What does MRI (Magnetic Resonance Imaging) stenosis mean?

MRI Stenosis: Definition and Clinical Significance

MRI stenosis refers to the narrowing of a canal, vessel, or passage in the body that is visualized and measured using Magnetic Resonance Imaging technology. This imaging finding has significant implications for patient morbidity, mortality, and quality of life depending on the location and severity of the stenosis.

Types of Stenosis Visualized on MRI

• Spinal Stenosis: Narrowing of the spinal canal that may compress the spinal cord or nerve roots, commonly seen in the cervical and lumbar regions 1, 2
• Vascular Stenosis: Narrowing of blood vessels, such as carotid artery stenosis or coronary artery stenosis 3
• Foraminal Stenosis: Narrowing of the neural foramina where nerve roots exit the spine 1, 2

Diagnostic Criteria and Grading

• MRI allows for precise measurement of stenosis severity using specific parameters:

  • For spinal stenosis, measurements include anteroposterior diameter of the spinal canal, with level-specific cut-off values (e.g., cervical spine: C3 < 12.9 mm, C4 < 11.8 mm, C5 < 11.9 mm, C6 < 12.3 mm, and C7 < 13.3 mm) 4
  • For vascular stenosis, measurements typically assess the percentage of luminal narrowing compared to normal vessel diameter 3

• Comprehensive grading systems exist for different types of stenosis:

  • Lumbar stenosis can be classified by location (central, lateral recess, foraminal) and severity (mild, moderate, severe) 2
  • Vascular stenosis is typically graded by percentage of narrowing (e.g., <50%, 50-69%, >70%) 3

Clinical Applications

Vascular Stenosis Assessment

• MRI angiography (MRA) is valuable for evaluating carotid artery stenosis, particularly when:

  • Multivessel cerebrovascular disease is present
  • Very severe stenosis exists that might cause artifactual measurements with other modalities 3
  • Anatomical features of plaque need assessment for stroke risk prediction 3

• For carotid stenosis, MRA has high sensitivity (90%) and specificity (94%) for identifying clinically significant stenosis (>70%) 3

• MRA may overestimate the degree of stenosis in severe cases, and contrast administration can sometimes reduce this overestimation 3

Spinal Stenosis Evaluation

• MRI is the preferred first-line imaging modality for spinal stenosis as it:

  • Does not require ionizing radiation or contrast injection 5
  • Provides excellent visualization of soft tissues including ligaments, discs, and neural elements 2, 5
  • Can detect dynamic compression with specialized techniques like flexion-extension MRI 6

• Multilevel developmental cervical spinal stenosis (≥3 stenotic levels) significantly increases the risk of developing degenerative cervical myelopathy (odds ratio 6.12) 4

Technical Considerations and Limitations

• Metal implants (like coronary stents) can cause local artifacts that may affect image quality but generally don't pose safety concerns 7

• Standard neutral-position MRI may miss dynamic stenosis that only appears during certain movements, necessitating specialized techniques like flexion-extension MRI in some cases 6

• For vascular stenosis, MRA may have limitations:

  • Overestimation of high-grade stenosis or near occlusion 3
  • Difficulty differentiating between high-grade stenosis and complete occlusion in some cases 3

Clinical Implications and Management

• Identification of stenosis on MRI guides treatment decisions:

  • For spinal stenosis: surgical decompression versus conservative management 1, 2
  • For vascular stenosis: medical management versus interventional procedures (angioplasty, stenting, endarterectomy) 3

• The degree of stenosis correlates with clinical symptoms and outcomes:

  • In carotid stenosis, >70% narrowing is generally considered hemodynamically significant and may warrant intervention 3
  • In spinal stenosis, the correlation between imaging findings and symptoms can be variable, requiring careful clinical correlation 2, 5

• Post-treatment surveillance with MRI can detect complications such as restenosis after interventional procedures 3