Diagnosing cerebral collateral flow patterns: accuracy of non-invasive testing

Objective: With routine use of non-invasive methods to assess the internal carotid artery, it becomes increasingly important to clarify the diagnostic accuracy of transcranial Doppler (TCD) ultrasound and magnetic resonance angiography (MRA) compared with intra-arterial digital subtraction angiography (iaDSA) for the detection of collateral flow via the major intracerebral collateral branches.

Subjects and methods: In a prospective study, we compared TCD via a temporal bone window and MRA (flow direction sensitive phase contrast and time of flight) examinations of the intracranial collateral flow with iaDSA in a cohort of 97 consecutive patients with recent transient or minor disabling cerebral ischaemia associated with an occlusion of the carotid artery (38 contralateral stenosis >70%).

Results: iaDSA allowed the evaluation of collateral flow via the anterior and posterior circle of Willis in 97 and 67 patients, respectively, TCD in 76 of 97 and 66 of 67 patients, MRA in 95 of 97 and 66 of 67 patients. MRA and TCD collateral flow measurements via the anterior part of the circle of Willis yielded a sensitivity of 83 and 82%, a specificity of 77 and 79% and a similar accuracy of 80%. MRA and TCD collateral flow measurements via the posterior communicating artery yielded a sensitivity of 33 and 76%, a specificity of 88 and 47% and an accuracy of 47 and 68%.

Conclusion: As compared with iaDSA, combined MRA and TCD has a moderate to good diagnostic value for the examination of intracranial collateral flow in patients with symptomatic carotid occlusion.