Cats may quite frequently show various conditions resulting in enlargement of oral or perioral tissues with a soft or hard consistency. These conditions may share similar clinical features which can lead to a wrong diagnosis unless thorough clinical examination is followed by diagnostic imaging and histopathology.

Because both benign dental diseases and cancerous lesions, such as squamous cell carcinoma, are frequently encountered in the feline oral cavity, early and thorough assessment is essential in achieving the correct diagnosis.

1. Diagnostic Approach

1.1 Signalment and History

Some disease processes are more likely to occur in young animals (pyotraumatic mucosal lesions, feline inductive odontogenic tumor) whereas others more frequently to affect older ones (malignant tumors). Breed is seldom a criterion of importance. History of previous recurrent diseases such as periodontitis, dental resorptions, eosinophilic oral lesions is to be taken into account as well as the slow or fast growing of the lesion.

1.2 Extraoral Examination

When the enlargement can be seen externally, facial structures should be palpated to assess its consistency and the presence of pain on palpation. Mandibular lymph nodes should be evaluated for unilateral or bilateral enlargement. With a maxillary deformation, nostrils and nasal airflow must be inspected to assess potential nasal involvement; ocular discharge, ocular inflammation and asymmetrical eyeball retropulsion must be assessed for potential periorbital diseases.

1.3 Intraoral Examination

Intraoral examination includes both assessment of mucosal surfaces and teeth. Any mass or bump must be clinically evaluated for its size, location pertaining to gingival or other oral mucosae, consistency (soft, fluctuant, firm, hard), appearance (smooth or irregular surface, ulcerative or proliferative aspect). Extension in the sublingual area, palatal area or oropharyngeal area must be noted; pharyngeal tonsils must be evaluated. When the lesion is close to or around a tooth, a thorough clinical dental examination is performed using dental probe and dental explorer; the tooth is assessed for evidence of fracture and pulpal exposure, tooth discoloration, dental resorption or periodontal pocketing.

1.4 Cytology and Histopathology

Cytology and/or histopathology are ways of achieving true diagnosis. Most of the time biopsy followed by histology is the preferred means. Cytology may be complementary to biopsy to evaluate lymph nodes (fine-needle aspiration), superficial masses (exfoliation cytology). The biopsy is performed under general anaesthesia and must sample the mass in its depth to avoid false diagnosis. When the mass is likely to invade bone structures, the biopsy is better performed after diagnostic imaging to make sure that the most representative tissues are sampled.

1.5 Diagnostic Imaging

Dental radiology is an essential diagnostic tool for assessing dental-related lesions. In cats, radiographs of teeth with clinical lesions yield additional or clinically essential information in 53.9% and 32.2%, respectively.¹ Masses localized along the dental arch or along the palate are eligible for diagnostic imaging. Depending on its localization, of its potential extent and on the presumptive diagnosis following clinical examination, dental radiographs, skull radiographs, CT scan or MRI may be indicated to assess lateral and deep extent of the mass. Isolated masses on oral mucosae may not require diagnostic imaging at first until identified as a potentially invasive lesion. Furthermore, CT scan and MRI allow assessment of locoregional extent and distant metastasis.

2. Different Clinical Conditions

2.1 Eosinophilic Granuloma Complex

Eosinophilic oral lesions may be found in cats in the perioral area (indolent ulcer on the maxillary lip facing the canine teeth and eosinophilic granuloma of the mandibular lip appearing as an enlarged "chin") and in the oral cavity. Slightly raised, red lesions with a yellowish patchy surface may be found on the surface of the tongue, sublingual mucosa, palatal or pharyngeal mucosa. They may appear as single or multiples nodules and be more or less spread over the mucosa.

2.2 Pyotraumatic Mucosal Lesions

Chronic traumatic lesions of the oral mucosa especially in the sublingual area or on the alveolar mucosa may appear as red proliferative or ulcero-proliferative lesions. Bacterial secondary infection may also give a suppurative aspect. Origins of the trauma include foreign bodies, laceration, or occlusal trauma. Brachycephalic cats have a tendency to have maxillary carnassials teeth inclined lingually, which may result in a traumatic contact with the alveolar mucosa along the mandibular carnassials teeth and result in the creation of a proliferative lesion.

