Diagnostic Imaging in Veterinary Dental Practice

Michael C. Congiusta from the Dentistry and Oral Surgery Service, Red Bank Veterinary Hospital, Tinton Falls, NJ 07724.

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Kevin L. Haggerty from the Dentistry and Oral Surgery Service, Red Bank Veterinary Hospital, Tinton Falls, NJ 07724.

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History and Physical Examination Findings

An 11-year-old 24.3-kg spayed female mixed-breed dog was evaluated for a recently developed darkly pigmented palatal growth. The client reported noticing a round black lesion adhered to the hard palate 1 month prior to examination.

Results of a general physical examination, CBC, and serum biochemical analysis were unremarkable. Intraoral examination revealed a darkly pigmented mass on the midpalate adjacent to the right maxillary second premolar tooth (Figure 1). The dog was anesthetized; CT images of the head and thorax were obtained before and after IV administration of contrast medium (iohexol solution, 700 mg of I/kg). The images were reviewed with soft tissue (window width, 400 HU; window level, 40 HU) and bone (window width, 1,500 HU; window level, 300) window settings. Selected CT images are provided (Figure 2).

Figure 1
Figure 1

Photograph of a darkly pigmented palatal mass just right of the midline at the level of the maxillary second premolar teeth in an 11-year-old 24.3-kg dog.

Citation: Journal of the American Veterinary Medical Association 259, 7; 10.2460/javma.259.7.729

Figure 2
Figure 2

Representative postcontrast transverse CT images of the head of the dog in Figure 1. The CT volume data were acquired and reconstructed in a series of contiguous transverse images with bone and soft tissue algorithms (slice thickness, 1.25 and 2.5 mm, respectively). The images are shown in panels A and B with soft tissue (window width, 400 HU; window level, 40 HU [A]) and bone (window width, 1,500 HU; window level, 300 HU [B]) window settings, respectively.

Citation: Journal of the American Veterinary Medical Association 259, 7; 10.2460/javma.259.7.729

Diagnostic Imaging Findings and Interpretation

Transverse images revealed a 6 × 12-mm, oval, mildly lobulated, and mildly heterogeneously contrast-enhancing mass in the palatal mucosa primarily on the right side and extending left of the midline at the level of the maxillary second and third premolar teeth (Figure 3). There was no evidence of osteolysis of the maxillary bone dorsal to the contrast-enhancing soft tissue mass. The lymph nodes were not enlarged and did not have peripheral contrast enhancement with central nonenhancing regions. There were no other clinically important abnormalities in the nasal cavities, pharynx, larynx, sinuses, ocular structures, cranial cavity, visible lymph nodes and salivary glands, tympanic bullae, ear canals, visible musculoskeletal structures, thyroid glands, or visible portion of the neck. Differential diagnoses for the oral mass included melanoma, other nonodontogenic tumors (ie, fibrosarcoma or extramedullary plasmacytoma), and nonneoplastic oral proliferative lesions (eg, fibroma).

Figure 3
Figure 3

Same CT images as in Figure 2 (A and B). A 6 X 12-mm mass (arrows) is outlined (dashed line) in the palatal mucosa. The mass is primarily on the right side but extends across the midline toward the left side of the oral cavity. There is no evidence of osteolysis of the nasal turbinates or maxillary bone of the hard palate.

Citation: Journal of the American Veterinary Medical Association 259, 7; 10.2460/javma.259.7.729

Treatment and Outcome

A complete periodontal treatment (charting, ultrasonic scaling, and polishing) was performed under the same anesthetic episode as CT, and an incisional biopsy of the palatal mass was obtained and submitted for histologic examination. Staging was recommended to assess for the presence of malignant neoplasia. Histologic evaluation of the mass and cytologic examination of the mandibular lymph node samples revealed melanocytoma and lymphoid hyperplasia, respectively. Computed tomography of the thorax revealed no evidence of metastasis. Abdominal ultrasonography was declined because of financial constraints.

