What Is Your Diagnosis?

Katie S. Barry Department of Small Animal Clinical Sciences, College of Veterinary Medicine, University of Florida, Gainesville, FL 32610.

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Daniel D. Lewis Department of Small Animal Clinical Sciences, College of Veterinary Medicine, University of Florida, Gainesville, FL 32610.

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Erin G. Porter Department of Small Animal Clinical Sciences, College of Veterinary Medicine, University of Florida, Gainesville, FL 32610.

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History

An adopted 1-year-old 22-kg (48.4-lb) neutered male mixed-breed dog was referred to the University of Florida Small Animal Hospital because of an inability to completely open its mouth. The dog had been adopted from a shelter 6 months prior to hospital admission. At the time of the adoption, no information was available on the dog's history. The owners noticed dysphagia when they acquired the dog; however, the dog was able to prehend and chew dry dog food. No treatment had been attempted before referral.

At the time of hospital admission, the dog was thin with a body condition score of 3.5 of 9, but was bright and alert. A hard, sessile swelling was palpated ventral to the right orbit. After sedation, the oral cavity was assessed. A large amount of dental tartar was adhered to the buccal surface of the right upper and lower dental arcades. The teeth on the left side of the mouth appeared normal. The rostral portion of the mouth could not be opened symmetrically. The right side of the mouth could be opened only 1 cm; therefore, the molar teeth and the lingual surface of the left arcade could not be examined. The left side of the mouth could be opened approximately 3 cm. A firm, immovable intraoral mass was observed caudal to the commissure of the lips on the right side of the mouth. Dental occlusion was normal both rostrally and on the left side of the mouth. No other abnormalities were found on physical examination. Digital radiographsa of the skull were made with the dog under general anesthesia (Figure 1).

Figure 1—
Figure 1—

Right dorsal–left ventral oblique (A), dorsoventral (B), and left dorsal–right ventral oblique (C) radiographic views of the skull of a 1-year-old 22-kg (48.4-lb) neutered male mixed-breed dog evaluated for inability to fully open its mouth.

Citation: Journal of the American Veterinary Medical Association 249, 7; 10.2460/javma.249.7.743

Determine whether additional imaging studies are required, or make your diagnosis from Figure 1—then turn the page.→

Radiographic Findings and Interpretation

Along the ventral margin of the mid to caudal aspect of the body of the right mandible, there is a moderate, smoothly margined osseous proliferation with a short zone of transition and well-defined margins (Figure 2). Additionally, there is mild, ventral angulation of the caudal aspect of the body of the right mandible at this site. Osseous proliferation with a granular appearance extends dorsally from the affected portion of the right mandible toward the right zygomatic arch. Delineation of a direct connection of this osseous proliferation with the zygomatic arch is limited by radiographic superimposition. The right temporomandibular joint space is mildly widened. These findings suggest that the dog had a chronic malunion fracture of the caudal aspect of the right mandible and a suspected synostosis with the zygomatic arch. Other differential diagnoses for these radiographic findings include a congenital abnormality, osteoma, osteosarcoma, or multilobular osteochondrosarcoma.

Figure 2—
Figure 2—

Same radiographic images as in Figure 1. On the right dorsal–left ventral oblique projection (A), there is osseous proliferation on the ventral aspect of the right mandible (arrow). Osseous proliferation with a granular appearance extends dorsally from the right mandible to the level of the zygomatic arch (black arrowheads). In the dorsoventral projection (B), there is smoothly margined osseous proliferation superimposed on the right zygomatic arch and lateral aspect of the right mandible (white arrowheads). The mottled material ventral to the mandible and rostral to the nasal planum is nonradiopaque gauze from surgical preparation.

