What Is Your Diagnosis?

Kelly Shaw From the Department of Surgical Sciences, College of Veterinary Medicine, University of Wisconsin-Madison, Madison, WI 53706.

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Travis Henry From the Midwest Veterinary Dental Services, Elkhorn, WI 53121.

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Sabrina H. Brounts From the Department of Surgical Sciences, College of Veterinary Medicine, University of Wisconsin-Madison, Madison, WI 53706.

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History

A 26-year-old 422-kg Arabian mixed-breed gelding was referred for evaluation of a left mandibular swelling that had progressively grown following extraction of multiple mandibular cheek teeth approximately 5 weeks earlier when the referring veterinarian had performed a radiographic examination (not shown) and diagnosed severe periodontal disease, mobility of teeth, and fractured mesial root of the right mandibular third molar tooth (M3). The referring veterinarian then digitally removed the left maxillary fourth premolar tooth (P4) and orally extracted the left mandibular P4, first molar tooth, and second molar tooth.

On referral examination, the gelding had swelling (approx 7 × 5 × 2-cm) along the ventral aspect of the left mandible, with ulceration and necrosis of the overlying skin, mild enlargement of the left mandibular lymph node, and partial paralysis of the left side of the tongue. The referring veterinarian’s radiographic images obtained of the gelding’s skull prior to the described extractions were reviewed; no lateral enlargement of the mandible or other abnormalities beyond those described by the referring veterinarian were observed. Radiographic images were obtained (Figure 1).

Figure 1
Figure 1
Figure 1

Left lateral (A) and left 45° dorsal–right ventral oblique (B) radiographic images of the skull of a 26-year-old 422-kg Arabian mixed-breed gelding with a history of severe periodontal disease; removal of the left maxillary fourth premolar tooth (P4), left mandibular P4, and left mandibular first and second molar teeth 5 weeks prior to these images; and progressive left mandibular swelling after the extractions.

Citation: Journal of the American Veterinary Medical Association 259, 12; 10.2460/javma.20.05.0267

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Radiographic Findings and Interpretation

The gelding had an irregular linear radiolucency ventral to the alveolus of the left mandibular P4, with ventral cortical interruption due to ill-defined moth-eaten lysis (Figure 2). From the level of the left mandibular P4 to the apex of the extracted left mandibular second molar tooth, the ventral mandibular cortex was irregular and thin, with surrounding bony response and associated soft tissue swelling. A second linear radiolucency with irregular margins and similar underlying sclerosis also converged toward the left ventral mandibular cortex, where a smooth, periosteal reaction was appreciable, indicative of a long-standing process. Differential diagnoses included osteomyelitis secondary to previous apical tooth root infections or severe periodontitis and chronic mandibular fracture. The linear radiolucency could have been indicative of a draining tract from a previous tooth root abscess of the extracted left mandibular P4 that resulted in a linear lucency with cloaca formation. Generalized sclerosis suggestive of severe osteomyelitis was not evident, nor was a focal, well-defined zone of geographic lysis, as would have been expected with a focal bone abscess. Additional radiographic changes supporting periodontitis were appreciable, including blunted apices and diastemata.

Figure 2
Figure 2
Figure 2

Same radiographic images as in Figure 1. The left mandible has a vertical linear radiolucency (arrowhead) that is ventral to the alveolus of the extracted P4, converges with a second linear radiolucency with irregular margins (arrow), and extends toward the ventral mandibular cortex, where there is surrounding smooth periosteal reaction (asterisk). Additionally, there is moth-eaten lysis and remodeling of the left mandibular cortex (number sign).

Citation: Journal of the American Veterinary Medical Association 259, 12; 10.2460/javma.20.05.0267

Treatment and Outcome

We performed aggressive curettage of the left mandible, bacterial culture and local wound management of the mandibular swelling, which was confirmed to be a chronic abscess. An intraoral plug was placed in the vacated alveolus of left mandibular P4, and treatment was initiated with phenylbutazone (2.2 mg/kg, PO, q 12 h, for 10 days), trimethoprim sulfa (25 mg/kg, PO, q 12 h, for 14 days), and metronidazole (15 mg/kg, PO, q 6 h, for 14 days). Heavy growths of an α-hemolytic Streptococcus sp, Actinomyces sp, and Fusobacterium necrophorum were identified on bacterial culture, and antimicrobial treatment was not changed.

