble other skin tumors such as basal cell carcinoma (2). Our case lacked a typical central pore-like opening feature clinically and revealed polymorphous vessels and white structures that correlate with the fibrovascular septae at stroma surrounding the tumor histopathologically. These dermoscopic features are non-specific and may also be observed in malignant tumors such as melanoma, metastases, and SCC. Therefore, histopathological examination remains the gold standard for diagnosing PSA. Our case findings show that PSA may have prominent vasculature on dermoscopy resembling malignant skin tumors. More reports are needed to define the typical features of PSA in order to differentiate this tumor from other malignant tumors just by dermoscopy and thus to avoid unnecessary excisions in the future.
- Pilar sheath acanthoma Mehregan AH, Brownstein MH. Arch Dermatol.1978;114(10):1495-7.
- Plaque-Like Pilar Sheath Acanthoma: Histopathologic and Immunohistochemical Study of 3 Unusual Cases Jo-Velasco M, Corrales-Rodríguez A, Francés-Rodríguez L, Alegría-Landa V, Eraña-Tomás I, Rütten A, Requena L. Am J Dermatopathol.2018;40(2):125-130.