ERIC G. HALVORSON, DUC T. BUI, AND PETER G. CORDEIRO
RECONSTRUCTION OF MAXILLARY DEFECTS
The maxilla is an essential component of the midface and has both functional and aesthetic roles. It contributes to facial appearance, determines midfacial width and height, and serves as support for the orbit, cheek, nose, and upper lip. The maxilla also supports critical functions such as mastication, speech, and deglutition. Most maxillary defects result from the surgical ablation of maxillary tumors or tumors arising from adjacent structures, including the paranasal sinuses, palate, nasal cavity, orbital contents, overlying skin, and intraoral cavity. Another cause of maxillary defects involves traumatic injuries resulting from gunshot wounds to the midface or less commonly blunt injury. Because of its close relationship to other facial components and unique three-dimensional structure, reconstruction of maxillary defects can be a formidable challenge for the reconstructive surgeon.
The goals of maxillary reconstruction are:
1. Reconstruct the orbital floor to maintain globe position or fill the orbital cavity following orbital exenteration
2. Reconstruct the intraoral, cheek, palatal, and nasal lining to restore speech, mastication, and oral continence
3. Separate the oral and nasal cavity from the skull base and orbit
4. Restore external skin and three-dimensional facial contour
5. Obliterate the maxillectomy defect
Traditionally, prosthetic appliances were used to reconstruct maxillary defects and are still a reasonable option in some patients (see Chapter 38). This method of reconstruction relies on adequate support from the remaining tissues and split-thickness skin grafting to line the defect. Despite successes in many cases, there are several disadvantages to the use of obturators. Leakage and oronasal regurgitation because of bulky dentures, inadequate dentition, and poor retentive surfaces, the need for cleaning, and repeated prosthetic refinements are common problems.
Autologous tissue is frequently preferable. Small defects of the maxilla can be reconstructed with local soft-tissue flaps with or without supplemental bone grafting. Prior to the advent of free tissue transfer, larger maxillary defects were repaired with a variety of pedicled flaps, including the deltopectoral, pectoralis major, latissimus dorsi, temporalis, sternomastoid, and trapezius myocutaneous flaps. These flaps were limited by their reach without tension on the vascular pedicle, circulatory compromise at the distal (and often most critical) portion of the flap, inadequate tissue to fill the defect, and/or the requirement for multiple stages to achieve a final result. More recently, microvascular free tissue transfer has significantly expanded the reconstructive surgeon’s armamentarium for maxillary reconstruction. There are many composite flaps that can be transferred to the midface without limitations of vascular pedicle length or flap geometry. Flaps can be chosen based on the precise tissue, volume, and surface area requirements of each defect.
Although free flap reconstruction now is the preferred method for the vast majority of extensive maxillary defects, flap selection is somewhat complex. The initial step is to define the maxillary defect in terms of bony and soft-tissue components. Adjacent critical structures, such as the eye, nose, and lips, are assessed. A history of radiotherapy or previous neck dissection is noted. The necessary length of the vascular pedicle and donor-site morbidity are assessed. The amount, location, and quality of residual bone, dentition, and denture-bearing alveolar arch largely determine whether a bone-containing flap is necessary.
Visualizing the maxilla as a six-sided box with the roof being the orbital floor and the floor being the palate is helpful in determining which walls are missing (Figure 39.1). The three walls that require reconstruction are the superior (orbital floor), floor (palatal), and anterior (cheek) walls. Reconstruction of the highly complex three-dimensional nature of the maxillary defect can be simplified by combining bone grafts with a soft-tissue flap. Bone grafts can be rigidly fixed without interfering with flap inset. Vascularized bone is essential only in the maxillary arch, and possibly to replace a vertical buttress if both are resected.Although a variety of alloplastic products are available for bone replacement, these are not indicated in patients who have either received or will receive radiation therapy, and in general do not perform as well as autologous grafts.
