Proliferating trichilemmal tumor mimicking squamous cell carcinoma: a case report of occipital reconstruction using a trapezius flap.

Introduction and importance: Proliferating trichilemmal tumors (PTTs) are rare cutaneous neoplasms that can mimic squamous cell carcinoma (SCC) clinically and histologically, posing a significant diagnostic challenge. We present a giant PTT of the nape initially misdiagnosed as SCC, highlighting diagnostic pitfalls and reconstructive management. Case presentation: A 61-year-old male presented with a 60 mm ulcerated, exophytic mass on the posterior neck. Initial superficial biopsy suggested a well-differentiated SCC. The patient underwent wide local excision. To cover the resulting 95 × 65 mm occipito-cervical defect, a pedicled lower trapezius musculocutaneous island flap was harvested. Definitive pathology revealed abrupt trichilemmal keratinization without a granular layer, correcting the diagnosis to a PTT with clear surgical margins. Clinical discussion: Superficial biopsies of PTTs often capture atypical squamous cell proliferation while missing deeper diagnostic features. Complete excision is necessary for accurate diagnosis. For massive posterior neck defects exposing underlying musculature, the lower trapezius flap provides reliable vascularity, adequate bulk, and minimal donor-site morbidity compared to free flaps or skin grafts. Conclusion: Surgeons and pathologists must be aware of PTTs mimicking SCCs to avoid overly aggressive oncological treatments. The lower trapezius island flap is an elegant and highly effective reconstructive option for large occipito-cervical defects.