Objective  This study aimed to provide the basic surgical guidelines for important injured nerves and vessels in the axilla during axillary lymph node dissection and reduce surgery-related complications by dissecting the variant latissimus dorsi (LATS) in the axilla.

  Methods  Data of 19 cases with LATS mutation from 128 breast carcinoma cases who underwent axillary lymph node dissection were collected and studied. The start and end points of the variation of muscle bundle (VOMB) were found by analyzing a full gross anatomy of the variant muscle bundle of LATS in the 19 cases. Length, width, and depth of VOMB were measured. Adjacent relationship among the axillary nerve, blood vessels, and lymph nodes in the axilla was observed.

  Results  Among the 19 cases with LATS mutation, each VOMB released a bundle of tendons from the lateral border of LATS, thereby stretching inward and upward as well as across the axillary neurovascular bundle. Above the bundle, a fan-shaped aponeurosis extended as a part of the fascia coracocleidopectoralis, which ended at the coracoid process. Among the 19 cases, 14 VOMBs were extended by a mode of a single muscle bundle. For the remaining five cases, VOMBs converged with a bundle from the outer margin of the pectoralis major muscle after VOMB was sent out from LATS. These VOMBs then extended upward. The VOMB and the insertion of LATS muscle retained the axillary neurovascular bundle in a forked form. The intercostobrachial nerves passed through the surface or the inner part of the vessels, which adjoined the thoraco-dorsal nerve and the sub-scapular blood vessels inward and inferolaterally. The lymphatic tissues were directed outside the sub-scapular blood vessels posteroexternally.

  Conclusion  LATS mutation may cause confusion in the anatomical structure of the dissected axillary lymph node and likely results in difficulties in the localization during surgery. Thus, determining the VOMB in the dissected axillary lymph node is important.