Citation: Journal of the American Veterinary Medical Association 249, 7; 10.2460/javma.249.7.743

The dog was later sedated, and CT examination of the head was performed by use of a 160-slice, multidetector-row, helical CT scannerb with 0.5-mm-thick slices. A comminuted fracture with poorly defined, sclerotic margins is present in the caudal aspect of the body of the right mandible, and there is smoothly margined osseous proliferation along the right mandible at the fracture site. In addition, there are ill-defined fractures at the junction between the right maxillary and zygomatic bones, immediately caudal to the right maxillary fourth premolar tooth. A well-defined, 1.5 (rostrocaudal) × 1.8 (mediolateral) × 3.5-cm (dorsoventral) region of osseous proliferation extends caudoventrally from the right maxillary fracture site to the right mandibular fracture site, forming a synostosis (Figure 3). Moderate atrophy of the right temporalis, masseter, and digastricus muscles is evident.

Figure 3—
Figure 3—

Transverse CT image of the skull of the same dog in Figure 1. Image was obtained in a bone window (window width, 2, 700 Hounsfield units; window level, 350 Hounsfield units) at the level of the maxillary second molar teeth with 3-mm slice thickness. Osseous proliferation extending between the right mandible (arrow) and zygomatic arch (arrowhead) is evident.

Citation: Journal of the American Veterinary Medical Association 249, 7; 10.2460/javma.249.7.743

Treatment and Outcome

The dog underwent surgery to excise the synostosis. The mass was approached from both the oral cavity and through a skin incision made dorsal to the swelling, paralleling the ventral border of the right zygomatic arch, and a 1-cm segment of bone was removed with a pneumatic burr. Additional burring of the proliferative bone was performed to establish more normal contours to the maxilla and mandible. The oral mucosa was closed over the remaining exposed maxillary and mandibular bone. Immediately after surgery, the mouth could be opened approximately 2 cm on the right side and the jaw opened more symmetrically rostrally. The dog was discharged from the hospital with instructions for the owners to gradually institute exercises to help improve opening of the right side of the mouth. The mouth was able to be opened 3.5 cm when the dog was reevaluated 3 weeks after surgery and 4.5 cm at 2 months after surgery.

Comments

Radiographic evaluation of the skull can be difficult because of complexity of the regional anatomy and superimposition of normal anatomic structures. Several ancillary projections can be used that help to obviate superimposition, such as rostrocaudal projections and 20° to 30° oblique dorsoventral projections. These projections are invaluable for precise localization if cross-sectional imaging is not available. Often, these projections require the mouth to be fully opened, which may not always be possible as a result of trauma or conformational anomalies,1 as was the case in the dog of the present report.

Radiographs should be obtained with the animal under general anesthesia; intubation may be difficult if there is underlying trauma or conformational anomalies. Computed tomography affords excellent spatial resolution because of its cross-sectional nature, thereby avoiding the problem of anatomic superimposition as seen with conventional radiography. For the dog of the present report, the mandibular fracture margins were difficult to evaluate on the radiographic images because of superimposition of the osseous proliferation creating the synostosis. Ancillary projections were attempted; however, the limited ability to open the dog's mouth and the fact that the mandible and maxilla had healed in a malunion made resolution of the superimposition difficult. Additionally, on the radiographs, the fractures involving the right maxillary and zygomatic bones were indistinct and the fracture margins could not be distinguished. Furthermore, although osseous proliferation could be seen extending dorsally from the mandibular fracture site, direct connection with the zygomatic arch could not be identified because of superimposition. In this dog, the CT examination was extremely valuable for diagnosing and more thoroughly evaluating the mandibular and maxillary fractures and for determining the sites where the osseous synostosis bridged the 2 fracture sites. Additionally, the CT examination was crucial for surgical planning to excise the synostosis in the dog of the present report.

