Mandibulectomy

Mandibulectomy is a procedure that is used to eradicate disease that involves the lower jaw or mandible. This procedure can be used in various settings, including infectious etiologies (eg, osteomyelitis), osteoradionecrosis, or a benign (eg, ameloblastoma) or malignant neoplastic process (eg, invasive squamous cell carcinoma) that involves the jaw. In cases of severe oral and maxillofacial trauma, if a section of the mandible is not salvageable, mandibulectomy may be an appropriate treatment.

In the last several years, the incidence of bisphosphonate-related necrosis of the mandible has increased, leading to the need for mandibulectomy to remove the affected section of mandible.[1]

It is important to differentiate the different types of mandibulectomy. Depending on the thickness of the native mandible and the specific disease process, the mandibulectomy can either be full thickness (segmental), in which both cortices in addition to the upper and lower surfaces of the mandible are removed en bloc, or partial thickness, in which either the inner or outer cortex of the mandible is spared in order to maintain some mandibular continuity (see image below).

Regardless of the degree of bone resection, it must allow the surgeon to encompass the involved disease process. Considerations for full thickness versus partial thickness mandibulectomy are discussed below.

Mandibulectomy is indicated in the following conditions:

• Malignant tumor invading the mandible, either a primary alveolar ridge tumor or from an adjacent site such as the floor of mouth

• Involvement of the mandible with a benign tumor of the jaw that has destroyed much of the mandibular integrity such that removal of the tumor would leave mandible so unstable as to lead to pathological fracture; in such cases, a full-thickness segmental mandibulectomy is most likely the best option

• Significant osteonecrosis related to bisphosphonate use that has led to significant mandibular deterioration

• Significant osteomyelitis that involves a significant portion of the mandible

• Osteoradionecrosis of the jaw following head and neck radiotherapy

• Severe mandibular trauma, either blunt or penetrating, that has devitalized a significant portion of mandibular bone and whose debridement will leave a full-thickness segmental defect in the mandible or an unstable framework

The most common contraindications to mandibulectomy are related to medical comorbidities. Cardiovascular hemodynamic instability or other metabolic comorbidities may prohibit the ability to get a patient to the operating room and to perform the procedure. In addition, an uncorrectable coagulopathy in a patient of already significant hemodynamic compromise would be a contraindication.

If the mandibulectomy is being performed to extirpate a malignant tumor, it should be undertaken only if the operating surgeon is relatively sure that the resection will be complete and that no residual gross (and hopefully microscopic) disease is left behind.

As noted above, either a full-thickness segmental mandibulectomy, which will result in a through-and-through bony defect of the jaw, or a less than full-thickness resection can be performed.[2] Several issues influence the degree of resection. In the management of malignant disease, the degree of mandibular invasion determines the extent of resection performed (see image below).

If the malignant process is suspected to have invaded through the outer cortex of the mandible, the lingual surface on the floor of mouth side or labially on the cheek side, it is essential that the mandible be resected as a full-thickness segmental mandibulectomy (see image below).

Once the outer cortex has been breached by the cancer and the medullary cavity has been accessed, full clearance of the tumor cannot be ensured with partial-thickness mandibulectomy. In addition, once the tumor has access to the central portion of the mandible, perineural invasion following the inferior alveolar nerve is a risk.[3] In this case, the tumor may track far beyond any radiographic or gross evidence of disease. Often, invasion of the bone is difficult to confirm. MRI is useful to show a change in the characteristics of the marrow cavity once the cancer has invaded the medullary cavity, but this is usually very late finding. A fine-cut/high-resolution CT scan using bone algorithm may be helpful to show erosion of the cortex of the mandible. Usually, this decision is made clinically (see image below).

If the tumor approaches the mandible from either the labial or the lingual surface yet appears to be mobile against the surface of the mandible, it is usually safe to assume that a subperiosteal resection or an inner table or outer cortex table resection will adequately encompass the tumor, as, under these conditions, it appears that the tumor has not invaded the mandible.[4] If the tumor appears mobile against the mandibular cortex, although it may be close, a subperiosteal dissection can be performed. If the tumor appears to be immobile against the outer cortex of the mandible despite all radiographic indications showing that the tumor has not invaded to the mandible, an inner-table mandibulectomy can be performed with hope that the tumor has been completely cleared.

