What is the typical pattern on MRI seen in multiple sclerosis (MS)?

Typical MRI Pattern in Multiple Sclerosis

The typical MRI pattern in multiple sclerosis (MS) is characterized by multiple round to ovoid T2-hyperintense lesions in characteristic locations: periventricular, juxtacortical, infratentorial, and spinal cord regions. 1

Characteristic Lesion Distribution

Periventricular Lesions

• Defined as T2-hyperintense cerebral white matter lesions in direct contact with the lateral ventricles, without intervening white matter 1
• Often have an ovoid shape and are oriented perpendicular to the ventricles (Dawson's fingers) 1
• Lesions abutting the ventricles and located in the corpus callosum are included in this definition 1

Juxtacortical/Cortical Lesions

• Juxtacortical lesions are defined as white matter lesions abutting the cortex without intervening normal white matter 1
• Cortical lesions involve the cortical ribbon and are best visualized using specialized sequences like double inversion recovery (DIR) or phase-sensitive inversion recovery (PSIR) 1
• These lesions are often missed on conventional MRI sequences 2

Infratentorial Lesions

• Defined as T2-hyperintense lesions in the brainstem, cerebellar peduncles, or cerebellum 1
• In the pons, MS lesions are typically located at the periphery, often contiguous with cisterns or involving the floor of the fourth ventricle 1
• In the midbrain, lesions are often located in the cerebral peduncles and close to the periaqueductal gray matter 1
• In the medulla, they typically have a uni- or bilateral paramedian location 1
• Cerebellar lesions frequently involve the middle and superior cerebellar peduncles 1

Spinal Cord Lesions

• MS spinal cord lesions are often multiple and short in cranio-caudal diameter 1
• The cervical portion of the spinal cord is more frequently involved than thoracic or lumbar regions 1, 3
• On axial MRI, most lesions are located in the periphery of the spinal cord, mainly in the lateral or dorsal columns 3
• Typical appearance is cigar-shaped on sagittal images and wedge-shaped on axial images 3

Lesion Characteristics

Morphology and Size

• MS lesions are typically round to ovoid in shape 1
• Range from a few millimeters to more than one or two centimeters in diameter 1
• Generally should be at least 3 mm in their long axis to satisfy diagnostic criteria 1
• Should be visible on at least two consecutive slices to exclude artifacts 1

Enhancement Pattern

• The pattern of gadolinium enhancement in MS lesions is variable but almost always transient (2-8 weeks, typically 4 weeks) 1
• Enhancement indicates active inflammation and breakdown of the blood-brain barrier 2

T1 "Black Holes"

• Hypointense lesions on T1-weighted sequences (black holes) represent areas of more severe tissue destruction and axonal loss 4
• Persistent black holes correlate with greater disability and are associated with more aggressive disease 5, 4

Diagnostic Criteria

• For the diagnosis of MS, there should be at least one typical MS lesion in at least two characteristic regions (periventricular, juxtacortical, infratentorial, and spinal cord) 1
• Serial imaging supports the diagnosis, as MS is characterized by the accrual of lesions over time and in new areas of the CNS 1
• T2 lesions can increase, decrease, or stabilize in size over time; small lesions may occasionally disappear 1

Advanced MRI Techniques

• Newer techniques provide increased sensitivity and specificity in detecting MS pathology 6, 2:
  • Double inversion recovery (DIR) and ultrahigh-field-strength MRI improve detection of cortical lesions 6
  • Diffusion tensor imaging helps assess white matter tract integrity 6
  • Magnetization transfer imaging may better reflect the extent of demyelination 6, 5
  • MR spectroscopy can detect metabolic changes in normal-appearing white matter 6, 7

Red Flags (Atypical Features)

• Symmetric central pontine lesions (suggestive of small-vessel disease) 1
• Periaqueductal lesions or area postrema lesions (suggestive of neuromyelitis optica spectrum disorders) 1
• Longitudinally extensive spinal cord lesions affecting more than three vertebral segments (suggestive of neuromyelitis optica spectrum disorder) 1, 3
• Extensive and selective involvement of lateral and posterior columns (suggestive of subacute combined degeneration) 3
• Diffuse spinal cord lesions with ill-defined borders 1, 3
• Multiple white matter lesions involving subcortical and deep white matter in a pattern suggestive of small-vessel disease 1
• Lesions with ill-defined borders in progressive multifocal leukoencephalopathy 1

Key MRI Sequences

• Key MRI sequences should include T2-weighted and T1 post-gadolinium images of the brain and spinal cord 1, 3
• 3D acquisitions or 2D with 3-mm thick slices and no gap between slices increase diagnostic yield 1
• Fat-suppressed MRIs of the optic nerves should be considered in atypical cases 1
• Axial imaging is particularly important to accurately localize lesions within specific spinal cord columns 3