Mark A. Varvares
INTRODUCTION
Restoration of function and acceptable cosmetic outcome are the two major goals of palatomaxillary reconstruction. The functional considerations include maintenance of an oral cavity of appropriate dimensions, the separation of the oral and nasal cavity to prevent nasal regurgitation and hypernasality, providing a framework to allow masticatory function, an osseous structure on which a prosthesis can be anchored and dental rehabilitation, and a structural foundation of the nasal base. The cosmetic implications related to this last point are obvious, to appropriately maintain the proper position of the midfacial structures including nasal support, premaxillary structure, and more superiorly and laterally structures related to midface skeletal contour. Ideally, total reconstruction of the palate would best be accomplished using a composite flap of soft tissue and bone.
Potential donor sites include the scapular osseofasciocutaneous flap, the fibular osseocutaneous flap, the radial forearm osseocutaneous flap, and the iliac crest osseomyocutaneous flap. The use of these sites would allow both the restoration of skeletal structure onto which one could build midfacial support and secure implants for dental rehabilitation as well as a soft tissue component to cover the transferred bone. However, in some patients, it may not be possible to reconstruct with a bone-containing flap. Such examples would be patients with severe medical comorbidities, not allowing the lengthier operative procedure usually required with the osseous flaps, or patients in whom the osseous donor sites are not available for whatever reason. For instance, patients with severe peripheral vascular disease, which would prohibit the use of a fibular osteocutaneous flap would be one example. A morbidly obese patient with an unavailable scapular donor site would be another example. In such cases, a soft tissue flap donor site may be the best option. Also, patients with palate defects that include a massive facial or periorbital component may be best served by transferring a soft tissue flap with an abundant quantity of tissue of different components (muscle and cutaneous tissue) to allow the successful reconstruction of a complex defect with multiple reconstructive requirements (palate, orbit, and facial skin). This chapter discusses the role of the rectus abdominis free flap for reconstruction of the entire palate.
HISTORY
The patient history is important in determining if there are any contraindications to harvesting from the rectus donor site. Prior abdominal surgery is the most common restriction. Other considerations include a history of an abdominal hernia that may preclude the use of this donor site.
PHYSICAL EXAMINATION
The physical examination entails an examination of the defect and the abdominal donor site. When using the rectus abdominis donor site to reconstruct a total palatal defect, the donor tissue may not be ideal if the patient is obese. Depending on the body habitus, the donor site may provide a flap that is too thick to comfortably reconstruct a palatal defect. In obese patients, the skin paddle can be removed to reduce the thickness of the flap and a skin graft can be placed over the vascularized muscle or the muscle can be left exposed in the oral cavity and be allowed to mucosalize. The physical examination is the only way to determine if the rectus is an appropriate donor site.
INDICATIONS
The rectus abdominis flap is indicated when a subtotal or total hard palate defect is anticipated and when osseous flap donor sites are not available. Other indications would include when a large volume of tissue is required for repair of a complex three-dimensional midface defect that may include the hard palate, orbital contents, and facial skin.
CONTRAINDICATIONS
Contraindications to this flap include patients who are morbidly obese, patients who have had previous abdominal surgery, or patients in whom previous inguinal hernia repair may have rendered the deep inferior epigastric vessels unusable.
PREOPERATIVE PLANNING
Preoperatively, it is important to measure the defect and determine the dimensions of the skin paddle required to reline the oral defect. In most cases of total palate reconstruction without a complicated midfacial defect such as orbital exenteration and midface resection, it is preferred to use the rectus abdominis free flap as a muscle-only flap. This prevents problems related to what in nearly all patients can be a very thick subcutaneous layer. A myocutaneous flap is used with more extensive facial and orbital defects when the abdominal wall subcutaneous tissues are of manageable thickness.
