Diagnostic Imaging in Veterinary Dental Practice

Amy Fulton Dentistry and Oral Surgery Service, William R. Pritchard Veterinary Medical Teaching Hospital, School of Veterinary Medicine, University of California-Davis, Davis, CA 95616.

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Nadine Fiani Dentistry and Oral Surgery Service, William R. Pritchard Veterinary Medical Teaching Hospital, School of Veterinary Medicine, University of California-Davis, Davis, CA 95616.

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History and Physical Examination Findings

A 10-year-old 40.0-kg (88.1-lb) castrated male Staffordshire Terrier was examined because of acute onset of pain and swelling involving the rostral aspect of the left mandible. The owner had noticed gingivitis at the level of the left mandibular premolar teeth approximately 1 month previously. Otherwise, there was no history of inappetence, reluctance to prehend, signs of pain during mastication, or changes in attitude.

Apart from intermittent lameness involving the left thoracic limb, the dog was reported to be otherwise healthy. The referring veterinarian had prescribed amoxicillin trihydrate–clavulanate potassium (6.25 mg/kg [2.8 mg/lb], PO, q 12 h) for treatment of mandibular swelling; the dog was also receiving carprofen (2.5 mg/kg [1.1 mg/lb], PO, q 24 h) because of osteoarthritis.

Results of a general physical examination were unremarkable, with the exception of left thoracic limb lameness that was localized to the elbow joint. Oral examination revealed substantial firm swelling of the ventral aspect of the left mandible, extending from the level of the canine tooth to the first molar tooth. A draining tract with a parulis was noted on the lingual aspect of the alveolar mucosa at the level of the second premolar tooth.

Results of a CBC, serum biochemistry panel, and measurement of urine specific gravity were within reference limits. The dog was anesthetized, and intraoral radiography and periodontal charting were performed. Select radio-graphic views are provided (Figure 1).

Figure 1—
Figure 1—

Lateral radiographic views (bisecting angle technique) of the rostral portion of the left mandible (A), left mandibular first through fourth premolar teeth (B), and caudal portion of the left mandible (C) in a dog examined because of left mandibular swelling and associated signs of pain.

Citation: Journal of the American Veterinary Medical Association 238, 4; 10.2460/javma.238.4.435

Determine whether additional studies are required, or make your diagnosis, then turn the page

Diagnostic Imaging and Interpretation

A large, ill-defined area of geographic bone loss with cortical bone expansion extending from the canine tooth to the fourth premolar molar tooth can be seen in the rostral portion of the left mandible (Figure 2). An unerupted first premolar tooth is evident distal to the canine tooth. External inflammatory resorption of the roots of the canine tooth and the second, third, and fourth premolar teeth is also present. The lamina dura of the canine tooth is absent, and the periodontal ligament space is substantially wider than normal. Ill-defined periapical lucencies are evident at the roots of the left fourth premolar tooth, along with well-defined periapical lucencies involving the roots of the first molar tooth. Both of these teeth had intact crowns, and there was no evidence to suggest primary endodontic disease.

Figure 2—
Figure 2—

Same radiographic views as in Figure 1. The rostral portion of the left mandible (A and B) is affected by a large area of geographic bone loss associated with expansion of the mandibular cortical bone. The affected area extends from the canine tooth to the fourth premolar tooth. Inflammatory root resorption (small black arrows) on all teeth from the canine tooth through the fourth premolar tooth and an unerupted first premolar tooth (large black arrow) are evident. In the caudal portion of the mandible (C), well-defined periapical lucencies can be seen at the roots of the first molar tooth (white arrows).

Citation: Journal of the American Veterinary Medical Association 238, 4; 10.2460/javma.238.4.435

The presence of an unerupted tooth within a cystic structure was strongly suggestive of a dentigerous cyst with secondary infection.1 In humans, benign lesions tend to result in tooth displacement, remodeling of the cortex of the mandible, and tooth root resorption as a result of pressure on neighboring structures.2 However, other conditions that could potentially cause aggressive bony destruction, including neoplastic conditions (eg, acanthomatous ameloblastoma) that have a cystic structure, osteomyelitis, and other cystic processes, were also considered in the differential diagnosis.

Treatment and Outcome

All teeth were sonically scaled supragingivally and subgingivally. Surgical extraction of the left mandibular canine, premolar, and first molar teeth was performed. Copious amounts of sanguineous and purulent fluid were found when the cystic structure was incised. The lining of the cystic cavity was curetted, and a sample was obtained and submitted for histologic examination.

