CAPTIVATING CASES

Issue 24 - June 2016

Equine Nuclear Medicine

Animal Imaging's use of nuclear medicine is particularly well suited for the diagnosis of equine lameness and pathologies involving the pelvis, back, cervical spine and head.

In diagnostic nuclear medicine, low dosage radioactive substances are administered to patients. These radiopharmaceutical "tracers" settle in particular organs or bones, where they can be detected by a gamma camera and provide diagnostic information about those areas. Importantly, equine patients do not experience pain or short-term side effects from these modalities. Equine scintigraphy is often the best diagnostic choice for subtle lameness and performance limiting conditions that are difficult to diagnose with conventional diagnostic modalities.

CT Imaging of the Equine Head

Patient History

A 9-year-old Quarter Horse gelding was presented to Animal Imaging in March 2016 for a CT examination of the skull. In February, he appeared to have a choking/retching episode with a few drops of blood coming from the right ear. Though this was confirmed to not be a true episode of choke, he was having pain and difficulty swallowing. Initially, he had a mildly increased rectal temperature of 101F for five days. He was then placed on anti-inflammatories and antibiotics. Clinical signs resolved and he was weaned off the medications. Three days after cessation of therapy, he showed signs of being painful on swallowing again.

On initial examination, the gelding was bright, alert, and responsive. All vital parameters were within normal limits. No cranial nerve deficits were appreciated. Overall the physical examination was unremarkable.

Findings

CT Findings:

A CT examination was performed under standing sedation. The right stylohyoid bone was markedly thickened along its entire length. There was a moderate amount of bony proliferation surrounding the right temporohyoid articulation. The proximal most portion of the stylohyoid bone was more proliferative than the mid to distal portion. No fractures of the stylohyoid bone were appreciated. The right ear canal and tympanic bulla were partially filled with soft tissue attenuating material. No abnormalities of the guttural pouches, teeth, or sinuses were identified. These findings were supportive of temporohyoid osteoarthropathy (THO).

Moderate-markedly thickened right stylohyoid bone.

Although CT is not necessary to diagnose THO, it does offer several advantages. It provides superior anatomic detail and may provide information that cannot be obtained from radiographs or endoscopy. One study that performed CT examinations identified that 94% of horses had bilateral disease. This is vastly different compared to the previous report of 21% of horses having bilateral disease detected on endoscopy and radiography.¹ CT also allows for the detection of unilateral or bilateral otitis, which is often noted in association with THO. CT may be especially helpful for horses where a ceratohyoidectomy is being considered. This procedure may be done prophylactically, to prevent fracture of the stylohyoid bone, or may be performed therapeutically after the fracture has already occurred.

For this gelding, a unilateral ceratohyoidectomy was recommended to prevent fracture of the right stylohyoid bone.

Hilton, et al. The computed tomographic appearance of equine temporohyoid osteoarthropathy.Veterinary Radiology & Ultrasound, Vol. 50, No. 2, 2009, pp 151-156.