SURGICAL TECHNIQUE
Whether the flap is taken as a muscle-only flap or as a myocutaneous flap, some basic anatomical landmarks need to be noted. The key anatomical landmarks for harvest of the rectus abdominis flap are the linea alba, the linea semilunaris, and the arcuate line (Fig. 21.1). The linea alba is the midline condensation of the rectus sheath. The linea semilunaris marks the lateral border of the rectus sheath, which contains the rectus muscle. The rectus sheath is composed of the aponeuroses of the three major muscles of the anterior abdominal wall: The external oblique, internal oblique, and transverses abdominis. At the horizontally oriented arcuate line, which is located halfway between the symphysis pubis and the umbilicus, the layers of the rectus sheath transition. Superior to the arcuate line, the anterior layer of the rectus sheath is composed of the entire aponeuroses of the external oblique and the split aponeurosis of the internal oblique. The posterior layer is composed of the posterior leaf of the aponeurosis of the internal oblique and the aponeurosis of the transversus abdominis. Deep to this is the transversalis fascia. Inferior to the arcuate line, all three muscle aponeuroses create the anterior layer of the rectus sheath, and the posterior layer is made up entirely of transversalis fascia (Fig. 21.2). This anatomical point of distinction that occurs at the arcuate line is important because any myocutaneous flap that will include in the harvest the anterior layer of the rectus sheath below the arcuate line requires that the anterior rectus sheath defect be reconstructed with mesh; otherwise the patient is at significant risk for formation of a hernia.
FIGURE 21.1 Schematic showing the key landmarks of the anterior abdominal wall and boundaries of the rectus sheath; the linea alba, the linea semilunaris, and the arcuate line.
FIGURE 21.2 Diagram showing the contents of the rectus sheath and the layers of the sheath above and below the arcuate line. A. Relationships of the aponeuroses of the muscles of the anterior abdominal wall above the arcuate line. Note that the middle layer splits to surround the rectus muscles. B. The anatomy of the rectus sheath below the arcuate line. Note that all 3 aponeuroses pass anterior to the rectus muscles and only the travsversalis fascia is found posterior to the rectus muscles.
It is important to palpate the femoral pulse prior to harvesting the flap. Just proximal to the femoral pulse will be the external iliac artery and vein. The deep inferior epigastric artery and vein take origin from the external iliac artery and vein to run on the deep surface of the rectus abdominis muscle. These vessels run the entire vertical length of the muscle and anastomose with the superior epigastric vessels, which are the terminal branches of the internal mammary artery.
The major musculocutaneous perforators that supply the skin overlying the rectus abdominis muscle are found in the periumbilical area. They radiate from the umbilical area, but the dominant vessels run in a posterior, lateral and superior direction toward the ipsilateral tip of the scapula. Any rectus musculocutaneous free flap must be harvested with preservation of these perforating vessels remaining in continuity as they pass out from the muscle through the anterior rectus sheath to supply the overlying skin and subcutaneous tissues (Fig. 21.3).
FIGURE 21.3 A. Diagram showing the primary vascular supply to the rectus muscle, the radiating periumbilical perforators, with the dominant vessels traveling in a trajectory toward the ipsilateral tip of the scapula. B–F. Options for the design of the skin paddle of the rectus abdominis myocutaneous flap.
When harvesting the rectus abdominis free flap as a musculocutaneous flap, the flap elevation proceeds as follows: The desired dimensions of the cutaneous paddle are outlined again in the area of the densest musculocutaneous perforators in the periumbilical area (Fig. 21.3A–F). The skin paddle may be used to replace palatal mucosa or facial skin or obliterate the orbit. Often, multiple cutaneous paddles may be created to reconstruct different aspects of the defect. If a desired dimension of the skin paddle is such that its length exceeds the width of the rectus muscle (as determined by the width of the defect), thereby requiring a portion of the flap that is not directly overlying muscle, this extension of the flap is drawn out in the direction of the vector from the umbilicus to the scapular tip. This allows capture of the axial vessels that penetrate through the anterior rectus sheath and travel in a plexus in this posterior, superior, and lateral direction.
