Vasospasm is a complication associated with subarachnoid hemorrhage (SAH). SAH is usually secondary to a ruptured cerebral aneurysm but can also occur secondary to trauma, arteriovenous malformations or tumors. Vasospasm develops over a multi-stage process. A vasoconstriction occurs in response to vasoactive substances being released as the subarachnoid blood is broken down. This leads to degeneration and inflammatory reactions of the vessel wall causing an organic vasculopathy with structural wall changes and luminal narrowing.
After the initial hemorrhage, a transcranial Doppler (TCD) exam is performed daily to monitor for vasospasm. Daily monitoring allows for intervention before a patient shows any symptoms.
Performing a Complete Exam to Assess for Vasospasm with TCD
To determine if vasospasm is present using TCD through the temporal window, first identify the middle cerebral artery (MCA) and “walk” the Doppler sample gate through the length of the vessel (throughout the red band in M-mode) saving an image every 3-5 mm. Vasospasm may be present at only a segment of a vessel and not the entire length of the vessel. Walk the sample gate throughout the M-mode band (vessel) to ensure vasospasm is not missed.
Continue through the temporal window and identify the anterior cerebral artery (ACA), terminal internal carotid artery (TICA), and posterior cerebral artery (PCA). The ACA should be walked every 3-5 mm. For the TICA and PCA, place the sample in the center, or “heart”, of the red or blue band in the M-mode and capture an image to document the mean flow velocity, pulsatility index, and contour of the waveform.
The suboccipital window is used to identify the basilar artery (BA) and the vertebral arteries (VA). The technique is repeated through the length of the BA and VA, walking the sample in 3-5 mm increments to identify if vasospasm is present.
The ophthalmic artery (OA) and siphon artery (SIPH) are assessed through the transorbital window with one image captured of each vessel on each side.
The submandibular window is assessed to obtain the extracranial internal carotid artery (ICA). One image is required to document the mean flow velocity and provide a Lindegaard ratio.
The Circle of Willis
Ensuring a Diagnostic Exam
It is important to ensure the envelope is accurately traced along the contour of the TCD waveform. When the envelope is traced accurately the TCD system will automatically provide accurate measures of the mean velocity and pulsatility index of the waveform. If the envelope does not trace correctly, it will result in inaccurate measurements.
Understanding Exam Results
Identifying vasospasm is done by looking for increased or elevated mean flow velocities, turbulent flow, and downstream effects. The level of increase in mean flow velocity correlates with the degree of vasospasm.
Lindegaard Ratio
The Lindegaard ratio is the calculated ratio of the highest mean velocities in the MCA and the ipsilateral extracranial ICA. This ratio compares inflow to outflow and determines the presence of vasospasm versus hyperemia. The MCA is obtained through the temporal window and the ipsilateral ICA is obtained through the submandibular window.
Lindegaard ratio = highest MCA mean velocity / highest ipsilateral extracranial ICA mean velocity
Categorizing the Degree of Vasospasm in the MCA and TICA
Mild vasospasm in the MCA and TICA is indicated when the mean flow velocities are 120 cm/s to 149 cm/s with the Lindegaard ratio between 3 and 6.
Moderate vasospasm in the MCA and TICA is indicated when the mean flow velocities are 150 cm/s to 199 cm/s with the Lindegaard ratio between 3 and 6.
Severe vasospasm in the MCA and TICA is indicated when the mean flow velocities reach 200 cm/s and greater with a Lindegaard ratio at 6 or greater.
Categorizing the Degree of Vasospasm in the ACA and Posterior Circulation
Vasospasm in the ACA will show mean flow velocities reaching 130 cm/s and above.
Vasospasm in the PCA will show mean flow velocities reaching 110 cm/s and above.
Vasospasm in the VA will show mean flow velocities reaching 80 cm/s and above.
Vasospasm in the basilar artery will show mean flow velocities reaching 85 cm/s and above. If the extracranial vertebral artery (ECVA) is obtained, the BA/ECVA ratio can be used according to the diagram below.
Case Examples
Case Example 1
56 year old Caucasian male, status post aneurysm coiling. Left MCA mean velocity of 132 cm/sec and a left Lindegaard ratio of 3.38 is suggestive of mild vasospasm. The right MCA of 103 cm/sec is within normal limits.
Case Example 2
75 year old Caucasian female, status post aneurysm coiling. Patient is on continuous monitoring EEG, intubated, with multiple IVs in place. Highest mean velocities found are in the left MCA at 164 cm/sec. This is suggestive of moderate left MCA vasospasm. The Lindegaard ratio of 5 confirms left MCA moderate vasospasm.
Case Example 3
44 year old Caucasian female, status post aneurysm coiling. The MCAs have mean velocities greater than 200 cm/sec bilaterally with Lindegaard ratio’s greater than 6. This is suggestive of severe MCA vasospasm bilaterally.
Citations
Ali, M.F. Transcranial Doppler ultrasonography (uses, limitations, and potentials): a review article. Egypt J Neurosurg 36, 20 (2021). https://doi.org/10.1186/s41984-021-00114-0
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