Comparison and clinical application of CT and MRI for evaluation of the equine cranial nerves

Reasons for performing study:

Advanced imaging modalities enable assessment of the equine skull and brain. Horses are susceptible to neurological dysfunction of the cranial nerves; however, our understanding of these structures’ imaging anatomy is limited.

Hypothesis:

Magnetic resonance imaging (MRI) will be superior to computed tomography (CT) for the identification of cranial nerves, but optimal assessment may depend on both modalities.

Objectives:

Identify cranial nerves and compare and contrast the utility of MRI and CT images of cadaver and clinical material. Interpret images from both modalities and determine the cranial nerve imaging anatomy.

Study design:

Prospective cadaver anatomical study combined with retrospective clinical case study.

Methods:

The head of a neurologically normal 9-yearold Thoroughbred gelding was scanned immediately following euthanasia (performed for reasons unrelated to this study). High resolution MRI (1.5 Tesla) and CT examinations were conducted over a 12 h interval following euthanasia. Images obtained were compared with selected clinical cases which were scanned during anaesthesia (MRI; approximately 30–60 min) or standing sedation (CT; approximately 30 s).

Results:

On a high resolution MRI scan of a cadaver equine skull, each of the 12 cranial nerves and their topographic location was readily appreciated. Cranial nerves 1, 2, 3, 5, 7 and 8 were more easily identified in clinically relevant MRI scans. CT allowed visualisation of the stylomastoid foramen, the inner and middle ear and cranial nerves 2, 3, 5 and 7.

Conclusions:

High field MRI allows for excellent visualisation of equine cranial nerves. CT allows for detailed visualisation of the osseous canals and foramina. This study advances anatomical knowledge of the normal equine cranial nerves to aid interpretation in horses that display neurological dysfunction localising to the brain and brainstem