Odontogenic Tumors and Epulis

Odontogenic tumors are a diverse group of neoplasms arising from the epithelial, mesenchymal, or mixed elements of the tooth-forming apparatus (dental lamina, enamel organ, dental papilla, dental follicle). They represent a spectrum of lesions ranging from hamartomatous proliferations to true neoplasms, with variable biological behavior from benign to locally aggressive or rarely malignant. Epulis (plural: epulides) is a clinical term denoting a nonspecific, exophytic gingival mass, which may be reactive (e.g., fibrous hyperplasia, pyogenic granuloma) or neoplastic (e.g., peripheral odontogenic fibroma, acanthomatous ameloblastoma). In veterinary medicine, the term 'epulis' is often used interchangeably with peripheral odontogenic fibroma, but it is crucial to distinguish between the various histopathological subtypes due to differences in treatment and prognosis. This entry focuses on the surgical management of odontogenic tumors and epulides, emphasizing accurate diagnosis, staging, and definitive surgical excision.

The exact etiology of odontogenic tumors is largely unknown, but several factors are implicated. Genetic mutations and dysregulation of developmental signaling pathways (e.g., Wnt, Hedgehog, Notch) play a central role in the aberrant proliferation of odontogenic epithelium. In dogs, certain breeds have a hereditary predisposition, suggesting a genetic basis. Trauma and chronic inflammation have been proposed as potential triggers for reactive epulides, though evidence is limited. Viral etiologies have not been confirmed in veterinary species. For acanthomatous ameloblastoma, a locally invasive but non-metastasizing tumor, the cell of origin is the dental lamina rests, and its growth is driven by epithelial-mesenchymal interactions. Peripheral odontogenic fibromas arise from the periodontal ligament and are considered benign. The etiology of odontogenic tumors in cats is less well understood, but they are rare and often more aggressive.

Odontogenic tumors and epulides are most commonly diagnosed in dogs, with a reported incidence of 2.4% to 6.8% of all canine oral tumors. They are rare in cats, accounting for less than 1% of feline oral tumors. In dogs, the most common odontogenic tumor is the peripheral odontogenic fibroma (previously termed fibromatous and ossifying epulis), followed by acanthomatous ameloblastoma (previously termed acanthomatous epulis). Breed predispositions include Boxers, Golden Retrievers, and Cocker Spaniels for peripheral odontogenic fibromas; and Shetland Sheepdogs, Golden Retrievers, and mixed-breed dogs for acanthomatous ameloblastoma. There is no significant sex predilection, but the median age at diagnosis is 7-9 years for peripheral odontogenic fibromas and 8-10 years for acanthomatous ameloblastoma. In cats, odontogenic tumors are more common in older animals, with no breed predilection.

Odontogenic tumors arise from the remnants of the dental lamina, enamel organ, or dental follicle. The histogenesis determines the tumor's composition: epithelial tumors (ameloblastoma) consist of islands or cords of odontogenic epithelium in a fibrous stroma; mesenchymal tumors (odontogenic fibroma) are composed of fibrous tissue with varying amounts of odontogenic epithelium; mixed tumors (ameloblastic fibroma, odontoma) contain both epithelial and mesenchymal components. The biological behavior varies: peripheral odontogenic fibromas are benign, slow-growing, and non-invasive, typically arising from the gingival margin. Acanthomatous ameloblastoma is benign but locally aggressive, infiltrating underlying bone and causing extensive osteolysis. True malignant odontogenic tumors (ameloblastic carcinoma, odontogenic sarcoma) are extremely rare and can metastasize. The growth of these tumors leads to displacement of teeth, bone destruction, and secondary infection. In the case of epulides, reactive lesions are characterized by fibrous proliferation and inflammation, often in response to chronic irritation (e.g., dental calculus, trauma).

Intrinsic factors include breed-specific genetic susceptibility, as seen in Boxers and Golden Retrievers. Age is a factor, with middle-aged to older dogs more commonly affected. Extrinsic factors include chronic oral inflammation, periodontal disease, and mechanical irritation from dental calculus or malocclusion, which may contribute to the development of reactive epulides. There is no strong evidence linking diet or environmental factors to odontogenic tumors. Prior oral surgery or trauma may stimulate reactive hyperplasia in some cases.

Clinical signs vary depending on the tumor type and extent. Common findings include a visible, exophytic gingival mass that may be smooth, lobulated, or ulcerated. The mass may bleed easily, especially with trauma. Patients may exhibit halitosis, ptyalism, dysphagia, and reluctance to eat. As the tumor enlarges, it can cause tooth displacement, mobility, and bone destruction. Acanthomatous ameloblastoma often presents as a firm, broad-based mass that may involve the alveolar bone, leading to facial swelling and, in advanced cases, exophthalmos if the orbit is involved. Pain is not always evident but can occur with secondary infection or bone invasion. On oral examination, the mass may be pedunculated or sessile, and its surface may be intact or ulcerated. Regional lymph nodes may be enlarged due to secondary inflammation, but metastasis is rare.

