Study on the subclavian artery and its branches in Japanese adults.

We examined the entire array of branches and the state of ramification of each branch of 144 subclavian arteries (Su) in 72 Japanese adults, and obtained the following findings. (1) The incidence of Type I -A(1) was 13.2%, the highest among the entire Su ramification. This was followed by Type I -B(1) at 9.0%, then Type I -A(2) at 6.9%, indicating considerable variation in the morphology of Su ramification. (2) Ontogenetic factors were implicated because of the existence of cases in which Su traversed the scalenus anterior muscle anteriorly (Type III: 0.7%), or was transfixed (0.7%). (3) Type 1-c was the form of thyrocervical trunk (Ttc) observed with the highest incidence of 31.3%. In addition, we propose that Types a-j (that were formed from a common trunk consisting only of the ascending cervical artery and inferior thyroid artery, and those in which another branch was included in this common trunk: 88.9%) be called Ttc. (4) The most common type of transverse cervical artery (Tc), which is formed from a common trunk consisting of superficial and deep branches, was found to be Type 1-a that branches from the first part of Ttc. It was observed with the highest incidence of 61.8%. Some of the superficial branches to the upper portion of the trapezius muscle that were independent and branched from Ttc (Types e, f: 2.8%), we called upper superficial branches. (5) The most frequently observed type of suprascapular artery (Ss) was Type b (38.2%), followed by Type a (25.7%), which branches independently from Su. We concluded that the sites at which Tc and Ss originate are the positions at which they traverse the brachial plexus (superior, transfixed to the plexus). (6) In cases in which the supreme intercostal artery (Is) and the deep cervical artery (Cp) were separate, (Types d-i excluding Type g: 31.9%), Is branched from a more proximal position than Cp.