18 The deep inferior epigastric artery perforator (DIEAP) flap
Perforator flaps have become increasingly popular over recent years. For this reason, they are positioned near the top of the reconstructive ladder and are considered a step advancement of musculocutaneous and fasciocutaneous flaps. Passive muscle and fascial carriers are no longer required to ensure flap vascularity and by virtue of their composition, perforator flaps permit excellent “like for like” tissue replacement with minimal aesthetic or functional donor morbidity. Perforator flaps are usually thin, pliable, easily moldable flaps that are well suited to resurfacing work. They are also ideal for reconstructing pliable organs such as the tongue or for molding to complex contours as in head and neck surgery. Perforator flaps with large quantities of subcutaneous fat have proved ideal for reconstructing the breast.
A perforator flap is defined as a flap of skin and subcutaneous tissue, which is supplied by an isolated perforator vessel. Perforators pass from their source vessel to the skin surface either through or between the deep tissues (mostly muscle). Any vessel that traverses through muscle before perforating the outer layer of the deep fascia to supply the overlying skin is termed a myocutaneous perforator. A vessel that traverses through septum, i.e., between the muscle bellies, is designated a septocutaneous perforator.
The deep inferior epigastric artery perforator (DIEAP) flap arose as a refinement of the conventional myocutaneous lower abdominal flap. The myocutaneous perforators of the inferior epigastric vessels were described1 soon after the first transverse rectus abdominis myocutaneous (TRAM) flap was performed for breast reconstruction by Holmström and Robbins.2,3 In the mid-1980s, following Taylor’s landmark work on the vascular territory of the deep inferior epigastric artery, it became apparent that the lower abdominal flap could be perfused solely by a large periumbilical perforating vessel. That assumption was confirmed in 1989 when Koshima and Soeda4 published two cases of “inferior epigastric skin flaps without rectus abdominis muscle”.
Initially the DIEAP flap met with animosity from many in the surgical community, as it challenged conventional teaching and was thought to be unsafe. However, we are now in an era where DIEAP flaps are routinely performed in plastic surgery units throughout the world.
In 1989, Koshima and Soeda4 reported the first clinical application of the inferior epigastric artery perforator flap. They demonstrated that it was possible to harvest the same amount of lower abdominal skin and fat as in the TRAM flap, without sacrificing the rectus abdominis muscle. Koshima et al.5 then reported another 13 cases with free thin para-umbilical perforator based flaps. Later, Pennington et al.6 used an anastomosis between the distal end of the ipsilateral pedicle and the contralateral pedicle to augment the blood supply of a free TRAM flap. Allen and Treece7 reported 22 successful breast reconstructions with the DIEAP free flap and finally, Blondeel8,9 improved the understanding of the flap and popularized its use in autologous breast reconstruction.10–13
The deep inferior epigastric artery arises from the external iliac, immediately above the inguinal ligament. It curves forwards in the sub-peritoneal tissue, and then ascends obliquely along the medial margin of the abdominal inguinal ring. Continuing its course upwards, it pierces the transversalis fascia, passing in front of the linea semicircularis, ascending between the rectus abdominis and the posterior lamella of its sheath.
The deep inferior epigastric artery finally divides into numerous branches, which anastomose, above the umbilicus, with the superior epigastric branch of the internal thoracic artery and with the lower intercostal arteries (Figs 18.1, 18.2).
Fig. 18.1 The vascular anatomy of the lower abdomen. In the right hemi-abdomen the skin is removed down to the superficial inferior epigastric vessels. The artery with its common veins and the superficial inferior epigastric vein can be found medial to the superficial circumflex iliac vessels. Around the umbilicus the perforators of the deep inferior epigastric system connect with arteries and veins of the superficial system. The anterior branches of the intercostal arteries and veins move anterior and distally from their origin at the midaxillary line. Variable anastomoses between these different vessels make up for a complex and intense random network between the skin and the deep fascia. On the left side of the abdomen, the deep fascia of the rectus abdominis muscle is removed and the fascia of the external and internal oblique have been retracted. The deep inferior epigastric artery and vein pass deep to the lateral board of rectus abdominis as they move more cranially and enter into the rectus abdominis a few centimeters higher. Segmental branches of the deep inferior epigastric system connect with the anterior branch of the intercostal artery and veins (specially the lateral branch of the deep inferior epigastric artery). The anterior intercostal nerves run together with the segmental branches and branch into sensitive branches that run with the perforators into the subcutaneous tissues and motor branches that run medial and distally in the rectus abdominis muscle. More cranially, the deep inferior epigastric vessels anastomose in the diffuse network throughout the muscle with the superior epigastric artery.
