Primary Malignant Perivascular Epithelioid Cell Tumor (PEComa) in the Mediastinum with Brain Metastasis: A Case Report and Literature Review

Background :Primary malignant perivascular epithelioid cell tumor (PEComa) is an extremely rare and highly aggressive tumor. Diagnosis is often difficult due to the lack of distinctive clinical features, which can lead to misdiagnosis. Imaging modalities such as CT, MRI, and PET-CT play a key role in diagnosis, but definitive diagnosis requires pathological analysis. Brain metastasis of PEComa is especially rare, making its diagnosis and treatment even more complex. Case Presentation :We report the case of a 32-year-old female who initially presented with intermittent chest pain and cough lasting for more than 10 days. Imaging revealed an irregular mass in the left mediastinum. CT scan demonstrated an ill-defined lesion measuring approximately 6.6 × 5.4 cm, adjacent to the pericardium and compressing the pulmonary artery. MRI showed heterogeneous signal intensity with progressive, uneven enhancement, suggestive of malignancy. Ultrasound-guided biopsy revealed a highly vascular tumor composed of perivascular epithelioid cells with active mitotic figures. Immunohistochemistry was positive for Melan-A and Desmin, establishing the diagnosis of primary malignant perivascular epithelioid cell tumor (PEComa) of the mediastinum. PET-CT confirmed hypermetabolic activity of the mass.The patient underwent tumor resection, which was technically challenging due to tumor adhesion to vital structures. Postoperatively, adjuvant radiotherapy was administered with a total dose of 50 Gy delivered in 25 fractions (2 Gy per fraction). Approximately 8 months after surgery, the patient developed confusion. Cranial CT revealed a hemorrhagic lesion in the left parietal lobe. Emergency hematoma evacuation and tumor resection were performed, and histopathology confirmed metastatic PEComa of the brain. Two months later, the patient was readmitted with headache. MRI demonstrated multiple nodular abnormal signals at and around the previous surgical site in the left parietal lobe, raising suspicion of tumor recurrence. Subsequent histopathological examination again confirmed metastatic malignant PEComa. Conclusion :Primary malignant PEComa in the mediastinum is extremely rare, and its clinical presentation lacks specificity. It is often misdiagnosed as thymoma, lymphoma, or teratoma on imaging. The final diagnosis relies on pathological and immunohistochemical examinations. A combination of various imaging methods is crucial for early detection and differential diagnosis. Clinicians should be aware of the imaging features of PEComa to avoid misdiagnosis and treatment delays. This case provides valuable insights into the clinical and imaging diagnosis of PEComa.