Pectoral Axillary Nodes

1. Overview

The pectoral axillary lymph nodes, also known as the anterior axillary nodes, form one of the primary groups of lymph nodes in the axilla (armpit). These nodes are mainly responsible for draining lymph from the anterior thoracic wall, including the majority of the breast (especially the lateral and central portions), making them especially significant in breast health and pathology. As the first nodes to receive lymph from the breast, they are frequently involved in the early spread of breast cancer.

2. Location

The pectoral (anterior) axillary nodes are located along the lateral edge of the pectoralis minor muscle, near the inferior border of the pectoralis major, and lie adjacent to the lateral thoracic vessels. Anatomically, they are positioned:

• Medial and anterior within the axilla

• Along the lateral thoracic vein

• Near the inferolateral border of the pectoralis minor muscle

There are typically 4–6 pectoral nodes, which receive afferent lymphatic vessels from the breast and the anterior thoracic wall. Their efferent vessels drain into the central axillary lymph nodes and then to the apical group.

3. Structure

Each pectoral lymph node is an encapsulated, bean-shaped structure composed of lymphoid tissue. Internally, they are organized into zones for processing lymph and mounting immune responses:

• Cortex: Contains follicles rich in B lymphocytes.

• Paracortex: Houses T lymphocytes and dendritic cells responsible for antigen presentation.

• Medulla: Contains macrophages and plasma cells, aiding in the final filtration and antibody production.

• Sinuses and trabeculae: Act as conduits for lymph to flow through and be screened by immune cells.

Multiple afferent vessels deliver lymph to each node, while a single or few efferent vessels carry filtered lymph toward the central axillary group.

4. Function

The pectoral axillary nodes serve as the first immune filtering station for lymph originating from:

• The skin and muscles of the anterior thoracic wall

• The lateral portions of the breast

• The upper abdominal wall (up to the level of the umbilicus)

Primary functions include:

• Lymph filtration: Removal of pathogens, cancer cells, and cellular debris from lymph before it reaches deeper nodes.

• Immune surveillance: Detection of foreign antigens and activation of lymphocytes to mount immune responses.

• Relay station: Transfers lymph to deeper nodes (central and apical axillary nodes) for continued filtration and eventual return to venous circulation.

5. Physiological Role(s)

The physiological importance of the pectoral axillary nodes lies in their strategic position and role in local immunity. Key roles include:

• Early immune response: First point of immune activation in cases of infection or inflammation involving the chest wall or breast.

• Fluid homeostasis: Helps return interstitial fluid to the circulatory system, preventing edema in the anterior chest and breast.

• Tumor surveillance: Monitors for malignant cells, especially from breast tissue, which may spread via lymphatics.

• Mucocutaneous defense: Helps maintain immunological integrity of the skin and subcutaneous tissues in the thoracic region.

6. Clinical Significance

Breast Cancer Metastasis

The pectoral nodes are among the most critical lymph nodes involved in breast cancer staging. Key points include:

• Sentinel lymph nodes: In many cases, pectoral nodes act as sentinel nodes — the first nodes where breast cancer may metastasize.

• Axillary lymph node dissection: Pectoral nodes are often removed and biopsied to assess the extent of cancer spread.

• Prognostic value: The presence or absence of cancer cells in pectoral lymph nodes directly influences staging, prognosis, and treatment strategy.

Lymphadenopathy

Pectoral node enlargement (lymphadenopathy) may be due to:

• Infections: Such as cellulitis, mastitis, or infected lesions of the chest wall.

• Malignancies: Breast carcinoma, skin cancers, and lymphomas.

• Autoimmune diseases: Including lupus or rheumatoid arthritis.

Imaging and Diagnosis

Due to their deep location, pectoral axillary nodes are typically evaluated via:

• Ultrasound: First-line imaging in evaluating breast lumps or axillary swelling.

• Mammography and MRI: Assess lymphatic spread in breast cancer.

• Fine needle aspiration (FNA) or core biopsy: Used for histopathological diagnosis when lymphadenopathy is present.

Surgical Relevance

During breast cancer surgery (e.g., modified radical mastectomy), the pectoral group is routinely removed if involved. Surgeons must avoid injuring nearby structures like the long thoracic nerve and lateral thoracic vessels.

Postoperative Complications

Injury or removal of pectoral nodes can lead to complications such as:

• Axillary web syndrome: Painful cord-like structures in the axilla due to lymphatic disruption.

• Lymphedema: Swelling of the breast or chest wall due to impaired lymph drainage.