From the Guidelines
Localizing a neurological lesion requires a systematic approach that begins with a thorough history and neurological examination, as emphasized by the most recent and highest quality study 1. To initiate this process, it is crucial to determine if the lesion is in the central nervous system (brain and spinal cord) or peripheral nervous system (nerves, neuromuscular junction, muscles). The next step involves identifying the specific anatomical structure involved by analyzing the pattern of symptoms and signs. For central lesions, it is essential to determine if they are unilateral or bilateral and whether they affect the cerebrum, brainstem, cerebellum, or spinal cord. In contrast, for peripheral lesions, one must establish if they involve a single nerve, multiple nerves (mononeuropathy multiplex), or follow a length-dependent pattern (polyneuropathy).
Key examination elements include:
- Mental status
- Cranial nerves
- Motor function (strength, tone, bulk)
- Reflexes
- Sensory testing
- Coordination
- Gait Upper motor neuron signs (hyperreflexia, spasticity, Babinski sign) suggest central lesions, while lower motor neuron signs (hyporeflexia, atrophy, fasciculations) indicate peripheral involvement, as noted in 1. The temporal evolution of symptoms provides additional clues—sudden onset suggests vascular etiology, while gradual progression may indicate degenerative or neoplastic processes.
The use of imaging studies, such as MRI, is crucial in localizing neurological lesions, particularly when the clinical evaluation suggests involvement of the brain or spine, as recommended by 1. In the setting of trauma, a head CT without intravenous contrast is the preferred initial imaging choice, while CTA of the neck can be helpful if vascular injury is suspected. For ataxia unrelated to recent trauma, MRI is the preferred imaging modality, tailored to assess the brain or spine depending on the area of suspected pathology. The use of intravenous contrast is generally helpful in these cases.
In evaluating cranial neuropathy, complete evaluation of the nerves from their brain stem nuclei to their “end organs” must be performed, as discussed in 1. This can be accomplished using MRI with intravenous contrast, and the primary plane of study for head and neck evaluation is usually the axial plane, with additional orthogonal planes required depending upon the course of the various nerves. High–field strength magnets (1.5-3.0T) are preferred due to achievable signal to noise ratios, gradient strength, and spatial resolution.
From the Research
Step-by-Step Approach to Localizing Lesion in Neurology
- The traditional approach to lesion mapping involves identifying overlap in lesion location across patients with similar symptoms, termed lesion mapping 2.
- A newer approach sensitive to network effects involves functional neuroimaging of patients, but this requires specialized brain scans beyond routine clinical data 2.
- An alternative approach involves three steps:
- Transferring the three-dimensional volume of a brain lesion onto a reference brain 2.
- Assessing the intrinsic functional connectivity of the lesion volume with the rest of the brain using normative connectome data 2.
- Overlapping lesion-associated networks to identify regions common to a clinical syndrome 2.
Imaging Modalities for Lesion Localization
- Magnetic Resonance Imaging (MRI) is a preferred diagnosis procedure for detecting and locating stroke lesions 3, 4, 5.
- Computed Tomography (CT) and MRI have been the standard studies in stroke imaging, which have been complemented by CT and MR angiography, diffusion-weighted MR imaging, and cerebral perfusion studies 5.
- Vessel wall magnetic resonance imaging (VW-MRI) can be used to determine the effects of thromboembolism and mechanical thrombectomy on the arterial wall 6.
Clinical Applications
- Lesion mapping can be used to localize neurological symptoms in the setting of brain lesions 2.
- Stroke lesion outcome prediction can be based on MRI imaging combined with clinical information 3.
- Aspirin treatment may be effective in preventing further small silent lesions in patients with nonvalvular atrial fibrillation 4.