What Doppler pattern suggests collateral flow compensating contralateral ICA stenosis?

• A. Increased flow everywhere including the ipsilateral ICA and CCA without turbulence.
• B. Increased flow only on the contralateral ICA with turbulence.
• C. Normal flow in both sides with no turbulence.
• D. Decreased flow on the contralateral side with normal on the ipsilateral.

Answer: (A)

Collateral flow through the circle of Willis can compensate when one ICA is stenosed, so the brain relies on the opposite side to supply blood. On Doppler, this shows up as higher flow volumes and velocities in both carotid systems because more blood is being delivered through shared pathways to the affected hemisphere. The key clue is that the spectra would be smooth and laminar, without the turbulent jet that comes from a locally significant stenosis. So seeing increased flow in both ICAs and CCAs with no turbulence points to redistribution of flow via collateral pathways rather than a single artery with a high-grade stenosis causing a turbulent jet.

If flow were increased only on the contralateral side with turbulence, that would suggest a focal stenotic jet rather than collateral compensation. Normal flow on both sides or decreased contralateral flow would not reflect active collateral redistribution.