Amelanotic Melanoma of the Sinonasal Region: Diagnostic Challenges.

Background & Objective: Sinonasal melanoma is an aggressive malignancy with a poor prognosis, largely due to its propensity for local invasion and early metastasis. Diagnosis is often difficult, particularly in the absence of melanin pigmentation. Histopathological and immunohistochemical (IHC) evaluation is essential for confirmation. This report describes a diagnostically challenging case of amelanotic melanoma of the sinonasal region. Case Presentation: A 56-year-old woman presented with a 5-month history of epistaxis, facial pain, and visual impairment of the left eye. Clinical examination revealed a mass in the left nasal cavity, initially diagnosed as sinonasal carcinoma. Histopathology suggested a differential diagnosis of non-Hodgkin lymphoma (NHL) and poorly differentiated squamous cell carcinoma (SCC). Imaging demonstrated a sinonasal tumor involving the left extraconal orbital wall and paranasal sinuses. A biopsy initially raised suspicion for NHL; however, IHC staining was negative for CD45, CD20, and CD3. Similarly, negative P40 and cytokeratin excluded SCC. Strong immunoreactivity for S100, HMB45, and Melan-A established the diagnosis of amelanotic melanoma. Conclusion: Amelanotic melanoma of the sinonasal tract poses a significant diagnostic challenge due to nonspecific clinical features and lack of pigmentation. This case highlights the indispensable role of IHC in achieving a definitive diagnosis.