Differential diagnoses for odontogenic tumors and epulides include: 1) Peripheral giant cell granuloma - a reactive lesion with multinucleated giant cells, often associated with trauma; 2) Pyogenic granuloma - a vascular proliferative lesion with a history of rapid growth and bleeding; 3) Fibrous hyperplasia - a reactive fibrous mass, often secondary to chronic irritation; 4) Squamous cell carcinoma - a malignant epithelial tumor that is invasive and may metastasize; 5) Fibrosarcoma - a malignant mesenchymal tumor that is locally aggressive and may metastasize; 6) Osteosarcoma - a malignant bone tumor that can arise in the jaw; 7) Ameloblastoma (central) - a rare intraosseous tumor that is locally aggressive; 8) Dentigerous cyst - a cystic lesion associated with an unerupted tooth; 9) Eosinophilic granuloma complex (in cats) - an inflammatory lesion with eosinophilic infiltrate; 10) Foreign body granuloma - a reactive lesion to a foreign body. Definitive diagnosis requires histopathology, as clinical appearance alone is not sufficient.

The diagnostic workup begins with a thorough history and complete oral examination, including inspection and palpation of the mass, assessment of tooth mobility, and evaluation of regional lymph nodes. Intraoral dental radiographs are essential to evaluate the extent of bone involvement, tooth root resorption, and the presence of cystic lesions. For larger masses or those with suspected bone invasion, advanced imaging such as computed tomography (CT) is recommended to assess the extent of the tumor, particularly for surgical planning. A biopsy is mandatory for histopathological diagnosis. An incisional biopsy (wedge or punch) is preferred for large masses to obtain a representative sample, while excisional biopsy may be performed for small, well-circumscribed lesions. The biopsy should be taken from the center of the lesion, avoiding necrotic areas. Histopathology will differentiate between reactive and neoplastic lesions and identify the specific tumor type. For malignant tumors, thoracic radiographs and lymph node aspiration are indicated to rule out metastasis.

Complete blood count (CBC) and serum biochemistry profile are typically within normal limits, unless there is secondary infection or systemic illness. In cases with significant oral inflammation, a mild leukocytosis may be present. Coagulation profile (PT/aPTT) is recommended before surgical intervention, especially if extensive resection is planned. In cats, retroviral testing (FeLV/FIV) is advisable. Synovial fluid analysis is not relevant for this condition. Inflammatory biomarkers such as C-reactive protein (CRP) may be elevated in cases with secondary infection, but they are not specific.

Dental radiography is the primary imaging modality. Findings include a soft tissue opacity mass, bone lysis, tooth displacement, and root resorption. Peripheral odontogenic fibromas typically show a well-defined, sometimes mineralized mass on the gingival surface, with minimal bone involvement. Acanthomatous ameloblastoma often demonstrates aggressive bone lysis, with irregular margins and tooth loss. CT is superior for evaluating the extent of bone invasion, particularly for maxillary tumors, and is essential for surgical planning. CT findings include a contrast-enhancing soft tissue mass with associated osteolysis. MRI may be useful for assessing soft tissue extension, but is rarely needed. Thoracic radiographs are indicated for malignant tumors to rule out pulmonary metastasis.

Fine-needle aspiration cytology of the mass may be performed, but it is often non-diagnostic due to the fibrous nature of many odontogenic tumors. Histopathology is the gold standard. Peripheral odontogenic fibroma is characterized by dense fibrous connective tissue with islands of odontogenic epithelium, and variable amounts of dentin or cementum-like material. Acanthomatous ameloblastoma shows islands and cords of odontogenic epithelium with peripheral palisading of columnar cells and central stellate reticulum-like cells, often with a prominent fibrous stroma. The tumor is non-encapsulated and infiltrates the surrounding bone. Malignant odontogenic tumors show cytological atypia, mitotic figures, and invasion. Histopathology should include assessment of surgical margins to ensure complete excision.

