Scalp Reconstruction with a Free Anterolateral Thigh Flap: Flap Dissection

Procedure: This procedure depicts the harvest of the anterolateral thigh flap to be utilized in the reconstruction of a post-extirpative scalp defect. Introduction: The anterolateral thigh (ALT) flap is often harvested as a fasciocutaneous flap off the descending branch of the lateral circumflex arterial (LFCA) system. The ALT flap is a versatile, durable option for free tissue reconstruction of the head and neck that results in minimal functional disruption of the lower extremity. Indications/Contraindications: Free tissue transfer is often indicated for large composite scalp defects that are not amenable to closure by rotational flap or tissue expander-based reconstruction. Contraindications include not suitable recipient vessels in the head and/or neck, any disruption to the descending branch of the LCFA or an absence of perforating vessels from the LCFA to the overlying skin. Materials and Methods: Using topographical landmarks, the septum is identified between the rectus femoris and the vastus lateralis, a fasciocutaneous island is harvested on musculocutaneous perforators from the transverse branch of the LCFA. This is a deviation from typical anatomy, as the pedicle normally arises from the descending branch of the LCFA. The length of the transverse branch is dissected proximally to obtain suitable pedicle length. Results: The fasciocutaneous flap was isolated musculocutaneous perforating vessels from the transverse branch of the LCFA and divided for transfer to the scalp. Conclusion: This report demonstrates the critical steps involved in ALT harvest.

Purpose of this technique: First described in 19841, the anterolateral thigh (ALT) flap has become a popular reconstructive option for patients requiring free tissue transfer.2 The ALT flap can be harvested as a fasciocutaneous, fascia-only, muscle-only or musculocutaneous flap based on perforating vessels from the descending branch of the lateral femoral circumflex artery (LCFA).2 Additionally, the flap can undergo sensory and/or motor neurotization3 and chimeric-type modifications can be made with any of the above components.2,4 As a result of the versatility of this flap, as well as the minimal donor site morbidity, the ALT flap has become an invaluable option for microvascular reconstruction.5 Proper patient/case selection (indications): Any patient with large composite defects not amenable to local or regional tissue rearrangement and/or grafting are candidates for free-tissue reconstruction based on the descending branch of the LCFA. Contraindications (absolute and relative): Absolute contraindications include an absence of perforating vessels from the descending branch of the LCFA and an inability to tolerate general anesthesia. Relative contraindications include prior surgery and/or trauma to the thigh. Advantages and disadvantages over alternative: Advantages of the ALT flap include a long pedicle length, which can exceed seven centimeters, and vessel luminal diameters of 1.5-2.5 millimeters, which are suitable for microsurgical techniques. A large skin paddle can be harvested, up to 8 by 25 centimeters, which can be thinned to adjust for recipient site thickness. The flap can be harvested in a chimeric nature and can be neurotized with the lateral femoral cutaneous nerve, or the nerve to the vastus lateralis if a muscular component is selected. Disadvantages include the perforator variability and the tedious dissection in the event of a musculocutaneous perforator.4,6-12 Complications and risks: Complications include those inherent to free-tissue transfer, most notably flap loss. Additional risks include temporary paresthesias of the donor site due to traction on the lateral femoral cutaneous nerve, which are rarely permanent. If the vastus lateralis is left intact, changes in lower extremity function are rarely discernable. Scar widening and compartment syndrome occur infrequently and even more rare is necrosis of the rectus femoris muscle as a result of inadvertent devascularization.13

