CHAPTER 131 Diagnostic Imaging in Neurologic Disease
Diagnostic imaging of horses with neurologic disease can be both rewarding and challenging. Although they are very useful for horses with traumatic injury or congenital malformations, conventional radiographic studies lack specificity and sensitivity for detecting one of the more common equine neurologic diseases, cervical stenotic myelopathy (CSM). Computed tomography (CT) and magnetic resonance imaging (MRI) are advanced imaging methods that have become the standard of care in smaller veterinary patients and in human medicine, but their use in horses is limited because of patient size. Nuclear medicine is very sensitive in detecting areas of abnormal bone physiology, but the modality is nonspecific and rarely yields a definitive diagnosis. Ultrasound has limited applicability in the diagnosis of neurologic disease in horses, but it has been used to assist in cerebrospinal fluid (CSF) sampling and for injection of corticosteroids into the cervical vertebral articulations.
SKULL
Radiographic Interpretation
Stylotympanohyoid disease may manifest as a head tilt, facial-nerve paralysis or paresis, or both. The stylohyoid bones and their articulation with the temporal bone are best assessed on a perfectly straight DV view and on oblique views. In most instances, preexisting and chronic disease have manifested in bony proliferation of the stylohyoid bone or bones at or near the articulation with the tympanic bulla; if severe, bony proliferation can extend distally along the shaft of the stylohyoid bone. Fracture of the stylohyoid bone can occur. These changes are usually evident on the radiographs. In more subtle cases, slight asymmetry in the opacity of the petrous temporal bone and tympanic bullae may be the only radiographic abnormality. Mild radiographic obliquity can mimic disease by yielding an asymmetric appearance of the stylohyoid bones, so confirmation of suspicious lesions should be made or refuted by obtaining two orthogonal oblique radiographs. In this circumstance, oblique views may be made as previously noted, which results in the articulations projecting above and below each other, or rostral 25-degree lateral to caudolateral oblique images can be made that project the stylohyoid bones rostral and caudal to one another. Nuclear medicine can be used to identify active bone metabolism, a so-called hot spot, in horses with stylotympanohyoid disease.
