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Veterinary Forum June 2007 (Vol 24, No 6)

Dental Dilemma: "Radical Maxillary Resection of Oral Squamous Cell Carcinoma in a Dog"

by Jan Bellows

    The most common oral tumors in dogs are malignant melanoma, benign odontogenic amelo­blastoma (epulides), squamous cell carcinoma, and fibro­sarcoma.1 Maxillectomy or mandibulectomy is often indicated for wide resection of these oral tumors.1-4

    Case presentation

    A 7-year-old, neutered miniature poodle (Figure 1) was referred for dental evaluation and treatment of a right maxillary oral mass of 3 weeks' duration. Two weeks earlier, squamous cell carcinoma had been diagnosed by the referring veterinarian after incisional biopsy. The dog's caregivers believed the dog was experiencing pain when touched and while eating.

    Clinical examination con­firmed a 20-mm oral mass of the gingiva and mucosa surrounding the right maxillary canine and second premolar (Figure 2). The right maxillary first, second, and third incisors and the first premolar were clinically missing. Palpation of the mandibular lymph nodes revealed normal shape, size, and consistency. Physical examination findings were within normal limits.

    The initial assessment plan included preanesthetic blood testing and urinalysis, along with three-view thoracic radiography and electrocardiography. All results were within normal parameters. Computed tomography (CT) of the tumor area was recommended but declined by the owner.

    Further assessment with the dog under anesthesia included full-mouth intraoral radiography; tooth-by-tooth examination for morphology, mobility, and probing depths; and fine-needle aspiration of both mandibular lymph nodes.

    The patient was premedicated with intramuscular hydromorphone at 0.1 mg/kg combined with intramuscular acepromazine at 0.01 mg/kg IM, and anesthesia was induced with 0.5 mg/kg of intravenous diazepam and 10 mg/kg of intravenous ketamine. The dog was placed in dorsal recumbency, intubated, and maintained on 2% isoflurane. The pulse, respiratory rate, blood pressure, and electrocardiographic parameters were monitored throughout the procedure. The patient's temperature was controlled with a warm-air Bair Hugger.

    Dorsoventral nasal films revealed an ill-defined, bilateral lytic area of tissue destruction with calcification in the rostral maxilla extending caudally to the second premolar. The maxillary incisor appeared to be unsupported by alveolar bone (Figure 3).

    Surgical treatment

    The client was advised of the findings and the overall guarded-to-poor prognosis because of the extent of disease caudally. Therapeutic options included radical surgery with a caudal margin of at least 1 cm with possible radiation and chemotherapy based on the results of the histopathologic margins and superficial tumor regrowth, antiin­flam­ma­tory medication without surgery, and euthanasia. The owner opted for surgery.

    The surgical margins were outlined by incising the gingiva and palatal mucosa at least 1 cm from the borders of the visible tumor extending through the hard palate. The mucosa was elevated from the underlying bone using Molt and Freer elevators.

    Figure 4 depicts the surgical procedure: The bone was cut along the margins of excision using a surgical cross-cut fissure bur on a high-speed, water-cooled handpiece. Transection of the infraorbital canal and ligation of associated vessels were performed. Excision of the caudal maxilla exposed the nasal cavity. The oronasal defect was closed using a labial mucosal-submucosal flap based at the lip margin. The flap was apposed with the cut edge of the hard palate mucoperiosteum without tension. The labial flap was sutured to the hard palate mucoperiosteum with two layers of simple, interrupted sutures (4-0 Biosyn). The first layer was placed in the submucosal tissue with the knots buried in the nasal cavity, and the second layer was placed in the mucosa with the knots in the oral cavity. After suturing, the nose was shorter because of removal of the rostral maxilla. To ensure patency of the nasal cavity, two 1.5-inch sections of intravenous catheter tubing were inserted through the nostrils into the ventral nasal meatus and sutured. Radiographs taken after surgical removal of the rostral maxilla confirmed clinical excision of the tumor (Figure 5). The tumor and the margins of excision were submitted for histopathologic evaluation (Figure 6).

    The oral cavity and pharynx were suctioned before recovery from anesthesia. During anesthetic recovery, the patient was monitored closely for dyspnea and excessive hemorrhage.

    Surgical follow-up

    Hydromorphone was administered twice daily as postoperative analgesia and was continued for 2 days. Water and soft food were offered the day after surgery, but intravenous fluid therapy was continued until the second postoperative day, after which the patient began eating and drinking. The patient was discharged from the hospital on the fourth postoperative day. Tramadol at 2 mg/kg bid, meloxicam at 0.1 mg/kg sid, and clindamycin at 1 mg/kg bid were dispensed for 1 week. The client was instructed to feed the dog a soft diet for 2 weeks.

