Malignant Solitary Fibrous Tumor of the Sinonasal Tract - A Rare Case with Diagnostic Challenges

Solitary fibrous tumor is a rare mesenchymal neoplasm, most commonly arising from the pleura, with infrequent involvement of the sinonasal tract. Malignant transformation is uncommon and poses significant diagnostic challenges due to overlapping histomorphology with other spindle cell neoplasms. We report a case of malignant solitary fibrous tumor of the sinonasal region in a 52-year-old male who presented with a recurrent nasal mass. Radiologic evaluation revealed an infiltrative lesion arising from the maxillary sinus. Histopathological examination and immunohistochemistry, including STAT6 nuclear positivity, confirmed the diagnosis of malignant SFT. This case highlights the importance of integrating clinical, radiologic, histopathologic, and immunohistochemical findings for accurate diagnosis of this rare entity. SFT (Solitary Fibrous Tumor) is a mesenchymal neoplasm of fibroblastic origin, classified as an intermediate (rarely metastasizing) tumor in the WHO Classification of Soft Tissue and Bone Tumors (5th edition).[1] While the pleura is the most common site, extrapleural locations such as the meninges, abdominal cavity, trunk, extremities, and head and neck region have been documented. Sinonasal involvement is particularly rare, accounting for approximately 5% of cases. Malignant SFTs exhibit aggressive behaviour with potential for local recurrence and distant metastasis. Due to histological overlap with other spindle cell neoplasms of the sinonasal tract, definitive diagnosis requires immunohistochemistry and molecular correlation. We present a rare case of malignant sinonasal SFT with emphasis on diagnostic approach and differential considerations.