Recent advances in magnetic resonance angiography of carotid and vertebral arteries

Practical noninvasive neurovascular imaging of the neck arteries in patients with stroke, transient ischemic attack, and suspected arterial disease that may lead to ischemia, infarction, or flow abnormalities

Stroke is the third leading cause of death in the United States, killing nearly 157,000 people a year with an estimated society cost of dollar 58 billion in 2006. A large percentage of ischemic strokes is secondary to extracranial carotid and vertebral arterial disease. While digital subtraction angiography has traditionally been used for the initial evaluation of the degree of stenosis, noninvasive imaging has moved to the forefront in the extracranial arterial evaluation. The importance of understanding the imaging techniques, findings, interpretation, artifacts, and pitfalls is essential to appropriate patient management.

The reliability of ultrasound measurements of carotid stenosis compared to MRA and DSA

OBJECTIVE

Carotid ultrasound (US) is a screening test for patients with transient ischemic attacks (TIAs) or stroke who then undergo Digital Subtraction Angiogram (DSA) or Magnetic Resonance Angiography (MRA). Gold standard DSA is invasive with inherent risks and costs. MRA is an evolving technology. This study compares reliability of MRA and US modes with DSA in determining degree of internal carotid artery stenosis.

METHODS

A five year retrospective analysis of 140 carotid arteries from patients who had carotid US and DSA, and possibly Magnetic Resonance Angiography was undertaken. Recorded US parameters were peak systolic velocity (PSV), end diastolic velocity (EDV), and ICA/CCA peak systolic velocity ratio. The MRA and DSA parameters used NASCET technique for measuring stenosis. Statistical analysis included ROC curves and Kappa computation.

RESULTS

US grading of carotid stenosis can be made more reliable by choosing appropriate parameters. The best combination of sensitivity and specificity for stenosis > 70% in our hospital was seen at PSV > 173 cm/s (sensitivity 0.87, specificity 0.8, Positive Predictive Value (PPV) 0.70, Negative Predictive Value (NPV) 0.93, kappa 0.64 and weighted kappa 0.71). MRA kappa was 0.78, (sensitivity 0.75, specificity 1.0, PPV 1.0, NPV 0.85).

CONCLUSIONS

US parameters should be validated in each centre. At best, US can only approximate the accuracy of DSA, probably due to inherent limitations of this modality. Magnetic Resonance Angiography has a perfect specificity and PPV but this technique needs to be standardized. Simultaneous use of MRA and US for screening increases sensitivity to over 0.9 without compromising specificity in > 70% stenosis.

Utility of Screening for Blunt Vascular Neck Injuries with Computed Tomographic Angiography

PURPOSE

To prospectively study the impact of implementing a computed tomographic angiography (CTA)-based screening protocol on the detected incidence and associated morbidity and mortality of blunt vascular neck injury (BVNI).

METHODS

Consecutive blunt trauma patients admitted to a single tertiary trauma center and identified as at risk for BVNI underwent admission CTA using an eight-slice multi-detector computed tomography scanner. The detected incidence, morbidity, and mortality rates of BVNI were compared with those measured before CTA screening. A logistic regression model was also applied to further evaluate potential risk factors for BVNI.

RESULTS

A total of 1,313 blunt trauma patients were evaluated. One hundred seventy screening CTAs were performed, of which 33 disclosed abnormalities. Twenty-three were evaluated angiographically, of which 15 were considered to have significant BVNIs, as were 4 of the 10 patients with abnormal CTAs and no angiogram. The incidence of angiographically proven BVNIs in our series was 1.1%. If four patients who were treated for BVNIs based on CTA alone are included, the incidence rises to 1.4%. This is significantly higher than the 0.17% incidence before screening (p < 0.001). In addition, the delayed stroke rate and injury-specific mortality fell significantly from 67% to 0% (p < 0.001) and 38% to 0% (p = 0.002), respectively. Overall mortality also fell significantly, from 38% to 10.5% (p = 0.049). Univariate logistic regression identified the presence of cervical spine injury as a significant predictor of BVNI (p < 0.001).

CONCLUSION

CTA screening increases the detected incidence of BVNI 8-fold, with rates similar to angiographically based screening protocols. CTA screening significantly decreases BVNI-related morbidity and mortality in an efficient manner, underlying its utility in the early diagnosis of this injury.

Imaging the vertebral artery

Although conventional intraarterial digital subtraction angiography remains the gold standard method for imaging the vertebral artery, noninvasive modalities such as ultrasound, multislice computed tomographic angiography and magnetic resonance angiography are constantly improving and are playing an increasingly important role in diagnosing vertebral artery pathology in clinical practice. This paper reviews the current state of vertebral artery imaging from an evidence-based perspective. Normal anatomy, normal variants and a number of pathological entities such as vertebral atherosclerosis, arterial dissection, arteriovenous fistula, subclavian steal syndrome and vertebrobasilar dolichoectasia are discussed.

