The cause of subclavian arterial aneurysms is most often:

C. Atherosclerosis.

DISCUSSION: The most common cause of subclavian aneurysms is atherosclerosis followed by trauma. The thoracic outlet syndrome may cause dilatation of the distal subclavian artery secondary to compression with poststenotic dilatation. Mural thrombi are quite common in these aneurysms and may cause embolism in an arm, a serious complication.