JPC SYSTEMIC PATHOLOGY
DIGESTIVE SYSTEM
September 2021
D-N01

Signalment (JPC #1698960): Adult boxer

 

HISTORY: The animal presented with an oral mass

 

HISTOLOGIC DESCRIPTION: Gingiva: Expanding the subepithelial connective tissue, elevating the overlying hyperplastic mucosa, and extending to cut borders is an unencapsulated, paucicellular neoplasm composed of spindle to stellate cells that are evenly spaced, arranged in loose, haphazard streams, and separated by an abundant collagenous matrix. Neoplastic cells have indistinct cell borders, a scant to moderate amount of eosinophilic, fibrillar cytoplasm, and an irregularly oval to elongate nucleus with finely stippled to hyperchromatic chromatin and an indistinct nucleolus. The mitotic count is less than 1 per 10 high power fields (2.37mm2). Focally within the neoplasm is an island of immature, woven bone (osseous metaplasia). Multifocally there are also few aggregates of homogenous, eosinophilic material up to 40 um in diameter (dental hard substance). There are multiple small subepithelial and perivascular accumulations of plasma cells, fewer lymphocytes, and occasional neutrophils. The overlying epithelium is moderately hyperplastic forming anastomosing rete ridges up to 2 mm in length with moderate acanthosis, spongiosis, multifocal epithelial intracellular edema, multifocal hyperkeratosis, neutrophilic exocytosis, and a focal area of erosion.

 

MORPHOLOGIC DIAGNOSIS:  Gingiva:  Peripheral odontogentic fibroma (POF), boxer, canine.

 

SYNONYMS:  Fibromatous epulis of periodontal ligament origin (FEPLO)

 

GENERAL DISCUSSION:

• Epulis is a nonspecific term that designates a tumor-like growth of the gingiva of any origin (i.e. neoplastic or non-neoplastic) that is common in dogs and infrequent in cats
• Epulis should not be used in morphologic diagnosis because it is nonspecific
• Non-neoplastic gingival growths include pyogenic granuloma, peripheral giant-cell granuloma, and fibrous hyperplasia
• Peripheral odontogenic fibroma (POF) is a tumor composed primarily of odontogenic mesenchyme
  • Common lesion in dogs, benign
  • Local excision curative
  • Unknown and chronically debated histogenesis and naming of this tumor; the name will likely be changed again in the future
  • Commonly has similar features of reactive fibrous hyperplasia or focal fibrous hyperplasia, a lesion secondary to chronic gingival trauma and irritation; the two are difficult to distinguish, and hybrid lesions exist

 

GROSS FINDINGS:

• Hard, pink, smooth, often lobulated mass that are always adjacent to teeth; the mass may displace teeth, but it does not invade bone

 

LIGHT MICROSCOPE FINDINGS:

• Neoplasm of odontogenic mesenchyme: regularly positioned stellate mesenchymal cells; localized deposition of collagen matrix is often seen and can have characteristics of osteoid/bone, cementum, or dentin; cords of odontogenic epithelium may be present; has considerable overlap with focal fibrous hyperplasia
  • Distinguished from fibrous hyperplasia by the immaturity of the stroma and their tendency to contain less inflammatory tissue and more hard tissue

DIFFERENTIAL DIAGNOSIS:

For oral/gingival mass:

• Fibrous hyperplasia: Secondary to localized chronic inflammation that produces a mass of mature fibrous tissue, often with a band of plasma cells adjacent to the overlying hyperplastic epithelium; common in dogs and usually does not recur following surgical excision; diffuse gingival hypertrophy is familial in boxer dogs
• Pyogenic granuloma: Reactive lesion of the gingival or mucosa; exuberant connective tissue proliferation in response to injury; bright red or blue mass; vascular granulation tissue covered by gingival epithelium; rare; usually does not recur
• Peripheral giant cell granuloma: Hyperplastic connective tissue response to gingival injury; smooth and sessile or pedunculated; dense, well-vascularized stroma with hemosiderin and numerous multinucleated giant cells with overlying hyperplastic epithelium; associated with the site of tooth extraction; rare; little chance of recurrence in the dog (similar behavior to POF)
• Ameloblastoma: Tumor composed of proliferating, palisading odontogenic epithelium, (may or may not have keratinization) with features of embryonic enamel organ; predominantly intraosseous; rare
• Amyloid-producing odontogenic tumors: Odontogenic epithelium with aggregates of amyloid +/- trabeculae of osteoid/dentinoid, +/- keratinization; rare
• Complex odontoma: Composed of disorganized dental tissue (poorly formed tooth like structures); rare but less so in horses and cattle
• Compound odontoma: Denticles (tooth like structures) within tumor containing enamel, dentin, cementum, and pulp (looks like more normal tooth); rare but less so in horses and cattle
• Feline inductive odontogenic tumor; Most common odontogenic neoplasm in kittens; typically occur in maxilla and cause osteolysis; rare; similar to ameloblastic fibroma but with distinctive features consisting of nodules of fibroblasts resembling dental papilla in a connective tissue stroma with clusters of odontogenic epithelium
• Squamous cell carcinoma (SCC): In dogs usually involves the gingiva or tonsils, locally invades bone and metastasizes to regional lymph nodes (second most common canine oral tumor); papillary form can appear similar but IHC (p63, AEI/AE3), and 34βE12) can differentiate (Thaiwong, Vet Pathol. 2018); in cats SCC is the most common oral malignancy and is usually located on the frenulum of the tongue
• Melanoma: Most common oral tumor of dogs; usually located on the gingiva, gums, buccal mucosa, lips, or palate; up to 90% metastasize to regional lymph nodes or lungs
• Fibrosarcoma: Occur on the gums of the upper molars and anterior half of the mandible; more common in younger dogs; about 35% metastasize to regional lymph nodes or lungs; second most common oral malignant neoplasm in cats

 

COMPARATIVE PATHOLOGY:

• Cats: Epulides occur less frequently compared to dogs; recurrence following excision is more common in cats than in dogs
• Lions: FEPLO is common in lions (Scott, Vet Pathol. 2020)

 

REFERENCES:

1. Bell CM, Soukup JW. Nomenclature and Classification of Odontogenic Tumors – Part II: Clarification of Specific Nomenclature. J Vet Dent. 2014; 31(4):234-243.
2. Monday JS, Lohr CV, Kiupel M. Tumors of the alimentary tract. In: Meuten DJ, ed. Tumors in Domestic Animals. 5th ed. Ames, IA: John Wiley & Sons, Inc.; 2017:533-543.
3. Murphy, BG, Bell CM, Soukup JW. Tumor-Like Proliferative Lesions of the Tooth Bearing Regions of the Jaw. In: Murphy, BG, Bell CM, eds. Veterinary Oral and Maxillofacial Pathology. 1^st John Wiley & Sons; 2020: 197-201.
4. Scott KL, Garner MM, Murphy BG, LaDouceur EEB. Oral Lesions in Captive Nondomestic Felids With a Focus on Odontogenic Lesions. Vet Pathol. 2020; 57(6):880-884.
5. Thaiwong T, Sledge DG, Collins-Webb A, Kiupel M. Immunohistochemical Characterization of Canine Oral Papillary Squamous Cell Carcinoma. Vet Pathol. 2018;55(2):224-232.
6. Uzal FA, Plattner BL, Hostetter JM. Alimentary system. In: Maxie MG, ed. Jubb, Kennedy and Palmer’s Pathology of Domestic Animals. Vol 2. 6th ed. St. Louis, MO: Elsevier; 2016:20-27.

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