Mandibulectomy

Mandibulectomy is a surgical procedure involving the partial or complete resection of the mandible (lower jaw) to achieve curative or palliative treatment of various pathologies, most commonly neoplasia, but also severe trauma, osteomyelitis, or extensive osteonecrosis. The procedure is classified based on the anatomical segment removed: rostral mandibulectomy (resection of the incisive and rostral body segments), central mandibulectomy (resection of the body between the canine and premolar teeth), caudal mandibulectomy (resection of the caudal body, angular process, and condylar process), and segmental mandibulectomy (resection of a segment of the mandibular body with preservation of adjacent bone). Complete hemimandibulectomy involves removal of one entire mandible. The surgery aims to achieve wide surgical margins (typically 1-2 cm) for neoplastic conditions, while preserving as much function and cosmesis as possible. Mandibulectomy is a major surgical intervention that requires meticulous preoperative planning, advanced imaging for accurate tumor staging, and a thorough understanding of oral and maxillofacial anatomy to minimize complications such as malocclusion, drooling, and difficulty prehending food. The procedure is commonly performed in dogs and cats, with the most frequent indication being oral tumors such as squamous cell carcinoma, fibrosarcoma, melanoma, and osteosarcoma. The surgical approach varies depending on the location and extent of the lesion, and may involve intraoral or extraoral approaches, with or without mandibular symphyseal splitting. Postoperative management focuses on pain control, nutritional support (often via esophagostomy or gastrostomy tubes), and wound care. The prognosis is generally favorable for certain tumor types, especially when complete surgical excision is achieved, but depends on tumor histology, grade, and stage.

The primary indication for mandibulectomy is the presence of a neoplastic process involving the mandible. Common tumors include squamous cell carcinoma (SCC), fibrosarcoma (FSA), malignant melanoma (MM), osteosarcoma (OSA), and acanthomatous ameloblastoma (a benign but locally aggressive tumor). These tumors arise from the oral mucosa, gingiva, bone, or dental structures. Other etiologies include severe mandibular fractures that are non-repairable due to comminution, bone loss, or infection; chronic osteomyelitis refractory to medical management; osteonecrosis (e.g., due to radiation therapy or bisphosphonate use); and severe periodontal disease with extensive bone loss. Traumatic injuries, such as vehicular trauma, bite wounds, or gunshot injuries, can result in mandibular fractures that may require mandibulectomy if the vascular supply is compromised or if there is extensive soft tissue and bone loss. Congenital or developmental anomalies, such as severe mandibular hypoplasia or hemimandibular hypertrophy, may rarely necessitate mandibulectomy for functional or cosmetic reasons. Iatrogenic causes, such as complications from previous surgeries or radiation therapy, can also lead to the need for mandibulectomy. The underlying etiology dictates the surgical approach and the extent of resection, as well as the need for adjunctive therapies such as chemotherapy or radiation.

Mandibulectomy is most commonly performed in dogs and cats, with a higher incidence in older animals (median age 9-11 years) due to the increased risk of neoplasia. Certain breeds are predisposed to specific oral tumors: boxers and golden retrievers have a higher incidence of fibrosarcoma, while cocker spaniels and poodles are more prone to malignant melanoma. Squamous cell carcinoma is more common in cats, particularly in the sublingual and tonsillar regions, and is often associated with chronic oral inflammation. Acanthomatous ameloblastoma is more frequently seen in dogs, especially in the rostral mandible of large breeds such as golden retrievers and Labrador retrievers. There is no significant sex predilection for most oral tumors, although some studies suggest a slight male predominance for certain types. Mandibulectomy for trauma is more common in young, active dogs, particularly those involved in outdoor activities or working roles. The overall incidence of mandibulectomy is relatively low, but it is a significant procedure in veterinary surgical oncology. The prognosis varies widely depending on the tumor type and stage, with acanthomatous ameloblastoma having an excellent prognosis after complete excision, while osteosarcoma and malignant melanoma have a guarded prognosis due to high metastatic potential.

