Chapter 78. Microvascular Reconstruction

The basic goal of head and neck reconstruction is to replace soft tissue and bony defects with similar tissue, restoring function, and optimizing cosmesis. Reconstructive surgical options are typically thought of in a hierarchy called the reconstructive ladder. (Table 78–1) Each step on the ladder increases the invasiveness and complexity of the reconstruction. Selection of the appropriate procedure depends on the defect and the goals of reconstruction.

Microvascular free-tissue transfer is a reconstructive technique in which tissue units are separated from their native blood supply and moved from one part of the body to a new location. The donor tissue has an identifiable artery and vein that are reanastomosed to recipient vessels, thus reestablishing blood flow. The potential for sensory reinnervation also exists through the reanastomosis of cutaneous nerves.

Refinements in free-tissue transfer over the last two decades have revolutionized the reconstruction of head and neck defects resulting from trauma, congenital anomalies, and ablative procedures for neoplastic processes. Free-tissue units are custom-designed for defects to provide characteristics similar to those of the original tissue. This versatility allows free flaps to serve multiple purposes, such as lining oropharyngeal defects and providing soft tissue support for maxillary defects. Free flaps offer other advantages because they do not have the anatomic constraints of regional pedicled flaps; they can be completed in a single stage, allow a simultaneous two-team approach, and have allowed ablative surgeons to expand their resection boundaries.

Important considerations in patient selection for free-flap reconstruction include age, comorbidities, and functional needs. Older patients are more likely to have comorbid factors that may increase their risk of exposure to prolonged anesthesia, affect wound healing, and decrease their tolerance for donor site morbidity. Some patients may not need the additional functional advantages gained from free-flap reconstruction. The risks and benefits of free-flap reconstruction must be considered for each individual patient.

Preoperative planning and communication with the anesthesia, nursing, and other involved surgical teams facilitate an efficient and well-executed surgical procedure. The tissue defect, functional needs of the patient, or both must be anticipated so that the optimal free flap is selected. Factors to be considered are donor tissue characteristics and composition, the length of pedicle, color match, soft tissue bulkiness, and the functional disability of the donor site. Communication about the patient's intraoperative position and the preservation of adequate recipient vessels in the head and neck for anastomosis should also be relayed with the appropriate teams.

Technical Considerations

Although careful preoperative planning, patient selection, and flap design are important factors in free-tissue transfers, a meticulous microvascular technique is essential for the successful insetting and revascularization of tissue units. Critical to the execution of microvascular techniques are proper instruments, an operating microscope, and the expertise of microvascular surgeons who are trained in the techniques of vessel selection, handling, and preparation.

Vessel Preparation

As a rule, vessel handling should be minimal to decrease the risk of trauma or injury. Vessels should be handled by the adventitia because direct contact with the intima may cause spasm, endothelial damage, and thrombosis, all with the potential of compromising blood flow to and from the transferred tissue. Vessels in the donor vascular pedicle are skeletonized, freeing the arteries from the veins within the vascular pedicle. Atraumatic vascular clamps are then placed. The ends of the vessels are transected and irrigated intermittently with dilute heparinized saline solution to prevent thrombosis. Finally, the excess adventitia is removed from the vessels to expose the media; adventitia trapped in the lumen at the suture line may initiate clot formation.

Microvascular Anastomosis

After both donor and recipient vessels are prepared, arterial anastomosis is followed by venous anastomosis. End-to-end anastomosis is the most commonly used technique, using appropriately sized monofilament sutures (8–0, 9–0, or 10–0). The end-to-side technique is used when there is a significant size mismatch between vessels (>3:1) or when the internal jugular vein is the recipient vessel. Significant tension should not exist at the suture line and vessels should be sutured to lie without twists or kinks.

Free-tissue flaps are generally categorized by the types of tissues that are included in the transfer. Flaps most commonly contain skin (cutaneo-), muscle (myo-), bone (osseo-), or fascia (fascio-). For example, a flap that primarily contained bone and skin would be described as a osseocutaneous flap. Enteric flaps contain visceral structures and fall into their own category.

