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.