Transcranial Doppler in a patient with subarachnoid haemorrhage on day 6 shows a mean flow velocity of 180 cm/s in the middle cerebral artery. The mean velocity in the ipsilateral extracranial internal carotid artery is 50 cm/s. This finding indicates:

• A Global cerebral hyperaemia
• B Middle cerebral artery vasospasm ✓
• C Normal study requiring no action
• D Raised intracranial pressure with preserved flow

Explanation

The Lindegaard ratio compares MCA velocity with ipsilateral extracranial ICA velocity. A ratio above 3 distinguishes true vasospasm from hyperaemia, because in hyperaemia both velocities rise proportionally and the ratio stays near 1. Here the ratio is 3.6 with elevated absolute velocity, confirming vasospasm. Hyperaemia would show a ratio below 3, and normal MCA mean velocity is below about 90 cm/s.

Reference: Greenberg's Handbook of Neurosurgery, 9th ed.

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