The cutaneous portion of each free-tissue flap is ultimately supplied by the main pedicle through perforating vessels. These small caliber perforators branch off the pedicle in somewhat predictable locations, although anatomic variation can exist. The perforating vessels travel from the pedicle to the skin to ramify in the subcutaneous plexus that then provides the vascular supply to the skin. Each perforator supplies a limited area of skin, therefore including an adequate number of these vessels in the flap design is essential for survival of the cutaneous paddle. Failure to do so can result in total or partial necrosis of the cutaneous portion of the flap. The course of these perforators from the main pedicle to skin must be preserved during flap elevation. They can travel through the fascial septum between muscles (septocutaneous perforators) or through the muscles themselves (musculocutaneous perforators). Similar vessels branch off the main pedicle to supply the periosteum of the osseous flaps.

Fascial and fasciocutaneous free-tissue flaps are commonly used flaps in head and neck reconstruction. They are characterized by thin, pliable fascia or skin without the bulk of pedicled myocutaneous flaps. Furthermore, they have the potential for crude sensation through the reanastomosis of an accompanying cutaneous nerve to nerves at the recipient site. They are primarily used for complex intraoral, pharyngeal, and cutaneous defects of the head and neck.

Radial Forearm Free-Tissue Flaps

The free-tissue flap of the radial forearm is based on the radial artery, its associated venae comitantes, and the cephalic vein. The skin is supplied by fasciocutaneous vessels in the intermuscular septum between the brachioradialis and flexor carpi radialis.

The main advantages of the radial forearm flap are its thin and pliable tissue characteristics. This flap is an excellent choice to reconstruct oral cavity and oropharyngeal defects without limiting mobility of the tongue or remaining structures. Furthermore, this tissue can be tubed for pharyngeal, laryngeal, and esophageal defects. Crude sensation may be achieved through the reanastomosis of the lateral and medial antebrachial cutaneous nerves to nerves at the recipient site.

Possible ischemic injury to the hand is the main disadvantage to this flap. Preoperatively, the Allen test is performed to verify collateral flow to the hand from the ulnar artery via the palmar arch. Other potential drawbacks include tendon exposure, dysesthesia, motor dysfunction of the hand, and cosmetic results at the donor site from coverage with a split-thickness skin graft (Figure 78–1).

Lateral Arm Free-Tissue Flaps

The fasciocutaneous flap of the lateral arm is supplied by the posterior branches of the radial collateral vessels from the profunda brachii artery. This flap has both a superficial and a deep venous system, the cephalic vein and paired venae comitantes, respectively. The perforators travel to the skin via the lateral intermuscular septum.

The advantages of this flap include a pliable skin paddle, the potential for sensory innervation through the posterior cutaneous nerve, and a donor site that can be closed primarily with minimal functional impairment. The disadvantages of this flap include smaller-caliber vessels and the variability of subcutaneous fat, which depends on the patient's body habitus.

Fasciocutaneous Flaps of the Lateral Thigh

The fasciocutaneous flap of the posterior lateral thigh receives its blood supply from the cutaneous perforators of the profunda femoris artery, with the dominating third perforator. Venous drainage occurs through paired venae comitantes that accompany branches from the third perforator. The lateral femoral cutaneous nerve may also provide some sensation to the skin paddle.

The advantage of this flap is the availability of a sizable amount of pliable skin. The long axis of the skin paddle is designed over the intermuscular septum between the long head of the biceps femoris and the vastus lateralis muscles. This flap has been used after laryngopharyngectomy, and the ample subcutaneous tissue is useful in total glossectomy and skull base defects. Donor site morbidity is minimal but may include wound dehiscence and compartment syndrome. Another disadvantage is the potential anatomic variation of the vascular bundle.

The anterior lateral thigh flap was initially described at the time of the lateral thigh flap, but it did not gain widespread acceptance and popularity until recently. This flap is similar to the lateral thigh flap in tissue characteristics, yet in a more favorable position for simultaneous harvest, since the approach is to the anterior thigh. The anterior lateral thigh flap is based on a septocutaneous or septomyocutaneous perforator off the circumflex femoral artery and vein. The vascular pedicle travels between the rectus femoris and vastus lateralis muscles until giving off perforating branches that supply the cutaneous segment. This perforator is situated within a 3 cm circle located midway between the anterior iliac crest and the lateral patella.