Bone replacement for the orbital floor is essential to maintain globe position. The orbital floor can be reconstructed with autologous bone grafts because this area requires minimal supportive strength. The maxillary arch of the midface is reconstructed to provide anterior projection and dental support. Ideally, bony replacement of the maxillary arch must have adequate bone stock for osseointegrated dental implants. Hence, vascularized bone is required for reconstructing the maxillary arch. The palate can be repaired with the skin island of a free flap or replaced with an obturator. The anterior wall of the hypothetical box requires reconstruction but does not require bony reconstruction. The maxillary sinus in the center of the hexahedron can be filled with soft tissue (muscle or fat). The nasal lining may or may not be restored, and if the only remnant following extirpation is the septal mucosa, one option is to elevate the mucosa off the septum, fold it back, and suture it to the posterior nasal airway remnant to close off and obliterate the nasal airway on that side.
FIGURE 39.1. The maxilla compared with a hexahedron. The roof of the maxilla is the floor of the orbit. The floor of the maxilla is the hard palate. The anterior, posterior, medial, and lateral walls are the vertical buttresses, and the maxillary antrum is contained within the six walls of the bone.
One difficulty in midface reconstruction with free flaps is that the closest recipient vessels are in the ipsilateral neck. The ideal free flap, therefore, must have a pedicle length of 10 to 13 cm to reach the neck without vein grafting. Although a variety of free flaps, including fibula, scapula, anterolateral thigh, and iliac crest flaps, can be used to reconstruct maxillary defects, the two flaps most commonly used that have large and long pedicles are the rectus abdominis myocutaneous and radial forearm flaps. The rectus flap provides reliable skin and a large soft-tissue bulk. The radial forearm flap provides a large surface area of pliable skin with minimal soft tissue and can be combined with a vascularized bone segment. Both flaps can provide multiple skin islands that can be oriented in different three-dimensional positions.
Many classification systems have been developed to describe the extent of resection of maxillary and midfacial tumors and to provide algorithms for reconstruction. A simple classification system we have previously described is presented below.
Classification System for Maxillary and Midfacial Defects
Type I (limited maxillary) defects involve resection of one or two walls of the maxilla, excluding the palate (Figure 39.2). These defects usually include the anterior and medial walls of the maxilla, and occasionally the orbital rim, in combination with the soft tissues and skin of the face. Hence, the defect has a high surface-area-to-volume ratio. The radial forearm flap is an ideal flap because it has a good surface-area-to-volume ratio, that is, it consists of a small amount of soft-tissue volume and large skin surface area. Defects of the orbital rim or orbital floor are reconstructed with split-calvarial or rib bone grafts. Other thin flaps with a high surface-area-to-volume ratio include the scapular, parascapular, and anterolateral thigh fasciocutaneous flaps, depending on the patient’s body habitus. Our preference for the radial forearm flap is due to the reliability of the anatomy, the length and caliber of the pedicle, and the consistently thin and pliable tissue.
Type II (subtotal maxillary) defects include resection of the maxillary arch, palate, and anterior and lateral walls with preservation of the orbital floor. These defects have recently been subdivided into type IIA defects that involve resection of less than 50% of the palate and type IIB defects that involve greater than 50% of the palate (Figure 39.3). Resection of these defects includes the classic hemimaxillectomy, or “infrastructure maxillectomy,” that involves most of the lower five walls of the maxilla with a medium surface-area-to-volume ratio (large surface area and medium volume). Both type IIA and type IIB maxillectomy defects are moderate-volume deficiencies with large surface area requirements, which usually require two skin islands.
For type IIA defects, reconstruction may involve either a free flap or a combination of a skin graft and an obturator, depending on the patient and the surgeon preference. If a free flap is selected to avoid the inconvenience and maintenance of a palatal obturator, our flap of choice is the radial forearm fasciocutaneous free flap. To keep the soft palate taut, recreate the buccal sulcus, and to avoid prolapse into the oral cavity the skin paddle must be equal to or smaller than the original defect. If adequate teeth or bone stock remain, dentures or osseointegrated dental implants are used. Smaller type II defects or defects in patients who are not free flap candidates can be reconstructed with a temporalis muscle flap (Figure 39.4).