The anatomy of the deep inferior epigastric artery system is very variable.14,15 The average pedicle length is 10.3 cm and the average vessel diameter is 3.6 mm. Normally, the deep inferior epigastric artery divides into two branches, with a dominant lateral branch (54%). However, if the deep inferior epigastric artery does not divide, the vessel has a central course (28%) with multiple small branches to the muscle and centrally located perforators. If the medial branch is dominant (18%), flow appears to be significantly lower than in a central system or in patients with a dominant lateral branch.16
Blondeel et al.16 found between two and eight large (>0.5 mm) perforators on each side of the midline. The majority of these perforators emerged from the anterior rectus fascia in a paramedian rectangular area 2 cm cranial and 6 cm caudal to the umbilicus and between 1 and 6 cm lateral to the umbilicus. Anatomical symmetry was hardly ever encountered. The closer a perforator is to the midline, the better the blood supply to the least vascularized part of the flap across the midline, as one choke vessel less has to be transgressed. However, the lateral perforators are often dominant and easier to dissect because they run more perpendicularly through the muscle. The sensory nerve that runs with these perforating vessels is also often much larger (Fig. 18.3). The medial perforators provide better perfusion of the flap but they have a longer intramuscular course, requiring more elaborate dissection with extensive longitudinal splitting of the muscle. An alternative is to extend the design of the flap to include more tissue from the flank. If one is uncertain as to whether or not enough volume can be transferred, the perforators can be dissected on both sides (Siamese flap).5
Fig. 18.3 (A,B) The anatomy of the intercostal nerves. The mixed intercostal nerves run below the fascia of the internal oblique and mostly enter the rectus abdominis muscle at its posterior surface at the level of the lateral branch of the deep inferior epigastric artery. They follow the intercostal and segmental vessels and mostly pass over the submuscular or intramuscular part of the lateral branch of the deep inferior epigastric artery. At that point it splits into two motor branches, one lateral and one medial, and additionally into a pure sensory nerve that accompanies the perforating artery and vein.
Preference is also given to perforators that pass through the rectus abdominis muscle at the level of the tendinous intersections. At this point, the perforators are frequently large and have few muscular side branches. The distance from the subcutaneous fat to the deep inferior epigastric vessels is also shorter, simplifying this most delicate part of the dissection.17
As a result, the design of a DIEAP flap is made over the most centrally located, dominant perforator, lateral or medial, as long as sufficient abdominal subcutaneous fat tissue is available and the least vascularized part of the flap across the midline can be discarded (Fig. 18.4). At the origin of the perforator, several nerves are encountered (Fig. 18.3). Although there is no constant anatomy, mixed segmental nerves run underneath or through the muscle from laterally and split into a sensate nerve running with the perforator into the flap and a motor nerve crossing on top of the deep inferior epigastric vessels distal to the bifurcation of the perforator, into the medial part of the rectus abdominis muscle.18 One should always expect and anticipate a variety of anatomical differences.
Fig. 18.4 Once the position of the dominant perforator is located on the abdomen, the flap is centered over this perforator. Finally, the incision on the abdomen will be symmetric over the midline but the least vascularized part of the flap will be discarded.
The superficial inferior epigastric artery (SIEA) originates 2–3 cm below the inguinal ligament directly from the common femoral artery (17%) or from a common origin with the superficial circumflex iliac artery (48%). It then passes superiorly and laterally in the femoral triangle lying deep to Scarpa’s fascia and crosses the inguinal ligament at the midpoint between the anterior superior iliac spine and the pubic tubercle. Above the inguinal ligament, the SIEA pierces Scarpa’s fascia and lies in the superficial subcutaneous tissue. During its course the SIEA lies deep to and parallel to the superficial inferior epigastric vein. The vein drains directly into the saphenous bulb.19
The superficial inferior epigastric artery is seen as a direct perforator to the skin while the perforators of the deep system are considered indirect perforators (Fig. 18.5). Of all vessels, it is important to choose the largest, most dominant perforator destined to vascularize the fat and skin, that has few or no side branches to the muscle.
