An Unusual Location and dermoscopy finding of a Pilar Sheath Acanthoma: A Case Report

Case presentation: Pilar sheath acanthoma is a rare, benign follicular hamartoma. They frequently present as an asymptomatic, flesh-colored papule with a central opening typically appearing on the upper lip of elderly patients although isolated cases have been reported on the forehead, cheek and postauricular area. Five neoplasams may arise from the infundibular part of the pilar apparatus. These include: pilar sheath acanthoma, dilated pore, inverted follicular keratosis, trichilemmoma, and the tumor of follicular infundibulum. We represent the case of a 55 years old, male patient, who came for consultation on nodular, keloid-appearing lesion on the upper leg, size of the lesion was 20x30 mm. It started developing five months prior the exam, at first as a small ulcer, patient did not report any previous injury at the site. The dermoscopic images revealed dotted and thin hairpin-like vessels on the periphery, polymorphous vessels including linear curved, rosetts, white circles with yellow center, and on nonpolarised mode, rainbow appearance. These dermoscopic features are non-specific and may also be observed in malignant tumors. Differential diagnosis included squamous cell carcinoma, inverted follicular keratosis and melanoma. An excision was performed and sent for routine H and E staining, which revealed distended, cystic, follicular structures, filled with keratin debris, part of them ruptured as well as abound inflammatory infiltrate, consistent with a pilar sheath acanthoma. In addition to being diagnostic, the excision was also curative, and no further treatment was required. More reports are needed to define the typical features of pilar sheath acanthoma in order to differentiate this benign tumor from other malignant tumors just by dermoscopy and thus to avoid unnecessary excisions in the future.

Keywords: Pilar sheath acanthoma