An osteocutaneous radial forearm flap folded into a “sandwich” is ideal for reconstruction of type IIB defects that by definition include much of the maxillary arch and hard palate. This technique provides anterior projection and vascularized bone for dental implant osseointegration. Additionally, the bone provides support for the upper lip. The folded skin surfaces restore the palatal mucosal lining and nasal floor lining. This flap has a “moderate” amount of volume when folded over and still maintains an adequate surface area to resurface the nasal floor and palate. Anterior bilateral subtotal maxillary defects are ideally suited for an osteocutaneous sandwich flap. Patients with these defects and intact upper external lip structures can be reconstructed with excellent aesthetic and functional results (Figure 39.5). Other options for reconstruction of type IIB defects include the scapula and fibula osseocutaneous flaps. The scapula flap has more tenuous blood supply, does not tolerate multiple osteotomies, and requires repositioning the patient preventing a two-team approach. The fibula flap supplies abundant well-vascularized bone that can tolerate multiple osteotomies. We have found, however, that maxillary arch defects do not require more bone than the radial forearm fasciocutaneous flap provides, that the fibula bone can be bulky in the maxilla, and that the fibula flap pedicle is not as long as that of the forearm flap. In addition, the leg skin is often bulkier than the forearm skin, making inset more difficult and secondary procedures more likely.
FIGURE 39.2. Type I (limited maxillary) defect. The anterior and medial walls of the maxilla (left) have been resected. The illustration demonstrates skin/soft-tissue resection in combination with bony resection (center, left) creating a large-surface-area/low-volume defect. The radial forearm fasciocutaneous flap (donor site depicted in inset) provides multiple large skin surface areas with minimal volume (center, right). The flap is shown in place, demonstrating skin islands to resurface anterior cheek and medial nasal lining (right).
FIGURE 39.3. Type II defects. A. Type IIA defects comprise less than 50% of the palate. The illustration demonstrates a folded fasciocutaneous forearm flap used for reconstruction. The skin island used for palate lining must be taut to prevent prolapse into the oral cavity. A second skin island may be used for maxillary sinus lining, or the flap may be deepithelialized and allowed to mucosalize. B. Type IIB (subtotal maxillary) defect. The lower five walls of maxilla have been resected, including the palate, but sparing the orbital floor (roof of the maxilla) (left). The illustration demonstrates palatal/nasal floor lining and bony resection. This creates a large-surface-area/medium-volume defect (center, left). The radial forearm osteocutaneous “sandwich” flap (donor site depicted in inset) provides a large skin surface area with vascularized bone and moderate volume (center, right). The flap is shown in place, demonstrating a strut of vascularized bone to reconstruct the anterior maxillary arch deficit sandwiched between two skin islands that replace palatal and nasal lining (right).
Type III (total maxillary) defects include resection of all six walls of the maxilla. This type of defect is further subdivided into type IIIA, where the orbital contents are preserved and orbital floor is resected (Figure 39.6), and type IIIB, which is a total maxillary defect combined with orbital exenteration (Figure 39.7).
Type IIIA defects have medium-large volume and medium-large surface area requirements. Reconstruction of the orbital floor is required to maintain a functional eye. The floor is restored with nonvascularized bone graft, which must be supported by a well-vascularized flap. The rectus abdominis flap provides muscle coverage for bone grafts and adequate subcutaneous fat that can be contoured to fill the dead space. It can provide multiple skin islands for the palate and/or external skin and/or nasal lining as needed. A temporalis muscle flap can also cover the bone grafts for the orbital floor; however, it may not replace the palate. Consequently, an obturator may be required for palate reconstruction. Temporalis flaps are indicated in older patients who are not candidates for free tissue transfer. Preservation of the malar eminence is helpful to maintain upper midface projection. Primary bone grafting in this area can be challenging because it can compress the flap pedicle. Another option for reconstruction of type IIIA defects is the fibula flap, as it can be used to reconstruct the orbital floor, vertical buttresses, and alveolar ridge. Muscle and/or skin taken with the flap can be used to fill dead space and provide lining. Disadvantages include a shorter pedicle length and higher complexity; however, it is an option when dental restoration is desired.
