18 Floor of Mouth Reconstruction
The floor of the mouth is a pliable mucosally lined surface spanning from the lower aspect of the ventral tongue to the fixed gingiva of the lingual surface of the mandibular alveolar ridge. Reconstruction of this area is critical following tumor resection in order to optimize postoperative function. The redundancy of this region provides freedom of motion of the tongue relative to the adjacent, rigid mandible. Repair options range from simple primary closure to complex reconstruction with composite free tissue transfer with the ultimate goal being to provide a healed epithelial-lined surface to minimize tethering of the adjacent tongue and allow for more natural speech and swallowing rehabilitation.
The floor of the mouth is a pliable mucosally lined surface that provides redundancy and freedom of movement of the oral tongue from the immobile mandibular arch. This flexibility allows the tongue to manipulate the food bolus during mastication and deglutition and also freely press against the gums, palate, lips, and teeth during speech to allow for clear articulation. It is fairly uncommon for defects resulting from oral cavity cancer resections to be limited just to the floor of the mouth. Many defects extend to involve the adjacent tongue and/or mandible and consequently have different reconstructive requirements. Reconstruction of such defects involving multiple sites will be covered in Chapter 31 entitled “Reconstruction of Multisite Defects.” Here we focus specifically on defects limited to the floor of the mouth, with or without associated communication with a concomitant neck dissection wound.
18.2 Diagnosis and Evaluation
18.2.1 Defect Evaluation
For the purposes of planning, evaluation of the primary tumor is essential for determining the likely approach that will be needed for reconstruction. Examination of the tumor’s proximity to the adjacent mandible and tongue is crucial, and bimanual palpation with one hand on the lesion and one in the submental/submandibular region will allow the surgeon to get a better sense of any endophytic component of the disease and the likelihood of needing a resection of the floor of mouth muscular sling to achieve adequate oncologic margins. Imaging with CT can assist in evaluating for bone erosion and to look for pathologic lymphadenopathy, but such images often provide little detail on the soft-tissue extent of the primary tumor, especially when significant dental artifact is present. When needed, MRI can be employed to provide additional soft-tissue detail on invasion into the floor of the mouth and tongue musculature and also can provide information on perineural invasion and mandibular involvement.
Intraoperatively, in determining the appropriate reconstruction following tumor removal of the floor of the mouth, the process starts with a careful analysis of the wound. Defects can range from simple mucosal loss with minimal associated muscle resection to larger composite defects with oral glossectomy and/or segmental mandibulectomy. For the purposes of this chapter, emphasis will be placed on defects limited to the floor of the mouth. In these instances, attention should be paid to look at the amount and location of mucosal surface area lost, the depth of the defect and extent of resection of the underlying floor of mouth musculature, and whether or not there is an associated defect of the adjacent mandible and/or the tongue musculature. Additional factors should include the status of the patient’s dentition, whether or not they had undergone prior surgery or radiation therapy, and if the submandibular duct papilla is affected (in situations where the gland is preserved).
As mentioned earlier, one of the critical factors to assess in floor of mouth reconstruction is the integrity of the underlying muscular sling. The mylohyoid muscle and hyoglossus muscles not only serve to suspend the larynx and support tongue movement, but, in the context of a floor of mouth resection, also can serve as a barrier, separating the oral cavity from the underlying neck dissection wound. In defects where this muscular layer has been removed, particular emphasis must be placed on achieving a watertight closure of the floor of the mouth, resuspending the tongue and/or hyoid bone, and providing adequate bulk to obliterate the created submental dead space. In addition, the surgical approach to the resection also must be taken into account. For example, for individuals undergoing a lingual release to allow for their resection, the detached musculature of the anterior floor of the mouth may need to be resuspended to the mandible to minimize posterior tongue displacement and to optimize postoperative function.
18.2.2 Donor Site Evaluation
Of all of the potential reconstructive approaches for lesions limited to the floor of the mouth, only the radial forearm free flap (RFFF) requires special preoperative evaluation. In such instances, typically the nondominant arm is assessed utilizing the modified Allen’s test. 1 Using this approach, both the radial and ulnar arteries are occluded with digital pressure and the hand is pumped multiple times to remove blood from the hand and fingers. The ulnar pressure is then released and the hand is assessed for refill of blood to the thumb and index finger over the next 15 seconds. Inadequate filling signifies an incomplete palmar arch circulation and is termed a “positive Allen test.” In such individuals, an alternative donor site should be found. For equivocal or delayed filling, the palmar arch can be formally assessed with Doppler testing 2 , 3 or pulse oximetry 4 to further assess the safety of graft harvest.