Advantages of the flap include the minimal donor site morbidity, since primary closure is usually achievable and minimal muscular loss is required. Disadvantages include the somewhat short vascular pedicle, requirement for delicate perforator dissection, and the somewhat small vessel diameter. The clinical uses of this flap are similar to those of the lateral thigh free flap.

Scapular Fasciocutaneous Flaps

The scapular fasciocutaneous flap is based on the circumflex scapular artery and vein and may be harvested either as a fasciocutaneous or an osseocutaneous flap (see the next section “Osseomyocutaneous Free-Tissue Flaps”). The circumflex scapular artery originates from the subscapular artery and terminates into the transverse and descending branches, which may be used to supply two separate skin islands—the scapular and parascapular flaps, respectively. Two skin flaps supplied by a single vascular pedicle offer an excellent choice when both intraoral and external coverage are needed. The scapular region provides a large amount of tissue (14–21 cm) useful for larger defects, large-caliber vessels, and an acceptable color match to facial skin.

The major drawback of this flap is the lateral decubitus position of the patient during flap harvest, which limits a simultaneous two-team approach. Furthermore, no potential for sensory reinnervation exists. Although the donor site can be closed primarily with minimal morbidity, patients may require an arm sling and need physical therapy for a short period of time postoperatively.

Temporoparietal Fascial Flaps

The temporoparietal fascial flap derives its blood supply from the superficial temporal artery and vein. The temporoparietal fascia is thin, pliable, and well vascularized, allowing it to mold into complex facial defects and drape over skeletal frameworks such as the ear. This flap also has the unique property of providing a viscous gliding surface that is excellent for tendon excursion. The temporoparietal fascial flap is most often used as a pedicled flap for reconstruction of lateral temporal bone, orbital, limited oropharyngeal, and intracranial defects. As a free flap, it can be used for orbital reconstruction and a nasal lining in the setting of total nasal reconstruction; it has recently been described for laryngeal reconstruction after partial laryngectomy.

The disadvantages of this flap include a donor-site scar, potential alopecia along the region of flap elevation, and a small-caliber vessel (Table 78–2).

A variety of composite flaps, comprising both soft tissue and bone, are available for mandibular, maxillary, and palatal defects. Because each flap has advantages and limitations, the surgeon needs to consider the soft tissue characteristics, the length of bone stock and vascular pedicle, and the suitability for osseointegration (ie, the placement of dental implants) of each flap.

The bony components of these composite flaps are vascularized by the periosteum, which in turn receives perforators from the main pedicle. The bone is plated to the viable remaining native bone, allowing primary bone healing. These free-tissue techniques, which include a bone segment, offer advantages over traditional techniques, which use reconstruction plates and myocutaneous pedicled flaps. Free-tissue techniques also provide an advantage to the potential complications of plate fracture and extrusion and wound breakdown associated with traditional techniques.

Scapular Osseocutaneous Flaps

As described previously, the circumflex scapular artery divides into the transverse and descending branches. The transverse branch of the scapular circumflex artery travels approximately 2 cm below and parallel with the scapular spine whereas the descending branch parallels the lateral border of the scapula. Approximately 10–14 cm of bone can be harvested from the lateral scapular border, which is suitable for osseointegration. The advantages and disadvantages are similar to the scapular fasciocutaneous flap described earlier. The vascular pedicle allows for significant mobility of the osseous portion of the flap relative to the cutaneous portion (Figure 78–2).

Osseomyocutaneous Flaps of the Iliac Crest

The iliac crest composite flap is based on the deep circumflex iliac artery and vein, which arise from the external iliac system. Perforators from the deep circumflex iliac artery supply the skin overlying the iliac crest and the ascending branch of this artery forms an arcade on the undersurface of the internal oblique muscle.

