Ramification patterns of the subclavian branches as the subclavian artery passes through the scalenus anterior muscle

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The subclavian artery branches to form the vertebral and internal thoracic artery and thyrocervical and costocervical trunk in this order and passes behind the scalenus anterior muscle. We report a case of the right subclavian artery passing through the right scalenus anterior muscle. Twenty‐five reports document the subclavian artery passing in front of the scalenus anterior muscle, with only eight instances of it passing through the scalenus anterior muscle. Therefore, we attempted to clarify the ramification pattern of the subclavian branches through the surrounding structures. Twenty cadavers (40 cases) were examined. In 39 cases, the subclavian artery passed behind the scalenus anterior muscle with five types of ramification patterns observed in the subclavian branches. In the remaining cases, the subclavian artery passed through the scalenus anterior muscle with a different ramification pattern than those previously reported. The first branch from the subclavian artery formed the vertebral artery, the second formed the thyrocervical trunk, the third formed the costocervical trunk, and the fourth formed the internal thoracic artery. These observations indicate that the ramification pattern of the subclavian artery passing through the scalenus anterior muscle in this case and in a previous case may be characteristic of this anatomical condition. (J Osaka Dent Univ 2019; 53: 49‐54)