31 Reconstruction of Multisite Defects
Summary
The reconstruction of oral cavity defects following cancer resection can prove challenging. The close spatial relationships between distinct tissue types found in the oral cavity can allow invasive malignancies to span multiple subsites. In these cases, reconstructive strategies that restore anatomic form as well as the specialized and coordinated function of each subsite are critical for success. Patient selection, preoperative planning, operative technique, and postsurgical care all greatly influence the ultimate success of multisite reconstruction of the oral cavity. This chapter will discuss the relevant challenges and potential solutions involved in the repair of these defects.
31.1 Introduction
Head and neck cancer has a yearly incidence of around 5%, although a disproportionate percentage of these malignancies arise within the oral cavity. 1 Dysfunction caused by oral malignancy is particularly problematic due to the high degree of coordination necessary for oral competence, digestion, swallowing, speech, and respiration. The highly specialized structures and distinct tissue types responsible for these functions are in close proximity and share tissue planes that extend across subsite boundaries. For this reason, invasive malignancies are likely to involve multiple oral cavity subsites. Surgical resection can therefore be expected to produce complicated and multifaceted defects that require careful planning and execution by the reconstructive surgeon.
The innovative architect Frank Lloyd Wright wrote in 1949 that “form and function thus become one in design and execution if the nature of materials and methods and purposes are all in unison.” 2 The same is true of surgical reconstruction, where the goal of unison between form and function is achieved only after appropriate choice of replacement tissue, flap type, design, and inset. This chapter will discuss surgical considerations important in the reconstruction of multisite oral cavity defects with this goal in mind.
31.2 Diagnosis and Evaluation
31.2.1 Patient Selection
The evaluation of the patient with oral malignancy should involve the comprehensive efforts of a multidisciplinary head and neck cancer team, including the head and neck surgeon, reconstructive surgeon, pathologist, radiologist, radiation oncologist, medical oncologist, oral surgeon, prosthodontist, psychosocial oncologist, nutritionist, and speech and language pathologist.
Evaluation of the patient by the reconstructive team attempts to assess the extent of the disease, predict the anticipated defect, and create a plan for repair. The guiding principles described by Millard and Gillies “to replace like with like” and to “think of reconstruction in terms of units” are particularly relevant in cases with multisite involvement. Keeping these tenets in mind will help to sort through the various reconstructive options and present the patients with the most suitable for their specific needs. A careful conversation about all options, including a discussion of the risks and benefits inherent to each, is critical for proper informed consent. The associated donor site morbidities, the need for additional procedures, and the timeline for recovery should be outlined. It is imperative to understand the patients’ goals for treatment, their motivations, and expectations. The possibility of postoperative functional and/or aesthetic deficits should be addressed so that expectations can be managed appropriately.
With the help of the head and neck cancer team, the patient’s medical fitness to undergo major surgery should be determined. Consultation with other specialists for risk stratification and preoperative work-up can detect patients who should not have surgery. Ancillary testing such as angiography to assess peripheral vascularity can be considered if free tissue transfer is necessary in the setting of peripheral vascular disease.
The overall nutrition status of the patient can be assessed through history, consultation with a nutritionist, or laboratory values such as albumin and pre-albumin that can indicate malnutrition. A swallow assessment by a speech and language pathologist is important to detect dysphagia that may cause aspiration. Some patients will benefit from immediate dietary modification, nil per os (NPO) status, or prophylactic gastrostomy tube placement. 3
A thorough history should be taken, with attention to past or current tobacco use, alcohol consumption, use of anticoagulants, prior radiation therapy, past head, neck, or extremity surgery, immunosuppression, systemic diseases such as Raynaud’s disease or scleroderma, as well as current medications and allergies.
Assuming a surgical treatment is indicated and the patient is medically fit to withstand an operation, a thorough examination of the oral cavity will help to determine the best reconstructive plan. The following section will discuss considerations by oral cavity subsite.