On histologic examination, the submitted tissue was found to contain islands and papillary projections of disorganized and thick squamous epithelium. There was moderate anisocytosis and anisokaryosis, with an average of 5 to 6 mitotic figures/10 hpf. There were large areas of hemorrhage, necrosis, and inflammatory cells, with a few spicules of mature mineralized bone or cementum surrounded by inflammation and thick, undulating fronds of presumed neoplastic epithelial cells. Findings were consistent with a diagnosis of squamous cell carcinoma.

Recommendations to the owner included oncological staging followed by computed tomography of the head and, depending on the results of staging and computed tomography, unilateral mandibulectomy. If imaging or staging results precluded surgery, palliative radiation therapy combined with piroxicam treatment was recommended. The owner declined further treatment.

Comments

Dentigerous cysts develop as a result of proliferation of the enamel organ remnant and accumulation of fluid between the crown of an unerupted or impacted tooth and the reduced enamel epithelium.3,4 They represent the most common form of odontogenic cyst in dogs and are most frequently found in the mandible in association with an unerupted first premolar tooth.1 These cysts can enlarge and cause expansile lesions with associated bone loss, leading to pain and occasionally pathological fractures of the mandible.3 Owing to its radio-graphic and clinical appearance, the lesion in the dog described in the present report was considered highly likely to be a dentigerous cyst. However, infection of a dentigerous cyst is an uncommon finding.1

Histologic examination of cyst samples confirmed that the lesion in this dog was actually squamous cell carcinoma. This is one of the most common oral neoplasms in dogs.5 Although the etiology is unknown, the gingival tissues are more frequently affected than the other soft tissues in the oral cavity.5 Squamous cell carcinomas of the oral cavity are typically locally invasive, affecting underlying bony structures, but late to metastasize. The exception is tonsillar squamous cell carcinoma, which has a high metastatic rate. The median age of affected dogs is 8 to 9 years, and there are no known breed or sex predilections.5

The diagnosis of squamous cell carcinoma is made on the basis of results of histologic examination of a biopsy specimen. Staging, including thoracic radiography, abdominal ultrasonography, advanced imaging of the tumor site, and lymph node aspiration or biopsy, should be performed prior to attempting treatment. The current standard of care is wide surgical excision and histologic evaluation to verify that margins are tumor free. One study6 found that the 1-year survival rate was 91% with surgery alone for dogs in which complete resection of a mandibular squamous cell carcinoma was possible. For dogs in which the tumor is inoperable or for which the owner declines surgery, radiation therapy is a reasonable option.7 There are also some data to suggest that administration of piroxicam alone or in combination with other chemotherapeutic agents can prolong quality of life in dogs with oral squamous cell carcinoma.8

In the dog described in the present report, the draining tract and parulis in combination with the irregular periapical lucencies of the affected teeth were clear indications of secondary infection and suggested that more than 1 disease process was present. In humans, the epithelial lining of untreated dentigerous cysts can, rarely, undergo transformation into ameloblastoma or carcinoma, although this has yet to be conclusively shown to occur in dogs.2 What is less clear is where the infectious component originated. One possibility is that the invading tumor disrupted the normal defense mechanisms that prevent periodontal infection, causing rapid progression of subclinical periodontal disease and allowing bacteria to invade the periodontal space and extend into the cystic structure. Another potential scenario is that the enlarging cystic structure resulted in death of these teeth and that the teeth were secondarily infected via anachoresis. There was no evidence to prove or disprove either of these theories; however, primary endodontic disease seems unlikely, given that the crowns of the teeth were intact. It is worth noting that there was little or no periodontal disease elsewhere in the oral cavity.

In the present case, the clinical picture was not clearly indicative of an aggressive neoplastic process. The radiographic and clinical appearance of the mandible was suggestive of a dentigerous cyst with secondary infection. The present report demonstrates the importance of histologic examination of a biopsy specimen in dogs with an aggressive bony lesion involving the oral cavity because differences between aggressive bony lesions are not always distinguishable on radiographs alone.

References

  • 1.

    Verstraete FJMZin BPKass PH, et al. Clinical-pathological study of odontogenic cysts in dogs: 41 cases (1995–2010). J Am Vet Med Assoc 2011; 238:in press.

    • Search Google Scholar
    • Export Citation
  • 2.

