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Microsurgical free tissue transfer has revolutionized head and neck reconstruction. It allows functions and esthetics to be preserved without compromising the principles of oncologic surgery. To this end, the anterolateral thigh (ALT) flap has recently gained increasing popularity. This article reviews the advantages of the ALT flap, its anatomy, and various methods of its elevation. We have successfully utilized the ALT flap for reconstructing a wide range of complex head and neck defects; a selection of our methods are outlined herein. Additionally, various configurations of the ALT flap, including the elevation of two independent cutaneous flaps from the same pedical, chimeric, and flow-through flaps, are described. The unique anatomy of the thigh allows unparalleled flexibility in flap design, useful for reconstructing defects of the tongue, buccal region, mandible, midface, scalp, and through-and-through defects of the cheek. Resultant donor site morbidity is low in comparison to other flaps that are commonly utilized for head and neck reconstruction.
Microsurgical free-tissue transfer has revolutionized head and neck reconstructive surgery. It gives oncological surgeons more freedom to perform radical tumor resections because single-stage reconstructive solutions are now available for the majority of defects.1,2,3,4 Patients who were previously thought inoperable, such as those with locally advanced or recurrent disease, can now be considered candidates for surgical treatment.2,4,5 Ablative surgery in such a complex anatomical site can cause severe impairments for the patient. An ideal reconstruction preserves both function and esthetic appearance without compromising the principles of cancer surgery. In recent practice, we have selected three workhorse free flaps for head and neck reconstruction: the anterolateral thigh (ALT) and fibula and radial forearm flaps.3,4,5,6,7,8,9
The ALT flap has only recently gained popularity because its original description preceded the development of perforator flap surgery. Song et al in 1984 described the ALT flap as being supplied by septocutaneous vessels originating from the descending branch of the lateral circumflex femoral artery.10 This was later demonstrated only to be true in 15% of cases, with the outstanding 85% majority supplied by a musculocutaneous perforator.3,11,12,13 Developments in intramuscular perforator and retrograde dissection techniques laid the foundations for the harvest of muscle-sparing ALT flaps.2,14,15 Koshima et al were the first to describe the use of the ALT flap to reconstruct head and neck defects.16,17 Since then, others have reported their experience, establishing the ALT flap as one of the major workhorse flaps used for head and neck reconstruction.1,3,9,18,19,20,21,22,23,24,25,26
The ALT flap is supplied by the descending branch of the lateral circumflex femoral artery, the largest branch of the profunda femoris system. Its artery, usually associated with two concomitant veins, traverses obliquely with the nerve to vastus lateralis within the groove formed between the rectus femoris and vastus lateralis muscles.12,13,27,28 The anterior branch of the lateral cutaneous nerve of the thigh can be included to create a sensory flap.29 The pedicle terminates near the knee joint in the vastus lateralis muscle after having provided septocutaneous vessels that pierce the fascia to access the ALT skin and perforators to the rectus femoris and vastus lateralis muscles. It is usually these musculocutaneous perforators that are encountered and dissected when harvesting a cutaneous or fasciocutaneous flap. ALT flap pedicle length (between 8 and 16 cm) and vessel diameters (at least 2 mm) are quite adequate for anastomoses12,13,27,28 (Fig. 1).
The unique anatomy of the thigh permits several methods of harvesting the ALT flap. The types of tissue to be included in the flap can be selected according to the defect to be reconstructed. The ALT flap can be harvested at the suprafascial level to include just skin and subcutaneous fat, which is useful when a thin flap is desired.3,12,27,28,30,31,32,33 When harvested at the subfascial level, the flap can bring additional tissue bulk including the fascia lata on the deep surface. The fascia is particularly useful in several situations, such as when repairing dural or tendon defects and when creating a sling to support the oral commissure.2,9,30,34,35 A musculocutaneous flap can be harvested by including part of the vastus lateralis muscle.3,12,17,27,28 The muscle can be attached to the overlying skin or splayed out on a separate vascular branch that arises from the same vascular pedicle to create a chimeric flap.3,35
The cutaneous vessels can be mapped out with a handheld pencil Doppler probe placed at the midpoint between the anterior superior iliac spine and the superolateral corner of the patella.1,3,30,36 The majority of skin vessels are located in the inferolateral quadrant of a circle with a 3-cm radius centered on this same midpoint, but they can also be located elsewhere.1,3,30,36 The flap should be centered over these vessels and designed with its long axis parallel to that of the thigh. A simultaneous two-team approach can be achieved with the patient supine as this usually allows the operation to be completed without altering the patient's position.
