Autologous breast reconstruction with the free TRAM flap

Fat layer, muscle and vessels of the lower abdomen

The fat layer of the lower abdomen is usually of sufficient thickness for breast reconstruction and is thickest just above or below the umbilicus. The abdominal fat layer is divided into the subcutaneous fat layer and sub-Scarpa fat layer, which are separated by Scarpa’s fascia or the superficial abdominal fascia. The subcutaneous fat layer is thicker than the sub-Scarpa fat layer. The attachment between the subcutaneous fat layer and Scarpa’s fascia is strong and usually resistant to separation, while the attachment between Scarpa’s fascia and the sub-Scarpa fat layer is loose and easily disrupted.

The anterior rectus sheath corresponds to the deep fascia of the abdomen and plays a crucial role in maintaining the integrity of the anterior abdominal wall. The rectus abdominis muscle is a key muscle for abdominal wall function. It is a long muscle with origins at the symphysis pubis and insertions at the 5th to 7th ribs and the xiphoid process. As a type III muscle. according to Mathes and Nahai classification, the rectus muscle is perfused by the superior and deep inferior epigastric vessels, which are usually connected by choke vessels; however, in some cases, they are continuous. The deep inferior epigastric artery originates from the external iliac artery and runs superiorly under the rectus muscle until it enters the rectus muscle near the arcuate line, and distinguishes the presence or absence of the posterior rectus sheath. The deep inferior epigastric vein originates from the external iliac vein and accompanies the inferior epigastric artery as the venae comitantes all the way up into the subcutaneous fat layer. The deep inferior epigastric vessels branch into two or three divisions as they run intramuscularly, but their branching pattern and intramuscular course are complex and variable ( Fig. 31.1 ). Each branch of the deep inferior epigastric vessel gives off multiple perforators, which ultimately supply blood to the adipocutaneous layer of the abdomen. The perforators have varying sizes and locations, but those close to the umbilicus are the largest and have a robust blood stream. The main blood flow to the free TRAM flap is directly supplied by the perforating vessels that originate from the deep inferior epigastric artery and veins. Therefore, the amount of blood supply to the adipocutaneous component of the flap depends on the size and number of perforators.

Structure of the free TRAM flap

The TRAM flap is composed of an ellipse of skin and subcutaneous fat as well as a part of the rectus abdominis muscle, which attaches underneath the flap. The skin and subcutaneous fat are the main functional part of the flap and provide both volume and dimension, whereas the small segment of the rectus abdominis muscle serves as a cushion for the perforators and contributes very little to the volume of the flap. Therefore, the process of harvesting the skin and subcutaneous fat of the flap is focused on maximizing volume and dimension, but during the muscle harvest, the focus is on incorporating essential blood vessels without damage to the perforators. Thus, in essence, the free TRAM is typically performed to minimize the risk of injury to the perforators and maintain a high rate of success

The simplest and safest way of muscle harvesting is full-width muscle harvest, but this can lead to excessive damage, loss of muscle continuity and functional deficits of the rectus abdominis muscle. Therefore, the free TRAM flap has evolved from the full-width muscle TRAM flap to the muscle-sparing TRAM flap, and most recently to the perforator-based DIEP flap, in order to reduce the amount of muscle damage, preserve continuity and maintain function. The classification of the abdominal flap has been developed based on the degree of muscle preservation. Full-width muscle harvesting is classified as MS-0. Preservation of the lateral or medial segment is classified as MS-1 (a muscle-sparing TRAM flap), and preservation of the lateral and medial segment is classified as MS-2 (a muscle-sparing TRAM flap). The preservation of the whole muscle is classified as an MS-3 (DIEP) flap ( Table 31.1 and Fig. 31.2 ).

The zones of the unilateral TRAM flap comprise four segments. The early zone classification was that zone 1 represented the area over the main pedicle and zone 2 was opposite the midline. Zone 3 was lateral to zone 1 and zone 4 was lateral to zone 2. The current zone classification is that zones 1 and 2 represent the medial and lateral portions of the ipsilateral flap and zones 3 and 4 represent the medial and lateral portions of the contralateral flap. With bilateral flaps, zone 1 is over the pedicle and zone 2 is lateral to zone 1 in each side ( Fig. 31.3 ).