There are a few situations in which inner-table mandibulectomy is not possible or is ill-advised. In a patient who has undergone previous high-dose (>50 Gy) radiotherapy for cure of a previously diagnosed head and neck cancer, inner-table mandibulectomy tends to result in osteoradionecrosis and pathological fracture of the residual mandible. In this setting, it is best to proceed with full-thickness segmental mandibulectomy and to perform mandibular reconstruction.

Partial-thickness mandibulectomy may also be difficult to perform in the case of an edentulous mandible. Once the patient has undergone full mouth extraction, the height and stock of the mandibular bone tends to decrease. In this case, it may be impossible to perform a partial-thickness mandibular resection and to leave enough viable bone to prevent a subsequent pathological fracture (see image below).

A successful mandibulectomy outcome is complete clearance of the involved disease process. In cases of malignant disease, this is complete resection of the malignant process.

Long-term follow-up is dictated by both the individual disease and patient risk factors. The primary goal of mandible reconstruction is that the reconstructed mandible maintains a degree of functionality, in addition to an acceptable cosmetic outcome. Of utmost importance is that the patient continue follow-up to monitor for wound breakdown, osteomyelitis, osteoradionecrosis, and tumor recurrence.

For optimal oncologic follow-up, physical examination is combined with an imaging modality such as CT scanning or positron-emission tomography (PET) scanning.

Management of patient expectations is important in any medical or surgical undertaking. This holds also true for patients undergoing mandibulectomy.

The potential sequela and postoperative symptoms vary by mandibular resection approach. Patients who undergo full-thickness segmental mandibulectomy will have permanent anesthesia of the affected lower lip postoperatively owing to the position of the inferior alveolar nerve in the core of the medullary cavity of the mandible. Some surgeons have attempted to reconstruct this with a segmental nerve graft using a donor nerve (eg, sural nerve or lateral femoral cutaneous nerve), with variable success.[5] In addition, in the setting of benign disease, some surgeons have attempted to mobilize the nerve out of the bone and to preserve it during mandibulectomy and reconstruction.[6]

The patient must be aware that, in all likelihood, the sensory defect will be long term. The author usually explains to mandibulectomy candidates that this sensation is similar to what they would experience after they have been to the dentist and local anesthetic has been infiltrated into the mandible. A temporary numbness of the lower lip is common when one leaves the dentist. This is an example nearly everyone can understand.

The patients need to be informed that, depending on the approach and the degree of reconstruction, the contour of the lower third to the face may be altered. In almost every situation today, some type of mandibular reconstruction is attempted, even in the patients with modest comorbidities.

In most cases of malignant disease, mandibulectomy is only one component of a more significant operative procedure. In many cases, as part of the oncologic resection, other surrounding tissue (eg, the floor of mouth, tongue, overlying facial skin, innervation to the lower lip) must be removed to obtain clear oncologic margins. Removal of these subsites has individual functional and cosmetic consequences. When the defect has been mapped out preoperatively, the surgeon should be able to anticipate the probable functional implications of the procedure. These need to be carefully explained to the patient and their family members so that appropriate expectations are established preoperatively. Most patients who undergo mandibulectomy will also undergo some form of neck dissection.

Typically, incisions need to be made on the lower face, particularly in the area of the chin and submandibular areas. Families need to be aware of this.

Airway management is a key component of the treatment of mandibular processes that will require mandibulectomy. Some patients may require tracheotomy, which is detailed below. Others may require nasotracheal tube intubation and overnight ventilatory support. The patients need to be adequately prepared for this possibility.

Preprocedure planning consists of several key elements. In the setting of mandibulectomy, the most important determination is how the airway will be managed.

Patients with limited disease that may involve only the mandible and does not extend into the adjacent floor of mouth who have an airway that can be easily visualized and managed by the anesthesia staff may undergo mandibulectomy with nasotracheal intubation and not require a temporary tracheotomy. This includes some patients who undergo immediate mandibular reconstruction with free-tissue transfers. These patients can usually be treated overnight with a nasotracheal tube in the ICU, with extubation the following day. In patients who will undergo significant floor-of-mouth resection with tongue and perhaps other adjacent areas in the oral cavity and oropharynx, tracheotomy is best advised and is the safest methodology to manage the airway.