    White SCPharoah MJ. Benign tumors of the jaws. In: White SCPharoah MJ, eds. Oral radiology—principles and interpretation. 5th ed. St Louis: Mosby, 2004;410457.

    • Search Google Scholar
    • Export Citation
  • 3.

    Regezi JASciubba JJJordan RC. Oral pathology—clinical pathologic correlations. 5th ed. Philadelphia: WB Saunders Co, 2008.

  • 4.

    Slootweg PJ. Dental pathology—a practical introduction. Berlin: Springer-Verlag, 2007.

  • 5.

    Liptak JMWithrow SJ. Oral tumors. In: Withrow SJVail DM, eds. Withrow & MacEwen's small animal clinical oncology. 4th ed. Philadelphia: Elsevier Saunders, 2007;455475.

    • Search Google Scholar
    • Export Citation
  • 6.

    Kosovsky JKMatthiesen DTMarretta SM, et al. Results of partial mandibulectomy for the treatment of oral tumors in 142 dogs. Vet Surg 1991; 20: 397401.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 7.

    Théon APRodriguez CGriffey S, et al. Analysis of prognostic factors and patterns of failure in dogs with periodontal tumors treated with megavoltage irradiation. J Am Vet Med Assoc 1997; 210: 785788.

    • Search Google Scholar
    • Export Citation
  • 8.

    de Vos JPBurm AGDFocker AP, et al. Piroxicam and carboplatin as a combination treatment of canine oral non-tonsillar squamous cell carcinoma: a pilot study and a literature review of a canine model of human head and neck squamous cell carcinoma. Vet Comp Oncol 2006; 3: 1624.

    • Search Google Scholar
    • Export Citation
  • Figure 1—

    Lateral radiographic views (bisecting angle technique) of the rostral portion of the left mandible (A), left mandibular first through fourth premolar teeth (B), and caudal portion of the left mandible (C) in a dog examined because of left mandibular swelling and associated signs of pain.

  • Figure 2—

    Same radiographic views as in Figure 1. The rostral portion of the left mandible (A and B) is affected by a large area of geographic bone loss associated with expansion of the mandibular cortical bone. The affected area extends from the canine tooth to the fourth premolar tooth. Inflammatory root resorption (small black arrows) on all teeth from the canine tooth through the fourth premolar tooth and an unerupted first premolar tooth (large black arrow) are evident. In the caudal portion of the mandible (C), well-defined periapical lucencies can be seen at the roots of the first molar tooth (white arrows).

  • 1.

    Verstraete FJMZin BPKass PH, et al. Clinical-pathological study of odontogenic cysts in dogs: 41 cases (1995–2010). J Am Vet Med Assoc 2011; 238:in press.

    • Search Google Scholar
    • Export Citation
  • 2.

    White SCPharoah MJ. Benign tumors of the jaws. In: White SCPharoah MJ, eds. Oral radiology—principles and interpretation. 5th ed. St Louis: Mosby, 2004;410457.

    • Search Google Scholar
    • Export Citation
  • 3.

    Regezi JASciubba JJJordan RC. Oral pathology—clinical pathologic correlations. 5th ed. Philadelphia: WB Saunders Co, 2008.

  • 4.

    Slootweg PJ. Dental pathology—a practical introduction. Berlin: Springer-Verlag, 2007.

  • 5.

    Liptak JMWithrow SJ. Oral tumors. In: Withrow SJVail DM, eds. Withrow & MacEwen's small animal clinical oncology. 4th ed. Philadelphia: Elsevier Saunders, 2007;455475.

    • Search Google Scholar
    • Export Citation
  • 6.

    Kosovsky JKMatthiesen DTMarretta SM, et al. Results of partial mandibulectomy for the treatment of oral tumors in 142 dogs. Vet Surg 1991; 20: 397401.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 7.

    Théon APRodriguez CGriffey S, et al. Analysis of prognostic factors and patterns of failure in dogs with periodontal tumors treated with megavoltage irradiation. J Am Vet Med Assoc 1997; 210: 785788.

    • Search Google Scholar
    • Export Citation
  • 8.

    de Vos JPBurm AGDFocker AP, et al. Piroxicam and carboplatin as a combination treatment of canine oral non-tonsillar squamous cell carcinoma: a pilot study and a literature review of a canine model of human head and neck squamous cell carcinoma. Vet Comp Oncol 2006; 3: 1624.

    • Search Google Scholar
    • Export Citation

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