Figure 8a. Radiologic findings in a 38-year-old man with shoulder pain who was found to have a left apical mass; biopsy revealed poorly differentiated adenocarcinoma. (a) CT image obtained at the thoracic inlet shows extensive involvement of the area with encasement of the left subclavian artery (arrowhead) but no evidence of osseous involvement. Abutment of the mass with the posterior aspects of more anterior vessels (arrows) does not confirm invasion of these structures. (b) Axial MR image shows encasement of the proximal left subclavian artery (arrowheads) and abutment of the mass with the trachea (T), a vertebral body (V), and anterior vessels (arrows). (c) Coronal MR image shows encasement of the left subclavian artery (arrowheads) by the mass. Proximal nerve roots of the brachial plexus (long arrow) appear intact. The appearance of invasion into a vertebral body (short arrow) is a volume-averaging phenomenon, as the vertebral body was intact at evaluation of the full set of coronal images.