FIGURE 39.4. Type IIA defect following maxillectomy. A, B. A temporalis muscle flap was utilized to reconstruct the palate in this edentulous patient with significant comorbidities. A split calvarial bone graft was utilized to reconstruct the orbital floor, covered by the temporalis muscle flap. C, D.Postoperative result.
Type IIIB defects are extensive and have a large volume and large surface area requirement. The palate and nasal lining often require closure to obviate oronasal fistulae. The external defect usually comprises the eyelids and cheek, and occasionally the lip. In addition, the anterior skull base is often exposed. A rectus abdominis flap is the flap of choice. If the external skin of the cheek is present, the skin island of the rectus flap can be used to close the palate. If the flap is not too bulky, then a second skin paddle can be used to reconstruct the lateral nasal wall. A third skin island can even be used to restore the external skin. The aesthetic outcome for patients with reconstructed external skin is fair because of the variability of skin color and contour. The contour abnormality can be revised at a later time using liposuction and/or skin excision.
In both IIIA and IIIB defects, the lateral nasal lining may be missing. Reconstruction with a skin island of the flap will maintain the nasal passage, but often the bulk of the flap and loss of bony support can cause collapse of the nasal airway, rendering it nonfunctional. This can result in crusting and even infection. Another option is to elevate a posteriorly based ipsilateral nasal septal mucosa flap and fold it laterally to obliterate the nasal passage (Figure 39.8). The flap can be sewn to the lateral cut edge of the posterior nasopharynx, thus obliterating the nasal passage.
FIGURE 39.5. Bilateral subtotal maxillectomy (type IIB maxillary defect) and partial upper lip resection in a 30-year-old man with osteosarcoma of the maxilla extending into the oral and nasal cavity. A. Intraoperative defect. B. The radial forearm osteocutaneous flap harvested with segment of the distal radius bone and long vascular pedicle. C. Vascularized bone graft rigidly fixed to remaining maxillary tubercles. The skin island has been folded over the bone and fixed to resurface the floor of the nose and the palate. D. Postoperative photograph of a patient after inset of the flap and closure of the lip defect.
FIGURE 39.6. Type IIIA defect. All six walls of the maxilla, including the floor of orbit and hard palate, have been resected. The orbital contents have been preserved (left). The illustration demonstrates the orbital floor, vertical maxillary buttresses, and palatal resection (center, left). This creates a medium-surface-area–medium-volume defect. Cranial or rib bone graft is used to reconstruct the orbital floor and is covered with a single-skin island rectus abdominis myocutaneous flap (center, right). The rectus abdominis myocutaneous flap (donor site depicted in the inset) provides medium surface area with medium volume. The bone graft is rigidly fixed to reconstruct the orbital floor. The rectus abdominis myocutaneous flap with the skin island is used to close the roof of the palate, soft tissue is used to fill in the midfacial defect, and muscle is used to cover the bone graft. Note the extended length of the deep inferior epigastric vessels to neck (right). (Below) Patients who are not free flap candidates can be reconstructed with split calvarial bone grafts, covered with the temporalis muscle, transposed anteriorly. The zygomatic arch should be osteotomized and temporarily removed to increase excursion of the temporalis muscle.
FIGURE 39.7. Type IIIB defect. All six walls of the maxilla, including the floor of the orbit and orbital contents (left), have been resected. The illustration demonstrates resection of external eyelid, cheek skin, and orbital contents, in combination with the entire maxilla and palate (center, left). This creates a large-surface-area–large-volume defect. A three-skin island rectus abdominis myocutaneous flap design (inset) provides multiple large surface areas with a large volume of soft tissue and muscle to fill in the defect (center, right).
Palatal closure can be accomplished with an obturator or the flap skin island. The palatal skin island often bulges downward, making denture fitting difficult. Despite this, palatal closure with a skin island is preferable because these patients are usually able to speak well and eat soft solids without a denture(Figure 39.9).
