Under-recognized soft-tissue structures inferior and lateral to the head of the clavicle: Anatomy with computed tomography correlation.

This study was undertaken to provide an anatomical explanation for two soft-tissue structures anecdotally found on axial computed tomography (CT) scan, which are inferior (SI) and lateral (SL) to the head of the clavicle and adjacent to the sternoclavicular joint (SCJ). Three sets of cryosection images were reviewed to identify the anatomical structures corresponding to SI and SL. To demonstrate that SI and/or SL communicate with the SCJ cavity in the living, 312 consecutive chest CT scans were assessed for coexistence of SCJ and SI/SL air. To prove that under-recognition of SI and SL is due to the use of thick-section CT scan, another 50 consecutive chest CT scans were evaluated: visibility of SI and SL, and continuity between them on thick (5 mm)-section images were compared with those on thin (0.75 mm)-section images. The anterior portions of SI and SL were extensions from the SCJ cavity in the cryosection images, with the articular cartilage and disc occupying variable volumes of SI. The posterior portions of the SI and SL corresponded to the thyroid strap muscles. Air was present in 1 SI, 6 SLs, and 10 SCJs. Four of five patients with SI or SL air had coexisting SCJ air. Thick sections provided significantly poor visibility of SI and SL and continuity compared with thin-section images. SI and SL are constant shadows on thin-section CT scan, and their anterior and posterior portions represent extensions of the SCJ cavity and the strap muscles, respectively. The use of thick sections may be responsible for the under-recognition of SI and SL on CT scan.