Imaging

Posterior Circulation Stroke

Preliminary Diagnosis: Posterior Circulation Stroke

I. What imaging technique is first-line for this diagnosis?

  • Non contrast CT of the head.

  • CTA of the head and neck may also be performed.

II. Describe the advantages and disadvantages of this technique for diagnosing posterior circulation stroke.

Advantages

  • Relatively fast and inexpensive imaging modality compared to companion MR imaging.

  • Highly sensitive to intracranial hemorrhage.

  • Offers exquisite detail of the osseous structures.

  • Highly sensitive and specific in localizing a focal area of significant hemodynamic stenosis, vascular malformation, or aneurysmal dilation (especially with 3-D vascular reconstructions.)

  • CTA of head and neck may help guide treatment planning and therapy.

Disadvantages

  • Less sensitive and specific in detailing a focal area of ischemia or infarct compared to MR imaging.

  • CTA exposes patients to larger quantities of ionizing radiation.

III. What are the contraindications for the first-line imaging technique?

  • May be contraindicated in pregnant patients.

  • Intravenous contrast is contraindicated in patients with abnormal renal function and elevated creatinine levels (institution dependent), and those not on an adequate dialysis regimen.

  • Relative contraindication of contrast in patients with a contrast allergy.

IV. What alternative imaging techniques are available?

  • MR of the brain, per stroke protocol.

  • MRA of the head and neck may also be performed.

V. Describe the advantages and disadvantages of the alternative techniques for diagnosing posterior circulation stroke.

MR of the brain, per stroke protocol

Advantages

  • Highly sensitive and specific in detecting and localizing a focal area of ischemia and infarction.

  • Highly specific and sensitive to micro hemorrhages.

  • Able to characterize the chronicity of an intracranial hematoma.

  • Does not expose patients to ionizing radiation.

  • MRA may be performed without intravenous gadolinium, utilizing time of flight protocol.

Disadvantages

  • MRA of the neck imaging is less sensitive and specific in detailing areas of significant hemodynamic stenosis, vascular malformation, and aneurysmal dilatation as compared to companion CT.

  • Expensive.

  • Time consuming.

  • Requires significant patient cooperation to minimize motion artifact.

VI. What are the contraindications for the alternative imaging techniques?

MR of the brain, per stroke protocol

  • Contraindicated in patients with non MR compatible hardware.

  • For MRA, gadolinium contrast is contraindicated in patients with a GFR ≤ 30.

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