31.2.2 Evaluation of Projected Subsite-Specific Defect
Oral cancer may present in a variety of forms, from seemingly small and superficial lesions to deeply infiltrative or submucosal masses. This variance adds to the challenge of predicting the final defect. Furthermore, the importance of obtaining negative surgical margins for oncologic control will necessarily lead to a defect larger than the size of the tumor itself. Intraoperative findings such as perineural involvement, metastatic lymphadenopathy, adherence to adjacent structures, or findings of unexpected progression can also lead to defects larger than anticipated. The concept of field cancerization represents a condition in which several tumor cells exist over a wide mucosal area, with potential segments of normal-appearing tissue in between. 4 Obtaining negative surgical margins can be difficult and may also lead to larger defects. Despite these uncertainties, “observation remains the basis of surgical diagnosis,” and a systematic and careful examination of each subsite will best inform the reconstructive plan. 5
Floor of Mouth
The floor of mouth represents a U-shaped mucosal lined space situated under the anterior ventral tongue and extending forward to the mandibular gingiva. Deep to this space, the mylohyoid muscle forms a sling which separates the floor of mouth from the submandibular and submental spaces. The sublingual frenulum bisects the floor of mouth, bordered by the paired papillae of the Wharton’s ducts. Sublingual folds of redundant mucosa as well as submucosal sublingual veins are found lateral to the frenulum. The floor of mouth extends posterolaterally adjoining the inferior lateral tongue and terminating at the anterior tonsillar pillar. 6 Due to the contiguous nature of the floor of mouth, advanced tumors may invade the base of tongue or anterior mandible. Palpation of mobile mandibular segments may suggest pathologic fracture if tumor invasion of the mandible is present. Loose teeth or edentulous areas adjacent to the primary tumor or firm and fixed lesions involving the gingiva or floor of mouth mucosa along the mandible are signs for probable bony invasion. Paresthesia of the chin may suggest tumor infiltration of the inferior alveolar nerve. Palpation of the submandibular and submental spaces may detect tumor invasion through the mylohyoid sling, and inspection of the external skin for signs of ulceration or induration can detect full-thickness involvement. Because the mucosa of the anterior ventral tongue is contiguous with the floor of mouth, the junction between these two subsites is important to assess. The same is true for the posterior where the floor of mouth abuts the tongue base. Assessment of tongue mobility and direct palpation can detect extension between these subsites as well.
Buccal Mucosa
The buccal mucosa is the membranous internal lining of the cheek extending from the inner oral commissure anteriorly to the pterygomandibular raphe found just lateral to the retromolar trigone. Medially, the buccal mucosa attaches to the upper and lower alveolar ridges to create the gingivobuccal sulci. The mucosa is bordered laterally by thin layers of soft tissue including the pharyngobasilar fascia, buccinator muscle, buccal fat, facial nerve branches, superficial musculoaponeurotic system (SMAS), and cheek skin. Low resilience of these tissues to infiltrating buccal lesions can allow lateral tumor extension, which may cause facial nerve paresis, orocutaneous fistulae, or skin changes. Stensen’s duct pierces the buccinator muscle and terminates at the papilla found within the buccal mucosa, creating another potential route of tumor egress. Additional routes of spread may occur in all directions to reach the alveolar ridge, retromolar trigone, ascending mandibular ramus, lateral tongue, and floor of mouth. 7
Hard Palate and Maxilla
The hard palate creates the roof of the oral cavity and extends from the gingiva of the upper dentition to its border with the soft palate. It consists of both the primary and secondary palate, which are separated by the incisive foramen. It is covered by a thick and adherent mucosal layer. Inspection and palpation of the palate is important because although ulcerative or exophytic masses are easily seen, minor salivary gland carcinomas arise submucosally and can be covered by normal-appearing mucosa. Palatal hypoesthesia may indicate perineural invasion through the sphenopalatine or pterygopalatine fossae. Anterior midline hard palate lesions may appear isolated but lateral or posterior lesions may involve adjacent subsites including the alveolar ridges, gingiva, maxilla, or pterygoid space. 8 Due to the dense adherence of the hard palate mucosa, most lesions will be relatively fixed even in the absence of bony invasion. Diagnostic imaging is helpful to assess bony invasion. Oroantral fistulae and loose or missing dentition may be noted.
Tongue
The tongue occupies the majority of the oral cavity and consists of eight muscles covered by mucosa containing minor salivary glands, papillae, and taste buds. The tip of the tongue is the pointed anterior-most portion which is highly mobile. The body of the tongue has dorsal, ventral, and lateral surfaces and contacts the floor of mouth. The oral tongue is also divided down the midline by the fibrous lingual septum which creates the median sulcus. The base of tongue, located posterior to the circumvallate papillae, is a structure of the oropharynx. The hypoglossal nerve supplies the motor innervation to the tongue and can be assessed by tongue mobility with hypoglossal palsy causing deviation toward the ipsilateral side. The vagus nerve contributes motor innervation to the palatoglossus muscle. The mandibular division of the trigeminal nerve contributes sensation to the oral tongue, and the chorda tympani, via the facial nerve, provides taste sensation. Tumors arising within the tongue can easily extend into the floor of mouth, gingiva, and mandible. 9
Mandible
The mandible is a horseshoe-shaped bone within the oral cavity that is covered by mucosa and gingiva and harbors the lower dentition. The muscles of mastication insert on the mandible as do the suprahyoid muscles. The bone itself is covered by a periosteal layer. The inferior alveolar nerve that enters the mandible through the mandibular foramen runs within the bone until it exits as the mental nerve through the mental foramen. The bone is subdivided into sections including the symphysis, parasymphysis, body, angle, ascending ramus, condyle, and coronoid process. The mandible has variable thickness and vertical height with both a lingual and buccal cortex. The retromolar trigone represents the region where the body of the mandible transitions to the ascending ramus and is located just posterior to the third molar. The gingiva and mucosa are tightly adherent to the bone but are contiguous with the mucosal surfaces of other subsites such as the floor of mouth and the buccal space. Inspection of the baseline occlusion is critical during the initial assessment of an oral malignancy. If the mandible is involved and requires reconstruction, restoring class I or premorbid occlusion is a major reconstructive goal. The degree of mouth opening and presence of trismus is assessed by measuring the inter-incisor distance. Tumor infiltration of the pterygoid space or pain in opening of mouth may cause severe trismus which can make airway management difficult as well as make surgery necessary.
