Master Techniques in Otolaryngology - Head and Neck Surgery: Reconstructive Surgery, 1ed.

42. The Rectus Abdominus Free Flap and Its Variations

Terry A. Day

INTRODUCTION

Major resections involving the lateral skull base present a complex challenge to the reconstructive surgeon. Over the past 30 years, advances in free tissue transfer techniques have improved both the safety of resection of the skull base and the quality of functional and cosmetic outcomes. Moreover, improvements in reconstructive methods have allowed for more comprehensive oncologic resection of advanced tumors of the skull base. Extensive resections involving the lateral skull base entail an array of reconstructive requirements, including the establishment of physiologic and structural separation between the neurocranium, the splanchnocranium, and the aerodigestive compartments; tissue volume replacement and contouring; and functional rehabilitation. Free tissue transfer of the abdominal musculature and its associated fasciocutaneous tissue are key techniques in reconstruction of the lateral skull base. This chapter presents an overview of the development and technical aspects of reconstruction of the lateral skull base using muscular, fascial, and cutaneous elements of the abdominal wall.

Characterization of Lateral Skull Base Defects

Defects of the base of the skull may be classified based on a system proposed by Irish and colleagues, which divides the base of the skull into three regions for the purpose of categorizing reconstructive requirements. Tumors arising in Region II tend to be centered on the infratemporal and pterygopalatine fossae and commonly feature extension through skull base foramina into the middle cranial fossa transversing the pterygoid muscular plane. Region III tumors most commonly originate from the temporal bone with extension into the middle or posterior cranial fossae. Broadly categorized, resection of the lateral base of the skull can encompass ablation of an array of anatomic features, including the lateral temporal bone, the infratemporal fossa, auricle, external auditory canal, masticatory musculature, and cranial nerves. Resulting defects therefore may entail multiple deficits, including insufficient dural coverage, exposure of the internal carotid artery, cavernous sinus or sigmoid sinus, cranial nerves with associated functional deficiencies, and loss of afferent sensory inputs. The most common etiologies for large defects of the base of the skull include extensive cutaneous malignancies, often involving the auricle or external auditory canal; neoplasms of the temporal bone; malignancies of the parotid with deep extension; tumors of the maxillary sinuses with invasion of the pterygopalatine or infratemporal fossae; carcinoma of the nasopharynx; and soft tissue sarcomas arising from the masticatory musculature. Tumor ablation involving the lateral base of the skull may entail extensive resections involving adjacent structures, such as orbital exenteration, auriculectomy, maxillectomy, palatectomy, or mandibulectomy, further complicating the reconstructive endeavor (Fig. 42.1).

FIGURE 42.1 Skull base defects by region.

In the 1960s, the development of local reconstructive flap techniques marked the opening of the modern era of skull base surgery. During the next two decades, innovations in regional flap techniques facilitated the adoption of more comprehensive resections of the skull base, but surgical complications remained prevalent. Since the 1980s, technical advancements in microsurgical techniques have facilitated broad adoption of free tissue transfer as the favored approach to reconstruction of the large defects of the base of the skull. Advantages to free tissue transfer approaches to reconstruction of the lateral base of the skull include the large volumes of tissue available for restoration of contour and obliteration of dead space, the location of donor sites outside irradiated fields, and the presence of well-vascularized tissue that is robust enough to withstand adjunctive radiotherapy and is well suited to the maintenance of effective separation between intra- and extracranial compartments. The development of free flap techniques for reconstruction of the base of the skull has allowed for the performance of increasingly extensive and complex resections. In many cases, functional and aesthetic outcomes in the reconstruction of major defects of the base of the skull may be achieved by combining both locoregional and free flaps in the design of tailored reconstructions.

Free tissue transfer techniques have emerged as the approach of choice for repair of defects of the lateral base of the skull given that effective reconstruction typically requires transfer of large volumes of tissue with aggressive contouring. The distal aspects of local and pedicled flaps, which are most susceptible to failure, are most frequently used in achieving coverage of critical defects. Given the dire consequences of flap loss in this region, the need for reliable coverage of the base of the skull has favored the increasing adoption of free transfer techniques over local or pedicled alternatives. Pedicled flaps, in general, are unlikely to provide adequate coverage for defects of the lateral temporal bone extending above the level of the external auditory canal or infraorbital rim. Whereas pedicled or local flap repairs required multilayer closure with fascial or pericranial grafts for dural repair and pedicled muscle flaps employed for bulk, a rectus abdominis myocutaneous free flap can provide both significant tissue bulk and vascularized lining for dural repair or reinforcement. The interposition of a vascularized layer of tissue yields a more robust partition that resists spread of infection, heals more effectively in a radiated bed, and better withstands adjunctive radiotherapy. A combined rectus muscle and fascial flap allow for one-stage repair of these defects even in patients with gross infection or osteomyelitis. Maintenance of intact vascularization in free tissue obliteration of defects of the skull base also facilitates enhanced delivery of antibiotics or chemotherapeutic agents to the wound site.

