Four-dimensional phase-contrast MRI can aid in the selection of candidates for surgery, study suggests.
An imaging approach that visualizes the entire cerebral arterial tree may help explain why degree of carotid stenosis does not always correlate with cerebral hyperperfusion by revealing the key sites of collateral recruitment. This technology, known as 4-dimensional phase-contrast magnetic resonance imaging (4-D PCMRI), can be used to identify which patients with carotid stenosis are the best candidates for endarterectomy, a new study suggests.
For patients being considered for endarterectomy to address severe carotid artery stenosis, today’s imaging strategy “is mainly based on the degree of stenosis in the symptomatic carotid artery,” Laleh Zarrinkoob, MD (Umeå University, Sweden), and colleagues write in their paper recently published online in Stroke.
Perfusion imaging has important limitations, however. “Perfusion studies have shown that the relation between the degree of carotid stenosis or occlusion is not always related to cerebral hypoperfusion because collateral recruitment plays an important role in preserving cerebral perfusion in patients with steno-occlusive disease of the carotids,” they explain.
PCMRI, on the other hand, allows for quantitative measurement of absolute blood flow rate (BFR). “By using this technique, “we have demonstrated that in healthy subjects, BFRs are distributed symmetrically in the carotids and along the cerebral arteries without signs of lateralization or influence by subject age or sex,” the investigators say, noting that it’s now possible to simultaneously assess BFR.
Zarrinkoob et al used 4-D PCMRI to evaluate 38 patients (mean age 72 years; 27 men) with symptomatic carotid stenosis ≥ 50% or occlusion. For each patient, BFR was measured in 19 arteries/locations, and the ipsilateral side to the symptomatic carotid stenosis was compared with the contralateral side.
Overall, carotid artery BFR was lower on the ipsilateral side than the contralateral side (134 ± 87 vs 261 ± 95 mL/min; P < 0.001). BFR in the anterior cerebral artery (ACA) A1 segment was also lower on ipsilateral side (35 ± 58 vs 119 ± 72 mL/min; P < 0.001).
Bilaterally, the ACA territory was primarily supplied by the contralateral internal carotid artery (ICA), while the ipsilateral ICA mainly supplied the ipsilateral middle cerebral artery (MCA) territory. The MCA was also supplied by a reversed blood flow rate found on the ipsilateral side in the ophthalmic (P = 0.001) and the posterior communicating artery routes (P = 0.03).
Despite these compensations, BFR in the MCA was lower on the ipsilateral side. This laterality was more pronounced in patients with severe carotid stenosis (≥ 70%), although there was no difference in BFR in the ipsilateral MCA between those with < 70% and those with ≥ 70% stenosis.
According to the authors, these findings demonstrate that “4-D PCMRI could simultaneously quantify BFR in individual cerebral arteries noninvasively and without anatomic restrictions. Thus, the present study demonstrates a new way to map, quantify, and understand the cerebrovascular impact of a significant carotid stenosis and the compensatory mechanism of the collaterals.”
They add that one key finding “was that contralateral ICA mainly secured the bilateral ACA territory and not only MCA on the ipsilateral side to the stenosis. Because of the collateral recruitment, compromised BFR in MCA is not necessarily related to the degree of carotid stenosis. These findings highlight the importance of simultaneously investigating the entire cerebral arterial tree.”
Source:
Zarrinkoob L, Wåhlin A, Ambarki K, et al. Blood flow lateralization and collateral compensatory mechanisms in patients with carotid artery stenosis. Stroke. 2019;Epub ahead of print.
Disclosures:
Zarrinkoob reports no relevant conflicts of interest.
