Autologous breast reconstruction with the superficial inferior epigastric artery (SIEA) flap

Introduction

The superficial inferior epigastric artery (SIEA) flap is very attractive for breast reconstruction because it provides the soft, pliable, and often abundant, skin and subcutaneous tissue from the lower abdominal donor site, just like the free or pedicled transverse rectus abdominis (TRAM) flap, and the deep inferior epigastric artery (DIEP) flap (see Figs. 32.1F & 32.2D ). The advantage of the SIEA flap over the TRAM and DIEP flaps, is that neither the anterior rectus fascia, nor the rectus abdominis muscle is incised nor excised, thus minimizing abdominal donor site morbidity. The SIEA flap is a true abdominoplasty flap, as it was first described for breast reconstruction in 1991. Strictly speaking, it is not a perforator flap because the superficial inferior epigastric vascular pedicle does not traverse, or perforate, through any muscle. The SIEA flap is a adipocutaneous flap. Another advantage of the SIEA flap is that the venous drainage of the flap through the superficial inferior epigastric vein (SIEV) is the dominant, and thus more reliable and robust, system of venous drainage of the lower abdominal skin and subcutaneous tissue compared with the deep inferior epigastric venous system. An occasional patient will have inadequate venous drainage through the deep inferior epigastric system, leading to venous congestion of a DIEP flap, and the SIEV will be needed to provide adequate venous drainage and relieve venous congestion and threatened flap loss by supercharging.

The major disadvantage of the SIEA flap is the well-documented higher risk of arterial microvascular thrombosis and total flap loss compared to free TRAM and DIEP flaps. This is thought to be due, at least in part, to the smaller diameter of the pedicle artery of the SIEA flap compared with the deep inferior epigastric artery of the TRAM and DIEP flaps. This mismatch of the arterial diameters, with the direction of blood flow in the direction from the larger recipient site internal mammary artery (IMA) into the smaller SIEA, is unfavorable for success of microvascular anastomosis. The author and others have employed spatulation of the SIEA, or end-to-side anastomosis of the SIEA to the IMA, and use of perforators of the IMA, but arterial thrombosis still occurs at a rate substantially higher than for deep inferior epigastric artery (DIEA) to IMA anastomosis when free TRAM or DIEP flaps are used. Therefore, there is some characteristic intrinsic to the SIEA, in addition to arterial diameter mismatch, that contributes to a high rate of arterial spasm, and microvascular anastomotic thrombosis. This increased risk for arterial microvascular anastomotic thrombosis, and total flap loss, may not be worth the benefit of decreased morbidity at the abdominal donor site, especially considering that there is not additional benefit at the reconstructed breast compared to free TRAM and DIEP flaps. In the author’s hands, the DIEP flap for breast reconstruction has a 0.5% risk of total flap loss, due mainly to venous thrombosis, whereas the SIEA flap carries a 6% total flap loss rate, due almost exclusively to arterial thrombosis. Surgeons must carefully consider this risk of increased flap loss when considering whether to perform an SIEA flap for breast reconstruction. The author has found that the decreased reliability of the SIEA flap is not worth the donor site advantages, especially since there is no advantage at the reconstructed breast.

There are secondary disadvantages of the SIEA flap. The vascular pedicle, in addition to having a smaller arterial diameter, is also shorter, typically roughly 7 cm in length, compared with over 10 cm in length for DIEP flaps. This shorter pedicle generally cannot reach the thoracodorsal recipient vessels, and in some obese patients with a very thick layer of subcutaneous fat at the lower abdomen, it can be challenging for the SIEA flap pedicle to reach the IM recipient vessels at the chest wall.

Another disadvantage of the SIEA flap is the inconsistency of its vascular anatomy. A clinically significant SIEA is only present in a minority of patients and is variably located within the middle third of a line drawn from the pubic symphysis to the anterior superior iliac spine (ASIS) (see Figs. 32.1B & 32.2B ). Even when it is present, it is often too small in caliber to be reliably used for an SIEA flap. The superficial circumflex iliac artery (SCIA) is consistently present about two-thirds of the distance along the line drawn from the pubic symphysis to the ASIS. The author, and others, require an SIEA with an exterior diameter greater than, or equal to, 1.5 mm measured intra-operatively at the level of the lower abdominal incision, to proceed with an SIEA flap. This is found in approximately one-third of patients, and despite this selection criteria, SIEA flap loss rates are multiple times higher than free for free TRAM or DIEP flaps. Another disadvantage is that the vascular territory (angiosome) of the SIEA is smaller than is possible with free TRAM or DIEP flaps.

Preoperative evaluation and indications

Preoperative evaluation and patient selection for SIEA flap breast reconstruction is nearly the same as for breast reconstruction with TRAM and DIEP flaps. This means the patient can safely tolerate 5–12 h of general anesthesia and does not have a known hypercoagulable state. Tamoxifen should be discontinued for 1 month prior to free flap surgery. The amount of lower abdominal donor tissue must be assessed for adequacy to reconstruct a breast or breasts of the desired volume. Preoperative imaging with computed tomography (CT) or magnetic resonance (MR) angiography can be used to determine the presence and adequacy of SIEA vessels, much like many surgeons use CT angiograms to evaluate the presence and location of DIEA perforators prior to performing DIEP flap breast reconstruction. However, preoperative imaging in not necessary, and is not used by the author. Smoking will increase the risk for wound healing complications, but it is not known to increase the risk for total flap loss of SIEA flaps.

Previous abdominoplasty or panniculectomy is a contraindication for use of any lower abdominal free flap, including an SIEA flap. One important difference with preoperative evaluation for DIEP flap breast reconstruction is that the common low transverse abdominal incision used by gynecologists for Cesarean section and hysterectomy most of the time will have divided the SIEV and likely also the SIEA, whereas this type of gynecologic incision rarely injures the deep inferior epigastric artery and vein. Therefore, a previous low transverse abdominal incision is a contraindication for an SIEA flap unless the SIEA and SIEV are deemed patent by vascular imaging studies. Previous abdominal liposuction is a relative contraindication.