The days of a simple X-ray being the only imaging option for the assessment of health issues in horses are long gone.
Appropriate treatment plans for rehabilitation and recovery from musculoskeletal injuries in horses are built on the foundations of an accurate diagnosis and detailed characterization of the pathology.
Radiography and ultrasonography are the cornerstones of the evaluation, but can fall short in the assessment of some conditions, according to Dr Fred Caldwell and Dr Robert Cole. from Auburn University in Alabama.
The pair, writing in the latest issue of Equine Disease Quarterly, said more advanced imaging options such as computed tomography (CT), magnetic resonance imaging (MRI), and nuclear scintigraphy may be beneficial in select cases.
Computed tomography usually requires the horse be placed under general anesthesia to prevent movement. Areas that can be imaged include the lower limbs (from the carpus or tarsus down to the hoof) and the head. This form of imaging is best suited for evaluating bone as it provides excellent bone detail, but can also be useful for assessing soft tissues. Common indications for CT scanning in horses include the characterization of distal limb fractures and paranasal sinus disease related to ethmoidal hematoma, cysts, neoplasia, or dental issues.
Contrast enhancement with CT is another technique that can further differentiate normal versus abnormal areas within soft tissues, according to the pair. With this method, iodine-based contrast media is injected intravenously and can help enhance visualization of pathology. Computerized three-dimensional models can also be generated from a study, which further aids in conceptualizing damaged tissues.
An exciting improvement to this technology, which currently has very limited availability, is a standing CT system for imaging horses without the need for general anesthesia.
Magnetic resonance imaging systems vary from standing low-field strength units that are used to image the horse under sedation to more powerful high-field units that require general anesthesia. Because of the unit configuration, areas that can be imaged in horses are limited to the lower limbs (carpus/tarsus or below) and head.
Similar to CT, MRI generates multiple two-dimensional cross-sectional image slices produced using a variety of sequences that uniquely highlight different tissues such as bone, tendon, cartilage, and synovium. When these images are evaluated collectively, they provide an excellent characterization of the area of interest.
The strength of MRI is its ability to provide detailed information of soft tissue structures and to highlight areas of injury that are not often seen with any other imaging options. In addition, it can provide unique information about various bone injuries.
The use of MRI has transformed veterinary medicine’s understanding of injuries to the distal limbs of horses and can be invaluable in the work-up of the equine athlete, they said.
Another useful imaging technique is nuclear scintigraphy, which can highlight differences in blood flow patterns, soft tissue inflammation, and active bone modeling. Abnormal bone modeling can occur because of localized injury (bone bruises, stress fractures), degenerative changes (bone spavin, ringbone), excessive stress on certain areas (pedal osteitis), or inflammation and infection.
These conditions can be apparent by scintigraphy well before radiographic changes are visible.
Scintigraphy also has proven useful in the diagnosis or characterization of acute suspensory desmitis, sacroiliac injuries, soft tissue and osseous conditions of the foot and navicular region, cervical spine osteoarthritis, overriding thoracolumbar spinous processes (kissing spines), bone spavin, stifle injuries, pelvic fractures, radial fractures, high and low ringbone, subchondral bone cysts, and even dental disease.
CT, MRI, and nuclear scintigraphy continue to be valuable diagnostic tools that are becoming more widely available to equine patients. They are complementary to a clinical examination and diagnostic analgesia, radiography, and ultrasonography in the diagnosis and characterization of musculoskeletal pathology in the horse.
Equine Disease Quarterly is funded by underwriters at Lloyd’s, London, brokers, and their Kentucky agents.