In evaluating patients under consideration for rectus flap harvest, it is critical to obtain a complete surgical history with particular attention to any previous abdominal procedures. Caution should be employed with regard to patients who have undergone prior abdominal surgery, particularly inguinal hernia repair. The patient’s performance status should be noted, and the overall suitability of the patient for performance of free tissue transfer should be assessed. Key considerations include factors that could adversely impact microvascular tissue transfer, such as coagulation disorders, severe vascular disease, and autoimmune disease. Moreover, adverse influences on wound healing such as smoking and poorly controlled diabetes should be identified. The patient’s nutritional status should be assessed and appropriate management of perioperative nutrition undertaken.

Preoperatively, the patient should be examined for abdominal scars. Prior abdominal incisions can compromise the abdominal flaps due to disruption of native vasculature. Moreover, violation of the rectus sheath during prior intra-abdominal surgery or elevation of an abdominal skin flap in the performance of abdominoplasty may increase the risk of formation of a postoperative abdominal hernia. Evidence of a previous Kocher incision is particularly concerning, as the entire thickness of the rectus abdominis has likely been divided. Preoperative arteriography may be employed to ensure vascular sufficiency of potential donor vessels. Body habitus is also a critical factor in selecting appropriate candidates for use of the rectus flap in lateral skull base reconstruction. Obese patients may not be suitable because of excessive tissue bulk, inadequate blood supply, or lipodystrophy. The risk of necrosis of adipose tissue is higher in obese patients when superiorly based flaps are used; thus, inferiorly based pedicles may be preferable in such patients. Performance of the “pinch test” yields a rough estimate of the extent of abdominal tissue that can be excised without undue tension on the abdominal closure.

Initially used exclusively as a pedicled rotational flap, the rectus abdominis was first employed as a free tissue transfer for breast reconstruction in the 1970s. Subsequent evolution of the technique entailed the development of muscle-sparing and perforator-based approaches. Advantages of the rectus flap in amelioration of defects of the lateral base of the skull include the following: Lengthy vascular pedicle; soft tissue bulk for effacement of cranial contour defects; anatomically distant from ablative site; little donor site morbidity in appropriately selected patients; potential for use of multiple skin islands; relative ease of harvest and reliable vasculature (Table 42.1). Harvest of the abdominal flaps may be performed concurrently with head and neck ablation. The incisions for these flaps tend to heal favorably and may be well camouflaged within the waistline. Remaining abdominal musculature is generally sufficient in maintaining capacity for abdominal flexion.

TABLE 42.1 Advantageous Features of Rectus Flaps for Reconstruction of Lateral Skull Base Defects

Weber, Kim, and Wax have proposed an algorithm for selecting donor sites for reconstruction of the base of the skull by the size of the defect and its location. They consider rectus abdominis flaps to be most suitable for reconstruction of large defects of the lateral base of the skull or maxillectomy defects, with the anterolateral thigh flap as an alternative for smaller lateral defects requiring less bulk. Rosenthal and colleagues described a classification system for describing defects of the lateral temporal bone and base of the skull. Under this system, Class I defects are limited in scope, encompassing mostly preauricular skin, partial auriculectomy, and parotidectomy defects. Class II defects involve significant resection of the lateral temporal bone with middle ear obliteration. Class III defects also include total auriculectomy with or without resection of the parotid gland. Among these categories, the authors characterized Class III defects as being most suitable for reconstruction with a rectus flap.

Defects of the lateral base of the skull present an array of reconstructive imperatives. Reconstructive objectives may be broadly categorized as physiologic/structural, functional, and cosmetic. Table 42.2delineates the specific imperatives to be considered in lateral skull base reconstruction. Among these diverse reconstructive goals, the establishment of an effective partition between the neural compartments and the aerodigestive tract is an overriding priority. Separation of these compartments is even more critical when large dural defects are involved or when healing is likely to be compromised by infection or irradiation.

TABLE 42.2 Reconstructive Goals in Addressing Lateral Skull Base Defects

Small to moderate defects of the lateral base of the skull may be suitable for reconstruction using locoregional or pedicled flaps such as temporoparietal fascia or pericranial flaps with or without calvarial bone grafts. However, local flaps have insufficient pedicle length and soft tissue bulk for the reconstruction of large defects. Moreover, the tissues most suitable for local flap reconstruction of defects of the lateral base of the skull, including galea, pericranium, temporoparietal fascia, and temporalis musculature, are often compromised during the ablative procedure.