When considering patients for an anterolateral thigh (ALT) flap, outside of inquiring about prior hip surgery or vascular surgery of the lower extremity, the other primary consideration is the patient’s body habitus and fat distribution. For floor of mouth repair, it is ideal to have minimal subcutaneous fat to allow for a more supple flap and less restriction of motion of the adjacent tongue.
18.3 Anatomic Considerations/Relevant Anatomy
Anatomically, the floor of the mouth extends from the lingual surface of the fixed gingiva of the mandible to the ventral surface of the tongue, with its posterior extent defined by the glossotonsillar fold (▶ Fig. 17.6).
Its inferior support is made up of a complex muscular sling including the mylohyoid muscle as well as additional contributions from the genioglossus, geniohyoid, and hyoglossus muscles. Lying deep to the mucosa and on top of the muscular floor are the sublingual glands, a network of veins, and the lingual nerves, as well as the paired submandibular ducts, which terminate near the midline at their respective papillae. Just beneath these structures course the terminal branches of the hypoglossal nerve providing motor function to the tongue musculature.
The mucosal surface of the floor of the mouth is redundant, creating a gravity-dependent sulcus that serves as a reservoir for food and liquid and also helps provide laxity and freedom to allow the tongue to move independently from the adjacent, more rigid mandible. Such tongue mobility is critical during mastication for food manipulation (▶ Fig. 18.1). It also allows for optimal bolus formation and transit to the oropharynx early during deglutition as the tongue moves toward the hard palate. With regard to speech, adequate tongue mobility is necessary to allow for articulation and clear pronunciation. More specifically, consonant sounds such as “K” and “T” can be particularly challenging in the absence of full tongue-tip mobility.
18.4 Surgical Considerations and Approaches
18.4.1 Management of the Sublingual and Submandibular Glands
The floor of the mouth, as previously discussed, contains the paired sublingual glands that empty either into the adjacent submandibular duct or through a network of smaller ducts directly to the surface above. In instances of floor of mouth resection, when possible, care should be made to minimize burying of sublingual salivary tissue in an attempt to avoid ranula formation. This may require removal of portions of the gland that have been unroofed.
Management of the submandibular ducts, when the associated gland has not been removed, requires reimplantation of the ducts by way of a sialodochoplasty. To accomplish this, the duct is ideally cannulated with a lacrimal probe to identify its tract. Once the mucosal resection is completed, the duct can be marsupialized with fine scissors or a scalpel. An initial absorbable anchoring suture is placed through the apex of the superficial aspect of the proximal portion of the duct to the adjacent mucosal edge, with additional sutures being placed to tack the other portions of the wall open to maximize patency. If needed, an angiocatheter can be placed for 1 to 2 weeks as a stent. ▶ Fig. 18.2 demonstrates a well-healed result of a bilateral submandibular duct sialodochoplasty following resection of an anterior floor of mouth carcinoma in situ.
18.4.2 Goals of Reconstruction and Development of a Reconstructive Algorithm
The primary goals of floor of mouth repair include the following:
Create a watertight closure of the floor of the mouth.
Replace missing mucosal areas with an epithelial-lined surface to allow for redundancy.
Provide adequate bulk and support for the adjacent tongue musculature.
To accomplish these goals, methods can range from simple to complex. Very limited surface defects with no communication with the neck can be closed primarily or left open to heal by secondary intention. For more significant resections, options include split-thickness skin grafts, local tissue rearrangement, regional rotational flaps, and free tissue transfer. For all graft inset and intraoral closure, absorbable sutures are typically employed using 3-0 vicryl sutures in either a simple or a horizontal mattress fashion. In situations where there is adequate cuff of mobile floor of mouth mucosa to allow for repair, the fixed gingiva on the lingual surface of the mandible can be resected to allow for circumdental sutures (dentulous patients) or repair to the fixed gingiva on the top of the alveolar ridge. This allows for more robust tissue to support the stitch and also prevents the suture line from being in the gravity-dependent sulcus of the floor of the mouth.