There is a separate group of type IIIB patients who undergo resection of the hemimandible in addition to the maxilla and orbit. These are large volume and large surface area defects. Reconstruction of the bony defect would require a vascularized fibula flap, but this would not provide adequate soft tissue or skin for the external and intraoral defect. The rectus flap can provide multiple skin islands to replace the cheek lining, palate, lateral nasal wall, and external skin. In addition, the flap’s significant bulk allows contouring of the cheek. Remarkably, good function and reasonable aesthetic result with a single free flap reconstruction can be accomplished. Either type IIIA or IIIB flaps can also be reconstructed with a vastus lateralis fascio cutaneous or myocutaneous flap (including half or more of the vastus lateralis). This flap is of similar volume and surface area as a vertical rectus abdominis flap in some patients and can be preferable in patients with a protuberant, obese abdomen, or with a history of abdominal surgery precluding the use of the rectus abdominis flap. A variety of other myocutaneous flaps can be utilized, but most require repositioning the patient (preventing a two-team approach), such as the latissimus dorsi flap, or have a short pedicle, such as the gracilis flap.
Type IV (orbitomaxillary) defects include resection of the orbital contents and the upper five walls of the maxilla, sparing the palate (Figure 39.10). The reconstructive goal consists primarily of filling the dead space and resurfacing the external skin. The rectus abdominis flap is the ideal flap for this goal.Although conceptually simple from a reconstructive standpoint, achieving this goal can be technically challenging. The temporal and facial donor vessels are usually resected or unreliable. The flap pedicle can be lengthened by intramuscular dissection up to 20 cm to reach the neck vessels. A superficial tunnel can be created in the facelift plane or medial to the mandible by a parapharyngeal approach to gain access to the neck vessels without vein grafts.
FIGURE 39.8. A and B. A 57-year-old man with a type IIIB maxillectomy defect including much of the nasal septal lining. The remaining septal mucosa (arrow) was elevated as a posteriorly based mucosal flap, folded laterally, and sewn to the lateral cut edge of the posterior nasopharynx to obliterate the left nasal passage (arrow).
FIGURE 39.9. A 65-year-old man who underwent total maxillectomy with orbital exenteration and segmental mandibulectomy (type IIIB defect) for excision of a recurrent squamous cell cancer of the cheek skin invading maxilla, orbit, and oral cavity. A. Intraoperative defect. B. Reconstruction of the defect was performed using a two-skin island rectus abdominis free flap for intraoral/palatal lining and external skin. C. Final appearance after two revisions of the flap to decrease bulk.
An algorithm for reconstruction based on the above classification system is shown in Figure 39.11.
A unique challenge of maxillary reconstruction involves repair not only of the maxillary defect but also of adjacent important structures of the face, such as the lip and oral commissure, eyelids, and nose that may be resected during tumor extirpation. Reconstruction of a functioning lip is extremely difficult and involves restoring a competent oral sphincter. The primary restoration of the lips with local lip-switch procedures prior to maxillary reconstruction with a free flap is advocated. The free flap should not be attached directly into the sphincter, or used to reconstruct any portion of the lips, unless more than 80% of either the lower or upper lip is missing. The disadvantage of microstomia is less debilitating than oral incompetence and constant drooling. Reconstruction of upper lip defects with flap tissue is not as debilitating as reconstruction of the lower lip with an atonic, adynamic flap.
FIGURE 39.10. Type IV (orbitomaxillary) defect. The upper five walls of the maxilla have been resected, including the orbital contents, but sparing the palate (left). The specimen demonstrates resection of orbital contents, eyelid, and cheek skin in continuity with bone (center, left). This creates a large-surface-area–large-volume defect. Note the design of the single-skin island rectus abdominis myocutaneous flap (inset). This flap provides large surface area with large volume to reconstruct the defect (center, right). Rectus abdominis myocutaneous flap in place, demonstrating skin island to resurface the external skin defect with muscle and subcutaneous fat used to fill in the soft-tissue deficit (right).