Lips
The lips form the anterior entrance into the oral cavity and have several crucial functions including articulation of speech, facial expression and aesthetics, oral competence during eating, and sensation. The orbicularis oris muscle courses circumferentially to create the upper and lower lips which join laterally at the oral commissure. The muscle is covered by skin, vermillion mucosa, and oral mucosa. This coverage is contiguous with the gingivolabial sulci and the buccal mucosa. Motor innervation to the lips is by the facial nerve, and sensation by the second and third divisions of the trigeminal nerve. Oral competence should create a watertight seal when the mouth is closed to prevent drooling or air escape during speech. The lips can be palpated and distracted away from the jaw in order gauge mobility. For primary lip cancers, determination of the percentage of the total lip length involved is important when choosing reconstructive options microstomia is to be avoided.
31.3 Determination of Reconstructive Options
The major goals of oral cavity reconstruction include: restoring lost volume, separating the oral cavity from the neck, allowing functional speech and swallowing, maintaining tongue mobility, establishing normal occlusion, allowing normal temporomandibular function without trismus, avoiding microstomia, and providing acceptable aesthetic appearance. Defects involving multiple subsites may demand attention to all or many of these challenges.
The reconstructive ladder represents a conceptual framework useful in the assessment of any defect. It includes every surgical option starting with the simplest and least invasive and moving toward the most complicated techniques. The smallest and most superficial defects can be addressed either by healing by secondary intention or primary closure, which make up the first two rungs of the ladder. However, as this chapter focuses specifically on multisite defects, the strategies of the higher rungs including local, regional, and free tissue reconstruction will be discussed.
The size and anatomic position of the defect, involved subsites, tissue types missing, degree of volume loss, and functional deficits are all used to determine the best reconstructive option. The need for bone, soft tissue, muscle, mucosal coverage, or any combination will make certain options more suitable than others. Flaps that allow motor or sensory innervation may better address functional losses than other options. Composite flaps containing several tissue types or the use of multiple flaps may be chosen. Local and regional flaps may involve less morbidity and perhaps lower risk than free tissue transfer, but rely on the availability of adequate nearby donor tissue and limitations on pedicle rotation. Free tissue transfer involves donor site morbidity, but can reliably provide the necessary bulk, specific tissue-type required, and options for innervation. Furthermore, the large primary tumors that create multisite defects often require postoperative adjuvant radiation therapy. Vascularized free tissue can resist the effects of radiation that lead to late complications. 10 A well-designed free flap containing all necessary elements and a resilient blood supply may ultimately involve less cost and morbidity than several local or regional flaps used over time that fail to achieve their goals.
31.3.1 Diagnostic Imaging
The major imaging modalities used for the diagnosis of head and neck cancer including CT scan, MRI, and angiography can be useful in planning multisite reconstruction. CT scan is especially valuable for detecting bony invasion that may require resection of the mandible or maxilla. MRI can assess tumor invasion into adjacent soft tissue spaces, such as the tongue and floor-of-mouth or buccal space. Protocols for three-dimensional reconstruction of both CT scan and MRI images are available that may illustrate the spatial complexity of the tumor and involved tissues. The role of angiography is mainly for assessing the vascularity of potential free flap harvest sites, such as the lower leg in patients with peripheral artery disease or the forearm in patients with history of prior trauma.
Virtual surgical planning (VSP) has evolved into a useful tool in craniofacial surgery, with potential benefits of decreased operative time and increased technical precision. Pretreatment planning using CT imaging, customized plating materials, and osteotomy cutting guides can be created to exact specification (▶ Fig. 30.4). However, in oncologic surgery, tumor progression can occur between planning and treatment, and resection margins may extend further than anticipated, making VSP no longer applicable. The learning curve for efficient use of the technology is another potential challenge. A recent review of the use of VSP in craniofacial free flap surgery found that the technology was completely abandoned in 4% of cases and only partially adhered to in 11%. 11
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