Benign Oral Tumors in Small Animals
Peripheral odontogenic fibromas (POFs, previously called fibromatous epulis or ossifying epulis) are the most common benign oral tumors. These periodontal ligament tumors manifest as firm gingival masses.
POFs are most common in dogs > 6 years old and are generally solitary, although multiple lesions may be present. Cats rarely develop POFs; however, when they do, they are generally multiple.
Some POFs develop centers of ossification, visible as distinct mineralizations within the soft tissue shadow on dental radiography.
Complete surgical removal usually necessitates conservative resection of the gingival mass, extraction of the affected tooth or teeth, and curettage of the alveolar sockets (ie, removal of the remaining periodontal ligament), followed by wound closure. Complete excision appears to be curative. Ossifying lesions are more challenging to remove because the tissue is substantially firmer and more difficult to excise.
Other less common benign oral tumors in dogs and cats include the conventional ameloblastoma, plasma cell tumor, granular cell tumor, lipoma, osteoma, adenoma, amyloid-producing odontogenic tumor, feline inductive odontogenic tumor, giant cell granuloma, and cementoma.
Odontoma is not a true tumor but a hamartoma (disorganized tissue made up of normal cells); it can be compound (toothlike structures present within the mass) or complex (unrecognizable as hard or soft dental tissue).
Canine acanthomatous ameloblastoma (previously called acanthomatous epulis), a benign neoplasm, is a much more locally aggressive tumor. Frequently, it invades the surrounding soft tissue and bone (see canine acanthomatous ameloblastoma photograph and radiograph).
Courtesy of Dr. Brenda Mulherin.
Courtesy of Dr. Ben Colmery III.
Canine acanthomatous ameloblastoma has a predilection for the rostral mandible but can be present anywhere in the oral cavity. Fortunately, this tumor does not metastasize; however, because it is locally aggressive, surgical excision should include a 1-cm margin of normal soft tissue and bone to be curative and prevent recurrence.
Radiotherapy can minimize disfigurement when treating large oral tumors in older dogs.
Malignant Oral Tumors in Small Animals
In dogs, the three most common malignant oral tumors are malignant melanoma, squamous cell carcinoma, and fibrosarcoma. The incidence of malignant oral tumors is higher in dogs > 8 years old. The appearance of oral tumors can vary; therefore, biopsy is imperative for accurate diagnosis.
Pearls & Pitfalls
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Malignant melanoma (MM) frequently presents as a pigmented or nonpigmented, ulcerative and proliferative mass of the gingiva, alveolar mucosa, labial and buccal mucosa, palate, or dorsum of the tongue. As masses increase in size, portions may become necrotic from outgrowth of blood supply. These tumors metastasize relatively quickly, and tumors > 2 cm in diameter have a poor prognosis due to the likelihood of metastasis to regional lymph nodes and other distant sites.
Dogs with heavily pigmented oral mucosa may be predisposed to developing oral MM. While this tumor commonly is palpably firm and appears pigmented black (melanotic), it can also be unpigmented (amelanotic). Many oral MM tumors show radiographic evidence of bony involvement. (See image of MM in a dog.)
MM is very rarely found in cats' mouths. As in dogs, tumors in cats can be melanotic or amelanotic. (See image of MM in a cat.)
Squamous cell carcinoma (SCC) is the most common malignant oral tumor in cats. SCC commonly involves the gingiva and underlying bone, as well as the tongue and sublingual region, alveolar mucosa, and palatine tonsil (unilaterally). These neoplastic lesions are invasive and commonly substantially involve underlying bone. Local recurrence after surgical resection is common; therefore, prognosis is generally poor. (See images of SCC in a cat, an elderly cat, and a dog).
SCC is the second-most common type of oral cancer in dogs. In dogs, SCC grossly appears as an irregular, raised, cauliflower-like mass that is present on gingiva, buccal mucosa, or labial mucosa. These lesions can also form on the hard and soft palate.
SCC is insignificantly slower to metastasize than MM. If abnormal tissue is associated with bilaterally enlarged tonsils, lymphosarcoma should be considered as a differential diagnosis.