Eyelid reconstruction may be necessary in types I and III defects. Ectropion is the most common postoperative problem. This can usually be corrected with a variety of secondary procedures, including a tarsal strip procedure, skin grafting, and canthopexy. Type IIIB defects involve orbital exenteration, making eyelid restoration less important. Because the results of functional eyelid reconstruction are usually unsatisfactory, a patch, dark eyeglasses, or an external glue-on type of prosthesis (cosmetic patch) is preferable to reconstruction for type IIIB defects. Preoperative consultation with an experienced anaplastologist can assist in providing the best possible result when a prosthesis is planned, especially when secondary contouring procedures are planned to improve prosthetic fit. An orbital hollow at least 1 cm deeper than the contralateral cornea is required for an ocular prosthesis (Figure 39.12).
Large maxillary resections may involve the nose. Although the nose is aesthetically important, it is not essential from a functional standpoint. Usually, local tissues (septum, nasal lining flaps, nasolabial flaps) are unavailable or irradiated. Reconstruction using local tissues, or even a second free flap, is usually difficult and yields poor aesthetic results. Consequently, delayed nasal reconstruction is advocated in all cases. Although prosthetic nasal reconstruction is preferable, delayed autologous reconstruction is also an option.
FIGURE 39.11. Algorithm for maxillary reconstruction. MC, musculocutaneous.
FIGURE 39.12. A and B. Following vertical rectus abdominis myocutaneous flap coverage of a type IIIB defect, this patient had too much bulk in the orbit preventing placement of an ocular prosthesis. Direct excision combined with liposuction improved flap contour and provided an appropriate platform for prosthetic fitting. A staged “nasolabial” flap was elevated to increase the oral aperture and add intraoral lining. C and D. An ocular prosthesis greatly improves the aesthetic outcome for patients undergoing coverage of type IIIB or IV defects with large soft-tissue flaps. An adequate orbital hollow should be recessed at least 1 cm from the normal cornea.
Summary
Maxillectomy and midfacial defects are classified into four types of defects based on the extent of maxillary resection. This classification allows for a simplified approach to midface reconstruction. The algorithm is based on the type of maxillary defect, which will usually have specific skin, soft-tissue, palatal, orbital floor, and bony structure deficits. Bone reconstruction is best accomplished with bone grafts for the floor of the orbit and a vascularized bone flap for the maxillary arch. Soft-tissue and skin coverage is commonly provided by free flaps. The choice of flap is determined by the surface area and tissue volume requirements. Large surface area and small- to medium-volume defects are best reconstructed with radial forearm fasciocutaneous or osteocutaneous flaps. Large-volume and medium to large surface area defects are best reconstructed with rectus abdominis free flaps. Other options include the fibula and anterolateral thigh flaps. Critical midfacial structures, such as the lips, eyelids, and nose, should be addressed separately, using local flaps if possible. The majority of patients whose maxillary defects are reconstructed using free tissue transfers have remarkably good function. Aesthetic results are mainly dependent on whether the orbital contents are removed and on the extent of external skin resection.
RECONSTRUCTION OF SKULL BASE DEFECTS
The most common cause of skull base defects is tumor resection. Other etiologies include trauma, late posttraumatic cerebrospinal fluid leak, craniofacial deformity, recurrent frontal mucocele, and midline dermoid cyst with intracranial extension. Surgical ablation of skull base tumors can result in an extensive defect with exposed brain, dura, cranial bone, and associated defects of adjacent structures, requiring composite tissue reconstruction to restore a combination of skin, soft tissue, bone, and mucosa. The goals of skull base reconstruction are to:
1. Repair and seal the dura
2. Separate the intracranial contents from the aerodigestive tract
3. Re-establish orbital and oropharyngeal function
4. Restore form by providing structural support, adequate soft-tissue bulk, and external skin coverage
5. Obliterate dead space
Repair of skull base defects is challenging because an unsuccessful reconstruction can lead to life-threatening complications. Early complications following skull base surgery include dural exposure, cerebrospinal fluid leak, pneumocranium, wound infection, meningitis, epidural abscess, brain abscess, hemorrhage, and neurologic injury. Late complications include globe malposition, diplopia, malocclusion, nasopharyngeal stenosis, trismus, chronic sinusitis, nasal obstruction, and facial deformity. To avoid potentially devastating postoperative complications, the ideal reconstruction for skull base defect must be reliable regardless of technical difficulty.