Prospective screening for blunt cerebrovascular injuries: analysis of diagnostic modalities and outcomes

OBJECTIVE

To prospectively examine outcomes associated with an aggressive screening protocol for blunt cerebrovascular injury (BCVI), and to compare the accuracy of computed tomographic angiography (CTA) and magnetic resonance angiography (MRA) versus conventional angiography with respect to BCVI diagnosis.

SUMMARY BACKGROUND DATA

In the past 5 years, BCVI (carotid and vertebral arteries) has been recognized with increasing frequency. Initial studies described blunt carotid injuries and their associated morbidity, while more recent reports have established the devastating potential of blunt vertebral injuries. It has been suggested that early diagnosis and anticoagulation will improve outcomes and that less-invasive diagnostic techniques than conventional angiography are desirable for screening. However, there are neither established screening criteria nor studies comparing optimal diagnostic modalities.

METHODS

The screened population included all patients with cervical spine fractures, LeFort II or III facial fractures, Horner's syndrome, skull base fractures involving the foramen lacerum, neck soft tissue injury, or neurological abnormalities unexplained by intracranial injuries. Patients underwent screening with four-vessel cerebral angiography. During the first half of the study, patients also underwent helical CTA. Selected patients during this same period underwent MRA. At the time of diagnosis, anticoagulant or antiplatelet therapy was instituted unless clinically contraindicated. Results of this screening protocol were compared to a previously published cohort with cerebrovascular injuries (1995-1999) from the authors' institution.

RESULTS

Two hundred sixteen patients were screened over a 2-year period (3.5% of all blunt trauma admissions). Angiography identified 24 patients with carotid artery injuries (CAI) and 43 patients with vertebral artery injuries (VAI) for an overall screening yield of 29%. While the incidence of CAI remained similar between the current study and the previous study group, the incidence of VAI diagnosis increased. Stroke rates in those with CAI were also similar between the two periods. The stroke rate in VAI, however, was markedly lower at 0% as compared to 14% in the previous group. Comparison of CTA and MRA with cerebral angiography in 143 patients demonstrated sensitivities of 47% and 50%, respectively, for CAI; sensitivities were 53% (CTA) and 47% (MRA) for VAI.

CONCLUSIONS

Aggressive screening of patients with blunt head and neck trauma identified an incidence of BCVI in 1.03% of blunt admissions. Early identification, which led to early treatment, significantly reduced stroke rates in patients with VAI, but provided no outcome improvement with CAI. More encompassing screening may be required to improve outcomes for patients with CAI. However, less-invasive diagnostic techniques (CTA and MRA) are inadequate for screening. Technological advances are necessary before abandonment of conventional angiography, which remains the standard for diagnosis.

Prospective screening for blunt cerebrovascular injuries: analysis of diagnostic modalities and outcomes

OBJECTIVE

To prospectively examine outcomes associated with an aggressive screening protocol for blunt cerebrovascular injury (BCVI), and to compare the accuracy of computed tomographic angiography (CTA) and magnetic resonance angiography (MRA) versus conventional angiography with respect to BCVI diagnosis.

SUMMARY BACKGROUND DATA

In the past 5 years, BCVI (carotid and vertebral arteries) has been recognized with increasing frequency. Initial studies described blunt carotid injuries and their associated morbidity, while more recent reports have established the devastating potential of blunt vertebral injuries. It has been suggested that early diagnosis and anticoagulation will improve outcomes and that less-invasive diagnostic techniques than conventional angiography are desirable for screening. However, there are neither established screening criteria nor studies comparing optimal diagnostic modalities.

METHODS

The screened population included all patients with cervical spine fractures, LeFort II or III facial fractures, Horner's syndrome, skull base fractures involving the foramen lacerum, neck soft tissue injury, or neurological abnormalities unexplained by intracranial injuries. Patients underwent screening with four-vessel cerebral angiography. During the first half of the study, patients also underwent helical CTA. Selected patients during this same period underwent MRA. At the time of diagnosis, anticoagulant or antiplatelet therapy was instituted unless clinically contraindicated. Results of this screening protocol were compared to a previously published cohort with cerebrovascular injuries (1995-1999) from the authors' institution.

RESULTS

Two hundred sixteen patients were screened over a 2-year period (3.5% of all blunt trauma admissions). Angiography identified 24 patients with carotid artery injuries (CAI) and 43 patients with vertebral artery injuries (VAI) for an overall screening yield of 29%. While the incidence of CAI remained similar between the current study and the previous study group, the incidence of VAI diagnosis increased. Stroke rates in those with CAI were also similar between the two periods. The stroke rate in VAI, however, was markedly lower at 0% as compared to 14% in the previous group. Comparison of CTA and MRA with cerebral angiography in 143 patients demonstrated sensitivities of 47% and 50%, respectively, for CAI; sensitivities were 53% (CTA) and 47% (MRA) for VAI.