Among patients who have large mandibular tumors that have destroyed the outer cortex of the mandible, thereby making it unusable as a template on which to bend a preresection bony mandibular internal fixation plate, a prebent plate using a computer generated model of the affected mandible may need to be obtained. In this setting, a plastic model is created that can then be used as a base onto which to create a template for the mandibular plate postresection. Typically, such models have an internal fixation system that allows stabilization of the fragments once the affected portion of the mandibular model is resected. These models are made to exact scale of the patient so the reconstruction bar can be bent to the perfect contour on the patient’s mandibular model and the plate can be sterilized and ready to use in the patient postresection (see image below).

This requires a few weeks of preoperative planning, with time allowing for the turnaround of the model in preform plates.[7]

Mandibulectomy entails an adequate mandibular reconstruction plating system, a sagittal or reciprocating saw, and a standard head and neck tray.

Anesthesia

Mandibulectomy is performed under general endotracheal anesthesia. The endotracheal tube must be positioned so as not to obstruct access to the anatomical components. Thus, in patients with a lesion limited to the mandible without adjacent floor-of-mouth or tongue involvement, who will not require tracheotomy, the endotracheal tube can be placed nasotracheally in nearly all cases. If the lesion is well lateralized, the tube can be placed transorally and secured to the contralateral side of the oral cavity, but only in patients who will not require intermaxillary mandibular fixation, which could be used to help maintain perfect occlusion throughout the course of the resection and postoperatively. in patients who require a large transoral resection with adjacent soft tissue, tracheotomy is appropriate.

Positioning

Generally, the authors position the patient supine and rotated 180° away from anesthesia so that the patient’s feet are adjacent to the anesthesiologist. This requires long ventilator tubing and allows the surgeon to take command of 280° of the patient’s operative field around the head and neck and potential free-flap donor sites. The patient’s head should be placed in a “donut” and a shoulder roll placed under the shoulders in a moderate degree of extension.

During mandibular resection and reconstruction, the patients are under general anesthetic and standard anesthetic monitoring. Special exceptions for free-flap cases include the necessity for an arterial line. In addition, the surgical team must communicate with the anesthesia team about location of line placement and judicious use of vasopressors, which negatively affect free-flap survival.

After the surgery and reconstruction is complete, if a free flap was used, a Doppler signal is detected and a single suture placed to ensure that both the medical and nursing team can properly assess the free-flap viability. In most cases, the patients are then transferred to the ICU, where they under frequent free-flap checks (Doppler, capillary refill, color, turgor). Once the patient is deemed stable and the free flap shows consistent viability, the patient is often transferred to a regular surgical ward until discharge.

The short-term follow-up regimen is surgeon-specific, but most patients are seen between 7 and 14 days after discharge for suture removal and dressing changes. Afterward, consistent follow-up plans are made every 1-2 months for the first year, mostly for oncologic surveillance and functional status inquiry.

Mandibulectomy can be performed transcervically, requiring face and neck incisions that allow external exposure to the mandible, or it may be performed transorally, in which all incisions are placed intraorally. In general, the disease process drives the approach taken.

For a benign process that involves the mandible and for small-to-moderate malignant processes, it is possible to perform the resection completely transorally in some patients.

For transoral approaches, particularly in benign disease, the mucosal incisions are made very close to the teeth that are to be resected or very close to the alveolar ridge in the patients who are edentulous. Incisions can be made farther than the limits of the bone resection to allow improved exposure and to place preresection and postresection mandibular plating devices. In patients with a benign process, once the mucosal incisions are made, both medial and lateral to the mandible and across the alveolar ridge at the point of resection, a periosteal dissector can be used to elevate the soft tissues off of the mandible. Once the mandible is completely exposed transorally, the appropriate plate can be placed preresection.

