Clinical Connections  –  Spring 2016

RVC Equine has a new, wider bore CT scanner, which improves the service’s diagnostic capacity for neck problems and will help generate a greater understanding of conditions affecting horses, which can help progress treatment methods.

Imaging is a key component of the diagnostic process in most patients, with more than 80% of cases undergoing one or more imaging procedure during their work-up.

Diagnostic imaging has undergone tremendous developments over the last decade, with more sophisticated methods such as CT and MRI becoming available for equine diagnostics.

Radiographs produce a 2D image of 3D structures, which means different anatomical and pathological features are superimposed on top of each other. This masks lesions and can make image interpretation difficult. This is especially the case in the equine head, where it is necessary to find very small but highly significant lesions (e.g. tooth root abscesses) amongst very complex anatomy.

CT and MRI get around this problem by producing virtual slices of structures resulting in a stack of images that can then be used to form a 3D picture. The RVC was the first equine hospital to install a CT scanner for horses, in 2003, and has since performed more than 2,000 scans, mainly of heads, but also of feet and part of the neck.

In 2009 the CT configuration at RVC Equine was changed to allow us to perform CT examinations of the head and part of the neck of the horse in standing position rather than having to put the horse under general anaesthesia (GA). Standing CT was a tremendous step forward and allowed RVC experts to identify new disorders, gain a better understanding of known problems and aided in the development of new treatments and the optimisation of existing treatment strategies. This has not only improved the welfare of the horses under RVC care but also internationally by sharing knowledge with the global veterinary community.

A standard CT scanner has an opening of 75cm, which is ample for the head and cranial part of the neck but limits its use for the rest of the neck to horses under GA. As GA carries a risk the benefits of an imaging procedure have to be balanced carefully against the risk associated with the procedure. For example, for horses suffering from compression of their spinal cord and impaired balance there is a risk associated with GA. Standing CT is therefore preferable in these cases.

Commenting on the value of the new scanner, Renate Weller, Professor in Comparative Imaging and Biomechanics, said: “Our new CT scanner is 10cm wider and while this may not sound much, it has a big effect on what we can fit into the scanner. The extra room allows us to include most of the neck, including the regions that are most commonly affected by problems in the standing horse.

She added: “We are very excited to be given this opportunity to improve our diagnostic ability for neck problems in the horse and expect that our understanding of these problems will improve tremendously. This will help the individual horse and also allow us to develop new treatment methods.”

Case Study

A 12-year-old cob cross, used for general riding, presented with neck pain and the owner reported stumbling. When RVC specialists examined the horse it showed mild ataxia and impaired neck movement. Radiographs showed marked enlargement of the left facet joint between the 5th and 6th cervical vertebrae. To further characterise this lesion and to evaluate the involvement of the spinal cord, a transverse CT image of the neck at the level of the 5th and 6th cervical vertebrae articulation was taken. The right joint was found to be markedly enlarged compared to the left, and bony protrusion was seen around the joint also extending into the vertebral canal. These indicated osteoarthritis of this joint. Changes towards the spinal cord are often impossible to appreciate on plain radiographs and in the past have required radiographs under general anaesthesia after the injection of a contrast agent around the spinal cord, often with unsatisfactory results. The new CT scanner enable the RVC to obtain a diagnosis in many cases without the need for more invasive techniques.

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