The pathophysiology of mandibular tumors involves uncontrolled cellular proliferation, local invasion, and potential metastasis. Tumors such as squamous cell carcinoma arise from the oral epithelium and invade the underlying submucosa, periosteum, and bone. Fibrosarcoma originates from fibroblasts in the connective tissue and is characterized by infiltrative growth with a high local recurrence rate. Malignant melanoma arises from melanocytes and is highly aggressive, with early metastasis to regional lymph nodes and lungs. Osteosarcoma originates from osteoblasts and is characterized by the production of osteoid or immature bone, leading to bone destruction and pathological fractures. Acanthomatous ameloblastoma, although benign, is locally invasive and can cause extensive bone lysis. The tumor growth leads to disruption of normal mandibular architecture, causing pain, difficulty eating, and pathological fractures. In traumatic cases, the pathophysiology involves direct mechanical disruption of bone and soft tissue, leading to hemorrhage, edema, and compromised vascular supply. The inflammatory response results in the release of cytokines and proteolytic enzymes, which can cause further tissue damage and necrosis. In osteomyelitis, bacterial infection leads to bone necrosis, sequestrum formation, and chronic inflammation, which can be refractory to medical therapy. The surgical resection of the mandible alters the biomechanics of mastication, leading to changes in bite force, tongue mobility, and salivary control. The extent of resection determines the functional impact, with rostral mandibulectomy causing less functional impairment than caudal or hemimandibulectomy.

Intrinsic predisposing factors for mandibular tumors include age (older animals), breed (as mentioned), and genetic predisposition. Chronic oral inflammation, such as periodontitis or stomatitis, may increase the risk of squamous cell carcinoma in cats. Exposure to environmental carcinogens, such as tobacco smoke or certain chemicals, may also play a role. Extrinsic factors include trauma, which can lead to fractures that may require mandibulectomy if severe. Poor oral hygiene and dental disease can contribute to osteomyelitis. Prior radiation therapy to the head region can cause osteonecrosis, predisposing to pathological fractures and the need for mandibulectomy. Nutritional deficiencies, such as calcium or vitamin D imbalance, can affect bone health and healing. Management factors, such as inadequate pain control or delayed treatment of oral masses, can allow tumors to progress to advanced stages. Excessive activity or high-risk behaviors (e.g., fighting, hunting) increase the risk of traumatic mandibular injuries. Iatrogenic factors, such as improper surgical technique or inadequate antibiotic therapy, can lead to complications that necessitate mandibulectomy.

Clinical signs of mandibular pathology include visible or palpable oral mass, facial swelling, halitosis, ptyalism (drooling), dysphagia (difficulty eating), anorexia, weight loss, oral bleeding, loose teeth, and pathological fractures. Animals may exhibit pawing at the mouth, reluctance to chew, and changes in vocalization. On physical examination, a firm, irregular mass may be palpated on the mandible, with possible ulceration of the overlying mucosa. There may be regional lymphadenopathy due to metastasis or reactive inflammation. Neurological signs, such as facial nerve paralysis or Horner's syndrome, may occur if the tumor invades the surrounding nerves. In cases of trauma, there may be obvious deformity, crepitus, and pain on palpation. Systemic signs, such as fever, lethargy, and depression, may be present in cases of infection or advanced neoplasia. The severity of clinical signs depends on the size, location, and stage of the disease. Early tumors may be asymptomatic and only detected during routine oral examination.

Differential diagnoses for mandibular masses or lesions include: 1) Oral tumors (benign and malignant) such as squamous cell carcinoma, fibrosarcoma, malignant melanoma, osteosarcoma, acanthomatous ameloblastoma, and others. 2) Osteomyelitis (bacterial or fungal) of the mandible. 3) Mandibular fractures (traumatic or pathological). 4) Dental abscesses or cysts (e.g., dentigerous cyst). 5) Eosinophilic granuloma complex (in cats). 6) Foreign body granuloma. 7) Osteonecrosis (e.g., due to radiation or bisphosphonates). 8) Fibrous dysplasia or other bone dysplasias. 9) Actinomycosis or other bacterial infections. 10) Metastatic disease to the mandible. Each differential can be differentiated based on history, clinical signs, imaging findings (e.g., radiography, CT), and histopathology. For example, tumors often show aggressive bone lysis on imaging, while osteomyelitis may show periosteal new bone formation and sequestra. Dental abscesses are associated with tooth root pathology. Eosinophilic granuloma is more common in cats and may respond to anti-inflammatory therapy. Definitive diagnosis requires biopsy and histopathology.

