New anatomical classification of the axilla with implications for sentinel node biopsy

Background: The exact anatomical location of the sentinel lymph node (SLN) in the axilla has not ascertained clinically, but could be useful both for teaching purposes and to reduce the morbidity of SLN biopsy. The aim of the study was to determine the position of the SLN in the axilla and to demonstrate that this location is not random. Methods: A consecutive series of 242 patients with stage I breast cancer (T1/T2 N0) or ductal carcinoma in situ who underwent SLN localization by peritumoral injection were included in a prospective study to map the location of the SLN in the axilla. A new anatomical classification of the lower part of the axilla based on the intersection of two anatomical landmarks, the lateral thoracic vein (LTV) and the second intercostobrachial nerve (ICBN), is described. These two constant elements form the basis of four axillary zones (A, B, C and D). Results: In 98.2 per cent of patients the axillary SLN was located medially, alongside the LTV, either below the second ICBN (zone A, 86.8 per cent) or above it (zone B, 11.5 per cent). In only four patients (1.8 per cent) was the SLN located laterally in the axilla. Conclusion: Regardless of the site of the tumour in the breast, 98.2 per cent of SLNs were found in the medial part of the axilla, alongside the LTV. This information should help to avoid unnecessary lateral dissections.