    Histopathology of the surgical specimen confirmed the diagnosis of squamous cell carcinoma. The surgical margins were clear of tumor. The patient was reexamined under sedation 2 weeks after surgery to clinically confirm that wound healing had progressed satisfactorily.

    Two weeks later, oral examination noted regrowth of the tumor on the soft tissue of the right edge of the rostral maxilla. CT to evaluate deeper structures and radiation therapy were recommended, and the owner agreed. The CT scan did not show bony invasion of the tumor. The dog is currently receiving treatments of 300 cGy megavoltage to the affected area three times a week for a total of 6 weeks. The radiation oncologist indicated that the prognosis is good, as there is no evidence of bony involvement (Figure 7).

    Discussion

    Signs of oral neoplasia can include halitosis, hem­orrhage, anorexia, weight loss, dysphagia, salivation, pain, epistaxis, coughing, sneezing, and dyspnea. Mobile teeth or a history of recent tooth extraction is common. Clinically, abnormal contours or enlargements of the mandibular or maxillary region may be noted.

    Tumors located in the rostral aspect of the oral cavity warrant a more favorable prognosis for canine squamous cell carcinoma, while tumors located in tonsillar or unresectable lingual sites warrant a poor prognosis. Maxillectomy and mandibulectomy are effective surgical techniques for the treatment of many oral tumors. Animals tolerate these procedures well, and oral function and cosmetic appearance after the procedures are generally acceptable to owners.2

    Surgery, radiation, and chemotherapy are all treatment options for canine oral squamous cell carcinoma. Tumors located in the rostral oral cavity can be excised with curative intent. Local recurrence is common with inadequate resection. The mean survival time is 15.8 months, with 80% of patients being clinically free of tumor at the time of their death. In one study,5 85% of the dogs were alive 1 year after surgery. Surgical margins greater than 1 cm (2 cm if possible) around the lesion are recommended. Remission of oral nontonsillar squamous cell carcinoma has been reported in another limited study using piroxicam and carboplatin.6-8 Squamous cell carcinomas are considered radiation sensitive. A combination of radiation and surgery may give the best control for gingival squamous cell carcinoma.

    Location of the tumor seems to influence radiosensitivity: Dogs with maxillary tumors had a longer response to radiation therapy (12 months) than did dogs with mandibular (3.4 months) or soft tissue tumors (1.8 months). Dogs with rostrally located tumors had longer1 survival times than did dogs with caudally located tumors or tumors extending rostrally to caudally.2

    In this case, conservation of functional nasal anatomy was important. The external nose is composed of paired dorsolateral and ventrolateral nasal cartilages, paired accessory cartilages, and a single cartilaginous nasal septum. There are three interconnected nasal meatuses in the dog: the dorsal, middle, and ventral meatus. The common nasal meatus is a longitudinal narrow space on either side of the nasal septum. The nasopharyngeal meatus is an extension of the ventral nasal meatus.

    The nasal cavity and external nose are supplied by an extensive capillary network, with an interconnecting network of arteries and veins. This extensive collateral network helps to maintain circulation to these tissues after radical surgery.

    Ideally, as part of the initial patient staging, oral CT should be conducted to adequately evaluate any extension of the tumor. This case was especially interesting, as CT was performed after surgery because of apparent tumor regrowth, which allowed the owner to agree to radiation therapy as part of the follow-up care to control local disease. After the radiation oncologist has completed the course of treatment, the patient will be followed closely for recurrence of disease.

    1. Salisbury SK, Richardson RC, Lantz, GC: Partial maxillectomy and premaxillectomy in the treatment of oral neoplasia in the dog and cat. Vet Surg 1986;15:16-26.

    2. Schwarz PD, Withrow SJ, Curtis CR, et al: Partial maxillary resection as a treatment for oral cancer in 61 dogs. JAAHA 1991; 27:617-624.

    3. Wallace J, Matthiesen DT, Patnaik AK: Hemimaxillectomy for the treatment of oral tumors in 69 dogs. J Small Anim Pract 1991;32:69-74.

    4. Pavletic MM: Atlas of Small Animal Reconstructive Surgery, ed 2. Philadelphia, WB Saunders, 1999.

    5. Withrow S: Oral tumors and their biology. Proc WSAVA World Congr:2001.

    6. de Vos JP, Burn AGD, Focker AP, et al: Piroxicam and carboplatin as a combination treatment of canine oral non-tonsillar squamous cell carcinoma. Vet Comp Oncol 2005;3(1):16.

    7. de Vos JP, Burn AGD, Focker AP, et al: Results from the treatment of canine oral non-tonsillar squamous cell carcinoma with piroxicam and carboplatin. J Vet Intern Med 18(5):775-796, 2004.

    8. Verstraete FJM: Non-odontogenic tumors. Proc WVC:2002.

    References »

    NEXT: Doctor to Doctor: "Buffing up behind-the-scenes"

    didyouknow

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