As the dissection begins, the incision is made circumferentially around the skin paddle to the level of the anterior layer of the rectus sheath. For those cutaneous paddles that extend lateral to the linea semilunaris because of the need for a paddle wider than the width of the rectus sheath, the initial incision to the depth of the deep fascia begins medial to the linea semilunaris and extends to the level of the anterior layer of the rectus sheath and lateral to this line, to the aponeurosis of the external oblique muscle. Elevation of the most lateral portion of the component can proceed from lateral to medial taking the cutaneous portion directly off of the aponeurosis of the external oblique muscle. Upon reaching the linea semilunaris, the anterior layer of rectus sheath that will support the cutaneous paddle can be outlined circumferentially and incised. Laterally, this incision is made just medial to the linea semilunaris. This requires that the fasciocutaneous extension that was mobilized lateral to this line be dissected just medial to this lateral anterior sheath incision. Following the anterior sheath incision around the proposed skin paddle, a vertical incision can be made from the midportion of the inferior edge of the skin paddle inferiorly toward the expected origin of the deep inferior epigastric vessels. This incision is made through the skin and subcutaneous tissue and to the anterior layer of the rectus sheath. The anterior layer of the rectus sheath is incised and opened exposing the entire rectus muscle on the ipsilateral side. The rectus muscle superior to the skin paddle can be identified through this opening in the anterior rectus sheath. The muscle at this point superiorly can be transected, and the muscle and attached skin paddle can then be mobilized out of the rectus sheath from superior to inferior.
As dissection proceeds inferiorly, it is important to take the entire muscle when the flap is harvested in this manner. At about the umbilicus, the deep inferior epigastric artery and vein will be visible on the posterior aspect of the rectus sheath. This dissection then continues inferiorly until the vessels can be dissected to the origin off of the external iliac vessels. The more inferiorly the dissection proceeds, the more lateral in relation to the rectus muscle the vessels become. To facilitate dissection at this point, it helps to divide the origin of the rectus abdominis muscle just above the symphysis pubis. This must be done with full knowledge and visualization of where the nutrient pedicle is located. This step improves the exposure and allows dissection of the inferior epigastric vessels fully to origin off the external iliac vessels. In most cases, this full pedicle dissection will result in the ability to harvest the deep inferior epigastric vein proximal to the point at which the two venae comitantes join to form a single vessel, which then empties into the external iliac vein. This larger caliber vein (3.5 mm) will facilitate an easier venous anastomosis.
Once the recipient site is ready, the flap can be harvested in the usual fashion with clamping of the artery first, then the vein, and then suture ligation of the origin of these vessels off of the external iliac vessels.
If a muscle-only flap is to be taken, a vertical incision is made paralleling the ipsilateral rectus muscle. This is carried down through skin and subcutaneous tissue down to the anterior layer of the rectus sheath. The rectus sheath can then be opened, the muscle transected superiorly and then mobilized out of the sheath, and the harvest completed, as described above.
Meticulous attention to closure of the donor site is important. In most cases, the anterior layer of the rectus sheath defect taken above the arcuate line can be closed directly with permanent Prolene sutures. If this cannot be accomplished, then typically one may repair this defect using Marlex mesh. The incisions in the anterior layer of the remaining rectus sheath then are closed directly using prolene suture. Suction drains are placed, and the subcutaneous and cutaneous tissues are closed.
Flap Inset
Usually adequate exposure of the palatal defect has been created by the ablative team. If a neck dissection has not been performed, the neck must be explored and the vessels isolated with recipient vessels identified for the microvascular anastomoses. An optimal vessel pair in the setting of palate reconstruction is the facial artery and vein, with the external jugular vein as a possible recipient vessel if necessary. An incision similar to what would be used for an excision of the submandibular gland may be used. Excision of the submandibular gland is usually done along with isolating the vessels, as it will help not only to isolate the facial artery and vein but also to create some working room, improving exposure to allow the microvascular anastomosis to be performed more easily. The main trunk of the facial artery can be preserved when excising the submandibular gland if care is taken only to divide the glandular branches of the facial artery as the main trunk passes over the superior portion of the gland. This will help to provide a longer recipient artery, keeping the anastomosis from being performed with the inferior border of the body of the mandible obstructing the view of the vessels through the microscope. For this reason, when the facial artery is used as a recipient vessel, the surgeon should not to be quick to divide the main trunk of the facial artery as it passes over the posterior belly of the digastric muscle as is frequently done in excision of the submandibular gland.