In most cases of resection of the lateral base of the skull, placement of an adequate volume of soft tissue with comprehensive dural coverage obviates the need for reconstruction of osseous defects. However, specific circumstances may require reconstruction with osseous flaps, bone grafts, or alloplastic implants. Such measures are more likely to be required in extended resections involving the orbitomaxillary structures or mandible. Indications for repair of osseous defects include the following: (1) Very large defects predisposing to gross cerebral herniation; (2) extensive defects of the roof of the orbit risking development of pulsatile enophthalmos; (3) large defects of the orbital or nasal wall; (4) large contour defects not amenable to repair with soft tissue alone; and (5) defects involving the maxilla, mandible, or glenoid fossa likely to interfere with occlusion or mastication.

With the exception of abdominal scarring that precludes harvest of the rectus abdominis flap, there are no strict contraindications to this option for reconstruction. It is reliable for most defects of the lateral base of the skull.

In designing a rectus flap, important surface landmarks include the umbilicus, the anterior iliac spine, the symphysis pubis, the linea alba, and the caudal margins of the fifth, sixth, and seventh costal cartilages. The presence of significant diastasis rectus, most common in multiparous females, should be noted. In addition to increasing the risk of abdominal wall herniation, diastasis recti may also necessitate modification of flap design. Multiple flap designs can be employed based on specific reconstructive needs, although consideration should be given to incorporating as much of the periumbilical perforator distribution and subdermal plexus vasculature as possible given particular design constraints. Major perforators should be demarcated preoperatively. This can generally be performed using a handheld Doppler at the time of surgery. However, preoperative imaging using either color flow Doppler or multiphase abdominal CT imaging may also be helpful; obtaining these studies preoperatively is particularly useful if a perforator-based rather than a myocutaneous flap is planned.

Anatomical Considerations

The rectus abdominis originates from the symphysis pubis and pubic crest and inserts on the fifth, sixth, and seventh costal cartilages. The arcuate line traverses the rectus abdominis at the midpoint between the umbilicus and symphysis—approximately 4 to 6 cm superior to the pubis. The extent of the rectus abdominis lying cephalad to the arcuate line is completely ensheathed in thick rectus fascia formed by the division of the internal oblique aponeurosis into anterior and posterior leaflets. Caudal to the arcuate line, the fascia of the internal oblique arises superficially to form the deep layer of the anterior rectus sheath, and the posterior rectus muscle is covered by transversalis fascia only. Longitudinally, the rectus abdominis is transected in the midline by the linea alba. Transversely, it has three tendinous inscriptions that are contiguous with the anterior rectus sheath, and it is thus separated into six muscular compartments. The entire length of the rectus abdominis musculature from xiphoid to pubis is potentially available for harvest and free transfer as a myocutaneous flap.

The rectus abdominis muscle features two dominant vascular pedicles, the deep inferior and superior epigastric arteries, along with an extensive arcade of perforators. The deep inferior epigastric artery (DIEA) originates from the external iliac artery approximately 1 cm cephalad to the inguinal ligament with an orientation toward the wall of the lateral rectus. As it ascends within a plane between the transversalis fascia and conjoint tendon superficially and the peritoneal fascia, the DIEA gently curves in a medial direction. It passes superficially to the arcuate line and then deep to the rectus abdominis within the posterior rectus sheath. It typically divides into lateral and medial branches. The lateral branch tends to be larger and often features anastomotic continuity with the deep superior epigastric artery (DSEA). The average caliber of the DIEA is 2.7 mm at its origin and 2.0 mm at the point where it penetrates the rectus sheath in its posterolateral aspect; typical pedicle length is 7 cm.

The DSEA is derived from the internal mammary artery at roughly the level of the sixth intercostal space. It descends superficial to the plane of the transverse thoracic muscle, running between its origins on the costal margin and xiphoid. It subsequently pierces the fascial envelope of the rectus and then arborizes within an intramuscular plane superficial to the posterior rectus sheath. The DSEA features an average caliber of 2.1 mm at its point of origin where it separates from the musculophrenic artery and 1.9 mm where it enters the deep surface of the rectus sheath. The DIEA is the largest artery of the abdominal wall, with a caliber (2.5 to 3.8 mm) that is generally twice that of the DSEA, and it is the preferred vessel for standard free transfer of a rectus myocutaneous flap. Both the DSEA and the DIEA are accompanied by consistent venae comitantes. Although venous drainage into the venae comitantes typically crosses the midline, the venae comitantes alone may be insufficient to prevent vascular congestion if the flap features significant contralateral extension. In these circumstances, harvest and incorporation of the superficial inferior epigastric vein (SIEV) decrease the risk of venous congestion and partial loss of the flap (Fig. 42.2).

