Helical computed tomography of the normal thoracic outlet

Purpose: This study was performed to determine the detailed anatomy of the thoracic outlet in normal subjects using helical computed tomography (CT), with particular attention to vascular compression with arm movement. Methods: Ten volunteers underwent detailed clinical evaluation and helical CT scanning of the upper thorax and neck with the arm in a neutral position and with the arm abducted 90 degrees or greater and externally rotated. Anterior scalene-clavicle distance (SC), costoclavicular distance (CC), and vessel diameters were measured with electronic calipers in each position. Comparisons were made with Student's t test. Results: With abduction the SC decreased from 18.4 ± 3.9 mm to 5.2 ± 2.4 mm (p < 0.001), and the CC decreased from 12.6 ± 2.7 mm to 6.3 ± 3.3 mm (p = 0.005). At these same anatomic planes, the vein diameter decreased from 11.0 ± 1.6 mm at the neutral position to 5.1 ± 1.5 mm (p < 0.001) and from 16.1 ± 3.0 mm to 7.4 ± 2.6 mm with the arm abducted (p < 0.001). The artery diameter changed from 6.6 ± 0.8 mm to 6.2 ± 0.5 mm (p = 0.08) and from 7.2 ± 0.8 mm to 6.0 ± 0.5 mm (p = 0.001) with arm movement. Conclusions: Both the distances between the anterior scalene muscle and the clavicle and between the clavicle and the first rib are significantly reduced with abduction of the upper extremity. Venous compression is universal at both the SC and CC spaces in normal subjects with this maneuver. Arterial narrowing occurs less frequently and appears to be minor. Minor changes in these thoracic outlet dimensions (SC/CC) may produce venous compression without movement.