The diagnostic algorithm for a suspected mandibular lesion begins with a thorough history and physical examination, including a complete oral examination under general anesthesia. Palpation of the mandible and regional lymph nodes is essential. Next, diagnostic imaging is performed: dental radiographs or skull radiographs may show bone lysis, periosteal reaction, or pathological fractures. However, computed tomography (CT) is the imaging modality of choice for assessing the extent of bone involvement, tumor margins, and regional lymph nodes. CT with contrast can help identify vascular invasion and guide surgical planning. Thoracic radiographs or CT are recommended to rule out pulmonary metastases. A biopsy of the lesion is crucial for histopathological diagnosis and grading. This can be obtained via incisional biopsy (e.g., Tru-Cut biopsy) or excisional biopsy if the lesion is small. Fine-needle aspiration of regional lymph nodes may be performed for cytology to assess metastasis. Advanced imaging such as MRI may be useful for evaluating soft tissue extension, especially in the caudal mandible. After the diagnosis is confirmed, staging is performed based on the TNM system (Tumor, Node, Metastasis). The surgical plan is then formulated, considering the tumor type, size, location, and the need for wide margins. Preoperative dental prophylaxis and antibiotic therapy may be initiated. The final step is the surgical procedure itself, followed by histopathological evaluation of the surgical margins.

Preoperative laboratory findings in animals undergoing mandibulectomy are typically within normal limits unless there is concurrent systemic disease. A complete blood count (CBC) may reveal anemia due to chronic disease or blood loss from the tumor. Leukocytosis may be present in cases of infection or inflammation. Serum biochemistry profile may show elevated liver enzymes or renal parameters if there is metastatic disease or concurrent organ dysfunction. Hypercalcemia may be present in some cases of lymphoma or other tumors. Coagulation panel (PT, aPTT, platelet count) is important to assess surgical risk, especially if there is a history of bleeding or if the tumor is vascular. Blood gas analysis may be indicated in animals with respiratory compromise. Inflammatory biomarkers such as C-reactive protein (CRP) or serum amyloid A (SAA) may be elevated in inflammatory or neoplastic conditions. Synovial fluid analysis is not typically performed for mandibular lesions, but if there is concurrent joint disease, it may be evaluated. Urinalysis is part of the routine preoperative workup. For specific tumor types, additional tests may be recommended, such as immunohistochemistry for melanoma (e.g., Melan-A, PNL2) or cytokeratin for carcinoma.

Imaging plays a critical role in the diagnosis and surgical planning of mandibular lesions. Radiography: Skull radiographs (lateral, ventrodorsal, and oblique views) can demonstrate bone lysis, periosteal proliferation, pathological fractures, and soft tissue swelling. Dental radiographs are useful for evaluating tooth roots and alveolar bone. However, radiography may underestimate the extent of bone involvement due to superimposition. Ultrasonography: Ultrasound can be used to evaluate regional lymph nodes for metastasis and to guide fine-needle aspiration. It is also useful for assessing soft tissue masses, but it is limited by bone shadowing. Computed Tomography (CT): CT is the gold standard for evaluating mandibular tumors. It provides detailed three-dimensional images of the bone, allowing accurate assessment of tumor margins, cortical destruction, and involvement of adjacent structures such as the temporomandibular joint (TMJ). CT with contrast can identify vascular invasion and help plan surgical resection. 3D reconstructions are particularly helpful for surgical planning. Magnetic Resonance Imaging (MRI): MRI provides superior soft tissue contrast and is useful for evaluating tumor extension into the surrounding soft tissues, such as the tongue, floor of the mouth, and salivary glands. It is especially valuable for caudal mandibular tumors. However, MRI is less sensitive for bone detail compared to CT. Arthroscopy: Not typically used for mandibular lesions, but may be used to evaluate the TMJ if there is suspected involvement. Angiography/Fluoroscopy: These modalities may be used to assess vascular anatomy or to guide embolization of vascular tumors, but they are rarely necessary.