FIGURE 42.2 Cross-sectional view of the vascular and muscular anatomy of the abdomen above and below the arcuate line.

The DIEA and the DSEA both contribute to a rich anastomotic network within the intramuscular plane and give off multiple perforators that travel though the rectus musculature toward the abdominal surface. As they emerge from the anterior rectus sheath, these perforators communicate with the subdermal plexus. An extensive watershed area exists between the DSEA and DIEA arcades above the level of the umbilicus. It is this watershed distribution, along with the shared territory of the subdermal plexus, that allows for versatility in using either DSEA or DIEA vessels as flap pedicles. Circumferentially, the subdermal plexus overlying the rectus musculature communicates via a system of choke vessels with multiple other regions of subdermal perfusion, including those distributions arising from the superficial superior and inferior epigastric arteries, the superficial circumflex arteries, and the intercostal vasculature. This extensive network of subdermal plexus vasculature allows for great variability for cutaneous flap design, with the potential for incorporation of adjacent angiosomes beyond those directly nourished by harvested perforators. Reliability of adjacent angiosome utilization can be increased by delayed flap elevation, which promotes dilation of the choke vessels prior to flap harvest.

The deep inferior epigastric perforator (DIEP) flap is based upon a constellation of periumbilical perforators emerging from the DIEA. There are typically five or six such large-caliber vessels (>0.5 cm in diameter). The largest periumbilical perforator is typically encountered lateral to or just caudal to the level of the umbilicus. While the course and orientation of these periumbilical perforators is highly variable, most emerge within 10 cm of the umbilicus and can be easily localized preoperatively with a handheld Doppler. If a territory is mapped in a half-circle shape extending out laterally and inferiorly around the umbilicus with a 6-cm radius, the major periumbilical perforators will be encompassed within this area in 90% of cases. Although DSEA-based flaps may be designed that incorporate the periumbilical perforators, they are generally less favored due to the fact that the perforators derive directly from the DIEA or its branches while their connection to the DSEA vascular arcades are attenuated by the periumbilical watershed anastomoses (Figs. 42.3 and 42.4).

FIGURE 42.3 Cutaneous perforators of the abdominal wall.

FIGURE 42.4 Distribution and localization of periumbilical perforators.

Additional blood supply to the lower area of the abdominal wall is derived from the superficial inferior epigastric artery (SIEA). The SIEA diverges from the common femoral artery, typically at a point 2 to 3 cm caudal to the inguinal ligament. However, the arterial course of the SIEA varies widely, and the SIEA is minor or absent in roughly one-third of patients. The SIEA traverses the femoral triangle, crossing the inguinal ligament roughly at its midpoint, and then ascends the abdominal wall within the subcutaneous layer, with its course becoming more superficial as it approaches the periumbilical area. Branches of the SIEA anastomose widely with both the main periumbilical perforators and the arterial network of the subdermal plexus. The average diameter and length of SIEA are 1.6 mm and 5 cm, respectively.

The superficial circumflex iliac artery (SCIA) is also derived from the femoral artery. Sharing of a common trunk by the SIEA and SCIA is a frequent anatomic variation. Most commonly, the SCIA diverges from the superficial femoral artery at a point approximately 3 cm caudal to the inguinal ligament and ascends in a trajectory roughly parallel to the inferior border of the inguinal ligament toward the anterior superior iliac spine (ASIS). Upon reaching the level where it traverses the sartorius, the SCIA tends to split into superficial and deep branches. The relative sizes of the superficial and deep SCIAs are highly variable. A series of perforators are emitted by both the superficial and deep systems. The SCIA is typically accompanied by paired venae comitantes.

The Rectus Abdominis Myocutaneous Flap

Multiple flap designs may be employed in the harvest of a myocutaneous rectus abdominis free flap, including the vertical rectus abdominis myocutaneous flap (VRAM), the transverse rectus abdominis muscle flap, and thoracoumbilical variations. Each of these flap designs uses the DIEA pedicle and should be fashioned such that the base is centered upon the rich perforator arcade of the periumbilicus. The standard VRAM flap is begun with a longitudinal incision extending from the level of the superior tendinous insertion superiorly to the inguinal ligament inferiorly. The upper portion is straight and centered over the midpoint of the ipsilateral rectus musculature in a transverse dimension. Below the level of the anterior–superior iliac spine, the incision is gently flared out laterally over the inguinal region so as to remain centered over the DIEA pedicle. Electrocautery is then used to deepen the incision through the subcutaneous plane and the anterior rectus sheath. Excision of rectus sheath below the arcuate line should be avoided, as leaving rectus sheath intact below this level decreases the risk of the subsequent development of a ventral hernia.

