Diagnostic Imaging in Veterinary Dental Practice

Travis J. Henry 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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Boaz Arzi Department of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California-Davis, Davis, CA 95616

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History and Physical Examination Findings

A 17-year-old 550-kg (1,210-lb) castrated male American Quarter Horse was evaluated because of a swelling below the right ear, slow mastication, and a history of bleeding from the right nostril. Evaluation by the referring veterinarian included oral examination, endoscopic evaluation of the upper airway, radiography of the skull, and a CBC and serum biochemical analysis. Other physical examination findings included a body temperature of 38.3°C (101.0°F) with heart and respiratory rates within expected ranges. The results of oral examination and evaluation of radiographs were deemed inconclusive. Endoscopic assessment revealed a small amount of hemorrhage and edema in the right auditory tube diverticulum (guttural pouch). The blood sample analysis revealed neutrophilia (9,730 cells/μL [reference range, 2,260 to 8,500 cells/μL]) and a high plasma fibrinogen concentration (950 mg/dL [reference range, 200 to 400 mg/dL]); the rest of the results were unremarkable.

The horse was admitted to the imaging facility of a veterinary teaching hospital 1 week later. Physical examination at the referral hospital revealed a body temperature of 37.8°C (100.1°F). Heart and respiratory rates were within the respective reference ranges. The body condition score was 6 of 9, and the horse was otherwise considered to be in excellent athletic condition. No neurologic or muscular abnormalities were detected. The horse appeared to be masticating well but resisted palpation of the right temporomandibular joint area. A swelling was detected beginning at the base of the right ear and extending over the region of this joint (Figure 1). The patient was sedated with detomidine (0.01 mg/kg [0.005 mg/lb]) and butorphanol (0.005 mg/kg [0.002 mg/lb]) administered IV, and a full oral examination and dental charting were performed. The mouth was carefully opened with a speculum, encountering little resistance, and complete intraoral examination revealed no abnormalities. Lateral and ventrodorsal radiographic views of the skull and tangential (right caudodorsal–left rostroventral oblique and left caudodorsal–right rostroventral oblique) views of each temporomandibular joint were obtained.1 The tangential radiographic views are provided (Figure 2).

Figure 1—
Figure 1—

Photograph of the head of a 17-year-old castrated male American Quarter Horse that was evaluated because of swelling in the region of the right temporomandibular joint (black arrow), slow mastication, and a history of bleeding from the right nostril.

Citation: Journal of the American Veterinary Medical Association 243, 3; 10.2460/javma.243.3.337

Figure 2—
Figure 2—

Tangential (right caudodorsal–left rostroventral oblique and left caudodorsal–right rostroventral oblique)1 radiographic views of the left (A) and right (B) temporomandibular joints of the horse in Figure 1.

Citation: Journal of the American Veterinary Medical Association 243, 3; 10.2460/javma.243.3.337

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

Diagnostic Imaging Findings and Interpretations

Osteolysis was detected radiographically the lateral margin of the mandibular head of the condylar process, with irregular linear lucency ing at the articular surface and extending into the dylar process (Figure 3). The full extent of the ease process at the right temporomandibular joint could not be appropriately evaluated via radiographic examination. Immediately following the diographic study, the horse was further sedated acepromazine maleate (0.02 mg/kg [0.009 mg/ and detomidine hydrochloride (0.01 mg/kg [0.005 mg/lb]), IV, and contiguous 1.3-mm colmated transverse CT images (120 k V, 200 mA, 0.8 second rotation) of the skull processed with a bone algorithm were obtained (Figure 4). Images were all viewed at a window level of 450 Hounsfield units and window width of 1,500 Hounsfield units.

Figure 3—
Figure 3—

Same radiographic images as in Figure 2. In both views (A and B), the mandibular head (black arrow) and temporal bone (white arrows) are indicated. In panel B, osteolysis of the right mandibular head (black arrowhead) is evident.

Citation: Journal of the American Veterinary Medical Association 243, 3; 10.2460/javma.243.3.337

Figure 4—
Figure 4—

Computed tomographic images of the head of the horse in Figure 1. A—Transverse image obtained at the level of the temporomandibular joint. B—Sagittal image obtained at the level of the right temporomandibular joint. Severe subchondral osteolysis at the head of the mandible (black arrows) and mild subchondral osteolysis at the mandibular fossa of the squamous part of the temporal bone (arrowhead) are seen. In panel A, notice soft tissue swelling over the right temporomandibular joint (white arrows).

Citation: Journal of the American Veterinary Medical Association 243, 3; 10.2460/javma.243.3.337

Examination of the CT images revealed marked loss of cortical details and severe subchondral osteolysis of the right mandibular head, indicating destruction of the articular surface at this region (Figure 4). Mild osteolysis of the mandibular fossa of the squamous part of the temporal bone was also observed. In addition, there was increased joint space with soft tissue swelling at the lateral aspect of the joint. Finally, mild enlargement of the right stylohyoid bone with osseous enlargement of the stylohyoid joint and irregular osseous enlargement of the petrous temporal bone were observed (image not shown).