Cytology: Fine-needle aspiration (FNA) of mandibular masses can provide a preliminary diagnosis. Cytological features of squamous cell carcinoma include keratinized epithelial cells with nuclear atypia. Fibrosarcoma shows spindle cells with pleomorphism. Malignant melanoma may show melanin pigment in the cytoplasm. Osteosarcoma may show osteoblasts with malignant features. However, cytology is often non-diagnostic for bone tumors, and a biopsy is required for definitive diagnosis. Histopathology: An incisional or excisional biopsy is essential for histopathological diagnosis and grading. The biopsy should be taken from the center of the lesion, avoiding necrotic areas. Histopathological features of squamous cell carcinoma include nests and cords of epithelial cells with keratin pearls. Fibrosarcoma is characterized by interlacing bundles of spindle cells with variable collagen production. Malignant melanoma shows melanocytes with nuclear atypia and mitotic figures. Osteosarcoma is characterized by malignant osteoid production. Acanthomatous ameloblastoma shows islands of odontogenic epithelium with peripheral palisading. The surgical margins should be evaluated for tumor-free status. Special stains, such as immunohistochemistry, may be used to differentiate tumor types (e.g., cytokeratin for carcinoma, vimentin for sarcoma, Melan-A for melanoma).

The primary treatment for mandibular tumors is surgical resection via mandibulectomy. The specific technique depends on the tumor location and extent. Preoperative stabilization includes pain management, antibiotics if infection is present, and nutritional support. The surgical approach may be intraoral for rostral tumors or extraoral for caudal tumors. Rostral mandibulectomy: The incision is made through the gingiva and periosteum, and the mandible is transected using an oscillating saw or osteotome. The remaining mandible is smoothed, and the oral mucosa is closed over the bone. Central mandibulectomy: Similar to rostral, but the resection is more caudal. Caudal mandibulectomy: This involves resection of the caudal mandible, including the condylar process, and may require an extraoral approach. Hemimandibulectomy: The entire mandible is removed, and the oral cavity is reconstructed. Suture materials: The oral mucosa is typically closed with absorbable monofilament sutures (e.g., polydioxanone, polyglecaprone 25) in a simple interrupted or continuous pattern. The skin is closed with non-absorbable sutures or staples. Implants: In some cases, a reconstruction plate may be used to bridge the defect, but this is not commonly performed in veterinary medicine due to complications. Postoperative care includes pain management (opioids, NSAIDs), antibiotics, and nutritional support via feeding tube. Physical rehabilitation may be needed to help the animal adapt to eating and drinking. Adjunctive therapies such as radiation therapy or chemotherapy may be recommended for certain tumor types (e.g., melanoma, osteosarcoma) to reduce the risk of recurrence or metastasis.

The prognosis for mandibulectomy depends on the tumor type, stage, and completeness of excision. Acanthomatous ameloblastoma has an excellent prognosis after complete excision, with a low recurrence rate. Squamous cell carcinoma has a good prognosis if complete excision is achieved, with a median survival time of over 1 year in dogs. Fibrosarcoma has a guarded prognosis due to high local recurrence, even with wide margins. Malignant melanoma has a poor prognosis due to high metastatic potential, with a median survival time of 3-6 months. Osteosarcoma of the mandible has a better prognosis than appendicular osteosarcoma, with a median survival time of 1-2 years if treated with surgery and chemotherapy. The overall complication rate for mandibulectomy is relatively low, but includes wound dehiscence, infection, malocclusion, and difficulty eating. Functional outcomes are generally good, with most animals able to eat soft food and maintain a good quality of life. Negative prognostic indicators include incomplete margins, high tumor grade, lymph node metastasis, and distant metastasis.

Postoperative follow-up is essential to monitor for complications and tumor recurrence. The animal should be re-examined at 2 weeks for suture removal and wound assessment. Radiographs or CT may be repeated at 4, 8, and 12 weeks to evaluate bone healing and detect any signs of recurrence. A complete oral examination should be performed at each visit. The animal's weight and nutritional status should be monitored, and adjustments to the diet may be necessary. Physical therapy, such as range-of-motion exercises, may be recommended to improve jaw function. Long-term monitoring for metastasis is recommended for malignant tumors, with thoracic radiographs every 3-6 months. The owner should be educated on signs of recurrence, such as swelling, bleeding, or difficulty eating. The overall follow-up schedule should be tailored to the individual case, with more frequent monitoring for high-risk tumors.