Although up to 16 cm of the bone stock can be harvested from the iliac crest, this flap is limited by the lack of maneuverability of the soft tissue component. The iliac crest flap was modified to include the internal oblique muscle. An osseomyocutaneous flap of the internal oblique-iliac crest offers increased flexibility of the soft tissue components as well as decreased bulk, making it a more versatile flap for oromandibular reconstruction. The iliac crest also provides a hardy bone stock suitable for osseointegrated implants.

The drawbacks of this flap are a short vascular pedicle, bulky skin island, and morbidity at the donor site. The donor site has an increased risk of abdominal hernias, even with the use of mesh, and gait abnormality.

Fibular Osseomyocutaneous Flaps

The fibular composite flap is based on the peroneal artery and vein. Perforators from the posterior intermuscular septum supply the thin overlying skin; sensation to the flap may be restored through the lateral sural cutaneous nerve. This flap offers the longest length of available revascularized bone (24 cm), allowing near-total mandibular reconstruction. Although the height of the fibular bone stock is shorter than the iliac crest, it can still support osseointegrated implants.

Preoperatively, angiography or magnetic resonance angiography is recommended to verify the collateral vascular supply to the foot. Approximately 6–8 cm of fibular bone should be left proximally to prevent injury to the common peroneal nerve and distally to prevent destabilization of the ankle.

Although the skin island is thin and pliable, it is somewhat limited by its linear orientation to the bone. However, technical modifications have made the skin harvest dependable. The donor site can usually be closed primarily, but a skin graft may be required. Functional mobility of the leg is expected postoperatively.

Osseocutaneous Flaps of the Radial Forearm

The fasciocutaneous flap of the radial forearm, described in the previous section, may also be harvested as a composite flap. The length of radius that may be harvested is limited to 10–12 cm in length and to 40% of the diameter to prevent donor site complications. The use of this flap has been limited by the risk of pathologic fracture and somewhat limited bone stock available (Table 78–3).

Before the advances in microvascular techniques, pedicled myocutaneous flaps, such as the pectoralis major and latissimus dorsi flaps, were the standard of care for head and neck reconstruction. Pedicle flaps still play an important role, but free-tissue myogenous and myocutaneous flaps offer greater versatility with fewer limitations. The following flaps may be harvested as muscle only or with skin and adipose tissue.

Myocutaneous Flaps of the Rectus Abdominis Muscle

Although the rectus abdominis muscle has a dual blood supply from the inferior and superior epigastric arteries, the harvested free-tissue flap is based on the larger caliber inferior epigastric system. These vessels arise from the external iliac vessels and send perforators to the skin through the rectus abdominis muscle.

This flap is used primarily for its significant muscle and soft tissue bulk, long vascular pedicle, and reliability. It is an excellent choice for large maxillary and skull base defects.

The main donor site morbidity is a potential ventral hernia, with the most susceptible region below the arcuate line. To decrease the risk of tissue and viscera herniation, the anterior rectus sheath below the arcuate line must be meticulously closed; mesh may be used as an adjunct to strengthen the abdominal wall (Figure 78–3).

Myogenous & Myocutaneous Flaps of the Latissimus Dorsi Muscle

The latissimus dorsi muscle receives its blood supply from the thoracodorsal artery and vein, which are branches of the subscapular system, with innervation from the thoracodorsal nerve. It is potentially the largest flap used in head and neck reconstruction.

An advantage of this flap is the versatility in the amount of muscle that is harvested, ranging from a small amount of muscle under the skin paddle to the entire muscle. Other advantages include its long pedicle length (9 cm), large-caliber vessels, and the ability to design a bilobed flap based on the medial and lateral branches of the thoracodorsal artery. This flap is used for glossectomy, the skull base, and large cervical cutaneous defects. Muscle only may be harvested and used with skin grafting for large scalp defects.

Disadvantages to this flap are the potential for seroma formation and wound dehiscence at the donor site. The lateral decubitus position of the patient, needed for flap harvest, limits the simultaneous two-team approach (Figure 78–4).

