Neurodiagnostic tests aid in determining both localization and diagnosis. The main neurodiagnostic tests are: neuroimaging, cerebrospinal fluid (CSF) analysis, electroencephalography (EEG), and electromyography/nerve conduction studies (EMG/NCS). EEG is discussed in the context of the diagnosis of seizures and epilepsy (Ch. 18) and EMG/NCS in the context of the diagnosis of neuromuscular disease (Ch. 15 for the principles; Chs. 16–17 and 27, 28, 29, 30 for clinical use). Neuroimaging and CSF analysis are discussed throughout this book, but an introduction to their use and interpretation is provided here.
NEUROIMAGING IN CLINICAL PRACTICE
Neuroimaging allows for visualization of the structures of the neuraxis, and is used as an extension of the neurologic examination. If a patient’s symptoms and signs localize to a particular part of the neuraxis, neuroimaging of that region can provide additional information about the underlying pathologic process. The disease-based chapters of Part 2 of this book discuss when neuroimaging should be obtained with regard to particular symptoms and diseases, and how it can aid in diagnosis of various neurologic conditions.
In clinical practice, many patients have undergone neuroimaging studies before a neurologist has evaluated them, and some patients may be referred for neurologic evaluation because of neuroimaging findings rather than clinical findings. In such scenarios, part of the clinical reasoning process is interpreting the neuroimaging in the context of the clinical findings: Do the neuroimaging findings correlate with the patient’s clinical presentation? Are there aspects of the patient’s clinical presentation that do not have a neuroimaging correlate? Are there incidental findings that have no relationship to the patient’s current presentation but require further evaluation or longitudinal clinical and radiologic surveillance? Whether neuroimaging is obtained and reviewed before evaluation of a patient or in the process of a patient’s evaluation, neuroimaging must always be interpreted in the context of the patient’s history and physical examination in order to prevent misinterpretation/overinterpretation/underinterpretation of radiologic findings.
The cornerstones of neuroimaging of the nervous system are computed tomography (CT) and magnetic resonance imaging (MRI), both of which can be performed with or without intravenous contrast, and both of which can be used to evaluate the cerebral vessels (CT angiography [CTA] and venography [CTV]; MR angiography [MRA] and venography [MRV]). More specialized radiographic techniques used in the evaluation of neurologic diseases include CT and MR perfusion studies, MR spectroscopy, nuclear imaging (positive emission tomography [PET] and single photon emission computed tomography [SPECT]), and transcranial Doppler ultrasound.
What follows is a primer on neuroimaging. It is not intended to be of sufficient scope and detail for radiologists and radiology trainees, but is meant to provide the clinician with an approach to interpreting neuroimaging studies of the brain and spinal cord (bone and extracranial soft tissues are not discussed).
OVERVIEW OF NEUROIMAGING INTERPRETATION