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Imaging the Feline Neurologic System
Shannon P. Holmes

Animal Cross-Sectional Imaging Specialists, Athens, GA, USA

6.1 Imaging the Feline seen as a hyperattenuating focus. It is also the modality
Neurologic System of choice for treatment planning with radiation therapy.
A primary benefit of CT is the speed of image acquisition.
Although clinical presentations of neurologic disease in With the multidetector CT units available, an entire cat may
feline patients are less frequent than in canine patients, be scanned within seconds with no compromise to image
the disease processes are similar and present similar sig- quality [2].
nificant risks to the quality of life of the cat. Full diagnos- Magnetic resonance imaging is widely recognized in
tic work‐up of feline patients with neurologic clinical both the human and veterinary fields to be the best modal-
signs will often require referral to a specialty practice due ity for evaluating the nervous system due to its superior
to the diagnostic imaging needs. Radiography and sonog- soft tissue contrast resolution. The small size of the feline
raphy ultimately have minor roles due to the osseous patient’s nervous tissue creates a major challenge in MR
enclosure of the central nervous system and the complex image acquisition, because smaller volumes of tissue are
skeletal anatomy of the calvarium and spine. These are sampled for high spatial resolution and to identify small
primarily used to screen for disease and/or to obtain sam- discrete structures. Lower resolution images overcome this
ples for definitive diagnosis. Similar to our human physi- issue of signal, but the resolution may be such that only
cian counterparts, magnetic resonance imaging (MRI) large lesions will be resolved (Figure 6.2a,b). Sampling of
and to a lesser extent computed tomography (CT) have smaller volumes of tissues means there are fewer protons
become the primary diagnostic imaging modality to best contributing to image generation. Therefore, longer scan
assess the nervous system. times or the use of stronger MR units (Figure 6.2c) are gen-
Diagnostic imaging of the feline nervous system is chal- erally required for feline patients due to their small size.
lenging because of the relatively small size of the anatomy. For the benefit of the patient, a balance must be struck
With CT imaging, areas of dense bone can create artifacts between image spatial resolution and the length of the
that hamper evaluation of certain areas of the nervous sys- scan, since all patients are anesthetized for MRI studies.
tem. This is best recognized where the density of the petrous If the osseous encasement of the nervous system is
temporal bone creates beam hardening artifact (Figure 6.1). removed or is extremely thin, ultrasound has proven benefi-
The use of reformatted high‐resolution thinly collimated cial in intraoperative delineation of tumors and their mar-
CT slices can reduce these artifacts. Some nervous tissue gins and confirmation of the completeness of removal of
may still be obliterated by the artifact, such as emerging cra- extruded intervertebral disc material [3]. Intraoperative
nial nerves in this area [1]. CT provides the best assessment ultrasound has also been used to facilitate intracranial
for the osseous anatomy of the calvarium (Figure 6.1a). The adeno‐associated virus (AAV) gene therapy (Figure 6.3) [4].
soft tissue resolution of CT is improved with the adminis- Anecdotally, some institutions will use intraoperative ultra-
tration of intravenous iodinated contrast, where contrast sound to sample tumors, presumably since neuronavigation
accumulates in highly vascular or permeable areas and is systems are still relatively limited in their availability.

Feline Diagnostic Imaging, First Edition. Edited by Merrilee Holland and Judith Hudson.
© 2020 John Wiley & Sons, Inc. Published 2020 by John Wiley & Sons, Inc.