The two edges of the split anterior rectus sheath are then retracted laterally to allow for exposure of the bulk of the ipsilateral rectus musculature. Dissection is carried inferiorly until exposure of the rectus abdominis origin at the pubis is achieved. The attachment of the muscle is carefully divided and the caudal end of the muscle retracted superiorly, revealing the underlying DIEA pedicle. The pedicle is dissected caudally and may be followed until its divergence from the external iliac artery. Division of the DIEA at this level provides an average of 10 cm of pedicle length. Once the pedicle is divided and protected, harvest of the muscle is performed in accordance with flap design, with the muscle preferentially divided along its fascial borders or tendinous inscriptions (Table 42.3; Fig. 42.5).

TABLE 42.3 Characteristics of DIEA-based Rectus Abdominis Myocutaneous Free Flaps

FIGURE 42.5 Dissection of the pubic origin of the rectus muscle and identification of the DIEA pedicle.

Muscle-Sparing Variations

The era of reconstruction using muscle-sparing abdominal flaps began in 1989 with Koshima and Soeda’s description of the DIEP flap. The primary advantage of the DIEP over traditional rectus flaps was that by sparing the bulk of the rectus musculature, the risk of postoperative abdominal wall weakness and herniation was reduced. Although the DIEP flap entails only skin and subcutaneous tissue, harvest still requires incision of the anterior rectus sheath and dissection through the abdominal wall musculature. With the advent of the superior–inferior epigastric artery flap, complete sparing of the abdominal musculature was achieved. A more recently described abdominal free flap, the SCIA flap, also spares dissection of both the rectus musculature and its fascial sheath. Woodworth and colleagues presented a series of head and neck reconstructions performed using muscle-sparing variations on DIEP, SIEA, and SCIA flaps. Advantages of these flaps included reduced morbidity of the donor site, a predictable volume of tissue transfer, and the favorable cosmetic result of a low-set transverse abdominal scar. The average size of the head and neck defect repaired was 74.5 cm². There were no postoperative abdominal hernias (Fig. 42.6).

FIGURE 42.6 SCIA, SIEA, and DIEA designs.

Deep Inferior Epigastric Perforator Flap

Preoperatively, the locations of the primary umbilical perforators and the course of the SIEA and SIEV are confirmed with handheld Doppler and marked. As with the rectus myocutaneous free flap, differing size and orientations of the skin paddle may be employed depending on defect-specific reconstructive requirements, but the design must incorporate a portion of the periumbilical perforator region of the abdominal wall. DIEP flaps utilized for head and neck reconstruction are typically based on 1 to 3 perforators, with an average of 1.5 perforators employed. The skin incision is performed circumferentially. Dissection is then carried down to the deep fascial layer. Generally, flap elevation begins at the most lateral or inferior aspects of the flap depending on the orientation of the skin paddle. As elevation progresses toward the periumbilicus, care is taken to identify and preserve the major perforators as they exit the anterior rectus sheath. The SIEV, which typically courses in a paramedian orientation approximately 4 to 5 cm lateral to the linea alba, should also be identified and preserved, as it may be useful in maintaining adequate venous drainage of large flaps. Up to three large-caliber perforators are then selected for preservation. Small, longitudinally oriented openings in the anterior rectus sheath allow for egress of the large perforators. The desired perforators are freed from the anterior rectus fascia with releasing incisions of the rectus sheath and then progressively followed through the rectus muscle using intramuscular dissection. In most cases, perforators can be freed by simply enlarging the natural disruptions in the fascial wall, which surround the perforators by inserting one blade of a small scissors and then splitting the fascia above and below to create a 2- to 3-cm longitudinally oriented fascial opening. A small cuff of rectus tissue is preserved around each perforator. Other perforators are then ligated, and the flap is progressively released from the anterior abdominal wall until it is tethered only by the preserved perforators. Separation of muscle fibers in their longitudinal plane allows for dissection of the perforators with only minimal damage to the surrounding rectus musculature. Segmental innervation of the rectus abdominis should be preserved when possible.