Instrumentation: Standard plastic surgery instruments are utilized for flap dissection and elevation. Both monopolar and bipolar electrocautery should be available. Ultrasonic scalpels can facilitate muscle transection. A standard handheld Doppler should be available as well as a full array of surgical clips and clip appliers. If the donor site is able to be closed primarily a multitude of sutures are available and acceptable. In the event that the donor site is not able to be closed a Dermatome should be available for skin graft harvest. Setup: The patient should be marked preoperatively in order to facilitate identification of muscular landmarks. Markings should be re-traced intraoperatively to confirm adequate flap size. The patient is generally placed in the supine position during flap harvest and a small bump under the ipsilateral hip can facilitate surgical dissection. There should be a separate set of instruments available for the harvesting team to allow for simultaneous flap elevation and extirpation/recipient vessel identification. Preoperative Workup: Preoperative consultation should be obtained with a reconstructive surgeon. A thorough history and physical should include examination of both thighs and a detailed vascular examination of both lower extremities. Signs of arterial and/or venous insufficiency should prompt angiography and/or Doppler venous studies. Computed tomography angiography (CTA) of the bilateral thighs can be obtained; however, the absence of visualized musculocutaneous or septocutaneous perforators off the descending branch of the LCFA does not preclude their presence. Anatomy and Landmarks: With the patient supine, a line should be drawn joining the anterior superior iliac spine (ASIS) to the superolateral border of the patella. This line approximates the septum between the vastus lateralis and rectus femoris. Perforators that nourish the overlying skin are generally found around this line. At the halfway point between the ASIS and patella, a point is marked. The highest concentration of perforators are generally found within a 3 centimeter radius of this mark. Perforators can be approximated transcutaneously using a conventional hand-held Doppler probe. Additional perforators can often be located 5-10 centimeters proximal and distal to this point. A skin flap is then designed based on the size of the defect to be reconstructed. Detailed Steps to Procedure: The medial flap border is often incised first and the incision can be extended proximally and distally along the marked line in order to facilitate anatomical exposure. Dissection is carried through the subcutaneous tissue and fascia to identify the rectus femoris muscle. The muscle fibers of the rectus femoris are arranged in an inverted “V” shape and perforators emanating through this muscle can be safely ligated. After the septum is identified between the rectus femoris and the vastus lateralis dissection can proceed along the loose areolar tissue lining the tendinous portion of the rectus femoris which allows the muscle to be retracted medially. At this point, the descending branch of the LCFA can usually be identified coursing along the medial border of the vastus lateralis and with careful dissection around the vastus lateralis in the area of the preoperative markings, either septocutaneous and/or musculocutaneous perforators are identified originating from the descending branch. Dominant perforators are selected based on pulse palpation and Doppler evaluation. Non-dominant perforators are ligated to liberate the pedicle. Musculocutaneous perforators are carefully dissected free from the vastus lateralis in the event that no muscle is to be included in the flap. In the event of a serpiginous intramuscular course, a cuff of muscle can be taken with the perforator for safety. Alternatively, a portion of vastus lateralis can be harvested in conjunction with the fasciocutaneous element. The descending branch can then be traced back and if needed, the transverse branch of the LCFA and the branch to the rectus femoris can be ligated to increase pedicle length. The lateral flap incision is then made and the flap is lifted on the pedicle, which is then divided. The donor site is then closed in layers over a closed suction drain and the skin is either reapproximated primarily or a skin graft is applied.

If elevated appropriately a standard fasciocutaneous ALT flap will contain skin, subcutaneous fat and fascia. Beneath the fascia the isolated perforators will often connect to the descending branch of the LCFA which will be of variable length depending on how far proximal it was clipped. Inappropriately harvested flaps may result from transection of the perforators that nourish the skin.

The ALT flap is one of the most commonly used flaps for scalp reconstruction. In addition to the advantages of microsurgical reconstruction, the fasciocutaneous ALT flap is easily contoured to fit the complex shape of the operated scalp. In addition, if employed for post-extirpative reconstruction and adjuvant radiation is planned, the fasciocutaneous composition is less susceptible to contracture than other muscular free flaps.13 The ALT flap is also useful in the reconstruction of numerous other defects spanning from the face to the feet. Frequent modifications of this flap include flap thinning to improve the contour as well as harvesting the flap as a fascia-only flap if the flap requires tunneling or for very small defects over critical structures. Such modifications facilitate intra-oral and extra-oral facial reconstruction. Additional modifications include harvesting a musculocutaneous flap which can provide additional bulk when reconstructing deeper defects. Alternatively the vastus lateralis can be harvested alone as a muscle-only flap, with or without its accompanying motor nerve. Chimeric principles allow for harvesting the flap with either multiple separate skin islands or a combination of skin and muscle islands. The skin component can also be harvested with the accompanying cutaneous nerve.13             Perhaps the most troubling situation is one in which no septocutaneous or musculocutaneous perforators are identified branching from the descending branch of the LCFA. In this circumstance it is possible to raise an anteromedial thigh flap (AMT) off perforators through or medial to the rectus femoris, a tensor fascia lata (TFL) flap based on perforators from the transverse branch of the LCFA or to use the contralateral ALT flap.14             Given the versatility and durability of the ALT and its modifications, applications for this flap are vast. Future modifications will likely expand on immediate flap thinning and contouring and expanding on chimeric principles to allow for more complex reconstruction based on a single vascular pedicle.

The authors have no funding for this project, relevant disclosures, or conflicts of interest.

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