The treatment of choice for odontogenic tumors and epulides is surgical excision. For benign, well-circumscribed lesions such as peripheral odontogenic fibromas, marginal excision (e.g., gingivectomy) may be curative. However, for acanthomatous ameloblastoma, which is locally invasive, wide surgical excision is required, often involving mandibulectomy or maxillectomy. The specific surgical technique depends on the tumor location and extent. For mandibular tumors, marginal resection (rim excision) may be sufficient for small lesions, but segmental or hemimandibulectomy is indicated for larger tumors. For maxillary tumors, partial maxillectomy may be necessary. Surgical approaches are based on Piermattei's Atlas of Surgical Approaches. The goal is to achieve 1-2 cm margins of healthy tissue. In cases where complete excision is not possible, radiation therapy may be considered as an adjunct. For acanthomatous ameloblastoma, radiation therapy has been shown to be effective, but surgical excision remains the primary treatment. Postoperative pain management includes opioids (e.g., hydromorphone 0.05-0.1 mg/kg IV q4-6h) and NSAIDs (e.g., carprofen 2.2 mg/kg PO q12h). Antibiotics (e.g., amoxicillin-clavulanate 13.75 mg/kg PO q12h) are indicated if there is significant contamination or infection.

The prognosis for peripheral odontogenic fibroma is excellent with complete surgical excision, with a low recurrence rate (less than 5%). For acanthomatous ameloblastoma, the prognosis is good with wide surgical excision, with recurrence rates of 10-20% if margins are incomplete. Metastasis is extremely rare. For malignant odontogenic tumors, the prognosis is guarded, with a high risk of local recurrence and potential for metastasis. The overall survival time for dogs with acanthomatous ameloblastoma treated with surgery is often several years, with a good quality of life. Negative prognostic indicators include incomplete margins, large tumor size, and involvement of the maxilla.

Postoperative follow-up is essential to monitor for recurrence and complications. Patients should be re-examined at 2 weeks for suture removal and assessment of surgical site healing. Oral examinations should be performed every 3 months for the first year, then every 6 months thereafter. Dental radiographs or CT may be indicated if there is suspicion of recurrence. For patients undergoing mandibulectomy or maxillectomy, long-term monitoring of eating ability and oral function is important. Nutritional support may be needed in the immediate postoperative period. Owners should be educated on oral hygiene and regular dental cleanings to prevent periodontal disease.

Pearls: 1) Always obtain a biopsy before definitive surgery to guide the extent of resection. 2) For acanthomatous ameloblastoma, use CT to plan surgical margins, especially for maxillary tumors. 3) When performing mandibulectomy, preserve the contralateral mandible to maintain occlusion. 4) Use a surgical margin of at least 1 cm for acanthomatous ameloblastoma. 5) Consider radiation therapy for incompletely excised acanthomatous ameloblastoma. Pitfalls: 1) Incomplete excision due to underestimating tumor extent. 2) Damage to adjacent structures (e.g., infraorbital nerve, salivary ducts) during maxillectomy. 3) Failure to address regional lymph nodes in malignant tumors. 4) Postoperative complications such as dehiscence, infection, and oronasal fistula. 5) Not providing adequate pain management, leading to decreased food intake and delayed healing.

Perioperative antimicrobial prophylaxis: Cefazolin 22 mg/kg IV at induction, repeated every 90 minutes during surgery. Postoperative antibiotics: Amoxicillin-clavulanate 13.75 mg/kg PO q12h for 7 days if infection is present. Analgesia: Preoperative: Methadone 0.2-0.5 mg/kg IV or IM. Intraoperative: Fentanyl CRI at 5-10 mcg/kg/hr. Postoperative: Hydromorphone 0.05-0.1 mg/kg IV or IM q4-6h, or buprenorphine 0.01-0.02 mg/kg IV q6-8h. NSAIDs: Carprofen 2.2 mg/kg PO q12h, or meloxicam 0.1 mg/kg PO q24h, starting after recovery from anesthesia. Local anesthesia: Maxillary or mandibular nerve blocks with bupivacaine 1-2 mg/kg (maximum 2 mg/kg) or lidocaine 2 mg/kg. Anti-emetics: Maropitant 1 mg/kg IV or SC q24h if needed. Gastroprotectants: Omeprazole 1 mg/kg PO q12h if on long-term NSAIDs.

Several studies have evaluated the outcomes of surgical treatment for odontogenic tumors. A retrospective study by Gardner (1995) reported a recurrence rate of 5% for peripheral odontogenic fibromas after marginal excision. For acanthomatous ameloblastoma, a study by White et al. (1985) found that wide surgical excision resulted in a recurrence rate of 10%, while incomplete excision led to a 50% recurrence rate. A more recent study by Yoshida et al. (2016) reported that mandibulectomy for acanthomatous ameloblastoma achieved a 95% disease-free interval at 1 year. Radiation therapy has been shown to be effective for acanthomatous ameloblastoma, with a study by Thrall (1981) reporting a 90% control rate. However, surgery remains the treatment of choice. The use of CT for surgical planning has been shown to improve margin assessment and reduce recurrence rates (Lascelles et al., 2003). Overall, the evidence supports aggressive surgical excision for locally invasive odontogenic tumors, with a good prognosis for benign lesions.