Left intercostobrachial nerve variation with dual communications: a cadaveric case report

To report a rare anatomical variation in which the left intercostobrachial nerve (ICBN) communicated with the lateral cutaneous branch of the third intercostal nerve and further formed dual communications with the medial brachial cutaneous nerve (MBCN), and to analyze its anatomical and clinical significance in light of the relevant literature.

During routine teaching dissection at the Department of Anatomy, layered dissection was performed on the left thoracic wall and axillary region of an adult Chinese male cadaver. The origin, course, branches, and communications of the ICBN were observed. Relevant distances were measured using a digital caliper with an accuracy of 0.01 mm. Each measurement was repeated three times, and the mean value was recorded.

The left ICBN arose from the lateral cutaneous branch of the second intercostal nerve. After emerging from the second intercostal space, it joined the lateral cutaneous branch of the third intercostal nerve at 51.68 mm from its exit point. The two then descended together for approximately 81.07 mm into the axilla and were distributed to the skin of the lateral thoracic wall. In addition, the nerve communicated with the main trunk of the MBCN at 61.53 mm from the exit point and again with one of its branches at 60.70 mm. The lateral cutaneous branch of the third intercostal nerve joined the second intercostal nerve system at 29.96 mm from its own exit point, while its remaining branches continued toward the axillary region.

This case suggests that the ICBN may present a complex configuration involving a T2 main trunk, T3 contribution, and multiple communications with the MBCN. This variation has practical implications for axillary lymph node dissection, breast surgery, transaxillary procedures, and regional nerve blocks. Intraoperatively, the ICBN should not be regarded simply as a single, constant sensory branch of T2.