18.4.3 Reconstructive Techniques
Local Tissue Closure
In instances where there is limited mucosal loss and no communication with the adjacent neck dissection wound, the defect can be closed primarily or left to heal using secondary intention. In such circumstances, it is critical to ensure that there is adequate mobile mucosa still remaining in this portion of the floor of the mouth and also that the defect does not significantly extend onto the lateral tongue in order to minimize tethering and associated oral dysphagia and dysarthria. This is especially important in dentulous patients as the resulting tongue deviation on protrusion will often result in significant trauma to the adjacent mucosal surface.
Skin Graft Closure
For larger mucosal defects that lack significant bone exposure or communication with the neck wound, a split-thickness skin graft can be employed. The purpose of the graft is to create an epithelial surface to minimize associated contracture and limitations in tongue mobility. In these instances, the graft is typically harvested as a split-thickness autograft from the thigh using a dermatome with the depth of harvest being between 0.015 and 0.0175 inches. The graft is then conservatively pie crusted to avoid fluid accumulating deep to the graft and interfering with the initial imbibition phase of healing. In all instances, it is critical to harvest a graft of adequate size to allow for significant redundancy. Once secured in place with absorbable sutures, a bolster should be secured to apply pressure to the graft, keeping it flush with the underlying muscular wound bed. The bolster can then be removed in the office on postoperative day 7. When needed, a sialodochoplasty can also be performed, placing the duct at the periphery of the graft or through a hole created within it. ▶ Fig. 18.3 shows a floor of mouth defect that was repaired with a split-thickness skin graft.
Regional Flap Closure
Locoregional flaps (LrFs) have regained popularity for closure of head and neck defects. There are multiple options for LrFs, each with their own benefits and disadvantages. LrFs are often touted as an equivalent replacement for a free flap. However, although LrFs offer the ability to close large defects with robust, vascularized tissue, without the need for microvascular expertise, they still suffer from a few shortcomings and lack the adaptability that is offered by free flaps. Specifically, they can be limited by the length and degree of rotation of their vascular pedicle and may be affected by defect size and location. The benefits of LrF over free flaps include quicker harvest, less operative time, 5 – 7 shorter hospital stay, and decreased health care costs. 8
Submental Island Flap
The submental island flap is a commonly used regional flap for reconstruction of the oral cavity. Its vascular supply is the submental artery that branches off the facial artery. The skin can easily be rotated into the oral cavity to fill defects. 9 One of the main critiques of the submental island flap for reconstruction after oral cavity cancer is risk of leaving pathological nodal disease in level I of the neck. However, if level I is shown to be clinically negative for disease, the submental island flap can still be used and the harvest of the flap allows for an appropriate level Ia and Ib neck dissection without compromising the flap pedicle. 10 A retrospective study by Howard et al showed that patients undergoing a submental island flap after oral cancer resection did not have an increased risk of locoregional recurrence. 11
The submental island flap can provide a large skin paddle of up to 11 × 11 cm 9 and the pedicle length is 5 cm, but it can be longer if the facial artery and vein are ligated distal to the takeoff of the submental vessels. 12 The boundaries of the skin that can be harvested include the lower border of the mandible to the hyoid and from angle to angle of the mandible. Although variations in harvest technique are described, the general steps are as follows: 9 , 11 , 12
The skin paddle is designed to fit the necessary defect.
The skin incision through the inferior edge of flap is performed and subplatysmal flaps are elevated.
The marginal mandibular nerve is found and preserved.
The facial artery is found as it traces over the mandible and then the submental arteries are identified branching off the facial and are traced to the anterior belly of the digastric.
The level I neck dissection can be completed, preserving the facial and submental vessels.
The anterior flap incision can be made and the mandibular attachment of the anterior belly of the digastric can be divided to help protect the pedicle. The depth of the flap dissection is to the mylohyoid muscle with branches of the submental artery supplying the mylohyoid needing to be ligated.
Once the flap is elevated, if necessary, any remaining nodal contents can be cleared carefully from the adjacent pedicle before being rotated into oral cavity for inset.
The donor site can be closed primarily.