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MANDIBULECTOMY AND MAXILLECTOMY
Overview
Mandibulectomy and Maxillectomy are surgical procedures where part of the lower jaw (the mandible) or the upper jaw (the maxilla) is removed. The most common reason for this operation in veterinary surgery is removal of oral cancer (tumors). Most oral tumors affect the underlying bone. The jaw bone must therefore be removed to provide margins free of cancerous cells.
In some animals without oral cancer, the surgeon may decide on mandibulectomy or maxillectomy to remove severely traumatized bone, which has lost the ability to heal and is causing pain to the pet. Severely infected jaw bone not responsive to antibiotic therapy may need to be removed. Oronasal fistula, a defect in the hard palate, resulting in communication between the mouth and nasal cavity may be another indication for maxillectomy in severe case.
Pathology
Oral cancer accounts for about 6% of all canine tumors and is the fourth most common cancer overall. In the cat, oral cancer represents 3% of all cancers. Cancer in the mouth can be malignant or benign. The four most common canine oral cancers are malignant melanoma, squamous cell carcinoma, fibrosarcoma and acanthomatous epulis. In the cat, the most common cancer in the mouth is squamous cell carcinoma, followed by fibrosarcoma. Each kind of cancer differs in its behavior and so the treatment options vary from cancer to cancer. It is up to the surgeon and his or her experience to decide on the most appropriate procedure and the extent of surgery.
Malignant melanoma (Figure 1)is most commonly located on the gum or gingiva and has a strong tendency to spread (or metastasize) to regional lymph nodes and then to the lung (80% of cases). Some breeds with dark mouths (pigmented oral mucosa) may be predisposed to this cancer. Melanoma affects older dogs (average age 9-11 years) and males are more commonly affected then females. Approximately 25% of dogs with malignant melanoma will survive 1 year or more with treatment. Dogs with small tumors (less than 2cm in diameter), have a better chance of survival with half the dogs surviving about 18 months or more. Dogs with cancerous tumors greater than 2 cm in diameter and that spread to the lymph nodes have a very poor chance of survival and often succumb to their disease within 5 months.
Figure 1. Malignant Melanoma on the gum.
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Fibrosarcoma (Figure 2) often also originates on the gum or palate. This cancer is very locally invasive but cancer spread to lungs is less likely compared to oral melanoma. Because of the invasive nature of this type of cancer, local control is a problem. The recurrence after surgery can be as high as 46%. The one year survival with treatment is about 50%with early wide resection offering the most optimistic prognosis. Unfortunately, these tumors are difficult to detect until they become large because they frequently occur at the back of the mouth.
Figure 2. Fibrosarcoma on the gum.
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Squamous cell carcinoma (SCC) (Figure 3) is the most common oral cancer in the cat and the third most common in the dog. This cancer readily invades the bone extensively. The location of the mass in the mouth predicts the prognosis. SCC of the tongue and tonsils carries a very poor prognosis, mainly because of cancer tendency to spread to regional nodes and lungs as well as a high rate of local recurrence after treatment. However, SCC of the front part (rostal) of the mouth in dogs can be curable with surgery or irradiation. In cats, oral SCC is nearly always bad with one year survival rates rarely exceeding 10%.
Figure 3. Sqaumous Cell Carcinoma in the dog.
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Signs and Symptoms
Most pets with oral cancer are presented to their veterinary surgeons for a mass in the mouth or swelling of the face noticed by the owner (Figure 4). However, veterinary advice should be sought for other signs, such as excessive salivation, difficulty chewing or swallowing, halitosis (very bad breath) or bloody oral or nasal discharge. Loose teeth can result from loss of bone caused by cancer, so it is important you ask your veterinarian to check out these problems early because many cancers can be cured if they are treated in the early stages.
Figure 4. Swelling of the face in the dog.
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Exam, Screening Tests and Imaging
If oral cancer is suspected, your veterinarian will undertake certain diagnostic procedures to assess the type of cancer and its extent. This is what oncologists call staging of the tumor. Staging will give the surgeon the necessary information to choose the best treatment and also allows the veterinarian to advise the owner of the prognosis.
Staging will involve obtaining a biopsy (a sample of tissue from the tumor) and this is usually done under general anesthetic. Other procedures for staging include fine needle aspirates or biopsy of the regional lymph nodes and chest X-rays to detect regional and distant metastasis (Figure 5). X-rays of the jaw will be taken before surgery to help in planning the operation (Figure 6). Sometimes three dimensional studies such as computed tomography (CT scan) (Figure 7) are done to help the surgeon to place the incision in the right position so the entire cancer is removed.