Fig. 18.5 The different types of perforators that can be found at the lower abdominal wall. (1) The branches of the superficial inferior epigastric artery are direct perforators that vascularize the subcutaneous fat and skin after perforating the deep and superficial fascia. All other perforators are indirect perforators; (2) perforators that have a predominant vascularization of the subcutaneous fat tissue and skin with few muscular branches; (3) perforators that branch off of side branches that have a predominant goal of nourishing the muscle; (4) perforators that pass through the rectus abdominis muscle without branching; (5) perforators that pass through the septum or around the rectus abdominis muscle with the sole goal of vascularizing the subcutaneous tissues.
The superficial inferior epigastric vein is the largest vein draining the skin paddle of the DIEAP flap. It is located below the dermal plexus but above Scarpa’s fascia, midway between the anterior superior iliac spine and the pubic symphysis. Harvesting an elliptical skin island transects this vein, redirecting the venous drainage through the smaller perforating veins. Connections between the superficial epigastric vein and the deep inferior epigastric system exist in every patient, but substantial medial branches crossing the midline have been found to be absent in 36% of cases.20,21 In these flaps, venous connections are only present through the subdermal capillary network. This explains why the portion of a flap farthest from the midline may suffer from venous congestion and why the presence of this problem is so variable and unpredictable.
The lymphatic drainage of the DIEAP flap can be divided into a superficial and a deep system. The superficial collectors are located directly underneath the reticular dermis. Deep cuts performed during de-epithelialization may injure this system. The superficial collectors drain to the superficial lymph nodes in the groin. The deep system drains the deep structures of the abdominal wall, i.e., the muscles and fascia and is located in close proximity to the arteries and veins. Careful dissection of the vascular pedicle avoids iatrogenic damage to this lymphatic vasculature. The deep system drains to the inferior epigastric artery and then to the deep iliac nodes.22
The internal mammary artery and its accompanying veins are the first choice for DIEAP flap breast reconstruction.9,11,23 Its central position on the chest wall facilitates microsurgery and offers the most flexibility during breast shaping. The vessels are easy to dissect and are usually protected from radiotherapy damage. In a number of irradiated vessels perivascular fibrosis can be encountered. Chest wall inflammation, following infected implant removal or extreme capsular fibrosis can sometimes cause severe peri-vascular scarring.
Although the artery is usually of sufficient caliber, the size of the veins is very variable. In general the veins on the left side of the chest wall are smaller than those on the right side. For this reason, we prefer to dissect the vessels at the level of the left third or fourth rib, but at the level of the fourth rib on the right side. A small segment of cartilage can be removed together with some intercostal muscles, both cranially and caudally (Fig. 18.6). This provides sufficient exposure of the vessels and adequate recipient vessel length. One can also limit the dissection and exposure to the removal of only the intercostal muscles. Wider exposure can be obtained by nibbling away the lower border of the superior rib and the upper border of the inferior rib.
At the level of the second and third intercostal space, large perforators sometimes emerge from between the intercostal muscles to perforate the medial part of the pectoralis major muscle. The size of these vessels is variable and it is estimated that they can only be used as recipient vessels for free flaps in about 5–10% of cases. These vessels can be identified and evaluated above and below the pectoralis during preparation of the recipient site. If no adequate perforators are found, the internal mammary artery and the accompanying veins are then prepared.
When designing a DIEAP flap, the main factor is the amount of viable tissue that can be harvested on a particular perforator. The most accurate indicator of this is preoperative localization of the dominant source of blood inflow by duplex Doppler or CT imaging. In addition to defining the “safe” flap territory, these techniques provide a degree of reassurance by avoiding intraoperative surprises and considerably reduce operative time. A reduction of operative costs significantly decreases the over-all expense of the reconstructive procedure.
More recently, magnetic resonance angiography has shown promise in the imaging of perforators. In addition to producing accurate and detailed images, there is no radiation exposure,24 unlike CT imaging.
Besides imaging with the purpose of identifying the main perforator, the conventional preoperative work-up includes blood work, oncologic screening and additional tests for concomitant diseases if necessary.
Grayscale imaging shows the anatomical detail of fixed points, axial vessels and perforating branches. The addition of color Doppler allows identification of blood flow, direction (towards or away from probe), pattern of flow (i.e., venous or arterial) and finally a measure of blood flow velocity.26–29
The disadvantages of color duplex lie in its lack of anatomical detail and operator dependence. It requires a detailed knowledge of three dimensional vascular anatomy, as well as expertise in the handling of the devise. Whilst it provides dynamic information about blood flow this may lead to a false sense of security. It is essential to look for vessels with a minimum size and select the largest perforator in the region of interest. This is necessary because of the constant humeral and nervous stimuli that affect the microcirculation and cause fluctuations in vessel flow. Hence, flow rates do not always correlate with the size of the perforator.