Once the vessels are isolated, a connection is created from the neck to the defect. In many cases that include resection of palate, facial skin, and orbit, only the inferior aspect of the tunnel need be created, as the resection has completed the most distal portion of the connection. There are essentially two different planes that can be used. In most cases, I prefer the subcutaneous tunnel. This dissection would proceed from the neck by dissecting in a supraplatysmal plane to the level of the midface. An advantage with this approach is that this supraplatysmal plane protects the marginal mandibular nerve and, as dissection proceeds more cephalad, all distal branches of the facial nerve. Once this dissection is adjacent to the defect, the tunnel must be connected with the recipient site of the midface, and typically, this does require a blunt dissection through the superficial musculoaponeurotic system into the oral cavity. This is done bluntly by spreading the tissue in the same direction as the branches of the facial nerve. The tunnel must be wide enough to allow the flap to be pulled from the neck into the midface or allow the vessels to be passed from the defect into the neck. Typically, a width equal to four fingerbreadths will be adequate. It is important to obtain meticulous hemostasis during creation of the tunnel to prevent bleeding into the tunnel postoperatively that could lead to a hematoma and flap compromise.
The second option for creating the tunnel connecting from the neck to the midface would be to use a deeper plane of dissection. This would require a subplatysmal dissection extending superiorly directly overlying the periosteum of the mandible and masseter muscle. This is a deeper layer of dissection and is deep to the branches of the facial nerve, thereby preventing potential injury to the nerve. Once the vessels are isolated and the tunnel is created, the flap is brought into the inset position. I prefer to pull the flap from the neck through the tunnel into the recipient site in the oral cavity. This approach allows certainty that there is not been any twisting of the vascular pedicle in the tunnel while the flap was being positioned. Retrograde placement of the vessels into the neck from the mouth by using a Penrose drain filled with normal saline is another approach.
This technique requires first passing the large Penrose drain from the defect into the neck, then clamping the drain inferiorly. The drain is then filled with normal saline, and the vascular pedicle is fed retrograde into the saline-filled drain. The drain with the pedicle contained in it is then slid through the tunnel into the defect. This technique is particularly useful if the distal component of the flap is too bulky to pass from the neck through the tunnel and into the defect, as can occur with some rectus abdominis myocutaneous flaps.
Vein grafts are rarely needed if the anastomosis is to be performed in the ipsilateral neck, given the considerable length of the rectus muscle that allows ample pedicle length. In cases in which there has been previous sacrifice of potential recipient vessels in the ipsilateral neck, a vein graft may be necessary to allow the anastomosis to be carried out in the contralateral neck.
In some cases, the superficial temporal vessels may be a very appropriate set of recipient vessels, depending on their caliber, which vessels remain available in the neck (such as in revision cases) and the exact details of the defect. Although the bigger the recipient vessels (as long as there is no size mismatch) the better, these vessels should be considered prior to using a vein graft to the contralateral neck.
The inset is relatively simple with suturing of the skin or muscle to the surrounding mucosal margins. This needs to be performed without redundancy to prevent prolapse or the muscle sagging into the oral cavity (Fig. 21.4). Attention should be paid to the point of the inset where the flap pedicle enters the defect such that a watertight repair is completed, decreasing the likelihood that saliva will enter the tunnel and result in an infection that could cause thrombosis at the anastomotic site that can rarely be salvaged in the setting of infection.
FIGURE 21.4 Appearance of right palate reconstructed with rectus muscle 18 months postoperatively.
In cases where there is a large midface or orbital defect, the cutaneous paddle is to be used to obliterate the orbit and the midface, and the muscle proximal to the skin paddle is the component that is used to repair the palate defect (Fig. 21.5A and B). Once the flaps are vascularized, hemostasis is obtained and neck closure can proceed as well as closure of the facial skin.