Perforators are followed down toward their origin from the DIEP vessels with ligation of small muscular branches. As dissection of the pedicle progresses, adjacent perforators may join into common vessels. Dissection is continued until appropriate pedicle and caliber length are obtained in accordance with the reconstructive requirements. Typical pedicle length is greater than 10 cm. If further pedicle length is required, incision of the inferior rectus sheath can facilitate tracing of the pedicle all the way back to the origin of the DIEA vessels. The perforators selected for the pedicle are then ligated and separated from surrounding DIEP vasculature with division of any anastomotic connections to the superior epigastric arcade. The perforator-based pedicle is then delivered through the previously fashioned apertures in the overlying rectus musculature and the anterior fascia (Figs. 42.7 and 42.8).

FIGURE 42.7 Preoperative marking of expected distribution of periumbilical perforators.

FIGURE 42.8 Elevation of flap with preservation and intramuscular dissection of perforators.

Superior–Inferior Epigastric Artery Flap

Preoperatively, the position of the SIEA, the SIEV, and the periumbilical perforators should be delineated with a Doppler. Initial elevation of the flap proceeds in a suprafascial plane, with early identification of the SIEA at the midpoint of the inguinal ligament. The caliber of the vessel should be assessed; if the SIEA is absent or features a diameter less than 1 mm, consideration should be given to conversion to conversion to a DIEP flap. Among patients in whom the SIEA is small or absent, the periumbilical perforators tend to be larger—making use of the DIEP flap more advantageous in such settings. If the SIEA is judged to be adequate, it can be carefully dissected to its takeoff from the femoral artery as needed, with division of the pedicle at a point where adequate caliber of the vessel and pedicle length have been achieved. Average SIEA pedicle length is 4 cm. The primary advantage of the SIEA flap as compared to the DIEP is the fact that the rectus abdominis musculature and the anterior rectus sheath are both left undisturbed. Disadvantages include a relatively small tissue volume and short pedicle length. Moreover, the SIEA is small or absent in a significant proportion of patients. Also, the fact that the SIEA pedicle emerges from the inferior aspect of the flap within a subcutaneous plane rather the deep surface of the flap can make orientation of the flap at inset and microvascular anastomosis more technically challenging, irrespective of relative pedicle caliber.

Superficial Circumflex Iliac Artery Flap

Preoperatively, the course of the SCIA inferior and parallel to the inguinal ligament from the femoral artery toward the ASIS and its major perforators are delineated and marked. The ASIS, inguinal ligament, and femoral artery are key anatomic landmarks. Flap design should encompass major SCIA perforators and the skin overlying the ASIS. Elevation of the flap is achieved in a suprafascial plane with careful preservation of major perforators. A dominant perforator is selected and traced back to the SCIA. Ideally, the superficial circumflex iliac vein (SCIV) should be dissected along with the venae comitantes, as the venae comitantes may be inadequate to provide sufficient drainage to avoid venous engorgement. Circumferential flap elevation is completed after the course of the selected SCIA perforator has been traced out. Dissection of the pedicle can be carried back to its takeoff from the femoral artery. Pedicle ligation and transfer should include the proximal SCIA and its venae comitantes along with a corresponding segment of the SCIV. Advantages of the SCIA flap include its thin profile, flexibility for folding and contouring, and the potential for rapid harvest. The major drawback to the flap is the small diameter of the SCIA, which may be 1 mm or less. In obese patients, the SCIA may be preferable to the DIEP and SIEA due to its less bulky relative volume and decreased risk of necrosis of adipose tissue.

Flap Inset

Options for arterial recipient vessels include superficial temporal, facial, lingual, and superior thyroid arteries. Priority may be given to preferential use of more cephalic vessels so as to preserve caudal options for possible future reconstructions. The superficial temporal vessels are a useful option based on their superior position and appropriate caliber.

The approach to dural repair varies depending on the size of the defect. If possible, primary dural repair yielding a watertight closure is optimal in protecting the dural contents from ascending infection. In the setting of large dural defects, grafts can be used, with preference given for autogenous grafts such as fascia lata or temporalis fascia. Alternatively, the fascial surface of the reconstructive free flaps may be used in patching dural deficiencies if defect and pedicle geometry allows. Free adipose tissue grafts harvested from the abdomen may be used to reinforce dural coverage in areas where defect dimensions make achievement of a tight dural seal difficult.

Following flap positioning to obliterate the defect, microvascular anastomosis is performed using standard techniques. Depending on the design of the flap and the characteristics of the defect, skin islands may be preserved as needed for cutaneous reconstruction. Other portions of the flap are deepithelialized. Any flap surfaces used in reconstruction of aerodigestive compartments should be meticulously deepithelialized to promote mucosal ingrowth. The fascial portion of the flap is suitable for use in creation of a watertight dural seal. If dura has been closed primarily, the fascial surface of the flap should be overlaid to reinforce a watertight repair. Alternatively, the fascial surface may be sutured directly to the free edges of the dura so as to obliterate directly the dural defect. The maintenance of an intact blood supply to the fascia is preferable to the use of a free rectus sheath fascial graft. If the complex dimensions of the defect require, the fascial portion of the flap may be pedicled on a sole perforator. The subcutaneous portion of the flap can also be positioned as a “cork” overlying the dural repair.

