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Magnetic Resonance Imaging (MRI) in Neurologic Disorders

By

Michael C. Levin

, MD, College of Medicine, University of Saskatchewan

Last full review/revision Jul 2021| Content last modified Jul 2021
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Topic Resources
  • Cranial nerves

  • Brain stem lesions

  • Abnormalities of the posterior fossa

  • Spinal cord

CT images of these regions are often marred by bony streak artifacts. MRI is especially valuable for identifying spinal abnormalities (eg, tumor, abscess) compressing the spinal cord and requiring emergency intervention. Also, MRI is better for detecting demyelinating plaques, early infarction, subclinical brain edema, cerebral contusions, incipient transtentorial herniation, abnormalities of the craniocervical junction, and syringomyelia.

Normal Brain MRI (Sagittal)

MRI is contraindicated if patients

  • Have had a pacemaker or cardiac or carotid stents for < 6 weeks

  • Have ferromagnetic aneurysm clips or other metallic objects that may overheat or be displaced within the body by the intense magnetic field

Visualization of inflammatory, demyelinated, and neoplastic lesions may require enhancement with IV paramagnetic contrast agents (eg, gadolinium). Although gadolinium is thought to be much safer than contrast agents used with CT, nephrogenic systemic fibrosis (nephrogenic fibrosing dermopathy) has been reported in patients with impaired renal function and acidosis. Before using gadolinium in patients with renal disease, clinicians should consult with a radiologist and a nephrologist.

Magnetic resonance angiography (MRA) uses MRI with or without a contrast agent to show cerebral vessels and major arteries and their branches in the head and neck. Although MRA has not replaced cerebral angiography Cerebral catheter angiography X-rays taken after a radiopaque agent is injected via an intra-arterial catheter show individual cerebral arteries and venous structures of the brain. With digital data processing (digital subtraction... read more , it is used when cerebral angiography cannot be done (eg, because the patient refuses or has increased risk). As a check for stroke, MRA tends to exaggerate severity of arterial narrowing and thus does not usually miss occlusive disease of large arteries.

Susceptibility-weighted angiography (SWAN) can be useful in evaluating bleeding. It allows better visualization of both large and small blood vessels, microhemorrhages, and deposits of calcium and iron in the brain.

Magnetic resonance venography (MRV) uses MRI to show the major veins and dural sinuses of the cranium. MRV obviates the need for cerebral angiography in diagnosing cerebral venous thrombosis and is useful for monitoring thrombus resolution and guiding the duration of anticoagulation.

Magnetic resonance spectroscopy can measure metabolites in the brain regionally to distinguish tumors from abscess or stroke.

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