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[Cerebrovascular Surgery Center]

Neurovascular Surgery
Brain Aneurysm & AVM Center

Carotid Endarterectomy without Cerebral Angiography
by Christopher S. Ogilvy, M.D.

Figure | Other sources of information

Carotid endarterectomy has now been shown to be effective in preventing subsequent ipsilateral strokes in patients with symptomatic severely stenotic (less than or equal to 70%) lesions at the origin of the internal carotid artery.(ref 1) Efficacy is achieved only if surgical morbidity is sufficiently low. Furthermore, endarterectomy is under study and may be considered in patients with hemodynamically significant asymptomatic atherosclerotic lesions at the origin of the internal carotid artery. Given the fact that safe, effective treatment is available, accurate diagnostic methods are necessary to evaluate structural lesions and flow at the bifurcation of the common carotid artery as well as along the course of the internal carotid artery in the intracranial branches. While conventional cerebral angiography is still the gold standard for diagnosis of cerebral vascular disease and assessment of collateral circulation, angiography has known risks. In fact, the patients at highest risk for stroke during angiography are those with atherosclerotic changes in the carotid vessels. Furthermore, the angiogram cannot be practically repeated in serial fashion. The safety and reproducibility of carotid noninvasive tests are very attractive in this respect, especially for asymptomatic disease. Carotid noninvasive testing comes in two forms. The first of these is a battery of three noninvasive testing modalities which can in most cases accurately provide the required assessment of extracranial internal carotid artery occlusive disease and associated intracranial hemodynamic changes. The three noninvasive tests are: 1) standard carotid noninvasive studies (CNIS), 2) transcranial doppler (TCD) assessment of intracranial arterial and ophthalmic artery flow, 3) MRI/MR angiography of the cervical and intracranial arterial system. Carotid noninvasive studies are divided into studies that assess flow and vascular morphology at the bifurcation of the common carotid artery (i.e. direct tests) and those that indirectly assess the hemodynamic effect of a stenotic lesion at the bifurcation of the common carotid artery or more distally in the internal carotid artery (indirect testing). Recently, direct tests have narrowed to two principle modalities: 1) duplex ultrasound scanning (B-mode ultrasound image combined with range gated assessment of flow at the bifurcation of the common carotid artery, and 2) triplex ultrasound scanning (duplex scanning combined with "real time" two dimensional flow images superimposed on the B-mode image). Continuous wave doppler spectral analysis of the flow at the bifurcation of the common carotid artery (CW doppler) is used less frequently. By combining the carotid noninvasive studies, a profile of the carotid bifurcation can be obtained in terms of residual lumen diameter as well as intracranial flow, however MRI/MR angiography has now added a new dimension to the analysis. Using the MRI/MRA, an image of the carotid bifurcation can be obtained which is reconstructed from the magnetic resonance angiogram itself. Two MRA bright blood techniques, time-of-flight and phase contrast MRA, are currently in widespread use. The most commonly employed technique, time-of-flight (TOF) uses repetitive radiofrequency pulses to suppress stationery tissues. The unsuppressed protons of flowing blood are then used to create a vascular image. The second technique, phase contrast (PC MRA) is also widely available although less frequently used than TOF. Phase contrast imaging is a subtraction technique in which moving protons acquire a phase shift proportional to their velocity during the application of a bipolar gradient. The net phase shift of stationery protons is zero. The phase contrast sequences therefore provide excellent background tissue suppression and can also provide velocity and directional information. Although the MR angiography provides information based on flow, patterns have emerged which when combined with the carotid noninvasive studies provide enough information to carry out endarterectomy safely and effectively. A typical MRA study of the carotid bifurcation in a patient with symptomatic stenosis is shown in Figure 1. At the MGH Aneurysm/AVM Center, we have now performed over 80 carotid endarterectomies in patients with carotid noninvasive studies and MRI/MRA alone. Initially, cerebral angiography was avoided in certain patients with renal dysfunction or those felt to be at extremely high risk from angiography. As experienced was gained operating on these patients, it became apparent that the MRA study could provide the anatomical location of the carotid bifurcation in the neck as well as the tortuosity of surrounding vessels. In one of the patient's operated on there was a 360o loop present distal to the stenosis which required excision at the time of the surgery. This was not predicted based on the MR studies. In one other case, MRA suggested no flow in the carotid artery, however the noninvasive studies documented a tiny residual lumen. The carotid bifurcation was explored and in fact excellent back flow from the internal carotid artery was obtained. We have had no complications related to using the combined techniques of carotid noninvasive studies and MRA for endarterectomy, however there have been patients where discrepancy between the two tests, or the suggestion of tandem stenosis with atherosclerotic narrowing of the carotid in the cavernous sinus, made it necessary to proceed with standard angiography. Although this was initially feared to be a potentially common cause of misreading the noninvasive studies, recent addition of TCD and high quality MRA often make the diagnosis of tandem lesions reliable even in the face of marked cervical ICA stenosis. When CNIS/TCD/MRA does not clarify surgical issues, then conventional angiography is required to guide surgical decision making. With increasing experience with noninvasive evaluation and growing confidence in its reliability, we now resort to conventional angiography only in cases with: 1) TIA/stroke and negative CNIS/TCD/MRA, 2) inadequate CNIS/TCD/MRA related to patient factors (marked obesity, severe claustrophobia), 3) no flow in ICA on 2D TOF, 4) discrepancy between CNIS/TCD and MRA, 5) complex or perplexing pathology (e.g. radiation induced bilateral carotid stenosis), or 6) other inadequately understood pathophysiology. We now rely on CNIS/TCD/MRA without conventional angiography in the evaluation of 90% of cases with symptomatic carotid stenosis and virtually all asymptomatic stenoses. Among 80 patient who underwent carotid endarterectomy without angiography, there has been no complication due to this approach, and the potential morbidity of 80 conventional angiograms has been avoided. With the ongoing improvement of CNIS, TCD, and MRA, we expect to use this approach even more widely in the future.

Figure 1. Time-of-flight based carotid MR angiography of a patient with symptomatic right carotid stenosis. The MR angiogram on the left shows both carotid arteries and vertebral arteries in the neck. The MRA on the right shows the right carotid artery bifurcation with a "skip sign" present where the signal of flow is not visible (arrow). In this region, the stenosis is extremely tight and the velocity of blood through the stenosis very high.

Other Information sources on carotid endarterectomy

1. North American Symptomatic Carotid Endarterectomy Trial Collaborators. Beneficial effect of carotid endarterectomy in symptomatic patients with high grade carotid stenosis. N Engl J Med 1991; 325:445-453.

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