Role of CT perfusion imaging in the diagnosis and treatment of vasospasm

Abstract

The current role of CT perfusion (CTP) imaging in the diagnosis and treatment of vasospasm in the setting of aneurysmal subarachnoid hemorrhage is discussed in this article, with specific attention directed towards defining the terminology of vasospasm and delayed cerebral ischemia. A commonly used CTP technique in clinical practice is described. A review of the literature regarding the usefulness of CTP for the diagnosis of vasospasm and its role in guiding treatment are discussed. Recent research advances in the utilization of CTP and associated ongoing challenges are also presented.

Figure 1. CT perfusion source images

CT perfusion was performed for the evaluation of possible vasospasm in this 55-year-old female with ruptured left middle cerebral artery aneurysm. The CT perfusion concept is illustrated. Multiple sequential images are performed during the first pass of the contrast bolus through a stationary slab of brain tissue demonstrating the baseline phase prior to arrival of contrast, at wash-in phase of contrast arrival, at peak arterial enhancement and in the wash-out phase of the contrast.

Figure 2. Arterial input function and venous output function

The arterial input function may be chosen in the A2 segment of the anterior cerebral artery (labeled 1) and the venous output function in the posterior aspect of the superior sagittal sinus (labeled 2).

Figure 3. Time–density curves

Time–density curves for the arterial input function (long white arrow) and the venous output function (short white arrow) are used to calculate the perfusion maps.

Figure 4. Perfusion maps

(A) Cerebral blood flow map depicts the volume of blood moving through a given volume of brain tissue per unit time. (B) Cerebral blood volume map depicts the total volume of blood in the arteries, veins and capillaries. (C) Mean transit time map depicts the average time of blood transit from the arterial inlet to the venous outlet.

Figure 5. A 66-year-old female with ruptured anterior communicating artery aneurysm and acute subarachnoid hemorrhage

(A) Posterior–anterior projection of the right internal carotid artery on post-hemorrhage day 1, at the time of aneurysm coiling, shows normal caliber of the M1 segment of the right middle cerebral artery and no evidence of vasospasm. The A1 segment of the right anterior cerebral artery is hypoplastic (black arrow). (B) CT perfusion examination performed on post-hemorrhage day 9, after the patient developed a left-sided pronator drift. There is delayed mean transit time (bottom right image), decreased cerebral blood flow (bottom left image) and preserved cerebral blood volume (top right image) in the right middle cerebral artery territory, consistent with a perfusion deficit (white arrows). (C) Emergent digital subtraction angiography performed just after the CT perfusion examination shows significant vasospasm of the M1 and M2 segments of the right middle cerebral artery (black arrow). The patient was treated with intra-arterial verapamil and experienced marked improvement, both clinically and on post-verapamil angiography.

Figure 6. A 78-year-old male with a ruptured anterior communicating artery aneurysm

(A) Baseline CT perfusion on post-hemorrhage day 4 was normal. (B) The patient developed symptoms of altered mental status on post-hemorrhage day 8, and a CT perfusion was performed, which shows diffusely decreased cerebral blood flow (white arrowheads). (C) Digital subtraction angiography was performed. Posterior–anterior projections of the cranium after right and left internal carotid artery injections show no significant narrowing of the medium- or large-sized cerebral arteries. The constellation of these findings is consistent with microvascular vasospasm.