When should I order a Magnetic Resonance Imaging (MRI) or Magnetic Resonance Venography (MRV)?

When to Order MRI/MRV

MRI and MRV should be ordered when evaluating suspected cerebrovascular disease, particularly when venous sinus thrombosis is suspected, for children with suspected pseudotumor cerebri syndrome, and for patients with unexplained intracranial hemorrhage to identify underlying vascular abnormalities.

MRI Indications

Suspected Stroke or Cerebrovascular Disease

• Acute ischemic stroke: MRI without IV contrast is the preferred imaging modality due to its superior sensitivity for detecting early ischemic changes 1
• Late-presenting stroke: MRI is useful to evaluate the extent of completed infarct and identify potential underlying etiology 1
• Thunderclap headache: When subarachnoid hemorrhage is suspected, non-contrast CT is first-line, but MRI with FLAIR and SWI/GRE sequences can detect acute and subacute SAH with sensitivity of 50-94% 1
• Parenchymal hemorrhage: MRI without IV contrast is highly sensitive for detecting hemorrhage, especially with susceptibility-weighted imaging (SWI) sequences 1

Pediatric Indications

• Headache with concerning features: MRI is indicated when headaches are associated with:
  • Abnormal neurological examination
  • Early morning or nocturnal occurrence with vomiting
  • Progressive worsening in frequency or severity
  • Changes in personality or school performance 1
• Seizures: MRI without IV contrast is indicated in the evaluation of patients with seizures 1
• Sickle cell disease: MRI with MRA is indicated for children with sickle cell anemia presenting with headache 1

MRV Indications

Venous Sinus Abnormalities

• Suspected cerebral venous thrombosis (CVT): MRV is the preferred first-line imaging modality for diagnosing CVT, showing both thrombus and parenchymal changes 2
• Pseudotumor cerebri syndrome (PTCS): MRV is indicated in conjunction with MRI for patients with suspected PTCS 1
  • A study of over 200 MRV studies found 52% of suspected pseudotumor cerebri cases showed evidence of venous obstruction in the dominant side of venous circulation 1
  • Follow-up MRV after CSF drainage may be helpful to assess reversibility of venous outflow obstruction 1

High-Risk Populations

• Mastoiditis: Children with mastoiditis are at particularly high risk for venous sinus thrombosis 1
• Intracranial extension of infection: MRV is indicated when there is concern for venous sinus thrombosis in children with intracranial extension of infection 1
• Oral contraceptive use: Girls using oral contraceptives are at increased risk for thrombosis 1

Evaluation of Intracranial Hemorrhage

• Proven parenchymal hemorrhage: MRV should be considered if there is concern for venous thrombosis or vascular malformation 1
• Unexplained intracranial hemorrhage: MRV is rated as "usually appropriate" (rating 7/9) for evaluation of proven parenchymal hemorrhage 1

Technical Considerations

MRV Protocols

• Contrast vs. non-contrast: The use of contrast in MRV depends on institutional preferences 1
• Contrast-enhanced MRV: May be helpful when evaluating areas such as the sigmoid venous sinuses, which are often degraded by artifact on non-contrast MRV 1
• Time-of-flight (TOF) technique: Non-contrast TOF MRV may miss intracranial sinovenous stenosis that can be detected with contrast-enhanced MRV 1

Alternative Imaging Options

• CT venography (CTV): If MRV is not possible or results are ambiguous, CTV is a reasonable alternative with high sensitivity and specificity (87% accuracy) for detecting venous sinus thrombosis 1, 2
• MRV advantages over CTV: MRV is generally preferred over CTV because of radiation concerns, especially in children and young adults 1

Follow-up Imaging

• Persistent symptoms: Early follow-up CTV or MRV is recommended for patients with persistent or evolving symptoms despite medical treatment 2
• Recurrent symptoms: In patients with previous CVT who present with recurrent symptoms, repeat CTV or MRV is recommended 2
• Recanalization assessment: Follow-up CTV or MRV at 3-6 months after diagnosis is reasonable to assess recanalization of the occluded cortical vein/sinuses in stable patients 2

Common Pitfalls and Caveats

• False negatives: CT or MRI brain alone may be normal in up to 30% and 23% of CVST cases respectively, while MRV of these patients will reveal the thrombosis 3
• Overestimation of stenosis: Non-contrast MRA of the neck tends to overestimate the degree of carotid stenosis compared with contrast-enhanced MRA 1
• Artifact considerations: Non-contrast MRV can have artifactual flow voids in the transverse sinuses that may mimic thrombosis 1
• FLAIR artifacts: Signal in the sulci on FLAIR sequence can be artifactually increased in children receiving propofol and supplemental oxygenation, potentially mimicking subarachnoid hemorrhage 1

By following these evidence-based guidelines for ordering MRI and MRV, clinicians can optimize diagnostic accuracy while minimizing unnecessary imaging studies.