Metastatic mediastinal neoplasm masquerading as aortic dissection: a skip sign on computed tomography for their distinction.

Four years after undergoing a left lower lobe lobectomy for squamous cell carcinoma, a 77-year-old man presented with a mass lesion in the left upper mediastinum associated with chest pain. Computed tomography revealed a homogeneous density immediately adjacent to the aortic arch and thoracic aorta consistent with aortic dissection. Upon thoracotomy, however, the lesion was found to be an oat cell carcinoma. Retrospective review of the computed tomography scans detected a normal segment of descending aorta, indicating the interruption of the paraaortic lesion. Such a skip sign can be used to rule out aortic dissection.