At a second visit 14 days later, the dog was anesthetized again and marginal excision (with 3-mm margins) of the mass was performed without removal of the maxillary bone of the hard palate. The excision site was allowed to heal by second intention. The mass was submitted to a veterinary diagnostic laboratory,a and a specialized immunohistochemistry panelb was requested to evaluate for histologic biomarkers reported to have valid prognostic utility for assessing the biological behavior of oral melanocytic neoplasms. Biomarkers exceeding given thresholds (nuclear protein Ki67 immunohistochemical staining index > 19.5, ≥ 30% atypical nuclei, and > 3 mitotic figures/10 hpf) have been associated with malignant behavior and an increased risk of death 1 year after diagnosis.1–3 Histologic diagnosis confirmed the diagnosis of melanocytoma, and biomarker testing of the mass revealed a Ki67 index of 1.4, < 30% atypical nuclei, and 0 mitotic figures/10 hpf.

The dog was discharged from the hospital, and the owner was instructed to administer carprofen (2.2 mg/kg, PO, q 12 h) and gabapentin (5 mg/kg, PO, q 8 h) for 3 days and to rinse the oral cavity with a chlorhexidine-containing oral rinse agent (1 mL, q 12 h) for 28 days. The owner was also instructed to feed a soft diet and restrict exercise to leash walking for the next 2 weeks and to schedule telehealth recheck appointments every 12 weeks for 2 years to follow up and monitor clinical progress. Five months after the diagnosis was made, there was no evidence of regrowth.

Comments

For the dog of this report, malignant oral neoplasms were included in the differential diagnosis list; thus, CT was performed to aid planning for possible surgical resection and assess for the presence of heterogenous contrast enhancement of soft tissue or neighboring bone, osteolysis, cortical bone destruction, invasion of neighboring structures, periosteal reactions, and pulmonary metastasis.4 The CT examination revealed a mildly heterogeneously contrast-enhancing mass in the palatal mucosa; there was no evidence of metastasis to regional lymph nodes, bone destruction, or contrast enhancement of the bone and soft tissue, all of which are features that may be found in patients with melanoma or other malignancies.5

A marginal excision was performed, and the mass was submitted for histologic examination to confirm the initial diagnosis, which was made through histologic evaluation of an incisional biopsy sample, and to ensure the desired tissue margins were achieved. In this case, marginal surgical excision of the mass and submission for histologic parameter analysis verified the diagnosis and helped establish an accurate prognosis.

The term melanocytoma refers to benign tumors of melanocytic origin. It is widely accepted that melanocytic neoplasms in the oral cavity are aggressive, but there is a subset of melanocytomas that have benign biological behavior.2,6 Melanocytomas are typically very well circumscribed and < 10 mm in diameter at the time of diagnosis.7 For the present report, it is important to note that there were no previous measurements or reporting of the mass prior to the initial examination described here. The diagnosis for the dog of this report was of an atypical-sized melanocytoma that was larger than the published general size range of < 10 mm.

Results from the histologic and immunohistochemical analysis supported that the mass had benign behavior; however, it is important to recognize there are no accepted criteria for prognostication, so these values should be interpreted with caution. The biological behavior and extent of involvement of the melanocytic neoplasm are often used to determine whether adjunctive immunotherapy (canine melanoma vaccine), radiation therapy, or surgical intervention is indicated.7 Although a high proportion of oral melanocytic neoplasms have malignant characteristics, benign melanocytic tumors have also been recognized in the literature.2,8 Although the term melanocytoma is currently in use, it should be interpreted with caution because it remains unclear whether benign melanocytic tumors have the potential to develop malignant behavior. The results for the dog of this report supported the diagnosis of oral melanocytoma with benign clinical behavior, which is an uncommon finding in dogs.9 Strict monitoring of the patient and follow-up should be implemented to check for evidence of disease recurrence or progression. Diagnostic imaging, histologic examination, cytologic tests, and prognostic immunohistochemical testing should be used to aid in the differentiation between benign and malignant melanocytic neoplasms. The use of CT to evaluate for evidence of osteolysis and lymphatic or pulmonary metastasis played a crucial role in this case with respect to surgical treatment planning and support of the diagnosis of a benign melanocytic neoplasm of the oral cavity.

Acknowledgments

The authors declare that there were no conflicts of interest.

Footnotes

a.

Michigan State University Veterinary Diagnostic Laboratory, Lansing, Mich.

b.

Melanoma Panel–Prognostic, Michigan State University Veterinary Diagnostic Laboratory, Lansing, Mich.

References

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    Murphy BG, Bell CM, Soukup JW. Tumors arising from the soft tissues. In: Murphy K, ed. Veterinary oral and maxillofacial pathology. Hoboken, NJ: Wiley-Blackwell, 2020;129133.

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