Treatment and Outcome

Recommended treatments included aggressive debridement of the joint with or without condylectomy. A right-sided condylectomy with joint debridement was performed, with histologic examination of a biopsy sample as well as culture and antimicrobial susceptibility testing. Histopathologic evaluation revealed a septic inflammatory process with no neoplastic cells detected. The results confirmed a diagnosis of septic arthritis with Streptococcus zooepidemicus infection. Following surgery, the horse masticated normally. The patient was treated for 30 days with chloramphenicol (45 mg/kg [20.5 mg/lb], PO, q 8 h), with strict instructions to the owners to wear protective gloves. Phenylbutazone (4 mg/kg [1.8 mg/lb], PO, q 12 h) was administered for 3 days. The horse was returned to competition 2 months after surgery.

Comments

The full nature and extent of temporomandibular joint disease in the horse of this report could not be adequately assessed by evaluation of conventional skull radiographs. However, the radiographic projections that had the highest yield from a diagnostic perspective were the tangential and ventrodorsal views of the right temporomandibular joint. The tangential projection was described by Townsend et al1 as a way to effectively image this joint in horses. In dogs and cats, CT has been proven to be a superior modality for imaging of the skull when compared with radiography.2 Further, CT has been demonstrated to be the imaging modality of choice in humans, dogs, and cats with suspected trauma to or pathological changes of the temporomandibular joint.3 In addition, in cases of temporomandibular joint destruction due to septic osteoarthritis in horses, CT was the imaging modality of choice.4,5

Advancements in the ability to perform CT scans in standing horses have greatly reduced the time involved in obtaining the images, the inherent risk of general anesthesia, and the associated costs. Computed tomography has been described as a superior imaging modality for assessment of the temporomandibular joint2,3,5,6 and is a valuable tool for evaluation of osseous lesions and spatial positioning of these bones. It also allows for images to be reconstructed into 3-D formats. This provides a greater amount of spatial information to allow adequate surgical planning. Magnetic resonance imaging is currently the standard-of-care diagnostic imaging method for the soft tissues of the temporomandibular joint in humans and may also provide superior images of this joint in horses.3,7 However, MRI of the equine skull requires the use of general anesthesia. In the horse of this report, the most adequate modality was CT, given the ability to acquire images and to detect bone lesions in a standing sedated patient.

Ultrasonography may have also been advocated in this case for evaluation of the temporomandibular joint and would have been helpful in guiding a needle to aspirate joint fluid for cytologic evaluation and culture. Ultrasound images may have provided superior detail of the articular disk, joint capsule, and lining.8 However, given the anatomy of the equine temporomandibular joint, the full extent of the bony changes would have been difficult to assess.8,9

The equine temporomandibular joint is divided into 2 synovial compartments, dorsal and ventral. Each compartment has a rostral and caudal component. The dorsal and ventral compartments are separated by the articular disk and do not communicate.10 Evidence of osteolysis and joint destruction was noted on the articular surface of the right temporomandibular joint of this horse, although lesions were most severe at the mandibular head. These changes were detected diffusely throughout the joint and would suggest that communication had been established between the dorsal and ventral compartments, possibly indicating that the articular disk was also affected. This was confirmed in surgery, where near total destruction of the articular disk was observed. Rule outs for the soft tissue swelling at the lateral aspect of the joint seen grossly and by use of CT could include an extension of joint inflammation or a neoplastic process.

Osteoarthritis of the temporomandibular joint is characterized by erosion, deterioration, and abrasion of the articular fibrocartilage with thickening and remodeling of the subchondral bone and presence of marginal osteophytes.3 Septic osteoarthritis is characterized by similar findings, except for a lack of subchondral bone remodeling and absence of marginal osteophytes.3 A neoplastic process may result in similar diagnostic imaging findings to those described for septic osteoarthritis. In 1 report, squamous cell carcinoma was found originating from the third eyelid in a horse, with extension to the temporomandibular joint.11 In previously reported cases4,12,13 of septic temporomandibular joint arthritis in horses, S zooepidemicus was isolated via microbial culture of samples from the affected joint, similar to the results for our patient. Furthermore, physical examination findings were similar in these horses, and all had neutrophilia and plasma fibrinogen concentrations greater than the reference range. However, septic arthritis of the temporomandibular joint is an uncommonly reported condition in humans and companion animals, as well as in horses.3,14

The hemorrhage in the guttural pouch, noted by the referring veterinarian, could not be fully explained. It is possible that the close proximity of the temporomandibular joint to the guttural pouch and the stylohyoid bone and joint, together with the extensive nature of the disease, may have contributed to bleeding in the guttural pouch. Another possibility was that trauma may have been an inciting cause of the entire disease process. However, the duration of the disease was unknown and the initiating cause could not be determined. Septic arthritis of this joint has been reported in horses with and without known trauma.4,12,13 Although the horse of the present report did not have a known history of trauma, this could not be ruled out.

In the few reported cases4,12,13 of septic arthritis of the temporomandibular joint in horses, those horses that underwent surgical treatment had favorable outcomes and returned to normal masticatory function. The case described here demonstrates that comprehensive high-definition CT imaging is critical for evaluation of equine temporomandibular joint diseases and is superior to radiography of the skull for this purpose. Our results also support the possibility of obtaining useful high-definition CT images of the head in standing sedated horses.

References

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