Vital Structures Preserved in the Axilla During Modified Radical Mastectomy

Modified radical mastectomy (MRM) removes the breast and axillary lymph nodes (levels I and II) while preserving the pectoralis major muscle and key neurovascular structures traversing the axilla. Injury to these structures causes significant functional morbidity, so their identification and preservation is a core surgical principle.

Analysis of Each Structure

• 1. Axillary vein: This forms the superior boundary of axillary dissection. It must always be preserved and skeletonised carefully — injury causes troublesome bleeding and risks lymphoedema of the arm.
• 2. Nerve to serratus anterior (long thoracic nerve of Bell): Runs along the medial wall of the axilla on the surface of serratus anterior. It must be preserved; injury causes winging of the scapula, a major functional disability.
• 3. Nerve to latissimus dorsi (thoracodorsal nerve): Runs with the subscapular vessels on the posterior wall of the axilla. It must be preserved to maintain latissimus dorsi function (important for shoulder movement and future use as a flap if needed).
• 4. Intercostobrachial nerve(s): These are purely sensory nerves supplying skin of the axilla and medial upper arm. They are frequently sacrificed during level I/II clearance to obtain adequate nodal clearance; their division only causes numbness over the medial arm/axilla, which is an acceptable trade-off and not a "vital" structure in the same sense as the vein and motor nerves. Hence they are not in the "always preserve" category.

Conclusion

The three structures that must always be preserved are the axillary vein, the nerve to serratus anterior, and the nerve to latissimus dorsi — corresponding to 1, 2 and 3. The intercostobrachial nerve, being purely sensory, may be sacrificed if it interferes with adequate nodal clearance, and is therefore excluded from the "always preserved" group.