Congenital maxillomandibular fusion, referred to as syngnathia, has been rarely reported for humans and is usually accompanied by additional congenital abnormalities of the head.2,3 Treatment of these patients involves osteotomy of the synostosis and use of a bite block to prevent reformation.4 We were unable to find any reports of congenital syngnathia in dogs, and we feel that the synostosis in the dog of the present report was likely due to trauma. To our knowledge, there is only a single case report of a 7-month-old dog that developed a mandibulo-zygomatic synostosis secondary to facial trauma.5 We strongly suspect that the dog of the present report sustained mandibular and maxillary fractures as a young puppy. We also suspect that the dog's fractures may have been managed with a muzzle before the dog was surrendered to the shelter. Muzzling would have immobilized the mandible and maxilla and allowed the synostosis to develop.

Footnotes

a.

CXDI-50 C detector and CXDI Control Software, version 7.0, Canon USA, Melville, NY.

b.

Toshiba Prime 160, Toshiba America Medical Systems, Tustin, Calif.

References

  • 1. Thrall DE. Principles of radiographic interpretation of the axial skeleton. In: Thrall DE, ed. Textbook of veterinary diagnostic radiology. 6th ed. St Louis: Elsevier Health Science, 2013;101113.

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  • 2. Daniels JS. Congenital maxillomandibular fusion: a case report and review of the literature. J Craniomaxillofac Surg 2004; 32: 135139.

  • 3. Fallahi HR, Naeini M, Mahmoudi M, et al. Congenital zygomatico-maxillo-mandibular fusion: a brief case report and review of literature. Int J Oral Maxillofac Surg 2010; 39: 930933.

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  • 4. Gupta RK, Jadhav V, Gupta A, et al. Congenital alveolar fusion. J Pediatr Surg 2008; 43: 14211425.

  • 5. Monteiro BP, Gibson T, Bratton A. Successful surgical treatment of mandibulo-zygomatic arch synostosis secondary to trauma in a dog. Can Vet J 2012; 53: 395398.

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  • Figure 1—

    Right dorsal–left ventral oblique (A), dorsoventral (B), and left dorsal–right ventral oblique (C) radiographic views of the skull of a 1-year-old 22-kg (48.4-lb) neutered male mixed-breed dog evaluated for inability to fully open its mouth.

  • Figure 2—

    Same radiographic images as in Figure 1. On the right dorsal–left ventral oblique projection (A), there is osseous proliferation on the ventral aspect of the right mandible (arrow). Osseous proliferation with a granular appearance extends dorsally from the right mandible to the level of the zygomatic arch (black arrowheads). In the dorsoventral projection (B), there is smoothly margined osseous proliferation superimposed on the right zygomatic arch and lateral aspect of the right mandible (white arrowheads). The mottled material ventral to the mandible and rostral to the nasal planum is nonradiopaque gauze from surgical preparation.

  • Figure 3—

    Transverse CT image of the skull of the same dog in Figure 1. Image was obtained in a bone window (window width, 2, 700 Hounsfield units; window level, 350 Hounsfield units) at the level of the maxillary second molar teeth with 3-mm slice thickness. Osseous proliferation extending between the right mandible (arrow) and zygomatic arch (arrowhead) is evident.

  • 1. Thrall DE. Principles of radiographic interpretation of the axial skeleton. In: Thrall DE, ed. Textbook of veterinary diagnostic radiology. 6th ed. St Louis: Elsevier Health Science, 2013;101113.

    • Search Google Scholar
    • Export Citation
  • 2. Daniels JS. Congenital maxillomandibular fusion: a case report and review of the literature. J Craniomaxillofac Surg 2004; 32: 135139.

  • 3. Fallahi HR, Naeini M, Mahmoudi M, et al. Congenital zygomatico-maxillo-mandibular fusion: a brief case report and review of literature. Int J Oral Maxillofac Surg 2010; 39: 930933.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 4. Gupta RK, Jadhav V, Gupta A, et al. Congenital alveolar fusion. J Pediatr Surg 2008; 43: 14211425.

  • 5. Monteiro BP, Gibson T, Bratton A. Successful surgical treatment of mandibulo-zygomatic arch synostosis secondary to trauma in a dog. Can Vet J 2012; 53: 395398.

    • Search Google Scholar
    • Export Citation

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