Rare Presentation of Proliferating Trichilemmal Tumor of the Left Shoulder Treated by Rhomboid Flap

Abstract

Background: Proliferating trichilemmal tumor (PTT), also known as giant hair matrix tumor or invading pilomatrixoma, is an uncommon adnexal neoplasm that is usually benign but occasionally shows malignant potential, for which postoperative histopathology is required to confirm diagnosis.

Case Presentation: A 53-year-old woman with an unremarkable medical and surgical history presented with a slowly enlarging lump on the posterior aspect of the left shoulder, present for 20 years.

Intervention: Ultrasonography showed a large, heterogeneous mass; fine-needle aspiration cytology (FNAC) was inconclusive, and incisional biopsy was performed prior to definitive excision with Rhomboid flap reconstruction.

Histology: Histopathological examination revealed a circumscribed nodule with proliferating squamous epithelium, abrupt trichilemmal keratinization, and mild focal atypia, features consistent with PTT.

Outcome: The patient recovered well after excision and flap reconstruction, with postoperative imaging showing no clinical evidence of recurrence.

Key Learning Point: PTT should be considered in the differential diagnosis of longstanding soft-tissue masses even at atypical extra-scalp sites such as the shoulder, where histopathological confirmation and appropriate reconstructive planning are essential for optimal outcomes.