2.3 Dental-Related Lesions

Dental resorptive lesions are frequently encountered in cats; 25–30% of cats show at least one tooth affected in the general random feline population, whereas the prevalence increases to 60–70% in cats presented for oro-dental diseases. Similarly, 70% of cats radiographically examined for oro-dental diseases show radiographic changes of periodontitis.² Dental infections due to pulpal necrosis or periodontitis as well as tooth root resorptive lesions may be associated with alveolar/jaw bone osteomyelitis. Clinically, a suppurative or nonsuppurative aspect can be observed altogether with soft tissue swelling and bony changes. Depending on chronicity of the lesion and balance between infection and host-defenses more or less bone apposition versus bone lysis can be seen. Additionally, buccal bone expansion has been described as an idiopathic condition in cats radiographically associated with vertical bone loss and appearing as an increase in the thickness of the alveolar bone and widening of the periodontal ligament space buccal to the canine teeth. Clinically, it appears as an enlargement of the bony crest, particularly visible on the maxillary teeth. The affected tooth may also present pathological eruption due to bone remodeling and subsequent tooth extrusion.

2.4 Oral Tumors

Oral tumors in cats comprise almost 10% of all tumors encountered in this species and the 3rd site of tumors after the hemolymphatic system and the skin. Squamous cell carcinoma is the most prevalent tumor and accounts for about 70% of oral tumors in cats.^3,4 Other tumors comprise odontogenic tumors, fibrosarcoma. Oral squamous cell carcinomas in cats are frequently observed on the sublingual, lingual, gingival and pharyngeal areas. Macroscopically they may appear as mostly ulcerative or ulcero-proliferative masses. Gingival carcinomas show bone invasion quite frequently and may present with an osteolytic or osteolytic and osteo-proliferative lesion, especially when the mandible is affected. In the caudal oral cavity, the tumor may spread to the orbital and zygomatic areas. Metastasis to the lymph nodes is observed in 30% of the cases and to the lung in 10% of the cases.⁵ Clinical presentation of oral squamous cell carcinoma in cats may be very confounding and can be misdiagnosed at first as an ulcerative lesion of the gingival or of the alveolar mucosa or as dental infection when bone lysis is present around the tooth. Prognosis is fair to poor depending on the local extent of the lesion at the time of diagnosis. It is therefore essential to use a thorough diagnostic scheme to avoid misinterpretation leading to a delayed diagnosis while wrongly attempting to treat the lesion as a benign mucosal or dental lesion.

The oral cavity in felines is peculiar because of the numerous inflammatory processes, dental related or not, that may be encountered and which may be confused with the development of a squamous cell carcinoma. Because of a huge difference in prognosis between these conditions, extreme care should be taken to reach as quickly as possible the correct diagnosis through a systematic diagnostic approach.

References

1.  Verstraete FJ, Kass PH, Terpak CH. Diagnostic value of full-mouth radiography in cats. Am J Vet Res. 1998;59(6):692–695.

2.  Lommer MJ, Verstraete FJM. Radiographic patterns of periodontitis in cats: 147 cases (1998–1999). J Am Vet Med Assoc. 2001;218:230–234.

3.  Stebbins KE, Morse CC, Goldschmidt MH. Feline oral neoplasia: a ten-year survey. Vet Pathol. 1989;26:121–128.

4.  Dorn CR, Priester WA. Epidemiologic analysis of oral and pharyngeal cancer in dogs, cats, horses, and cattle. J Am Vet Med Assoc. 1976;169:1202–1206.

5.  Soltero-Rivera MM, Krick EL, Reiter AM, Brown DC, Lewis JR. Prevalence of regional and distant metastasis in cats with advanced oral squamous cell carcinoma: 49 cases (2005–2011). J Feline Med Surg. 2014;16(2):164–169.