CONCLUSIONS

Aggressive screening of patients with blunt head and neck trauma identified an incidence of BCVI in 1.03% of blunt admissions. Early identification, which led to early treatment, significantly reduced stroke rates in patients with VAI, but provided no outcome improvement with CAI. More encompassing screening may be required to improve outcomes for patients with CAI. However, less-invasive diagnostic techniques (CTA and MRA) are inadequate for screening. Technological advances are necessary before abandonment of conventional angiography, which remains the standard for diagnosis.

Magnetic resonance angiography of thromboembolic stroke in rats: indicator of recanalization probability and tissue survival after recombinant tissue plasminogen activator treatment

Magnetic resonance angiography (MRA) was performed in a thromboembolic stroke model of the rat to characterize intracranial vessel occlusion patterns and to test its predictive power for tissue recovery after recombinant tissue plasminogen activator (rt-PA) treatment. After rt-PA-treated selective middle cerebral artery (MCA) occlusion, full recanalization was observed in two of three animals, whereas additional occlusion of the circle of Willis (CW) resulted in full vascular flow restitution in only one of six rats. Tissue reperfusion markedly lagged the onset of treatment, and the delay correlated with the pattern of vessel occlusion (20 to 23 minutes for selective MCA occlusion vs. 71 to 79 minutes for combined MCA/CW occlusion). In lateral cortex and striatum the apparent diffusion coefficient decreased to 78 +/- 15% of control after embolization, recovered to 80% to 85% after rt-PA treatment of selective MCA occlusion, but further declined to 66% to 69% after combined MCA/CW occlusion. Correspondingly, T2 relaxation time increased to 107% to 118% of control after selective MCA occlusion and to 112% to 124% after combined MCA/CW occlusion in these regions. The present investigation shows that MRA provides valuable information on the severity of thromboembolic stroke and has the power to predict, before the initiation of treatment, the functional tissue outcome after rt-PA-induced thrombolysis.

Magnetic resonance angiography and evaluation of cervical arteries

Multiple clinical trials have demonstrated the efficacy of endarterectomy in selected groups of patients based primarily on percent diameter stenosis. Although measurement of stenosis in the clinical trials was established by conventional angiography, there is considerable interest in noninvasive alternatives. Magnetic resonance angiography, performed using time-of-flight methods or with contrast enhancement, is one of several alternatives for noninvasive carotid evaluation. Screening examinations are routinely performed for carotid stenosis. Preoperative evaluations based on one or a combination of noninvasive tests have been proposed, although these proposals are the subject of ongoing controversy. Evaluation of the vertebral arteries is more difficult and less well studied: however, the increasing availability of therapies for posterior circulation atherosclerotic narrowing is resulting in increased interest in this problem.

Aneurysmal forms of cervical artery dissection : associated factors and outcome

BACKGROUND AND PURPOSE

The natural history of aneurysmal forms of cervical artery dissection (CAD) is ill defined. The aims of this study were to assess (1) clinical and anatomic outcome of aneurysmal forms of extracranial internal carotid artery (ICA) and vertebral artery (VA) dissections and (2) factors associated with aneurysmal forms of CAD.

METHODS

Seventy-one consecutive patients with CAD were reviewed. Aneurysmal forms of CAD were identified from all available angiograms by 2 neuroradiologists. The frequency of arterial risk factors, of multiple vessel dissections, and of artery redundancies was compared in patients with and without aneurysm. Patients with aneurysm were invited by mail to undergo a final clinical and radiological evaluation.

RESULTS

Of the 71 patients, 35 (49.3%) had a total of 42 aneurysms. Thirty aneurysms were located on a symptomatic artery (ICA, 23; VA, 7) and 12 on an asymptomatic artery (ICA, 10; VA, 2). Patients with aneurysm had multiple dissections of cervical vessels (18/35 versus 7/36; P:=0.005) and arterial redundancies (20/35 versus 11/36; P:=0.02) more frequently than patients without aneurysm. They were also more often migrainous (odds ratio=2.7 [95% CI, 0.8 to 8.5]) and tobacco users (odds ratio=2.2 [95% CI, 0.7 to 6.3]). Clinical and anatomic follow-up information was available for 35 (100%) and 33 patients (94%), respectively. During a mean follow-up of >3 years, no patient had signs of cerebral ischemia, local compression, or rupture. At follow-up, 46% of the aneurysms involving symptomatic ICA were unchanged, 36% had disappeared, and 18% had decreased in size. Resolution was more common for VA than for ICA aneurysms (83% versus 36%). None of the aneurysms located on an asymptomatic ICA had disappeared.

CONCLUSIONS

Although aneurysms due to CAD frequently persist, patients carry a very low risk of clinical complications. This favorable clinical outcome should be kept in mind before potential harmful treatment is contemplated.

Postoperative neurologic assessment and management of the cardiac surgical patient

The neurologic evaluation of patients in the immediate postoperative period and postanesthetic state is unique and challenging. Neurologic assessment is complicated by the lingering residual effects of anesthetics as well as by the effects of narcotic analgesics, anxiolytics, and muscle relaxants, especially in ventilated patients. In this review we examine the suspected causes, clinical manifestations, diagnostic options, and intervention schemes for the common neurologic syndromes seen after cardiac operations.