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Surgery of Oral Tumors

Stephen Withrow United States

Cancer of the oral cavity is a common occurrence in dogs and is less common in cats. No anatomic area is prone to such a wide variety of cancers with as varied a response to therapy. Preoperative biopsy and accurate staging are critical to proper treatment. Most oral cancers are treated with surgery, although radiation has a limited but definite role in management of radiation sensitive cancer, unresectable disease, or postoperative residual disease. The key to long-term remission is: 1) diagnosis at an early stage (small volume); and 2) aggressive surgical resection at this stage, which is often curative. Wide removal of cancer of the mandible/maxilla is achievable with bone removal. A large array of curable and nonmalignant conditions exists that needs to be recognized so that inappropriate euthanasia or therapy does not take place.

Large wedge biopsies of healthy tumor are often necessary to make a diagnosis. Two common biopsy result problems in the oral cavity are: 1) amelanotic melanoma may be interpreted as undifferentiated neoplasia (special stains may help resolve these cases); and 2) fibrosarcoma of the maxilla of large breed dogs (especially Golden Retrievers) may look very benign histologically yet is aggressive in the patient and needs radical resection in spite of the biopsy result.

Malignant cancer on or in the mandible or maxilla requires bone-removing procedures if permanent local disease control is to be expected with surgery. Fixation of a soft tissue mass to bone strongly suggests bone invasion regardless of what regional radiographs demonstrate (remember that 30-40% of the bone must be destroyed before it is obvious on plain radiographs). Accurate preoperative staging is enhanced by the use of CT or MRI scans, especially for lesions caudally located in the mouth, orbit, or vertical ramus of the mandible. Preoperative biopsies are crucial but must not contaminate the buccal mucosa since it will serve as the primary means of wound closure. Mandibulectomy procedures in common usage include unilateral rostral, bilateral rostral, segmental, vertical ramus, and total unilateral resection. Complications include wound dehiscence (especially if previously irradiated or if electrocautery is used in excess), “ranula” formation (which spontaneously resolves), tongue lag, cheilitis, and medial drift of remaining mandible. Maxillectomy procedures include unilateral premaxilla, bilateral premaxilla (± nasal planum), and unilateral lateral maxilla. To date, a well-established method to reconstruct bilateral caudal palatine lesions is not available. Closure is with buccal mucosal transposition grafts. The major complication is wound dehiscence (~ 10%), which is generally readily re-sutured if the buccal flap is viable.

Attention needs to be paid to tailoring the correct surgery to the correct tumor type and stage. Access to blood transfusions, intensive care units, and analgesics is desirable. Owner satisfaction with cosmetic and functional results (not always the oncologic results) is uniformly good.

The long-term results from an oncologic perspective are presented in Table 1.

TABLE 1: Summary of Various Papers on Mandibulectomy or Maxillectomy


 % Local

Median Survival

 Number

 Recurrence

 (months)

 % 1 year

Acanthomatous epulis

149

4

36

90

Squamous cell carcinoma

92

15

18

70

Osteosarcoma

69

25

8

50

Melanoma

126

25

8

35

Fibrosarcoma

92

46

11

35



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