Rectus Abdominis Flaps and Pudendal Thigh and Related Flaps




BACKGROUND



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Reconstruction of the vulvovaginal and pelvic region can be a complex and formidable undertaking. Defects from oncologic resection can be extensive and variable. The increasing use of adjuvant radiation therapy and chemotherapy further adds to the challenge of achieving uncomplicated wound healing. Trends indicate that patients are being diagnosed with gynecologic malignancies at younger ages, and with better treatments, long-term survival has increased.1,2,3,4 Longer survival results in a higher risk of local recurrence, which can complicate reconstruction, because the operative field in such patients is often scarred and radiated. The goals of reconstructing vaginal defects are manifold: to restore normal anatomy, to facilitate primary wound healing, to fill in dead space in the pelvis with healthy tissue, to restore support of the pelvic floor, and to create a neovagina that allows for sexual activity.



Vaginal reconstruction comprises techniques designed to ameliorate defects not just from extirpative procedures but also from congenital vaginal agenesis. However, regardless of the cause of the defect, the ultimate goal is the same: to restore a vagina that maintains sexual function and body image. From the original nonoperative technique of stenting and dilatation by Frank5 to skin graft inlay combined with stenting by McIndoe6,7, to some of the more established flap techniques—including the gracilis myocutaneous flap,8,9,10,11,12 the medial thigh flap, the rectus flap, the omentum, and various fasciocutaneous flaps—there is no one ideal method for reconstruction.13,14,15,16,17,18,19,20 However, flaps must be able (1) to provide a reliable amount of skin and subcutaneous fat and/or muscle into the defect, to produce a functional outcome, (2) to provide a sensate flap, when needed, (3) to minimize donor site morbidity, and (4) to achieve an aesthetic outcome.



Vaginal defects can be reconstructed using a number of locoregional flaps. A detailed assessment of the wound must be performed before selection of the flap. To better visualize the range of vaginal defects, the vagina can be represented as a coned cylinder, as shown in Figure 17-1.21,22 The opening of the cone is the introitus. The anterior wall of the vagina is adjacent to the bladder, the lateral walls are next to the pelvic musculature, and the posterior wall is in proximity to the rectum. Vaginal defects are classified, on the basis of these anatomic considerations, into 2 general categories: partial defects (type I) and circumferential defects (type II; see Figure 17-1). Type I defects are further classified as either anterior or lateral wall defects (type IA); these often result from bladder or urinary tract malignancies or from primary vaginal malignancies. Type IB defects are posterior wall defects and often are caused by colorectal cancers. Type II defects are circumferential defects and are further divided into type IIA, which are located in the upper two-thirds of the vagina and are usually caused by uterine and cervical malignancies, and type IIB, which result from total, circumferential vaginal resections related to pelvic exenterations.




Fig. 17-1.


To better visualize the range of vaginal defects, the vagina can be represented as a cylinder. Defects can be categorized as type I partial defects, which involve the anterior or lateral wall (type IA) or the posterior wall (type IB), or type II circumferential defects, which involve the upper two-thirds of the vagina (type IIA) or total vaginectomies (type IIB).






INDICATIONS AND CLINICAL APPLICATIONS



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A reconstructive algorithm can be used to simplify the choice of flap on the basis of the type of defect (Figure 17-2). Three regional flaps can be used to reconstruct the vast majority of vaginal defects. The Singapore or pudendal thigh fasciocutaneous flap is ideal for type IA defects, which involve the anterior or lateral wall.13,23,24,25,26,27,28 This flap is well vascularized and reliable, and it is thin, which allows for easy insertion and insetting into the anterior/lateral defect. Type IB defects involve the posterior wall of the vagina, and the rectus abdominis flap provides well vascularized skin to cover the posterior vaginal wall and good muscle bulk to obliterate the dead space between the abdominal and pelvic cavities.29,30 Type IIA defects can also be reconstructed using the rectus abdominis flap. For type IB defects, it provides a good skin paddle and good muscle bulk. However, for type IIA defects, this flap is best conformed into a rolled or tubed flap to form the neovagina. Type IIB defects, which result from circumferentialtotal vaginectomies, are best reconstructed using bilateral myocutaneous gracilis flaps. There is usually a large amount of vaginal surface area that needs to be replaced after a type IIB resection.




Fig. 17-2.


An algorithm approach based on the type of vaginal resection.