Fibrosarcoma (FSA) is the second-most common oral malignancy in cats. In dogs, it is highly invasive and tends to occur in young adult to middle-aged large breeds and older small breeds. This oral tumor commonly affects the gingiva, lip/cheek mucosa, and the hard and soft palate. (See image of FSA in a dog.) These tumors are usually flat and firm but can be ulcerated and multilobular. Occasionally, FSA arises from the lateral surface of the incisive bone and maxilla, developing as a slowly enlarging, firm mass at the muzzle.
Fibrosarcoma has less metastatic potential than MM or SCC. However, if extensive, FSAs carry a poor prognosis.
Courtesy of Dr. Ben Colmery III.
Courtesy of Dr. Ben Colmery III.
Courtesy of Dr. Ben Colmery III.
Courtesy of Dr. Brenda Mulherin.
Courtesy of Dr. Ben Colmery III.
Courtesy of Dr. Ben Colmery III.
Other less commonly found oral tumors in dogs and cats include osteosarcoma, multilobular tumor of bone, peripheral nerve sheath tumor, lymphosarcoma, adenocarcinoma, hemangiosarcoma, rhabdomyosarcoma, and anaplastic or undifferentiated neoplasia.
In dogs and cats, mast cell tumors (MCTs) arising from the oral mucosa are rare compared with cutaneous MCTs. MCTs in the oral cavity are substantially more aggressive and have a higher metastatic rate (see oral mast tumor image).
Courtesy of Dr. Ben Colmery III.
Clinical Findings
Clinical signs of malignant oral tumors vary depending on location and extent of the neoplasm. Halitosis, reluctance to eat, and hypersalivation are common. If the oropharynx is involved, dysphagia may be present. These tumors frequently ulcerate and bleed. The face may become swollen as the tumor enlarges and invades surrounding tissue. Regional lymph nodes (parotid, mandibular, medial retropharyngeal) often become enlarged before oral and oropharyngeal tumors are observed.
Diagnosis
Visual inspection
Diagnostic imaging
Tissue biopsy
Oral tumors are diagnosed and staged by visual inspection and palpation of the primary tumor and regional lymph nodes, diagnostic imaging of the thorax (with standard radiography, CT), diagnostic imaging of the primary tumor (with dental radiography, CT), and cytological or histological examination (of the primary tumor, regional lymph nodes). (See SCC radiograph.)
Courtesy of Dr. Brenda Mulherin.
Because of the varied behavior of oral tumors, staging is imperative to determine the extent of disease and to plan and discuss appropriate treatment options with the owner.
Biopsy with histological examination of the primary tumor is the most reliable method to obtain a definitive diagnosis. A cytological diagnosis from impression smears or fine-needle techniques (insertion or aspiration) is possible if the lesion is comprised of cells that easily exfoliate.
Evaluation of regional lymph nodes and thoracic imaging should be performed to check for regional and distant metastasis.
Treatment
Surgical removal and reconstruction
Radiotherapy, chemotherapy, and immunotherapy
Surgical removal of the oral tumor with clean margins and functional reconstruction of the resulting wound are the main treatment goals. Radiotherapy, chemotherapy and immunotherapy may be used in conjunction with surgery or when surgery is not an option.
Preoperative workups, in addition to staging, include routine blood tests, blood type determination and crossmatching, coagulation profiles, buccal mucosa bleeding time, and diagnostic imaging of the surgery site.
Conservative resection should be restricted to peripheral odontogenic fibromas that are removed together with the associated tooth (which is extracted) and its periodontium (through curettage of the alveolus). Invasive tumors require radical resective surgery (mandibulectomy, maxillectomy, glossectomy, lip and cheek resection, etc) in efforts to provide clean, tumor-free margins.
Electrocoagulation should be avoided along incised mucosal edges that will be sutured. Bone should be resected with power instruments (rotating burrs, sagittal and oscillating saws, piezoelectric surgery) or an osteotome and mallet for a clean cut to the bone. It is often safer to "break out" the piece to be resected rather than to burr or saw through any remaining bony attachments, particularly when the attachments cover the bony channels containing neurovascular bundles.
Various maxillectomy procedures are possible ranging from partial resection of the rostral upper jaw on one or both sides (rostral maxillectomy), to resection of a central or caudal portion of the maxilla (central or caudal maxillectomy) or the entire dental arch on one side, including the palate to midline (total maxillectomy), to resection of the entire palate and both sides of the dental arch. For more caudally located lesions that extend onto the side of the face, the bones forming the ventral and lateral limits of the orbit can be resected (partial orbitectomy).
