[[Supravalvular pulmonary stenosis as a manifestation of a mediastinal germ cell tumor: a case report]].

Extrinsic compression of the pulmonary artery by a mediastinal mass is an exceedingly rare cause of pulmonary stenosis. We report the case of a 22-year-old man with no relevant medical history who, during a pre-surgical evaluation, presented with a three-month history of exertional dyspnoea. Echocardiography demonstrated supravalvular pulmonary stenosis, and chest computed tomography revealed a giant mediastinal mass encasing the great vessels and causing collapse of the left pulmonary artery branch. Mediastinal biopsy and immunohistochemical analysis were consistent with a primary mediastinal germ cell tumour of seminomatous morphology, accompanied by serum alpha-fetoprotein elevation, leading to its classification as a high-risk extragonadal germ cell tumour. This case highlights the importance of multimodal imaging in the differential diagnosis of mediastinal masses with compressive cardiac involvement, as well as the value of histopathological correlation and tumour marker assessment in guiding prognosis and multidisciplinary management.