When selecting the flap for reconstruction, patient characteristics must also be taken into consideration. In patients who are obese, thin, pliable flaps such as the Singapore or pudendal thigh flap may be more optimal than the rectus flap, on account of the unreliable vascularity of the rectus flap’s skin paddle in this population. For patients who smoke, careful consideration must be taken when selecting a regional flap to ensure reliability of the skin portion of the flap. In patients with prior vaginal reconstruction, the use of pedicled flaps may be limited. In radiated patients, because of scarring and the higher risk of problems with wound healing, the rectus flap may be used to fill pelvic dead space and to improve revascularization. For patients who do not plan to resume sexual activity, vaginal vault reconstruction can be excluded, and the rectus myocutaneous flap can be placed in the pelvis to obliterate dead space and to provide healthy, vascularized tissue to promote healing.



In patients with prior abdominal incisions, care must be taken when harvesting the flap to first ensure that the vascular pedicle is patent. For patients with a history of vascular surgery or inguinal hernia repairs (especially those in whom mesh was used), it may be prudent to obtain a preoperative angiogram to evaluate the inferior-based pedicle of the rectus flap.




RECTUS ABDOMINIS FLAP



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Anatomic Considerations



The rectus abdominis is a long, flat muscle that extends vertically along the length of the anterior abdomen. Superiorly, the muscle inserts into the xiphoid process and attaches to the anterior surfaces of the fifth, sixth, and seventh costal cartilages. The paired rectus abdominis muscles are key postural muscles. Together they are responsible for flexing the lumbar spine when the muscles of the posterior trunk are relaxed. By contrast, when both the paired rectus and posterior trunk muscles contract, intra-abdominal cavity pressure is increased. Thus, the rectus muscles play an important role in coughing, defecation, and childbirth. Their dimensions measure approximately 26 cm in length and 6.6 cm in width. The muscle is enclosed by the anterior and posterior rectus sheaths, which are formed by the three fascial layers of the abdominal wall: the external oblique, the internal oblique, and the transversus abdominis. Of note, below the arcuate line, the anterior sheath is composed of aponeurotic contributions from all 3 fascial layers. However, there is no posterior sheath below the arcuate line; the posterior rectus muscle is separated from the peritoneal cavity by only the transversalis fascia. This is important to take into consideration when closing the fascia, once the muscle flap is harvested and inserted into the pelvis, in order to prevent herniation.



1. Blood supply and innervation


The rectus abdominis muscle is a class II muscle with a dual blood supply (Figure 17-3).31,32,33 One dominant pedicle involves the superior epigastric artery and vein, which arise from the internal mammary vessels. This pedicle is approximately 2 cm in length and 1.8 mm in diameter. It lies beneath the muscle insertion at the costal margin and usually enters the muscle at the medial to midposterior third of the muscle. The other dominant pedicle involves the deep inferior epigastric artery and vein (DIEA/DIEV), which come from the external iliac artery and vein. This pedicle is approximately 5 to 6 cm in length and 2.5 mm in diameter. It enters the lateral edge of the muscle 4 cm superior to the groin origin. Minor pedicles that also ­contribute to the blood supply involve the subcostal and intercostal vessels. When using the pedicled rectus abdominis flap in pelvic and vaginal reconstruction, the muscle is usually detached superiorly at the costal margin, thereby making the deep inferior epigastric vessels the main blood supply to the flap.




Fig. 17-3.


The rectus abdominis muscle has a dual blood supply: superiorly from the internal mammary vessels and inferiorly from the deep inferior epigastric vessels.





The rectus muscles are innervated in a segmental fashionby intercostal nerves T7 through T12, which contain both motor and sensory fascicles. This segmental innervation ­prevents the use of this flap as an innervated muscle or sensory skin flap.



2. Skin territory


A musculocutaneous flap of varying dimensions can be designed along the entire length of the muscle and/or along any axis radiating from the umbilicus. The rectus muscle will perfuse a very wide vertical skin flap, with excellent reliability. The maximum width of the vertical island is typically dictated by the ability to obtain primary closure of the abdominal donor site (Figure 17-4); this is generally a width of 6 to 8 cm. Alternatively, a horizontal and/or oblique skin paddle can be placed anywhere along the length of the rectus abdominis muscle, but it is important to note that the concentration of perforators below the arcuate line is not as great. However, the flaps used for vaginal reconstruction are, in general, best designed either with muscle alone or with a vertical skin paddle and are, therefore, known as vertical rectus abdominis myocutaneous flaps. Perforating vessels arise along the course of both the superior epigastric and the deep inferior epigastric artery, piercing the anterior rectus abdominis fascia 2 to 3 cm from the lateral border of the muscle. A cluster of large (> 0.5 mm) periumbilical perforating vessels, representing terminal branches of the DIEA, is present within a rectangular area 2 cm cranial and 6 cm caudal to the umbilicus, and from 1 to 6 cm lateral to the umbilicus. A musculocutaneous flap should be designed to include at least one of these perforating vessels; thus, it is wise to make the skin island at least 6 cm in diameter and to include the direct periumbilical skin.




