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4 Advanced Imaging: Intracranial Surgery

Simon Platt and J. Fraser McConnell

Introduction Overview of Intracranial Imaging
Diagnostic imaging is important in the characterization and identi- Techniques
fication of gross structural abnormalities affecting the nervous system.
All imaging studies in the neurological patient should be preceded by Survey Radiography
clinical assessment aiming at ruling out nonneurological causes of Survey radiography of the cranium provides information largely
signs or systemic disease, determining the lesion localization within limited to the osseous component of the skull. Nonetheless plain
the nervous system, and identifying possible concurrent injuries. As radiographs are quick to obtain and relatively inexpensive but often
with anatomical imaging elsewhere in the body, functional disorders in neurological emergencies have a low diagnostic yield. The cor-
and diseases that do not result in a gross structural change in an organ relation between radiological abnormalities and neurological status
may not be visible on images. Such imaging is only useful if inter- is poor and fractures are often missed [1].
preted along with the patient’s signalment and history and with the Radiography has a very low diagnostic yield for the diagnosis
information provided by a comprehensive neurological examination. of intracranial pathology (Figure 4.1) and survey radiographs are
The choice of imaging modality depends upon multiple factors, not not usually indicated unless there is external swelling or known
least expense. Advanced neuroimaging is expensive and interpretation history of severe head trauma. Even with skull fractures, radiog-
is dependent on correlation of the neurological examination with the raphy will not provide information on severity of brain injury
imaging findings. Magnetic resonance imaging (MRI) or computed and many skull fractures may be missed. Depressed fractures or
tomography (CT) should not be used as substitutes for a thorough neu- swellings will only be visible if the X‐ray beam is tangential to the
rological evaluation. MRI requires general anesthesia and imaging may lesion. A specific lesion‐orientated oblique view may be required.
need to be delayed until the animal is stable. If the neurological exami- This is obtained by angling the X‐ray beam so it skylines the
nation indicates a central lesion, advanced imaging will be required to swelling or depression.
confirm or exclude a gross structural lesion. Other than in cases of Skull radiographs can be used in the investigation of peripheral
known or suspect trauma, MRI is the preferred imaging modality vestibular syndromes and facial nerve paresis due to otitis media‐
because it provides excellent soft tissue contrast. In the majority of cases interna (albeit with relatively low accuracy) but have limited value
of intracranial disease, radiography is of limited or no value. in the investigation of most cranial nerve or peripheral nerve
When considering using imaging during an intracranial surgical lesions. Survey radiography to assess the bullae in cases of peripheral
procedure, the aims of imaging and the type of surgery will help vestibular disease involves a rostro‐caudal open mouth oblique
determine the technique that should be chosen. However, the avail- or lateral oblique views and a dorsoventral view. The sensitivity
ability of intraoperative imaging at an individual center will limit of radiography for the diagnosis of otitis media compared with
the choices that can be made as will the user’s experience in inter- CT was only 0.85 in one study, with a specificity of 0.68 [2]. Bullae
pretation, which can be quite different from more standard intrac- radiographs are more difficult to interpret in large dogs because of
ranial imaging. This chapter addresses the use of radiography, the large amounts of overlying soft tissue and radiographs provide
ultrasound, CT, and MRI for intracranial imaging both prior to and no information about the intracranial extension of otitis media
during surgery. Additionally, from the perspective of what is cur- (Figure 4.2). Soft tissue/fluid opacity within the bullae may also
rently done in human medicine, we discuss what may be possible in be nonsignificant as primary secretory otitis media is a common,
veterinary patients in the future. apparently incidental finding in brachycephalic dogs.

Current Techniques in Canine and Feline Neurosurgery, First Edition. Edited by Andy Shores and Brigitte A. Brisson.
© 2017 John Wiley & Sons, Inc. Published 2017 by John Wiley & Sons, Inc.
Companion website: www.wiley.com/go/shores/neurosurgery

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