Incise the skin and subcutaneous tissue. Visualize the breast as lying encapsulated in a separate layer of subcutaneous fat that lies 0.5 to 1.0 cm below the skin. Often, this layer can be defined as the skin incision is made. Place Lahey clamps on the dermal side of the upper flap and have an assistant place these under strong upward traction (Fig. 17.2A). Apply countertraction by pulling the breast tissue down and toward you strongly with a lap sponge. Avoid manipulating the breast overlying the biopsy site. Develop flaps by sharp dissection using a shaving motion with a sharp knife or electrocautery. If a knife is used, change blades frequently. Dissection in the proper plane is surprisingly bloodless. A network of large subcutaneous veins is often visible on the underside of the flap and will be preserved if dissection progresses in the proper plane. Ligate occasional bleeders on the underside of the flap. (Use electrocautery with caution on the flap because it can burn through the thin flap to damage the overlying skin surface.) Confirm the thickness of the flap by palpation as the dissection progresses.

An alternative technique uses slightly opened Mayo scissors to develop the flaps by a push-cut technique. This is particularly useful when the skin incision is small, as during skin-sparing mastectomy.

In the axilla, the skin flap will be crossed by hair follicles and apocrine glands. Divide these sharply. Raise flaps to the level of the clavicle superiorly, the midline medially, the anterior rectus sheath inferiorly, and the anterior border of the latissimus dorsi muscle laterally (Fig. 17.2B). Of these, the lateral border of the latissimus dorsi is generally the most difficult to find.
Identify this muscle by palpation of a longitudinal ridge of muscle tissue. Dissect sharply down to confirm its identity by visualizing longitudinal muscle fibers. Trace the muscle up toward the axilla. Check the upper flap for hemostasis and place a moist laparotomy pad under the flap. Place Lahey clamps on the inferior skin incision and develop the inferior flap by the same technique. The plane between breast and subcutaneous tissue is frequently less well defined inferiorly, and unless care is taken, the inferior flap may be cut too thick. Guard against this by constant palpation of the thickness of the flap. If white fibrous tissue (breast or suspensory ligaments of the breast [Cooper’s ligaments]) is seen, the flap is too thick and must be cut thinner.

Draw a line around the margins of the dissection by incising the fascia at the perimeter of the field with electrocautery. This will prevent your dissecting too far in any direction. Recheck both flaps for hemostasis and place warm moist lap pads under them. Take care throughout the operation not to allow the subcutaneous fat of the underside of the flaps to become exposed and desiccated.

The breast is a conical ectodermal derivative limited to superficial fascia. The base of the breast overlies the chest wall from the second rib to the sixth and from the edge of the sternum to the midaxillary line. A lateral tongue of breast tissue—the axillary tail of Spence—extends into each axilla from the otherwise conical breast. This tail sometimes passes through the deep fascia of the axilla and approaches the pectoral group of axillary lymph nodes. Superficial to the breast is the superficial layer of the superficial fascia, whereas deep to the breast is the deep layer of superficial fascia. The subcutaneous fat lobules are small and easy to differentiate from the larger fat lobules of the breast itself.