Sequential evaluations over the following 5-month period showed enlargement of the swelling over the left mandible, primarily laterally, and increased mobility of the left mandibular third premolar tooth (P3) and M3. Radiography performed 5 months after the initial referral examination revealed a large expansile multicavitary lesion of the lateral aspect of the left mandible, with severe cortical lysis and lateral extension of the mass beyond the level of the cheek teeth, consistent with neoplastic changes (Figure 3). The differential diagnosis list included primary bone lesion (eg, aneurysmal bone cyst) or primary bone neoplasia (eg, ameloblastoma, osteosarcoma, fibrosarcoma, or chondrosarcoma). Furthermore, the irregular linear radiolucency identified earlier could have been a pathological fracture secondary to neoplasia. Ultrasonography of the mandibular swelling revealed well-encapsulated masses with a homogenous soft tissue architecture that filled in the regions of cortical lysis (not shown). The left mandibular P3 and M3 were extracted orally, and a biopsy specimen was obtained from the bottom of the P3 alveolus. Histologic results indicated sarcoma with variable differentiation, a rare malignant mesenchymal tumor that tends to be highly aggressive. Palliative care was provided. Three months later, the owners elected euthanasia for the horse because of declining quality of life.

Figure 3
Figure 3
Figure 3

Dorsoventral (A) and left 45° dorsal–right ventral oblique (B) radiographic images of the skull of the horse described in Figure 1 obtained 5 months later. Compared with the previous images, the multicavitary expansile lesion (arrowheads) of the left mandibular body has severe progressive cortical lysis and enlargement.

Citation: Journal of the American Veterinary Medical Association 259, 12; 10.2460/javma.20.05.0267

Comments

Unilateral mandibular swelling, particularly along the mandibular body, in horses is a common sign usually caused by cheek teeth apical infections.1 Less common differential diagnoses include external trauma, fractures, and neoplastic or nonneoplastic mandibular growths.1,2,3 Of these conditions, both dental-related and traumatic causes of mandibular swellings are typically easy to diagnose and often respond favorably to extraction of the affected teeth combined with supportive care. The neoplastic or nonneoplastic mandibular growths, however, tend to be diagnosed at advanced stages for which treatment tends to be palliative and not curative.1

Radiography is the most commonly used ancillary technique for diagnosing mandibular growths in horses.4 In the horse of the present report, cortical lysis along the left mandibular body and the linear radiolucency associated with the extracted left mandibular P4 indicated a destructive process that resulted in pathological fracture due to increased weakness of the bone structure and decreased mechanical resistance. The pathognomonic findings of a periapical infection (ie, periapical sclerosis, apical blunting, and periapical halo formation) were contrarily not identified in the horse of the present report. Sequential radiography can also help to further distinguish between differential diagnoses, as seen in the present report in the progression of the neoplastic process over time.

Limitations of radiography are the superimposition of complex anatomic structures and potential underestimation of the true extent and severity of the lesion.2 Considering these constraints, CT is increasingly used to establish a diagnosis and to demarcate the margins necessary for surgical treatment and radiotherapy.5 However, CT is not always readily available or feasible, whereas successive radiography can be diagnostic, as seen in this case. Ultrasonography used in conjunction with radiography and CT may provide additional information on the soft tissue architectural changes, as seen in this case where multifocal well-encapsulated masses of soft tissue echogenicity were identified, filling in the regions of mandibular cortical lysis.

Histologic examination revealed sarcoma with variable differentiation. Accurate characterization of mandibular neoplasia in horses is invaluable for determining appropriate treatment recommendations and prognosis, which varies depending on classification and the extent of the tumor. If the tumor is detected early, treatment for affected horses may include surgical excision, mandibulectomy, or radiation therapy.1 Therefore, to achieve the most favorable results, it is important to recognize mandibular neoplasia as a differential diagnosis for mandibular swelling in horses early on and acquire an accurate diagnosis with imaging and histologic examination. Findings for the horse of the present report demonstrated the need to expand the differential diagnosis list to both include and prioritize neoplasia, especially in older horses that are refractory to extraction treatment when mobile teeth and mandibular enlargement are present.

References

  • 1.

    Dixon PM, Reardon RJ. Equine mandibular growths. Equine Vet Educ. 2015;27(1):1621.

  • 2.

    Bass K, Mochal-King CA, Cooley AJ, Brinkman E. Equine mandibular fibrosarcoma in two horses: clinical, diagnostic, and therapeutic considerations. J Equine Vet Sci. 2017;48:3138.

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  • 3.

    Pirie RS, Dixon PM. Mandibular tumours in the horse: a review of the literature and 7 case reports. Equine Vet Educ. 1993;5(6):287294.

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  • 4.

    Dixon PM, Loh N, Barakzai SZ. Swellings of the angle of the mandible in 32 horses (1997–2011). Vet J. 2014;199(1):97102.

  • 5.

    Knottenbelt D, Kelly D. Oral and dental tumors. In: Equine Dentistry. 3rd ed. Elsevier Saunders; 2011:127148.

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