The first incision is placed on the medial side of the designed flap outline and continued down to just above the fascia lata. Skin and subcutaneous tissues are then gently dissected away from the fascia laterally until the vessels to the skin are revealed. The identified skin vessel is dissected back to the main pedicle, leaving a small piece of fascia encircling the vessel. Intramuscular dissection proceeds if the vessel is a musculocutaneous perforator. Such vessels always give several branches from their lateral and posterior aspects to supply the neighboring vastus lateralis muscle, with fewer arising anteriorly. The musculocutaneous perforator can therefore be easily traced by incising the muscle over the perforator and ligating each branch to the muscle arising laterally and posteriorly. Dissection is even easier if instead the skin vessel is septocutaneous and dissection is performed between the vastus lateralis and rectus femoris muscles back to the main pedicle. It is possible to elevate a cutaneous flap as thin as 3 to 5 mm; however, excessive thinning should be avoided in less experienced hands to avoid marginal necrosis.3,33,37
The skin is incised down to the fascia lata, which is included in the flap. The cutaneous vessel from the lateral circumflex femoral artery system is identified beneath the fascia. Flap elevation proceeds similarly as described for suprafascial dissection.
Dissection of the perforator or septocutaneous vessel is not necessary when elevating a musculocutaneous flap, because the portion of vastus lateralis muscle within which the skin perforator travels is included. The necessary portion of vastus lateralis muscle is divided away while paying attention to the intramuscular branches that require ligation. Again, the main pedicle is dissected as before.
Numerous chimeric ALT flap combinations are possible because the lateral circumflex artery provides lateral, medial, and descending branches. Most involve an ALT flap in combination with rectus femoris muscle, tensor fascia lata, anteromedial thigh skin, or the vastus lateralis muscle; thus chimeric ALT flaps can be musculocutaneous, fasciocutaneous, or cutaneous only with more than one skin island.35 Chimeric ALT flaps are a versatile choice for reconstructing three-dimensional defects because two or more separate tissues can be harvested on one pedicle, which maximizes the flexibility of flap inset (Fig. 2).35
Usually the pedicle terminates distally into the vastus lateralis muscle by branching into cutaneous vessels. This distal end of the pedicle can be dissected to the required length clear of the vastus lateralis muscle to serve as recipient vessels for a second free flap (Fig. 3).3,38
As the descending branch of the lateral circumflex femoral artery provides multiple septocutaneous vessels and myocutaneous perforators to the thigh, two independent skin flaps can be harvested from the same donor site, reducing both the total time of flap harvests and overall donor-site morbidity. Two separate cutaneous vessels are required for this, and each needs to be dissected back to the main pedicle. If longer or wider vessels are needed, the dissection can be continued to reach the descending branch of the lateral circumflex femoral artery. To maximize the length of the pedicle for the distal flap, its origin should be defined as being located immediately distal to the origin of the branch supplying the proximal flap (Fig. 4).
The vascular anatomy of the thigh allows considerable flexibility when designing an ALT flap for a given defect in the head and neck. It can be harvested as thinly as the radial forearm flap or augmented by inclusion of subcutaneous tissue, fascia lata, or the vastus lateralis muscle.3,9 Chimeric ALT flaps are available for defects demanding reconstruction in even greater than three dimensions. Although flap size can range from just a few centimeters up to the length of the thigh, its width should be limited to between 8 and 13 cm if primary donor-site closure is to be achieved, as larger donor sites usually necessitate skin grafting.1,3,6,30
The tongue is one of the sites most frequently affected by oral cancer. Invasion into the floor of the mouth, oropharynx, and hypopharynx is common.39,40 A thin ALT flap is the first choice in our center for reconstructing defects smaller than that of a hemitongue. For larger defects, such as a total glossectomy, more tissue is readily available.3,9 Muscle inclusion facilitates obliteration of dead space, such as in the submandibular and neck regions following neck dissection. Furthermore, the flap can be de-epithelialized and folded for extra volume, and sensation can be provided by inclusion of the lateral cutaneous nerve of the thigh.3 The ALT flap can provide as much tissue volume as the rectus abdominis myocutaneous flap; however, it is easier to inset because it can be harvested with two separate skin islands or with a separate mass of muscle based on the same pedicle (Fig. 5), and it causes less donor-site morbidity.30
Buccal defects created from cancer ablation can be divided into two major categories: those that are partial and those that are full thickness. The ALT flap can be safely thinned intraoperatively, making it applicable for reconstructing partial-thickness cheek defects.3,30,37 Although the radial forearm flap is also good in this setting, the ALT flap leaves a less conspicuous donor site with less morbidity. Full-thickness cheek defects, which involve the oral lining, buccal fat, masseter muscle, and facial skin, are more challenging to reconstruct, particularly if the oral commissure is involved. Reconstruction of such defects with the radial forearm flap usually results in inadequate functional and esthetic outcomes. When the oral commissure is not involved, the folded ALT flap is our preferred option. Again, a segment of vastus lateralis muscle can be included for additional volume. Involvement of the oral commissure calls for a well-designed chimeric ALT flap to increase the flexibility of flap inset, resulting in improved oral continence and quality of speech (Fig. 6).3,35
Composite mandibular defects are ideally reconstructed with an autogenous bone flap, most commonly the vascularized osteoseptocutaneous fibula flap.41,42,43 Another option is to bridge the bony gap with a reconstruction plate and gain coverage with a soft tissue flap.44,45 This is usually indicated for short or lateral mandibular segmental defects, older patients, or patients with a poor prognosis.46
From our experience and the work of others the ALT flap is the first choice the soft tissue reconstruction.3,4,30,35 Radical treatment for extensive T3 and T4 cancers creates large composite defects requiring both bone and extensive soft tissues for reconstruction.46,47 Although a composite vascularized osteoseptocutaneous fibula flap can provide intraoral and external coverage, its volume is usually inadequate for larger resections or for through-and-through cheek defects. The simultaneous use of a second free flap has been advocated by several authors as a means of overcoming this soft tissue deficiency.4,5,48,49,50 The second flap can obliterate the dead space resulting from resection of the masticator muscles, buccal fat, and parotid gland and prevents the accumulation of fluid that leads to secondary infection or an orocutaneous fistula.4,5 Adequate volume and quality of soft tissue is important to prevent bone and plate exposure, especially in patients scheduled for radiation therapy.4,5
A particular advantage of the ALT flap is that it provides a good contour for the face. Although it may have a bulky appearance at first, it will usually shrink after radiotherapy (Fig. 7).
