A 38-year-old woman comes to the office after feeling a lump in her left breast while showering. Examination reveals a firm, 3-cm (1.2-in) mass with ill-defined margins in the upper outer quadrant of the left breast. Enlarged lymph nodes are present in the left axilla, and fine-needle aspiration of the lymph nodes reveals adenocarcinoma. The patient undergoes left modified radical mastectomy including left axillary lymph node dissection, with removal of levels I and II axillary lymph nodes. During the surgery, which of the following muscles is used to distinguish between the different levels of axillary lymph nodes?

Question

A 38-year-old woman comes to the office after feeling a lump in her left breast while showering.  Examination reveals a firm, 3-cm (1.2-in) mass with ill-defined margins in the upper outer quadrant of the left breast.  Enlarged lymph nodes are present in the left axilla, and fine-needle aspiration of the lymph nodes reveals adenocarcinoma.  The patient undergoes left modified radical mastectomy including left axillary lymph node dissection, with removal of levels I and II axillary lymph nodes.  During the surgery, which of the following muscles is used to distinguish between the different levels of axillary lymph nodes?

Quizplus · Accepted Answer

Explanation: 11ec25c8_d8d0_ebd3_bc81_0bd01e5d751a_MD0003_00 The axillary lymph nodes receive the majority (~85%) of the breast lymphatic drainage and are the most commonly involved lymph nodes with breast cancer lymphatic invasion. For this reason, axillary lymph node sampling is performed in most patients diagnosed with invasive breast cancer. In general, patients with clinically negative nodes (ie, no enlarged nodes on clinical examination) undergo axillary sentinel lymph node biopsy ("sentinel" refers to the first group of lymph nodes draining the cancer). In contrast, patients such as this one with clinically positive and biopsy-proven (eg, fine-needle aspiration) nodes undergo axillary lymph node dissection (ALND). The spread of breast cancer to the axilla usually mirrors the course of the breast lymphatic drainage. The lymphatic drainage passes along the lateral edge of the pectoralis major muscle to reach lymph nodes lateral/inferior to the pectoralis minor muscle and/or posterior to the muscle. It then continues medially/superiorly to reach the infra- and supraclavicular lymph nodes, lymphatic ducts, and venous circulation. Therefore, the surgical classification of the axillary lymph nodes, which corresponds to their likelihood of harboring tumor cells, uses the pectoralis minor muscle as its landmark: Level I: lateral/inferior to the pectoralis minor Level II: posterior to the pectoralis minor Level III: medial/superior to the pectoralis minor ALND typically resects only levels I and II lymph nodes; this limits morbidity (eg, lymphedema) while providing an adequate sample for tumor staging by removing the lymph nodes most likely to be involved. If there is clear (ie, on palpation or imaging) involvement of the level III nodes, these may also be resected; however, level III involvement is associated with a poorer prognosis because they are the final group in the lymphatic chain prior to drainage into the systemic circulation. (Choices A, C, D, and E) The latissimus dorsi, subscapularis, and teres minor muscles form the posterior boundary of the axilla. The subclavius muscle, together with the pectoralis major and minor muscles, forms the anterior boundary of the axilla. Although these muscles help define the posterior- and anterior-most extent of the ALND, they do not distinguish between the surgical levels (ie, levels I, II, and III) of the axillary lymph nodes. Educational objective: Lymphatic drainage from the breast passes primarily to the axillary lymph nodes, with drainage traveling from lateral to medial, posterior to the pectoralis minor muscle. The pectoralis minor muscle is the landmark for distinguishing the surgical levels of axillary lymph nodes during axillary lymph node dissection. References: Contemporary evaluation of breast lymph nodes in anatomic pathology. (http://www.ncbi.nlm.nih.gov/pubmed/29746624)

A 38-Year-Old Woman Comes to the Office After Feeling a Lump