In patients with extensive malignant disease that will require wide resection, a transcervical approach with lip splitting or visor flap incisions are most appropriate. Key to the ability to render the patient disease free of oral cavity carcinoma is complete extirpation of the tumor with histologically clear margins. The authors expect a minimum of 5 mm on permanent fixed section to truly call a margin clear. Bony resection margins must also be histologically clear, and at least a 1-cm gross margin should be taken at the time of tumor resection.

As noted above, a reconstruction plate should be placed, if at all possible, prior to any full-thickness resection of the mandible. In patients with an intact lateral mandibular cortex, the lateral surface of the mandible may be used as the template on which to bend a conforming mandibular reconstruction plate.

Typically, the soft metal template that comes with the plating system is used to obtain the general shape and form of the lateral mandibular cortex; the actual fixation plate is then bent based on the dimensions of the soft metal template. Once the gross changes are made in the mandibular plate, it is fine-tuned by applying the plate directly against the lateral border of the mandible. Knowledge of the anticipated osteotomy sites is helpful, since it is generally desirable to have 3 screws present on either side of the mandibulectomy (see image below).

This requires that 3 solid hole purchases are placed into the native mandible. In patients in whom a preoperative computer-generated prebent plate has been made, it will be placed after the mandibulectomy is performed.

Prebent plates are now available from some vendors that are said to conform to the vast majority of human mandibles and may require only minimal contouring (see image below).[7]

In patients with a tumor that has “blown out” the lateral cortex of the mandible, the authors often use an external fixation device. By fixing the mandible on either side of the proposed resection site to the external fixation device, proper occlusion can be maintained by maintaining the proper alignments across the defect of one mandibular remnant to the other.[8] The external fixation set can be used to allow maintenance of the proper mandibular segment relationship, even when a computer-generated mandibular reconstruction plate is available, as this allows, during all portions of the resection, for mandibular segments to be in proper alignment with one another. In addition, an external fixator device allows the mandibular condyles to be in proper position in the glenoid fossa (temporomandibular joint) during the reconstruction (see image below).

Soft-tissue exposure is important for allowing excellent visualization of resection of the benign tumor or a malignant process. Gross 1-cm margins are desirable both on soft tissue and bone. Therefore, the resection is performed with a 1-cm minimum margin of what is believed to be healthy mandible on either side of the tumor. The cuts are either made with a sagittal or reciprocating saw, depending on the surgeon’s preference. Once the inferior alveolar neurovascular pedicle is divided, this will need to be addressed with cautery.

It is common practice to shape and place a reconstructive plate onto the native mandible before the mandible is resected. In doing this, the surgeon must drill holes in the native mandible and place screws to secure the plate to the underlying bone. Just prior to resection, any plates and screws that had been placed preresection are removed. The advantage of drilling the holes preresection is that, when the plates are reapplied postresection, the holes that have been previously drilled and the mandibular segments are maintained at proper alignment with one another, thereby sparing the occlusion.

In patients undergoing less than full-thickness segmental mandibulectomy, the inner table alone can be resected. In general, teeth in patients who are undergoing inner-table mandibulectomy may need to be extracted, and the sagittal saw can then be used to take the inner cortex of the mandible. The fresh dental-extraction socket generally makes an excellent parasagittal plane on which to place the saw and to resect the medial half of the mandible, leaving the lateral half of the marrow cavity and the lateral cortex intact.

Reconstruction of the mandible is beyond the scope of this discussion.

In some cases, nothing more than a reconstruction bar is used for rigid reconstruction of the mandible. In these cases, the mucosal edges of the resection can be closed onto themselves. Generally, it is best to close the lateral buccal mucosal margin to the medial lingual mucosal margin using absorbable 3-0 Vicryl sutures.

Postoperatively, patients are kept NPO for a variable period to allow the intraoral suture line to close before stressing it with chewing and movement, as well as bolus in the oral cavity. Among patients who have undergone a mandible reconstruction using a free-tissue transfer, 7-10 days should generally elapse before an oral intake diet is begun. The same will hold true for patients closed primarily.

One of the dangers of closing the mucosa primarily over a reconstruction bar is that a dead space is created that is nonvascularized, which will lead to mucosal breakdown and plate extrusion.