In addition to preoperative imaging, it is possible to use a unidirectional hand-held pencil probe for identification of superficial vessels in the operating theatre. The perforators identified can be marked on the patient’s skin to allow accurate flap design and aid intraoperative dissection. This is a simple and inexpensive technique, which provides a useful intraoperative adjunct.30 There can, however, be false negative and positive signals as a result of interference from axial vessels or perforators that run parallel to the fascia, before entering their suprafascial course.
Multidetector-row helical CT is a recent innovation that permits rapid delineation of an anatomic area of interest, giving excellent resolution and low artifact rating. It takes less than 10 min to perform and is well tolerated by patients. This has become the modality of choice for the identification of abdominal wall perforators.31–33 The use of magnetic resonance imaging to avoid the high X-ray dose is promising but still needs further sophistication.34
The scanning is performed in conjunction with intravenous contrast medium and allows evaluation of the donor and recipient vessels. Information collected includes the exact location and intramuscular course of vessels from their origin, the caliber of the perforators and also identifies the dominant vessel. Delineation of the relative dominance of the deep and superficial systems allows the surgeon to consider different options preoperatively. Not only can this modality be used to select suitable patients preoperatively but also operative times are reduced by a mean of 21%, with the obvious associated cost benefits.35
The disadvantages of multidetector-row helical CT lie in the X-ray dosage and use of intravenous contrast media, with the resultant risk of anaphylaxis. The X-ray dose, albeit significant, is less than a conventional liver CT scan and can be combined with staging investigations to reduce the overall exposure. Interpretation of the images can be done before and during surgery by the surgeon him/herself and correlated to intraoperative findings (Figs 18.7, 18.8).
Fig. 18.7 Different views and 3-dimensional reproduction of a pararectal perforator on the right side. The sagittal view shows the course of the vessel through the rectus abdominis muscle. The location of the perforator is referenced to the umbilicus.
Fig. 18.8 CT-angio of a supraumbilical lateral perforator on the left side, symmetrical to a similar perforator on the right side, vascularizing only the most lateral parts of the lower abdomen. The sagittal view shows a relatively easy dissection as the vessel penetrates through the muscle relatively easy but choosing this perforator implies that tissues over the midline will certainly not be vascularized.
Patients eligible for an autologous breast reconstruction with a DIEAP or SIEA flap are mainly those with sufficient lower abdominal subcutaneous fat tissue at the lower abdominal wall. Fortunately in our modern Western Society, many women are good candidates. Cultural differences may apply however. For example, Asian women are generally slimmer and might prefer other donor areas like the anterolateral thigh area. At the top of our preference list, the lower abdomen is our number one choice for autologous breast reconstruction. In microsurgical centers, the DIEAP flap is a preferred choice over implants. Only in very slender women or in cases where multiple scarring of the abdominal wall endangers the normal blood circulation of the free flap or the abdominoplasty flap, secondary options like gluteal perforator flaps or internal thigh flaps are considered. Pedicled latissimus dorsi or thoracodorsal artery perforator flaps combined with an implant is at the bottom of the preference list. Contraindications concerning general health can also influence the decision. Morbid and severe obesity, uncontrolled diabetes, debilitating cardiovascular diseases and uncontrollable coagulopathies are the most frequent examples of absolute contraindications. Smokers and nonmotivated patients will be asked to postpone their surgery if oncologically possible. Implant reconstruction is recommended in patients with a limited oncological prognosis or with a limited life span because of age or concurrent diseases. Also, patients refusing additional scars at the donor site, refusing complex surgery or accepting the possible microsurgical complications, are seen as candidates for implant surgery. All other patients are good candidates for lower abdominal wall breast reconstruction.
The patient is marked in a standing position. A fusiform skin island is drawn on the abdomen, similar to the one used for breast reconstruction with a free TRAM flap but the bulk of the flap is centered over the selected perforator. Although the size and shape may vary slightly, the borders of a DIEAP flap are generally located at the level of the suprapubic crease, the umbilicus and both anterior superior iliac spines, but the flap may be extended laterally to the mid-axillary lines.