Reconstruction of the midface can be challenging as the defect is usually three dimensional and involves more than one tissue type.9 The flaps most commonly described for midface reconstruction are the radial forearm for small defects and the rectus abdominis or latissimus dorsi for larger defects; however, the ALT flap is suitable for a range of defect sizes.9 A cutaneous or fasciocutaneous ALT is suitable for reconstructing small defects; however, an almost unlimited area of skin is available for larger defects and the vastus lateralis muscle can be included as necessary for bulk. The muscle component is useful for obliterating the maxillary sinus and for providing well-vascularized coverage for bone grafts used when reconstructing the orbital floor (Fig. 8).
When only the exposed calvarium needs coverage, a large ALT flap can be harvested.30,31 The flap can be thin and provide good-quality skin without excessive bulk, unlike when myocutaneous flaps such as the rectus abdominis or latissimus dorsi are used.9,51 The skin quality of the ALT flap is superior to a muscle flap covered with split-thickness skin graft. Furthermore, the functional impairment related to muscle harvest is avoided. For defects involving both the calvarium and dura, fascia lata can be included to reconstruct the dura and seal against cerebrospinal fluid leakage (Fig. 9).
Radical tumor ablations in the head and neck region can significantly impair function and esthetics and usually require complex reconstructions. In the past, options for soft tissue coverage were limited only to pedicled flaps. Traditional free flaps were either too thin or too bulky, or were not ideal for texture matching. The introduction of perforator-based flap harvest and the chimeric flap concept allowed the surgeon to choose a more accurate single-stage reconstruction that could both restore good function and achieve an esthetically acceptable result in the majority of patients.
During the past 10 years, we at Chang Gung Memorial Hospital, Taipei, Taiwan, have performed more than 2600 cases of ALT flaps, 70% of which were for head and neck reconstruction. We have found that the ALT flap possesses many of the important properties that make a flap ideal for head and neck reconstruction, namely: (1) anatomically constant with a long and sizeable pedicle; (2) good match for recipient-site tissue characteristics; (3) flexibility of tissue volume, be that thick, bulky, or thin and pliable; (4) flexibility in design, including the availability of different tissue types for harvesting on the same pedicle, as in a chimeric flap; (5) the option to harvest two separate flaps from the same site; (6) insignificant donor-site morbidity; (7) simultaneous flap harvest and tumor ablation afforded by a two-team approach; and (8) the option for sensory reinnervation.3,6,8,9 We have only rarely encountered cases that required vein grafts, even when reconstructing cases following recurrent cancer, difficult neck dissections, or when having to turn to the contralateral neck to find suitable recipient vessels. A particularly important advantage of the ALT flap is the relatively low donor-site morbidity that accompanies even a substantial flap harvest. An increase in the size of a cutaneous flap does not appear to cause a proportional increase in donor-site morbidity. Dissection and protection of the nerve to the vastus lateralis muscle should be performed carefully to preserve maximal quadriceps function when harvesting a cutaneous ALT flap. The inclusion of a segment of the vastus lateralis muscle might be expected to increase donor-site morbidity; however, it was objectively demonstrated at long-term follow-up with a kinetic communicator machine that only a minimal weakness of the thigh results.52 In our experience, no significant functional deficits were noted either by the patient or examining physician.
Although numerous other soft tissue flaps have been described, most are less useful than the ALT flap for head and neck reconstruction, because they variably fail to offer a sufficient number of these advantages. The diversity that the ALT flap offers allows its use for most indications in head and neck reconstruction, including those of the intraoral, tongue, buccal, midface, and scalp regions. Resultant donor-site morbidity is low when compared with other available flaps.