Confronting Upside-Down Video-Assisted Thoracic Surgery for Anterior Mediastinal Leiomyoma.

[INTRODUCTION] Leiomyoma is a benign smooth muscle tumor typically arising in the uterus or gastrointestinal tract; its occurrence in the anterior mediastinum is extremely rare. The differential diagnosis of anterior mediastinal tumors usually includes thymoma, germ cell tumors, and lymphoma, whereas leiomyoma is rarely considered.

[CASE PRESENTATION] A 50-year-old woman with no notable medical history presented with chest pain and cough. Chest radiography showed a mass in the left lower lung field. Tumor markers (HCG, CEA, AFP, CYFRA 21-1, ProGRP, anti-AchR antibody, sIL-2R) were normal. CT revealed a 2.8 × 1.8 × 2.3 cm solid mass in the left anterior mediastinum, and MRI showed a fibrous lesion with mildly high T2 signal intensity and gradual contrast enhancement. These findings suggested a solitary fibrous tumor or neurogenic tumor. Thoracoscopic surgery was performed using the confronting upside-down video-assisted thoracic surgery (VATS). Intraoperatively, a well-defined, whitish, pedunculated mass arising from pericardial fat was identified. En bloc resection of the mass and surrounding pericardial fat was completed, while the phrenic nerve was entirely preserved. Histopathological examination revealed spindle-shaped smooth muscle cell proliferation. Immunohistochemistry was positive for desmin and α-smooth muscle actin (αSMA), partially positive for CD34, and negative for S100, confirming leiomyoma. The postoperative course was uneventful, with discharge on day 2.

[CONCLUSIONS] Primary leiomyoma of the anterior mediastinum is extremely rare. Because primary mediastinal leiomyomas have nonspecific imaging features, distinguishing them from other anterior mediastinal tumors is challenging; thus, surgical resection is required for both diagnosis and treatment. Compared with the conventional look-up method, the confronting upside-down VATS technique utilizes higher intercostal access to provide a comprehensive thoracic view while minimizing diaphragmatic interference. The 180-degree rotated assistant monitor allows both surgeon and assistant to share a thoracotomy-like visual field, enhancing intraoperative coordination. In this case, it facilitated a stable operative field and phrenic nerve preservation despite the tumor's proximity without diaphragmatic interference. The confronting upside-down VATS technique may be particularly advantageous for anterior mediastinal tumors located along the phrenic nerve and in close proximity to the diaphragm.