Superficial inferior epigastric vein and dominance of the venous drainage system

Similar to some other flaps, the TRAM flap has a dual venous drainage system. The first is the deep venous drainage system, which drains venous outflow through the venae comitantes of the perforators, culminating in the deep inferior epigastric vein. The second is the superficial venous drainage system, which collects venous outflow via the superficial inferior epigastric vein, which runs vertically along the paramedian lower abdomen in the superficial fat layer. The vein can be easily identified at the lower margin of the flap ( Fig. 31.4 ). Of the two drainage systems, the superficial system is considered the dominant drainage system based on anatomic analysis. This means that the superficial inferior epigastric vein can collect and drain the complete venous outflow of the flap, but perforator veins might not be capable of that. However, there are connections between the superficial inferior epigastric vein and the perforator veins, which have been proven by multiple anatomic and imaging studies. Therefore, ultimately, the venous outflow of the flap is collected by the superficial inferior epigastric vein and transferred to the perforator veins via the connection between them, and then drained into the deep system. However, not all perforator veins are connected to the superficial inferior epigastric vein. If only those perforators without connections to the superficial vein are chosen, serious venous insufficiency can occur, which can be noticed immediately after flap elevation. This venous insufficiency results in intraoperative venous congestion. Intraoperative venous congestion is uncommon because periumbilical dominant perforators with a large caliber tend to be connected to the superficial vein. A meta-analysis estimated the occurrence rate as approximately 1% in free TRAM flaps and 3% in DIEP flaps. The lower rate in TRAM flaps can be attributed to the higher number of perforators incorporated in TRAM flaps than in DIEP flaps and thus a higher chance of the perforators having connections to the superficial system. Intraoperative venous congestion can be diagnosed when there are signs of venous congestion without any microsurgical cause. Unless adequately remedied by incorporating a dual drainage venous system, total flap loss is likely. Congestion can be relieved by establishing an additional venous drainage route using the superficial epigastric vein. Anastomosing the superficial vein to any available chest vein or to one of the deep inferior epigastric veins has been proposed.

Midline cross-over vessels

The free TRAM flap is a bisymmetrical flap, but embryologically, the two sides of the TRAM flap develop separately and fuse only in the later stages. There is no consistent vascular structure that crosses the midline below the umbilicus. Thus, the blood flow to the contralateral side is random and sometimes unpredictable, and a single-sided pedicle does not guarantee the survival of the contralateral side of the flap. If the degree of perfusion to the contralateral side can be assessed, the incidence or amount of fat necrosis can potentially be reduced, and the decision to supercharge or turbocharge can be properly made. One of the best ways to assess midline cross-over blood flow is real-time indocyanine green infrared fluorescence angiography (discussed in detail later in this chapter).

Recipient vessels in breast reconstruction

The most common recipient vessels for breast reconstruction are the internal mammary artery and vein. The internal mammary vessels have a large caliber and very robust blood flow and run vertically along the lateral border of the sternum just under the costal cartilage. The internal mammary vessels can be approached by splitting the pectoralis major muscle along the fiber direction and removing the third or fourth costal cartilage. The vessels can be readily identified after excision of the posterior costal perichondrium ( Fig. 31.5A ). The internal mammary vessels can also be approached through the intercostal space. Division or resection of the intercostal muscle exposes the vessels and secures the working space ( Fig. 31.5B ). The second and third intercostal spaces are commonly used for this approach. The second intercostal space is the widest and provides sufficient space for microanastomosis, but the pleura under the vessel is thin and care must be taken to not tear it. The third intercostal space is sometimes too narrow to achieve a working space, and widening by rongeuring the costal margin is often necessary.

The artery lies lateral to the vein, but when the vein divides into two branches, the artery lies between the two veins. The left internal mammary vein tends to be smaller than the right vein. The internal mammary vein has multiple valves, but the majority of valves are located higher than the third rib, which makes a retrograde venous anastomosis possible.

The perforators of the internal mammary vessels can be used as a recipient vessel if they are large enough for anastomosis and are not damaged during mastectomy. The perforator in the second intercostal space is the largest.

An alternative to the internal mammary recipient vessels is the thoracodorsal artery and vein that are the second most commonly used recipient vessels that also have sufficient caliber and blood flow. They are readily identifiable if axillary lymph node dissection was performed ( Fig. 31.5C ). If not, searching through the axillary fat tissue is required. The main trunk of the thoracodorsal vessels is the most ideal recipient, but the branch to the latissimus dorsi muscle, after giving off the branch to the serratus anterior muscle, can also be used. As the thoracodorsal vessels are located far from the anterior chest, securing the maximal length of the pedicle is needed in order to minimize the likelihood of a laterally positioned flap.

The lateral thoracic vessels are other important vessels in the axilla. They directly branch off the axillary vessels and run caudally along the anterior axillary line. The lateral thoracic vessels can be very easily identified just lateral to the pectoralis minor muscle if they have not been injured during mastectomy or axillary lymph node dissection. The lateral thoracic vein invariably has a large size and thick wall and is a very good venous recipient. The lateral thoracic artery, however, tends to be too small (or often absent) as the main arterial recipient.

The pectoral branch of the thoracoacromial vessels can also be used as recipients for breast reconstruction, but only in exceptional cases due to its high location and relatively small caliber.