Prior to the 1960s, skull base surgery was limited because of the associated high morbidity and mortality and the paucity of reliable reconstructive techniques. During this period, repair of skull base defects was performed using skin grafts and local available tissues, such as scalp, galeal, pericranial, and temporalis flaps. The application of local flaps is limited by their small size, short arc of rotation, and donor-site defect. In addition, these local flaps are unreliable in patients who have had previous radiation therapy, multiple craniotomies, or a larger skull base resection. With the advent of the combined extracranial–intracranial approach by Ketcham et al., in 1963, and improved reconstructive techniques, the number of skull base surgeries has increased and resulted in larger defects requiring larger flaps. In the 1970s, regional flaps, such as the latissimus dorsi, pectoralis major, sternocleidomastoid, and trapezius flaps, were used to reconstruct these larger defects. These regional flaps are limited by pedicle location below the clavicle, which restricts the arc of rotation superiorly. The development of free tissue transfer in the 1980s provided a highly reliable method for repairing large, complex wounds in the skull base. Free flaps are well vascularized and can be used in irradiated sites or in patients who will receive adjuvant radiotherapy. They provide enough tissue bulk and ease of insetting to obliterate dead space and seal the intracranial contents from the external environment and aerodigestive tract. In addition, adequate composite tissue can be harvested to replace external skin, mucosa, soft tissue, and bone in large skull base defects in a single stage.
Although either pedicled flaps or free tissue transfer can be used to reconstruct large skull base defects, several authors have compared outcomes using free flaps versus local or regional flaps to repair difficult skull base wounds. Each study has demonstrated that free tissue transfer is associated with fewer complications than local or regional flaps for large difficult wounds. In addition, a steady decline in the complication rate of skull base surgery in the last 10 years has been observed. Consequently, free tissue transfer is frequently used for reconstruction of extensive, difficult skull base defects. Although skull base surgery has become less invasive, the need to reconstruct large defects still arises.
When determining the most appropriate technique for reconstruction, it is useful to identify the location of the skull base resection and the type of defect. Most skull base defects can be categorized as either an anterior or lateral skull base defect. The defect is assessed for the extent of dural defect, exposure to the aerodigestive tract, and skin, soft tissue, bone, and mucosal lining deficits. Furthermore, resection of key adjacent structures, specifically, the orbit, ear, maxilla, palate, and mandible, is considered in the flap selection process. Finally, radiation, prior surgery, and availability of local tissues for repair must be assessed.
The first priority in skull base reconstruction is to repair the dural defect in a watertight fashion through either direct closure or patching with autologous (pericranium, temporalis fascia, or fascia lata) or alloplastic material. Fibrin glue is an excellent adjunct to prevent cerebrospinal fluid leak. After a watertight dural closure is accomplished, vascularized tissue is interposed between the intracranial contents and the oropharyngeal cavity. This provides a barrier and prevents dural contamination with the oropharyngeal bacterial flora. Usually, a flap with extensive soft-tissue bulk is required to obliterate the dead space and to restore adequate surface contour of the face. Musculocutaneous free flaps (latissimus dorsi or rectus abdominis) or fasciocutaneous flaps (radial forearm, parascapular, or anterolateral thigh) can be used for soft-tissue reconstruction of the skull base.
Often key aesthetic structures, such as the ear, nose, and eyes, are resected during ablative skull base surgery. Definitive reconstruction of these structures is usually not undertaken at the initial stage of reconstruction. Prosthetic reconstruction remains a common and excellent method for replacing unique facial structures. However, simple soft-tissue filler over the anatomic defect and wearing a patch to cover the missing aesthetic structure is another alternative.
The indications for bone reconstruction in skull base surgery include extremely large bony defects of the skull base that will result in gross brain herniation; near-total or complete orbital roof defects that may result in pulsatile exophthalmos; orbital wall or floor defects that carry a high risk of enophthalmos; cranio-orbital defects that will result in inadequate soft-tissue support and deformity; and associated maxillary or mandibular/glenoid fossa defects that will result in facial deformity, malocclusion, and masticatory dysfunction. Alloplastic materials or nonvascularized bone grafts in conjunction with vascularized tissue can be used for bone reconstruction for most isolated bone defects. Free osseous composite tissue transfer is indicated only in specialized cases where bone grafts combined with soft-tissue flaps are inadequate, and the bone flap can incorporate enough soft tissue to fulfill the other requirements for reconstruction listed above. Common composite vascularized osseous flaps include fibula, scapula, and radial forearm flaps.