Figure 5. Chest X-ray of Metastasis.
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Figure 6. X-ray of the jaw.
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Figure 7. CT image of maxilla.
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Treatment Options
Surgery, cryosurgery (freezing) and irradiation are the most useful therapies for dealing with oral cancer. Surgical excision is the most commonly used treatment modality. The surgeon must remove the entire tumor with a margin of healthy normal tissue to ensure no cancer is left behind. This often means some of the jaw must be removed. These surgeries, known as mandibulectomy and maxillectomy, surprisingly cause little ill effects. Dogs usually return to eating within a day or two of the surgery and we have found the owner's satisfaction with the functional and cosmetic results is higher than 85%. (Figures 8.1 and 8.2).
Figure 8.1. Dog after Rostral Mandibulectomy.
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Figure 8.2. Dog after Caudal Maxillectomy.
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Surgery
Food is generally withheld for 12 hours prior to surgery. A general anesthetic will be given that best suits your pet's health status and certain laboratory tests may be performed prior to the anesthetic to ensure the best drugs and techniques are used. Pain prevention is important so various drugs and local anaesthetic techniques will likely be used before, during and after surgery to ensure comfortable recovery.
The extent of the bone removed depends on the staging and location of the tumor. The operation to remove the lower incisors, lower canines and first two premolar teeth on one side is called Rostral Mandibulectomy (Figure 9). Often the tumor has crossed the midline of the mandible so both sides need to be removed. This is called a Bilateral Rostral Mandibulectomy . For extensive tumors spreading into the cavity of the bone, the entire side of the jaw is removed and this procedure is called a Total Hemimandibulectomy (Figure 10). Sometimes only part of the side of the jaw needs to be removed and this is called a Body Segmental Mandibulectomy (Figure 11).
Figure 9. Rostral Mandibulectomy.
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Figure 10. Total Hemimandibulectomy.
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Figure 11. Body Segmental Mandibulectomy.
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Maxillectomy is the surgical removal of various portions of the upper jaw and palate. Tumors in front of the second premolar could be removed via Premaxillectomy (Figures 12.1 and 12.2), either one-sided - for lesions not involving the midline or on both sides if necessary. Very extensive Hemimaxillectomy or Lateral Maxillectomy (Figure 13) will be necessary to remove large tumors of the side of the upper jaw. Central Maxillectomy (Figure 14) is indicated for tumors located between the upper canine tooth and the first molar on one side. Tumors behind the third premolar tooth on one side can be removed by Caudal Maxillectomy. Sometimes part of the bone surrounding the eye must be removed when there are tumors in this location and then the procedure is a Maxilectomy-Orbitectomy combination.
Figure 12.1. Premaxillectomy.
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Figure 12.2. Premaxillectomy Bilateral.
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Figure 13. Hemimaxillectomy.
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Figure 14. Central Maxillectomy.
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After the tumor and bone is removed, the adjacent soft tissue is used as a flap which is sutured in place with absorbable suture material.
Postoperative Care and Complications
Complications are relatively rare. The rich blood supply to the mouth helps prevent infection and ensure speedy healing. Animals usually remain on intravenous fluids overnight but most are drinking and eating within 24 to 48 hours. The best food in the early days after surgery is “meat balls” made from canned pet food which can be easily swallowed without the need to chew. Ranula (pocket of saliva) or edema on the side of the tongue after surgery can happen but this complication is temporary and resolves within a few days.
If a large segment of the lower jaw is removed (cut behind the second premolar tooth) drooping of the tongue and drooling can occur. (Figure 15) When the front part of the upper jaw is excised, some nose shortening and drooping of the muzzle is expected. Tear duct damage can cause crusting of the muzzle or tear overflowing from the eye. These problems are minor and animals quickly adapt to their new setting.
Figure 15. Drooping of the tongue.
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Nose bleeds may occur after various maxillectomy surgeries for the first few days but this is also temporary with resolution without treatment. The soft tissue flap can come away requiring further surgery in 20-30% of cases but reconstruction usually involves a minor second surgery. Other rare complications include malocclusion and mandibular drift sometimes requiring dental procedures. Overall, however, mandibulectomy and maxillectomy are well tolerated, cosmetic and very effective in controlling cancer of the oral cavity in selected canine and feline cases.
Aftercare
After surgery your pet will be closely watched for tumor recurrence. We recommend visits at your local veterinarian monthly for 3 months and then every 3 months for a year.
—Martin Havlicek, MACVSc
—Rod Straw, BVSc
Diplomate ACVS
Posted 8/13/2004
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