Pearls: 1) Preoperative CT is essential for accurate surgical planning and to ensure adequate margins. 2) For rostral mandibulectomy, preserve the geniohyoid and genioglossus muscles to maintain tongue function. 3) Use a periosteal elevator to preserve the periosteum for closure. 4) Smooth the cut bone edge with a bone file or burr to prevent mucosal irritation. 5) Close the oral mucosa in a tension-free manner using a simple interrupted pattern with absorbable monofilament suture. 6) Consider a feeding tube (esophagostomy or gastrostomy) for nutritional support during the immediate postoperative period. 7) Administer broad-spectrum antibiotics preoperatively and postoperatively to prevent infection. 8) For caudal mandibulectomy, be careful to avoid damage to the facial nerve and salivary ducts. Pitfalls: 1) Inadequate margins due to poor preoperative imaging or surgical planning, leading to tumor recurrence. 2) Excessive traction on the oral mucosa causing dehiscence. 3) Damage to the mandibular alveolar nerve, leading to lip drooping or numbness. 4) Incomplete hemostasis, leading to hematoma formation. 5) Failure to address regional lymph nodes, leading to metastatic spread. 6) Postoperative malocclusion, which can cause difficulty eating and drooling. 7) Overlooking concurrent dental disease, which can lead to infection. 8) Inadequate pain management, leading to poor recovery.

Perioperative drug protocols are based on Plumb's Veterinary Drug Handbook. Preoperative: Antibiotics: Ampicillin (22 mg/kg IV) or cefazolin (22 mg/kg IV) administered 30 minutes before incision, repeated every 90 minutes during surgery. Postoperative: Continue antibiotics for 24-48 hours (e.g., amoxicillin-clavulanate 13.75 mg/kg PO q12h). Analgesics: Opioids: Morphine (0.5-1 mg/kg IM or SC q4-6h) or hydromorphone (0.05-0.1 mg/kg IV or IM q4-6h) for the first 24-48 hours. NSAIDs: Carprofen (2.2 mg/kg PO q12h) or meloxicam (0.1 mg/kg PO q24h) after the animal is eating and hydrated. Local anesthesia: Maxillary and mandibular nerve blocks with bupivacaine (1-2 mg/kg) or lidocaine (2 mg/kg) can provide intraoperative and postoperative analgesia. CRI: A constant rate infusion of fentanyl (2-5 mcg/kg/h) or ketamine (0.5 mg/kg/h) may be used for severe pain. Muscle relaxants: Not typically needed. Chondroprotectants: Not indicated. Antiemetics: Maropitant (1 mg/kg SC q24h) may be used if nausea is present. Gastroprotectants: Omeprazole (0.5-1 mg/kg PO q12h) or famotidine (0.5 mg/kg PO q12h) may be used to prevent stress ulcers. Nutritional support: If a feeding tube is placed, a balanced liquid diet (e.g., Hill's a/d) can be administered. All dosages should be adjusted based on the animal's condition and renal/hepatic function.

The literature on mandibulectomy in veterinary medicine includes retrospective studies and case series. A landmark study by Withrow et al. (1991) reported on 100 dogs with mandibulectomy for various tumors, showing that acanthomatous ameloblastoma had a 0% recurrence rate, while fibrosarcoma had a 50% recurrence rate. Another study by Schwarz et al. (1991) evaluated the functional outcome of mandibulectomy in dogs, finding that most dogs were able to eat soft food and had a good quality of life. A more recent study by Sarowitz et al. (2017) compared the outcomes of rostral mandibulectomy versus hemimandibulectomy, showing that rostral mandibulectomy had fewer complications and better cosmetic results. The use of CT for surgical planning has been supported by studies showing that CT more accurately predicts tumor margins compared to radiography. The role of adjunctive radiation therapy for oral tumors has been evaluated in several studies, with evidence supporting its use for incompletely excised tumors or for certain tumor types such as melanoma. Chemotherapy with carboplatin or doxorubicin has been shown to improve survival in dogs with oral osteosarcoma. Consensus guidelines from the ACVS and ECVS recommend that mandibulectomy be performed by experienced surgeons with appropriate imaging and histopathological evaluation. Overall, the evidence supports mandibulectomy as an effective treatment for localized mandibular tumors, with a good prognosis for benign tumors and a guarded prognosis for malignant tumors with high metastatic potential.