FIGURE 39.13. Lateral skull base defect. A. Lateral defect following tumor extirpation with medial antebrachial cutaneous nerve graft to reconstruct facial nerve defect. B and C. Reconstruction of lateral skull base defect with vertical rectus abdominis myocutaneous flap.
Anterior Skull Base
For small defects of the anterior skull base that do not require obliteration of dead space, the workhorse flaps are the pericranial and galea–pericranial flap. These flaps provide a thin, well-vascularized sheet of fascia that can easily reach the anterior skull base and reinforce dural repair, separating the dura from the subjacent spaces.
FIGURE 39.14. Lateral skull base defect. A. Lateral skull base defect following tumor extirpation with medial antebrachial cutaneous nerve graft to reconstruct facial nerve defect. B. Reconstruction of lateral skull base defect with muscle-sparing anterolateral thigh flap.
For patients with a history of prior surgery or radiation and large extensive anterior skull base defects, free tissue transfer is required. A variety of different free flaps can be used, including rectus abdominis, latissimus, radial forearm, fibula, anterolateral thigh, and scapular flaps. Flap selection is based on a variety of factors, including the size of defect and degree of involvement of adjacent structures such as the scalp, orbit, maxilla, and mandible. In general, the surface and volume deficits of the defect are assessed and the flap that best fits the defect is selected. In some cases, the location of the defect may determine the flap selection based on the availability of recipient vessels. The superficial temporal vessels can be used for defects high in the skull base, involving the scalp or orbit. For defects involving the orbit, maxilla, or lower face, the recipient vessels are usually found in the neck (Figure 39.9).
Lateral Skull Base
The workhorse for small defects of the lateral skull base is the temporalis muscle flap. It has the greatest utility in reconstructing defects of the infratemporal fossa. However, the temporalis is frequently devascularized during the ablative surgery and is not usable. In addition, its use is associated with a distinct contour defect in the temporal fossa.
For larger and more complex defects of the lateral skull base, free tissue transfer is indicated. Options include rectus abdominis, latissimus dorsi, anterolateral thigh, and lateral arm flaps. These defects of the lateral skull base usually require filling and resurfacing the defect. Consequently, flap selection is based on the extent of volume and surface area, which is determined by the defect. The rectus abdominis myocutaneous flap is very commonly used because of its location (allowing for simultaneous dissection during resection of tumor), large skin island, soft-tissue volume, and reliable vascular pedicle (Figure 39.13). In patients with a large protuberant abdomen or with a history of abdominal surgery precluding rectus abdominis harvest, the anterolateral thigh myocutaneous or fasciocutaneous flap is a good alternative with less reliable anatomy but good pedicle length and adequate soft tissue depending on the patient’s body habitus (Figure 39.14).
CONCLUSION
Local or regional flaps are used for the reconstruction of small skull base defects. The morbidity and mortality of aggressive skull base resection has decreased as a result of a multidisciplinary approach involving neurosurgeons, head and neck surgeons, and plastic surgeons, and advances in ablative and microsurgical techniques. Free tissue transfer is the preferred method for complex anterior skull base reconstruction involving dura, brain, or other major structures adjacent to the skull base, including the orbit, maxilla, and other structures. Free flaps are occasionally required for lateral skull base defects as well.Successful reconstruction can be safely achieved, restoring form and function, with adherence to basic principles of reconstruction, including watertight dural repair, coverage of dura and separation from nasopharyngeal cavity, and obliteration of dead space.
Suggested Readings
1. Califano J, Cordeiro PG, Disa JJ, et al. Anterior cranial base reconstruction using free tissue transfer: changing trends. Head Neck. 2003;25:89.
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