Odontogenic tumors (OTs) arise
from those embryonic tissues destined to develop into teeth and associated
structures. They originate from remnants of ondontogenic epithelium (rests of
Malassez and rests of Serres located within the periodontal ligament stroma and
gingiva) in the tooth-bearing areas of the mandible and maxilla. OTs are
considered neoplasms that range from benign to invasive in biologic behavior.
Historically, OTs have been
categorized as being epulides or an epulis. These terms have no specific
histopathologic connotation and are clinical terms used only to describe any
localized swelling on the gingiva. Many veterinarians and pathologists commonly
use both terms incorrectly today. The term epulis should not be used in defining a diagnosis. Confusion exists as several different
pathologic entities are categorized as epulides, and they are often mistakenly
considered benign and inconsequential.
Many epulides are
actually odontogenic tumors (or cysts) and definitive diagnosis requires a
biopsy and histopathologic assessment by a pathologist with formal training in
the pathology of odontogenic tumors and cysts. Treatment planning should occur
only after a definitive diagnosis has been established.
non-inductive, soft tissue tumors that, in spite of their benign appearance, should
be considered locally invasive neoplasms that do not metastasize. In dogs, two
subtypes may be encountered: 1) central (intraosseous) ameloblastoma and 2) peripheral
(acanthomatous) ameloblastoma. The central (intraosseous) ameloblastoma often presents as a facial swelling with bony distortion,
however, the main complaint may be an obvious tooth displacement or
malocclusion. Because they are usually painless, patients are
usually asymptomatic. On X-rays, it is common to see bone lysis with unilocular
or multilocular cystic structures around tooth roots. Peripheral (acanthomatous) ameloblastomas
(PAs) are often noted as gingival enlargements discovered as incidental
findings during routine dental screening exams. They are considered to be
benign tumors with invasive properties into surrounding bone. The infiltration
of bone distinguishes the PA from other ameloblastomas. On X-rays, patterns
are characterized by bony infiltration, alveolar bone resorption and tooth
displacement. The preferred treatment modality is surgical excision with
appropriate margins. Recurrence is common and may be disastrous. Incomplete
surgical removal, before a diagnosis is established, is the most common reason
considered rare in cats and those that do exist are sometimes confused with
other more common types of ondontogenic tumors in this species.
Peripheral Odontogenic Fibroma
Many of the gingival
enlargements previously described as fibromatous and ossifying epulides have
been reclassified as peripheral odontogenic fibromas (POFs). POFs are slowly
growing, benign neoplasms that are common in dogs and may be seen in cats. Histopathology
is necessary to definitively diagnose POFs. These tumors contain proliferative
fibroblastic connective tissue as well as proliferative ondontogenic epithelium
associated with foci of a variety of hard tissues, suggesting induction. Complete
surgical excision, with appropriate margins, is usually curative.
Amyloid Producing Ondontogenic Tumor
This OT type is rare in
dogs and cats and presents as a gingival swelling on either jaw in patients
between 8 to 13 years of age. These tumors are locally invasive, however, not metastatic. On radiographs, the lesions are often cystic and may resemble an ameloblastoma.
The presence of amyloid (Congo red stain), which tends to calcify, is a
characteristic histopathological finding of this tumor. Surgical excision, with
appropriate margins, is necessary to completely remove this invasive neoplasm.
Feline Inductive Odontogenic Tumor
This tumor is unique to
young cats (usually 8 to 18 months). Feline inductive odontogenic tumors (FIOTs)
are raised, submucosal, soft tissue masses most commonly located on the rostral
maxilla. This tumor is considered locally invasive, however, it does not metastasize.
Complete surgical excision is required.
Odontomas are benign inductive
tumors diagnosed in young dogs and cats of 6 to 18 months. Some consider
odontomas as actually being malformations and not neoplasms. These are well-differentiated,
non-invasive tumors characterized by the simultaneous occurrence of soft and hard
dental tissues (enamel, dentine, cementum, dental papilla). An odontoma in
which rudimentary tooth-like structures (denticles) are present is referred to
as a compound odontoma. An odontoma
in which the arrangement of dental tissues is haphazard, is called a complex odontoma.