Imaging and pathological diagnosis of primary intracranial malignant melanoma: A case report and literature review

Primary intracranial malignant melanoma (PIMM) is a rare malignant tumor that lacks specific clinical manifestations. Preoperative diagnosis is difficult to differentiate from meningiomas on computed tomography (CT) scans. Magnetic resonance imaging (MRI) usually shows typical characteristics with high signal intensity on T1WI and low signal intensity on T2WI. PIMM is highly invasive, insensitive to chemoradiotherapy, and has a poor prognosis. A 27-year-old woman was admitted to the hospital with a headache for 10 days. She did not experience nausea, vomiting, dizziness, or any other discomfort. A computerized tomography (CT) scan demonstrated a high-density mass in the left cerebellum with patchy calcification at the posterior edge, and heterogeneous enhancement was observed on a contrast-enhanced scan. MRI revealed typical characteristics of high signal intensity on T1WI and low signal intensity on T2WI. The signal characteristics of FLAIR were similar to those of T2WI, and diffusion-weighted imaging (DWI) sequence showed limited diffusion of the tumor. Magnetic resonance spectroscopy revealed increased choline (Cho) and decreased creatine (Cr) and N-acetyl aspartate (Naa) in the tumor. The patient underwent tumor resection and postoperative chemoradiotherapy and immunotherapy. Histological and Immunohistochemistry (IHC) tests confirmed the diagnosis of PIMM. In addition, genetic testing revealed GNAQ gene variation. No recurrence or complications were observed during the follow-up for 6 months. PIMM is rare, and its pathological diagnosis should be closely combined with clinical and medical history. GNAQ is a common variant of PIMM and is expected to be a therapeutic target.