What is the superior limit of dissection in a modified radical mastectomy (MRM)?

Superior Limit of Dissection in Modified Radical Mastectomy

The superior limit of dissection in a modified radical mastectomy is the axillary vein, with lymph node dissection including tissue inferior to the axillary vein extending from the latissimus dorsi muscle laterally to the medial border of the pectoralis minor muscle (level I/II). 1

Anatomical Boundaries of Axillary Dissection

The NCCN guidelines consistently define the superior boundary as follows:

• Superior limit: The axillary vein serves as the cranial boundary of dissection 1
• Lateral limit: Latissimus dorsi muscle 1
• Medial limit: Medial border of the pectoralis minor muscle (for level I/II dissection) 1
• Inferior limit: The dissection extends inferiorly to encompass level I and II nodes 1

Level-Specific Dissection Requirements

For standard modified radical mastectomy, level I and II axillary lymph node dissection is recommended, requiring removal of at least 10 lymph nodes for accurate staging. 1

When to Extend to Level III

• Level III dissection (extending medial to the pectoralis minor muscle) should only be performed if gross disease is apparent in level II or III nodes 1
• In the absence of gross disease in level II nodes, extending the dissection to level III is not indicated 1
• Level III dissection requires splitting the pectoralis major muscle approximately 2 cm inferior to the clavicle to adequately expose the subclavian region 2

Critical Structures at the Superior Boundary

When dissecting to the axillary vein, the following structures must be identified and preserved:

• Axillary vein: The primary superior landmark that should be clearly exposed 1
• Medial pectoral nerve: Traverses craniomedially near the lateral edge of the pectoralis major and should be preserved 3, 4
• Long thoracic nerve: Must be preserved to prevent winged scapula 1
• Thoracodorsal nerve and vessels: Should be preserved to maintain function 1, 2

Technical Considerations

Circumferential stripping of the axillary vein is unnecessary and may increase the incidence of lymphedema. 1

• The dissection should include removal of lymphoid adipose tissue along the fascial space while skeletonizing the subclavian/axillary vein 2
• A small vein adjacent to the medial pectoral nerve can be followed craniomedially to identify the axillary vein, facilitating safe dissection 3
• The fascia on the surface of the axillary vein should be lifted to allow complete removal of lymphoid tissue 2

Common Pitfalls to Avoid

• Do not extend dissection superior to the axillary vein, as this provides no additional staging benefit and increases morbidity 1
• Avoid routine level III dissection in the absence of gross disease, as it increases complications without survival benefit 1
• Preserve the intercostobrachial nerve when possible to reduce postoperative numbness and dysesthesia in the upper medial arm 4, 2
• Do not perform circumferential dissection of the axillary vein, which increases lymphedema risk 1