Alterations of anatomic relationships on chest computed tomography as a function of arm position

To determine the effects of arm position on the appearance of structures in the upper chest as seen on computed tomography (CT), such as clavicular angle, course of axillary vessels, pectoralis major muscle, and bicipital groove.

The study consisted of 52 chest CT examinations (32 from men and 20 from women; mean [SD] age, 64 [20] years) performed with 1 or both arms at or above the shoulder (n = 44 arms) or by the side of the body (n = 60 arms). Three chest radiologists assessed randomized CT examinations for specific anatomical structures including orientation of the bicipital groove of the humerus, appearance of the pectoralis major muscle, and the course of the axillary vessels. Orientation of the clavicle and the scapula were assessed by measuring their angles with the mid-sagittal plane. Data were analyzed using the Student t test.

There was a significant difference in the mean angle of the clavicles with the mid-sagittal plane in arms at or above the shoulder level (41.3 +/- 11.7 degrees) compared with arms-by-side position (54.8 +/- 14.7 degrees; P < 0.0001), but no significant difference was found in scapular angles (P = 0.4). All 3 radiologists found anteriorly directed bicipital groove, flat pectoralis major, and straight course of the axillary vessels from the chest to the axilla when arms were by the side. With arms at or above the level of the shoulder, however, the bicipital groove was directed posteromedially, the pectoralis major was buckled, and the axillary vessels had an angulated course.

The bicipital groove, the pectoralis muscles, the axillary vessels, or the angle of the clavicle with the mid-sagittal plane on transverse CT images can help predict the position of the arms in patients undergoing chest CT.