Relationship between circle of Willis morphology on 3D time-of-flight MR angiograms and transient ischemia during vascular clamping of the internal carotid artery during carotid endarterectomy

Abstract

Background and purpose: A potential source of complication at carotid endarterectomy (CEA) is cerebral ischemia caused by hypoperfusion during clamping of the carotid artery. Configuration of primary collateral pathways may be a major risk factor for development of transient cerebral ischemia during clamping. We investigated whether circle of Willis morphology on 3D time-of-flight (TOF) MR angiograms can reliably predict transient ischemia during vascular clamping of the internal carotid artery (ICA) in patients undergoing CEA.

Methods: Three-dimensional TOF MR angiography and CEA were performed in 117 patients. Patients had unilateral stenosis (n = 86), unilateral stenosis with contralateral occlusion (n = 21), or bilateral severe stenosis (n = 10) of the ICA. Circle of Willis morphology on preoperative 3D TOF MR angiograms was analyzed and correlated with intraoperative history of ischemia during vascular clamping of the ICA.

Results: Patients with unilateral stenosis or bilateral severe stenosis experienced transient ischemia during clamping of ICA at a low rate (11 [11%] of 96). In these groups, we found no specific circle of Willis patterns associated with development of intraoperative ischemia. However, patients with contralateral ICA occlusion experienced ischemia frequently during clamping of the ICA (12 [57%] of 21). In this group, incompleteness of the circle of Willis was significantly related to the risk of intraoperative ischemia (P =.005).

Conclusion: In patients without contralateral ICA occlusion, circle of Willis morphology on 3D TOF MR angiograms cannot predict the development of intraoperative ischemia. However, in patients with contralateral ICA occlusion, incompleteness of the posterior part of the circle of Willis is a significant risk factor for development of ischemia during vascular clamping of the ICA.

Fig 1.

Schematic views of anatomic variations of the anterior (A) and posterior (B) parts of the circle of Willis. Only the right side is presented. The left side is a mirror image of the right side. A, Demonstrable anterior communicating artery (a), approximated both proximal A1 segments without demonstrable anterior communicating artery (b), hypoplastic contralateral A1 segment (c), widely separated both A1 segments with no demonstrable anterior communicating artery (d), absence of contralateral A1 segment (e). The anterior part of the circle of Willis is considered as complete in types a and b, incomplete in types d and e, or indeterminate in type c. B, Demonstrable ipsilateral posterior communicating artery and P1 segment (a), hypoplastic ipsilateral posterior communicating artery or ipsilateral P1 segment (b1 and b2), no demonstrable ipsilateral posterior communicating artery (c), no demonstrable ipsilateral P1 segment (d). The posterior part of the circle of Willis is considered as complete in type a, incomplete in types c and d, or indeterminate in type b (b1 or b2).

Fig 2.

A 62-year-old man with a history of sudden loss of consciousness immediately after vascular clamping during CEA. A, Contrast-enhanced MR angiogram shows focal severe stenosis of the left proximal ICA and occlusion of the contralateral ICA. B, Three-dimensional TOF MR angiogram demonstrates incomplete anterior and posterior patterns of the circle of Willis with absence of the right A1 segment of the anterior cerebral artery and the left posterior communicating artery.

Fig 3.

A 65-year-old man without any neurologic symptoms during CEA. A, Contrast-enhanced MR angiogram shows short segmental severe stenosis of the left proximal ICA. The contralateral ICA is occluded at the level of the carotid bifurcation. B, Three-dimensional TOF MR angiogram shows intact both A1 segments, anterior communicating artery, and ipsilateral posterior communicating artery. The circle of Willis is complete in both anterior and posterior parts.