Myogenous Flaps of the Gracilis Muscle

The dominant vascular supply to the gracilis muscle is the adductor artery, which arises from the profunda femoris. Venous drainage occurs via accompanying venae comitantes. Motor innervation to the gracilis is supplied by the obturator nerve, which divides into fascicles to different portions of the muscle.

The gracilis muscle is a medial rotator and superficial adductor of the medial thigh whose primary role in head and neck reconstruction is for facial reanimation. The main advantages of the gracilis flap for facial reanimation are the fascicular neuroanatomy of the obturator nerve, the long vascular pedicle (up to 6 cm), and the ability to allow a simultaneous two-team harvest. Donor morbidity is minimal (Table 78–4).

The jejunal enteric free-tissue flap was the first example of head and neck free flap reconstruction in humans (1959). The unique aspect of jejunal and omental-gastroomental tissue in head and neck reconstruction is the availability of a mucosal surface that may be used to reconstruct the aerodigestive tract. Both jejunum and gastroomentum flaps may be used as a tubed flap or mucosal patch. In reconstruction of pharyngeal defects that extend into the mediastinum, a gastric pull up procedure is preferred to avoid placing the distal anastomosis within the thoracic cavity.

Jejunal Enteric Free-Tissue Flaps

The jejunal enteric free-tissue flap is based on arborizing vessels from the superior mesenteric artery and vein. The antimesenteric border of this flap may be filleted, exposing a mucosal surface and providing a pliable and secretory flap for pharyngeal and oral cavity reconstruction. This tubular flap has been used extensively for pharyngoesophageal defects and the diameter of the jejunum makes it appropriate for this purpose.

The disadvantages of this flap include its fragile vessels, poor tolerance to ischemia, and the risks associated with the laparotomy required for harvest: bowel adhesions, obstruction, and wound dehiscence (Figure 78–5). In addition, voice outcomes with a tracheoesophageal puncture are considered to be inferior as compared to the radial forearm free flap for reconstruction of total pharyngeal defects.

Omental & Gastroomental Free-Tissue Flaps

The omental flap derives its vascular supply from the right and left gastroepiploic vessels. This flap includes the double layer of peritoneum that hangs off the greater curvature of the stomach. A segment of the greater curvature is included in the gastroomental flap.

Because of its excellent blood supply, the omentum has a wide variety of uses in the head and neck, including reconstruction of the skull base and large scalp defects, carotid coverage, the management of wounds with osteomyelitis and osteoradionecrosis, and facial contouring. The gastroomental tissue includes gastric mucosa, which provides potential secretions useful for oropharyngeal defects.

Donor site morbidity includes potential intra-abdominal complications such as a gastric leak and gastric outlet syndrome.

Once the microvascular unit has been successfully transplanted and vessels have been reanastomosed, the viability of the flap depends on the maintenance of arterial and venous flow. Factors that may reduce vascular flow, such as external compression from hematoma and edema, hypotension, vasopressors, and vessel spasm, need to be minimized (Table 78–5).

Postoperative Monitoring

The dreaded complication of microvascular reconstruction is flap loss from vascular compromise. Early detection may mean the difference between flap salvage and flap failure, with most surgeons favoring the frequent monitoring of flap viability for the first 48–72 hours. The vast majority of flap failures occur within this period. Venous congestion usually precedes arterial insufficiency owing to a low-flow system with an increased risk of thrombus formation. The most commonly used monitoring techniques are clinical assessment of the cutaneous paddle and Doppler ultrasound flowmeter.

Clinical evidence of venous congestion includes a purplish, turgid flap with rapid capillary refill (less than 1 second). Arterial insufficiency manifests with a pale, cold flap with prolonged (>3–4 seconds) or no capillary refill. Pinprick of the cutaneous portion of the flap with an 18-gauge needle is also an excellent means of assessing the quality of blood flow to and from the flap. A congested flap rapidly bleeds dark blood, whereas a flap with arterial insufficiency may not bleed at all or may bleed bright blood after a significant delay (>4 seconds).

