Clinical application of multidetector computed tomography and magnetic resonance imaging for evaluation of cranial nerves in horses in comparison with high resolution imaging standards

Abstract

Summary Although horses are affected by cranial nerve disease, our understanding of these structures' imaging anatomy is limited, and the optimal modality for imaging of each of these nerves is unclear. The aim of this study was to describe the imaging appearance of the equine cranial nerves on high‐resolution 1.5T magnetic resonance imaging (MRI) and computed tomography (CT) scans of a cadaver head, and with these as standards, examine the utility of MRI and CT performed in clinical cases. High‐resolution MRI and CT images were prospectively acquired of the head of a normal Thoroughbred gelding following euthanasia. Ten clinical cases undergoing high‐field MRI under general anaesthesia and 10 clinical cases undergoing CT in the standing horse under sedation were retrospectively evaluated by three reviewers to assess cranial nerve visibility. On high‐resolution, thin‐slice, MRI scans of the normal cadaver head, each of the 12 cranial nerves and their topographic location could be appreciated. On high‐resolution cadaver CT, cranial nerves II, V and VII were clearly visible, but others were less easily identified; osseous structures were clearly visualised. Clinical MRI and CT allowed for variable visualisation of the cranial nerves, dependent on the sequence and the orientation of scan planes. High‐field MRI allowed excellent visualisation of equine cranial nerves, whereas CT allowed for more detailed visualisation of the osseous canals and foramina. In live horses, the ability to identify all 12 nerves is challenging with either MRI or CT; however, high‐field MRI enables better visualisation of the nerve bundles than CT.

Application and indications of magnetic resonance imaging and computed tomography of the equine head

“…2015; Dixon et al . 2017b). The transverse plane was found to be the most useful plane and the acquisition of MRI high‐definition sequences with thin slice thickness improved nerve identification ( Fig ) (Dixon et al .…”

Unusual pathophysiological mechanisms of ptyalism in two horses

“…Prescribing antimicrobials in the absence of a confirmed infectious cause is not good practice, but the risks of general anaesthesia or of withholding treatment to the individual patient were considered to outweigh the harm of possible unnecessary use of antimicrobials, in this case. Head MRI was not available (Dixon et al 2017). As stimulation of both autonomic systems acts to increase saliva secretion (Proctor and Carpenter 2007), it is difficult to explain how dysfunction could cause ptyalism although a denervation hypersensitivity, for example enhancing the response to circulating catecholamines, is a possibility.…”

Use of cone‐beam computed tomography for advanced imaging of the equine patient

“…Despite the increasing availability and use of MR units in practice for imaging of the distal limbs, comprehensive imaging of the equine proximal appendicular and axial skeletons remains a challenge. An increasing number of studies have been published using MRI for evaluation of the equine skull 56 including studies reporting the normal anatomy, 57,58 cranial nerves and various neurologic diseases, 59,60 sinonasal disorders, 61 and pulp cavity of normal and diseased cheek teeth 62 . Clinical use of MRI of the equine skull is primarily limited to single case reports 63‐67 or small case series, 68,69 although one large, multicentre study 70 has been published describing MRI use for a variety of different disorders of the skull.…”