Lindegaard ratio

Last revised by Gregory George Westin on 20 Dec 2021

The Lindegaard ratio refers to the calculated ratio of the mean flow velocities in the middle cerebral artery and the ipsilateral extracranial internal carotid artery, as measured by transcranial Doppler 1. Its primary utility is, in the context of increased MCA velocities after subarachnoid hemorrhage, to confirm the presence of vasospasm


A Lindegaard ratio above 3 supports the diagnosis of vasospasm in the presence of an increased MCA mean flow velocity, with a ratio above 6 classified as severe 2. A ratio of less than 3 may indicate the presence of an alternate etiology to the increased flow velocities measured, including 3:

  • cerebral hyperemia
  • hypertension
  • hypervolemia

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