The relatively small size of the skull and the short and tight upper lip make radical maxillectomy in cats far more challenging than in dogs.
Various mandibulectomy procedures are possible ranging from partial resection of the mandible on one or both sides (unilateral or bilateral rostral mandibulectomy and partial mandibular body resection), to resection of one entire mandible (total mandibulectomy), or resection of one entire mandible and a portion of the mandible on the other side.
For caudally located lesions, the mandibular ramus or a portion of it can be resected by means of a dorsolateral approach through the zygomatic arch and the masseter and temporal muscles. Bilateral rostral mandibulectomy to the level of the first premolars in dogs (rostral aspect of the diastema between canines and third premolars in cats) provides good function and esthetics. Bilateral resection caudal to this level results in progressively greater problems with retaining the tongue within the mouth, as well as with eating and grooming. Resection of the symphysis causes the two remaining mandibular sections to "float," which can be functionally and aesthetically acceptable.
Lingual tumors are resected with good results if the resection can be confined to the free rostral or dorsocaudal portions of the tongue. Clamping the tongue caudal to the excision site with noncrushing forceps aids in hemostasis. Surgical principles for resection of tumors of the lip and cheek include the following:
maintenance of a functional lip commissure so that the mouth can open adequately
separate closure of mucosal and haired skin incisions
avoidance of parotid and zygomatic salivary gland ducts or ligation of ducts when avoidance is not possible
cosmetic closure of resulting facial defects by advancing or rotating tissue from the lower lip and side of the face, head, or neck
Pain control is achieved with a combination of intraoperatively administered longer-acting local anesthetics, centrally acting opioids, and NSAIDs. Chlorhexidine digluconate solution or gel can be administered (0.1–0.2%, PO, 2 weeks). Oral antimicrobial administration is not required after oral and maxillofacial surgeries in otherwise healthy patients.
Water can be offered once the patient has recovered from anesthesia. Soft food should be offered 6–8 hours after surgery and maintained for approximately 2 weeks, as the surgical sites heal. Dogs usually eat the same day or the next day; cats may benefit from placement of an esophagostomy tube to ensure proper nutrition and facilitate medication administration during the immediate postoperative period.
Elizabethan collars, tape and nylon muzzles, or other restraining devices may be used to prevent disruption or self-trauma at the surgical sites.
Reexaminations are scheduled at 2 weeks (removal of skin sutures) and at 2, 6, 12, 18, and 24 months postoperatively, followed by annual reevaluation.
Key Points
Clients must be informed about intra- and postoperative complications regarding surgical resection of neoplastic lesions including follow-up care, longterm function and quality of life, and prognosis.
Combined treatment (surgery plus radiotherapy, chemotherapy, and/or immunotherapy) may be indicated, particularly for tumors with regional or distant metastasis. The treatment of choice for most oral and maxillofacial tumors is wide surgical excision. Large portions of upper and lower jaws and associated soft tissues can frequently be removed without compromising quality of life.
Depending on the tumor type, surgical resection should include at least 1–2 cm of apparently healthy tissue surrounding the tumor. Due to their highly invasive nature, fibrosarcomas should ideally be resected with even wider margins.
The surgical site should be closed with a labial or buccal flap that is undermined until it can cover the defect without tension. A two-layer suture closure is preferred, with the first layer apposing connective tissues to relieve tension on the mucosal edges and the second layer closing skin.
Collaboration with an oncologist is helpful after histopathological diagnosis to discuss the need for further treatment (surgery, radiotherapy, chemotherapy). Palpation of nonresected lymph nodes (with cytological or histological examination of enlarged nodes) and thoracic radiographs should be performed to monitor for regional and distant metastasis, depending on the tumor type.
For More Information
Munday JS, Thomson NA, Luff JA. Papillomaviruses in dogs and cats. Vet J. 2017;225:23-31.
Bilgic O, Duda L, Sánchez MD, Lewis JR. Feline oral squamous cell carcinoma: clinical manifestations and literature review. J Vet Dent. 2015;32(1):30-40.
Farcas N, Arzi B, Verstraete FJM. Oral and maxillofacial osteosarcoma in dogs: a review. Vet Comp Oncol. 2014;12(3):169-180.
Also see pet owner content regarding disorders of the mouth in dogs.