Fig. 17-4.


A vertical or horizontal skin paddle can be designed over the rectus muscle.





Preoperative Preparation



Box 17-1 KEY SURGICAL INSTRUMENTATION FOR FLAP INSET




  • A lighted retractor can be used in the pelvic region during flap inset for better visualization.



  • The Lonestar retractor system can be used to help flap insetting in the vaginal wound and to allow for a simultaneous, 2-team approach for closing the abdomen while the flap is sutured in place and the perineal wound is closed.




The presence of long abdominal scars may interfere with flap design or preclude the use of the flap altogether. Furthermore, the placement of such scars may indicate that the vascular supply to the flap has previously been transected. For patients at risk for pulmonary complications and/or back pain or weakness, harvest of the flap should be carefully considered, because abdominal wall strength will be weakened following harvest of one or both rectus muscles. In cases in which ostomy sites are already present or are planned in the concurrent procedure, the contralateral muscle should ideally be harvested for the flap.



1. Muscle flap


The approximate location of the rectus abdominis muscle to be harvested is outlined. The lateral border of the muscle is indicated by a line drawn from the pubic tubercle, intersecting the midpoint of another line drawn from the anterior superior iliac spine, to the umbilicus. The medial border is typically represented by the midabdominal line, or linea alba; however, the border may lie more laterally, depending on the degree of diathesis between the paired rectus muscles. The arcuate line is located approximately midway between the umbilicus and the symphysis pubis or at the level of the anterosuperior iliac spine. Typically, a midline or paramedian vertical incision is planned.



2. Myocutaneous flap


A vertical cutaneous paddle can be designed over the rectus abdominis muscle. The flap is designed so that primary ­closure is permitted. The umbilicus should be maintained on the same side as the stoma. Therefore, the medial part of the vertical skin incision should be lateral to the umbilicus (Figure 17-5). The average flap width measures 5 to 6 cm, and the average length is 12 to 14 cm. The length of the skin paddle is determined according to the amount of vaginal wall surface area that is needed to be replaced after resection.




Fig. 17-5.


The skin island should be on the side contralateral from the stoma site. The umbilicus should remain on the same side as the stoma.





Surgical Procedure



Box 17-2 MASTER SURGEON’S PRINCIPLES




  • Before flap elevation, the pedicle should be palpated at the iliac takeoff to ensure viable donor flap vessels. Retraction during the pelvic portion of the procedure should be performed without applying too much force and pressure, which can cause pedicle compression and thrombosis.



  • To preserve the musculocutaneous perforators, elevation of the skin paddle of more than 1 cm on either side of the rectus muscle should be performed under direct vision.



  • During flap elevation, the skin paddle can be sutured to the muscle to prevent shearing or separation of the skin island from the muscle underneath.



  • To avoid pedicle tension and to prevent hernia formation, the fascia must be closed carefully—a breadth of 1 finger should be able to comfortably fit into the fascial defect at the flap base after primary closure.



  • If the fascia is attenuated or if primary closure results in tearing of the fascia, mesh should be applied as reinforcement.




1. Muscle flap


Flap elevation is performed with the patient in the supine or lithotomy position. In general, for cases involving pelvic and vaginal reconstruction, the patient will already be in the lithotomy position from the oncologic resection portion of the case. The skin is incised, and subcutaneous tissue is dissected. Once the anterior rectus sheath is visualized along the length of the incision, the sheath is incised 1 cm lateral to the linea alba. This exposes the rectus abdominis muscle. The anterior rectus sheath is then sharply elevated from the anterior surface of the muscle. The muscle must also be freed from its close attachments to the anterior sheath at its inscriptions. The lateral border of the muscle is located. At a level just above the arcuate line, the rectus muscle is bluntly elevated from the posterior rectus sheath. Dissection is carefully continued distally to expose the vascular pedicle entering the posterior rectus sheath from a lateral direction. The DIEA and DIEV are readily seen coursing beneath the transparent transversalis fascia, approximately 3 to 4 cm below the level of the arcuate line.

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Jan 12, 2019 | Posted by in GYNECOLOGY | Comments Off on Rectus Abdominis Flaps and Pudendal Thigh and Related Flaps
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