Preoperative Misdiagnosis of Malignant Mucosal Melanoma of the Nasal Septum by MRI.

Malignant sinonasal mucosal melanoma is a rare and aggressive neoplasm. As it shows nonspecific clinical symptoms, magnetic resonance imaging (MRI) is the most effective diagnostic tool. Before a mass is histopathologically confirmed, MRI is regarded as the optimal differential diagnostic procedure, especially in patients who present with a unilateral sinonasal cavity mass. However, we recently treated a patient who showed atypical MRI findings, resulting in a preoperative misdiagnosis of a vascular tumor. By pathologic examination, the patient was confirmed to have a malignant mucosal melanoma that originated from the nasal septum. This case demonstrates that unilateral nasal cavity masses that present with nonspecific symptoms, such as epistaxis, should be evaluated for possible malignant neoplasms, even if the mass has benign-looking characteristics in preoperative endoscopic findings and MRI images.