Innominate artery: angiocardiographic study.

Abstract

The Radiologist is familiar with the problems involved in the differential diagnosis of roentgenographically demonstrated right superior mediastinal prominences. Similar shadows may represent a variety of neoplastic, infectious, granulomatous, vascular, and other lesions (Fig. 1). Aneurysm, dilatation, or buckling of the innominate artery may produce roent-genographic findings which simulate those of retrosternal thyroid enlargement, mediastinal lymph node enlargement, mediastinitis, or disease within the apex of the right lung. In the past it has occasionally been necessary to resort to exploratory thoracotomy in order to distinguish between innominate artery aneurysm and superior mediastinal tumor; this distinction may be made with ease through the use of angiocardiography (1). The present report summarizes our experience with contrast visualization as it bears upon the innominate artery. Normal Innominate Artery The normal innominate artery is the largest branch of the arch of the aorta, having been found in postmortem studies to measure from 3.7 to 5.0 cm. in length. It arises as the first of the three great brachiocephalic arteries from the ascending portion of the aortic arch; its point of origin is approximately on a level with the upper border of the second right costal cartilage. It takes an oblique course upward, backward, and to the right, to the level of the upper border of the right sternoclavicular junction, where it bifurcates to form the right common carotid and subclavian arteries. Anteriorly, the innominate artery is related to the left innominate and right inferior thyroid veins and the right vagus nerve. Posterior to it is the trachea, which it crosses obliquely. To the right are the right innominate vein, the superior vena cava, the right phrenic nerve, and the pleura. To the left are the thymic remnant, the left common carotid artery, the inferior thyroid veins, and the trachea (2, 3). The conventional postero-anterior chest roentgenogram does not reveal the normal innominate artery, since it does not project to the right of the spine and since the superior vena cava and the right innominate vein form the right superior mediastinal border in this projection. In the left anterior oblique projection, the innominate artery forms the anterior, superior portion of the cardiovascular silhouette, above the curve of the ascending aorta. Its posterior border is invisible. Elongation and dilatation of the artery may result in its becoming border-forming in the frontal projection (4). Angiocardiographic findings are in conformity with the anatomical and roentgenographic descriptions given above (Fig. 2). Due to its relatively small caliber (in comparison to that of the aorta), the innominate artery is not invariably well demonstrated by angiocardiography. Serial studies are of special value in this connection.