During inset, the flap should be carefully secured to the surrounding tissues to prevent the graft from falling away and compromising coverage of the base of the skull. The flap may be directly sutured to the adjoining temporalis musculature. Burr holes may be established in the bony cranial perimeter of the defect through which anchoring sutures may be placed to suspend and secure the flap. Suspension of the flap via drill holes placed around the craniectomy defect can facilitate secure placement of the free tissue transfer over the dura. If necessary, a channel may be drilled in the cranial wall to allow the vascular pedicle to drape away from the anastomotic site without undue kinking, torsion, or tension. When recipient vessels within the neck are used, the pedicle should be threaded into the neck through a tunnel between the angle of the mandible and the oral mucosa.

If the defect of the base of the skull extends to involve the orbit, the rectus myocutaneous flap may be employed in primary reconstruction of the orbit. If facial nerve resection is required for tumor extirpation, reanimation measures including the placement of gold or platinum weights in the upper lid, lid-tightening procedures such as wedge resection or canthoplasty, and static sling procedures may be performed in a single stage along with rectus flap reconstruction.

Primary closure of the donor site is preferred and is feasible in nearly all cases. If the rectus sheath was incised during flap harvest, it must be securely reapproximated. If significant rectus musculature is harvested or there is a sizable defect in the anterior rectus sheath, placement of a synthetic mesh as part of the donor site closure decreases the risk of postoperative hernia. Consideration should be given to placement of a lumbar drain and application of compressive dressing in circumstances where a reliable watertight dural seal has been impossible to establish. This measure counters the force of normal CSF pulsations, which will tend to promote dissection between tissue closure planes with a resulting increased risk of CSF leakage and susceptibility to ascending infection (Fig. 42.9).

FIGURE 42.9 Closure of donor site with alloplastic mesh.

Technical Innovations and Variations

Fasciocutaneous and perforator-based variations upon the rectus flap afford greater flexibility in reconstructive design, particularly in circumstances where less bulk is required. One key distinction between myocutaneous and perforator-based variations is that the perforator flaps allow for precise establishment of cranial and facial contours at the time of initial reconstruction without the expectation of significant atrophy as would occur with a myocutaneous flap. The degree of denervation atrophy likely to occur over time with the myocutaneous rectus flap is unpredictable, thus complicating decisions regarding the amount of bulk appropriate for initial reconstruction. Moreover, the absence of muscle bulk allows for more complex folding for three-dimensional reconstruction and increased independent mobility if multiple skin paddles are employed. Although muscle-sparing variations of the rectus flap have been widely adopted in the performance of breast reconstruction, their use in the reconstruction of head and neck defects is relatively new. DIEP and SIEA flaps have been shown to yield reduced morbidity at the donor site, length of stay, and hospital costs as compared to traditional myocutaneous rectus flaps in breast reconstruction. Recent published series of cases have also demonstrated the safety and effectiveness of muscle-sparing variants in head and neck reconstruction.

Although reconstruction of bony elements is not often required for reconstruction of defects of the lateral base of the skull, bony support may be desirable if defects extend to involve orbitomaxillary structures. In such cases, bone grafts from other sites such as the iliac crest may be incorporated into myocutaneous rectus free flaps prior to inset. Malar reconstruction may also be achieved using osteomyocutaneous composite free rectus flaps including a costochondral component. If bony elements are required for reconstruction, portions of the 7th, 8th, 9th, and 10th ribs, which derive their blood supply from their corresponding intracostal vessels, may be harvested in conjunction with abdominal flaps. These vessels are nourished primarily by the costomarginal artery, which features anastomotic connections with DSEA on the deep surface, allowing for incorporation of rib elements into the rectus flap. Free rectus flaps incorporating 7th to 10th rib elements have been successfully used in craniofacial reconstruction. Alternatively, vascularized bone can be incorporated into the DIEP flap with harvest of a portion of the superior pubic ramus, which receives arterial supply from the DIEP vessels. Use of the rectus abdominis as a free flap with efferent neural innervation as a one-stage procedure for reconstruction of facial defects with reanimation has been described, and the division of the rectus abdominis by tendinous inscription into multiple functional segments with separate neural fascicles holds the potential for complex facial reanimation.