FIGURE 21.5 A. A patient with recurrent squamous cell carcinoma of the palate and maxilla. The lesion involves the infraorbital and eyelid skin and the entire maxillary sinus and palate. Defect involving orbit, facial skin, and entire right hard palate. B. Rectus abdominis myocutaneous flap obliterates the entire orbit and replaces resected infraorbital skin and provides lining for the ipsilateral hard palate.
POSTOPERATIVE MANAGEMENT
The donor site requires relatively little care. Suction drains are placed both into the donor site and into the deck, which are left in place until the output is less than 10 mL over 10-hour shift. I find the use of an abdominal binder to be helpful in early mobilization of the patient to help manage the pain at the donor site. Monitoring of the flap should be done in accordance with the operating surgeon’s regimen. Most recently, I have incorporated the Synovis implantable venous Doppler, which is attached to one of the two rings of the venous coupler. This allows monitoring using a more objective signal and does not require the nursing staff (which does most of our flap monitoring) to go hunting for a signal using a handheld Doppler probe even when the flap vessel is marked with a suture. Monitoring is usually discontinued after 5 days, and the Doppler wire is removed at the bedside.
Patients are fed via a nasogastric tube and should be NPO for at least 5 to 7 days depending on the defect, the health of the recipient bed, and the confidence the team has in the healing at the flap/recipient site interface.
COMPLICATIONS
The two most significant complications related to this procedure are the development of a hernia at the donor site and flap compromise related to hematoma developing in the tunnel connecting the neck and the recipient site.
Hernias can be prevented by meticulous closure of all defects involving the anterior layer of the rectus sheath. It is also important to avoid using the anterior layer of the rectus sheath below the arcuate line as the posterior layer of the rectus sheath is significantly weaker and the risk of hernia at that location is greater. To prevent hematoma in the connecting tunnel, it is very important that hemostasis be obtained during creation of this tunnel and during flap harvest.
RESULTS
Typically, the use of rectus abdominis free flap achieves the desired goal of reconstructing the palate and separating the oral cavity from the nasal cavity. For more extensive ablations that include the palate and other midface components, it provides abundant soft tissue that can be useful for not only reconstructing the palate but also reconstructing the other related defects. This nonosseous flap is not the optimal reconstruction for defects in this area, but typically, the patients who undergo this reconstruction are unlikely to go on to full dental reha-bilitation with an implant-borne dental prosthesis.
PEARLS
• Appropriate flap design is the most important point to keep in mind when using the rectus abdominis free flap for this specific defect.
• For patients who require reconstruction of the palate only and who do not necessarily require reconstruction of the midface or orbit, a muscle-only flap is ideal. This provides very well-vascularized muscle that will beautifully and reliably reconstruct the palatal defect.
PITFALLS
• Donor site morbidity can be significant if there is a breakdown at the donor site, so careful attention to the closure of the donor site is important to avoid donor site morbidity.
• It is critical to be certain that the tunnel is appropriately placed and that appropriate hemostasis is obtained.
INSTRUMENTS TO HAVE AVAILABLE
• Standard head and neck surgical set
• General surgery tray
• Marlex mesh
SUGGESTED READING
Pennington DG, Pelly AD. The rectus abdominis myocutaneous free flap. Br J Plast Surg 1980;33:277–282.
Chicarilli ZN, Davey LM. Rectus abdominis myocutaneous free-flap reconstruction following a cranio-orbital-maxillary resection for neurofibrosarcoma. Plast Reconstr Surg 1987;80:726–731.
Urken ML, Turk JB, Weinberg H, et al. The rectus abdominis free flap in head and neck reconstruction. Arch Otolaryngol Head Neck Surg 1991;117(9):1031.
Nakatsuka T, Harii K, Yamada A, et al. Versatility of a free inferior rectus abdominis flap for head and neck reconstruction: analysis of 200 cases. Plast Reconstr Surg 1994;93(4):762–769.
Yokoo S, Komori T, Furudoi S, et al. Indications for vascularized free rectus abdominis musculocutaneous flap in oroman-dibular region in terms of efficiency of anterior rectus sheath. Microsurgery 2003;23:96–102.