The Doppler ultrasound flowmeter is also a convenient tool to assess vascular flow. The quality of the Doppler signal can give evidence of the velocity of blood flow. Other monitoring methods, such as temperature probes, oxygen tension measurement, implantable dopplers, and color-flow Doppler, have been used.

Thrombus Prevention

The use of pharmacologic adjuncts to prevent thrombus formation is controversial. However, a variety of agents exist and their use is left to the discretion of the surgeon. Aspirin is an antiplatelet agent that has been used postoperatively to prevent thrombus formation. Heparin can be given as a low-dose intraoperative bolus followed by 5–7 days of intravenous infusion, or as a perioperative, subcutaneous injection of 5000 units three times a day. Dextran has been used for its antithrombin and antifibrin effects. An intraoperative bolus is followed by 5 days of intravenous infusion at 25 mL/h. Numerous other agents have been investigated with varying effects.

Flap Salvage

If there is evidence of flap compromise due to either arterial or venous insufficiency, the patient is taken back to the operating room for exploration. The cause of problems vary and can include hematoma, clot within the vascular pedicle, or inappropriate vessel geometry. In cases where adequate venous outflow of the flap cannot be established, leech therapy can provide a temporary solution.

Medicinal leeches (Hirudo medicinalis) are useful for congested flaps and salvaging areas of marginal viability. Leeches release hirudin, an agent that inhibits the conversion of fibrinogen to fibrin at the bite site. The bite wounds then slowly ooze venous blood for up to 6 hours, relieving venous congestion. Patient hematocrit levels must be monitored to prevent significant blood loss, and an antibiotic, third-generation cephalosporin or ciprofloxacin is given intravenously for prophylaxis against specific gram-negative bacterial infection unique to the leech bite. The leech is removed from its attachment to the tissue after withdrawing approximately 5–10 mL of blood by exposing it to an alcohol swab. Each leech is used only once and disposed of using universal precautions. Frequency and duration of leeching is variable and must be based on clinical assessment of the flap. Leeching generally continues until the venous drainage of the flap is established through inosculation to the recipient tissue bed.

Perforator Flaps

Perforator flaps represent an evolving option for further refinement of donor tissue units. These flaps are cutaneous flaps that are created by tracing a single or multiple perforators supplying an area of skin back toward the larger vascular pedicle from which they branched. During the dissection, the muscle through which the perforator travels is separated and not included in flap elevation. The versatility of these flaps is the ability to harvest discrete amounts of skin and subcutaneous tissue from a much larger variety of perforating vessels throughout the body. It avoids the associated tissue bulk and donor site morbidity of harvesting the underlying muscle. These flaps tend to be more technically demanding, and their indications in the head and neck are developing.

Biomedical & Tissue Engineering

Biomedical engineering has continued to rapidly evolve and provide reconstructive surgeons with new tools. Computer-aided design and computer-aided manufacturing of stereolith models based on preoperative imaging has given surgeons a template with which to plan and design bony reconstructions. Robotic surgery has been described for assisting with flap inset in patients who have undergone transoral resection of cancers. Tissue engineering uses cells, scaffolds and growth factors to create replacement tissues. Although this modality remains in its infancy, bioengineered structural elements such as bone and cartilage could be used to prefabricate flaps at distant sites, which can then later be transferred to the head and neck using microsurgical technique.

Allotransplantation

As our experience with and understanding of immunosuppression grows, our ability to transplant non-vital structures has expanded. In 2005, a French group reported the first successful allogenic face transplant for a woman suffering from traumatic soft tissue deficits. Since then, interest in this procedure has continued to grow, with two additional transplants having been performed in the US and one in China. Many new challenges arise in facial transplantation, the most important of which is the need for life-long immunosupression to prevent graft rejection. Balancing the risks of life-long immunosuppression against the outcomes from traditional reconstructive techniques has been a source of debate. Tongue, larynx, and tracheal transplants have been described but also remain experimental. Discovery of new immunosuppressive agents that are more selective and with fewer side effects or induction of tolerance may alter the clinical utility of allogenic transplantation for head and neck defects.

We would like to acknowledge Jeannie Hye-Joon Chung, MD for her contribution to this chapter in the previous editions of CDT.