Anterior Axillary Arch: An Anatomic Variant Every Surgeon Operating in the Axilla Should Be Aware of

Background: Anterior axillary arch (AAA) is a slip of latissimus dorsi muscle, of variable thickness, which crosses anterior to the axillary vessels and brachial plexus. It is the most common anatomic variant in the axilla and surgeons operating in this area should be familiar with this finding to prevent confusion and complications. The aim of this study is to enhance surgeon's awareness of AAA, report the prevalence, and to describe our experience with this anomaly. Methods: An institutionally maintained database was used to identify patients with AAA in a single surgeon's experience, from 2008 to 2019. Patient characteristics, including tumor type, laterality, and pathologic node counts were determined and compared with patients undergoing axillary lymph node dissection (ALND) without this anatomic anomaly. Results: Nineteen patients with AAA were identified (13 on ALND and 6 during sentinel lymph node biopsy). Indications for ALND included breast cancer (12), melanoma (5), and Merkel cell carcinoma (2). In patients with AAA undergoing an ALND, the median number of lymph nodes pathologically identified was 23 and similar to those without AAA (27, P = 0.14). The prevalence of AAA in patients who underwent ALND was 3.1% (13/422). Conclusions: Surgeons who operate in the axilla are likely to encounter an AAA. Knowledge of this variant should improve operative efficiency and may prevent technical errors during an ALND or sentinel lymph node biopsy.