Invagination of the left subclavian artery into the left upper lobe--a normal variant.

A rare variant of the left subclavian artery is presented, in which the usually intramediastinal portion of the artery ascended in the medial aspect of the left upper lobe in a 44-year-old woman. A septum, presumed to represent a quadruple layer of visceral and parietal pleurae, connected the mediastinum to the intrapulmonary course of the artery.