Postoperatively, patients should be admitted to an intensive care unit to monitor both the flap and the neurologic status. If the dural envelope was violated, a postoperative CT is indicated to evaluate for pneumocephalus. CSF leaks are an uncommon complication and generally resolve with lumbar drain decompression when they do develop. Neurosurgical consultation is necessary if a lumbar drain has been placed. Standard techniques for monitoring of free flaps should be employed with frequent flap checks in the immediate postoperative period. The neurologic status of the patient should be closely monitored for evidence of meningitis or other cerebral complications. Nutritional status should be optimized in the perioperative period to maximize healing. Manipulation of intraperitoneal contents during flap elevation may cause postoperative ileus, in which case enteral feeding must be temporarily suspended. Donor site care requirements are minimal, although strenuous activity should be limited until incision sites are well healed. Abdominal exercises should be deferred for several weeks.

Generally, I have found that complications are rare and typically are restricted to abdominal hernia. The closure of the donor site must be achieved with meticulous attention to the fascial closure, or the risk of hernia is high.

The results with the technique have been outstanding. In over 100 cases, I have has had excellent results. The anatomy and reliability are excellent. Free tissue reconstructions using the rectus abdominis myocutaneous free flap or its muscle-sparing variants are reliable techniques for ameliorating large defects involving the lateral base of the skull. The musculature of the abdominal wall and associated fasciocutaneous tissues can yield a large volume of highly vascularized tissue that can effectively protect neural elements of the base of the skull while also addressing complex associated functional and aesthetic deficits. Innovative techniques for the harvest and inset of abdominal flaps have been established that provide the reconstructive surgeon with tremendous flexibility in designing reconstructive procedures tailored to the specific needs of patients with defects of the lateral base of the skull.

• Achievement of a watertight dural seal and establishment of a physiologic barrier protecting the dural compartment is a critical factor in reconstruction of defects of the lateral base of the skull.

• In most cases, osseous elements are not required in reconstruction of the lateral base of the skull, and transfer of an adequate volume of vascularized soft tissue is sufficient.

• Muscle-sparing abdominal flaps such as the DIEP, SIEA, and SICA flaps provide greater flexibility for reconstruction of complex three-dimensional defects of the lateral base of the skull and minimize the risk of postoperative donor site complications.

• The rate of abdominal hernia following performance of a rectus myocutaneous free tissue transfer is low. However, placement of an alloplastic mesh during donor site closure should be considered in high-risk patients.

• Preoperative imaging with either color flow Doppler or CT may be helpful in ensuring adequate vascularity for free transfer of abdominal tissue and in identifying the locations and course of key perforator vessels.

• The major periumbilical perforators can generally be identified within a 6-cm radius of the umbilicus.

• Perforator-based abdominal flaps for reconstruction of the lateral base of the skull most commonly incorporate one to three periumbilical perforators. The largest perforator is typically located just lateral to the umbilicus, either directly on or slightly caudal to the transumbilical plane.

• Postoperative CSF leaks following free tissue reconstruction of lateral skull base defects are rare, and when they occur, they generally resolve rapidly with lumbar drain decompression.

• Previous abdominal surgery is a relative contraindication to the use of the rectus abdominis flap or its variants in free tissue transfer.

• Perforator-based abdominal flaps may lack adequate bulk for amelioration of large defects of the lateral base of the skull.

• Significant volume loss will occur with transfer of a free rectus abdominis myocutaneous flap due to denervation atrophy, although the degree of loss is variable and difficult to anticipate.

• Ascending infection may lead to meningitis or other cerebral complications if sufficient insulation and partition of the neural compartment is not established.

• Abdominal flaps employed in reconstruction may be weighty, and secure attachment to the skull base may be challenging to achieve.

• Placement of a lumbar drain and application of compressive dressings should be considered if the dural seal is of questionable integrity.

• Standard head and neck surgical set

I gratefully acknowledge the contributions of Barry T. Malin, MD MPP.

SUGGESTED READING

Gal T, Kerschner J, Futran D, et al. Reconstruction after temporal bone resection. Laryngoscope 1998;108(4 pt1):476–481.

Day T, Davis B. Skull base reconstruction and rehabilitation. Otolaryngol Clin North Am 2001;34(6):1241–1257.

Marchetti C, Gessaroli M, Cipriani R, et al. Use of perforator flaps in skull base reconstruction after tumor resection. Plast Reconstr Surg 2002;110(5):1303–1309.

Leonhardt H, Mai R, Pradel W, et al. Free DIEP-flap reconstruction of tumor related defects in head and neck. J Physiol Pharmacol 2008;59:59–67.

Rosenthal E, King T, McGrew B, et al. Evolution of a paradigm for free tissue transfer reconstruction of lateral temporal bone defects. Head Neck 2008;30(5):589–594.