The Utility of Brain Magnetic Resonance Imaging/Angiography and Neck Magnetic Resonance Angiography in Patients with Suspected Acute Stroke



 

Mark Harris; Alyssa Finger; Emily Nishimura; Blake Watabe; Hyo-Chun Yoon, MD, PhD

Perm J 2021;25:20.214

https://doi.org/10.7812/TPP/20.214
E-pub: 03/01/2021

Background: In our health maintenance organization, we have seen a trend among our referring physicians to order simultaneous brain magnetic resonance imaging (MRI), head magnetic resonance angiography (MRA), and neck MRA in the evaluation of patients for acute stroke. However, there are little data to demonstrate any improvement in patient care resulting from ordering this triple study. The objective of this study was to analyze the utility of the triple MRI/MRA study for patients who experience stroke-like symptoms.

Methods: We reviewed all triple-study cases between January 1, 2013 and December 31, 2016. We recorded whether or not an acute stroke occurred, the presence or absence of a major stenosis in the intracranial and/or neck arteries, subsequent percutaneous endovascular or open surgical intervention within 90 days, and any follow-up computed tomography angiography or carotid ultrasound studies within 30 days.

Results: During the studied period, 591 triple studies were ordered, and 162 patients (27.4%) were found to have moderate or severe stenosis. Of the patients who had an acute stroke, 100 (48.3%) also had a major stenosis. Of 591 patients, only 15 (2.5%) underwent percutaneous endovascular or open surgical intervention within 90 days. Of these, 4 patients had an intervention in less than a week; in all of the cases, the triple study did not need to be ordered simultaneously to achieve the same clinical outcome.

Conclusion: Brain MRI, head MRA, and neck MRA studies should not be ordered simultaneously as a generalized response to patients presenting with acute stroke-like symptoms.

INTRODUCTION

Magnetic resonance imaging (MRI) has been shown to be an excellent method for the detection of acute stroke as well as for the evaluation of intracranial and cervical arterial anatomy.1-3 In our health maintenance organization (HMO), we have seen a trend among our referring physicians to order all 3 studies simultaneously in the evaluation of patients for acute stroke. The reason for this trend is unclear but may be related to a perceived benefit in providing timely interventions or reducing patient inconvenience associated with having to return for multiple studies. However, there are little data to demonstrate any improvement in patient care resulting from ordering this triple MRI study. At a time when health care costs are under increasing scrutiny, the use of multiple expensive imaging studies is not warranted unless there is clear clinical benefit to patients. We hypothesized that the use of this triple study should result in a substantial (> 10%) proportion of patients undergoing some type of open surgical or percutaneous endovascular intervention on the intracranial or cervical arteries within the following 90 days to justify performing all 3 studies simultaneously rather than order them sequentially as the clinical need arose.

METHODS

Our institutional review board approved this study with a waiver of consent. This retrospective analysis was performed on patients who all belonged to a geographically isolated HMO where all imaging is provided within the HMO and where all inpatient and outpatient information is available on an electronic medical record (EMR). We reviewed the results from all adult patients who underwent brain MRI, brain magnetic resonance angiography (MRA), and neck MRA simultaneously for the assessment of acute stroke from the emergency department or inpatient setting. All information was obtained from the EMR for triple studies performed between January 1, 2013 and December 31, 2016.

Data collected at the time of the triple MRI/MRA examination were as follows: age, sex, presence or absence of acute stroke, presence or absence of a major stenosis in the intracranial and/or cervical arteries, subsequent percutaneous endovascular or open surgical intervention within 90 days, and any follow-up computed tomography angiography (CTA) or carotid ultrasound studies within 30 days. Children who presented stroke-like symptoms were excluded, as they are unlikely to have atherosclerotic disease of the cervical or intracranial arteries.

All imaging was performed on 1 of 3 MRI scanners: GE Signa 1.5T (GE Medical Systems, Milwaukee, WI), Philips Intera 1.5T (Philips Medical Systems, Andover, MA), or Philips Ingenia 3T. Intracranial MRA was performed using a 3-dimensional time-of-flight (TOF) technique without intravenous contrast. Neck MRA was performed using a 3-dimensional TOF technique with intravenous contrast.

All magnetic resonance images of patients who presented with major intracranial arterial disease or cervical arterial disease were reviewed. Patients were considered to have major arterial disease when specifically reported by the radiologist as a stenosis of greater than 50% or as “severe.” Furthermore, one of the authors reviewed the images that were reported as “moderate” or “mild” stenosis and measured the stenosis severity. Those stenoses greater than 50% were considered major. The EMRs of patients with major stenoses were reviewed to determine whether percutaneous endovascular or open surgical intervention occurred within 90 days.

Any CTA or carotid ultrasound study performed within 30 days of the triple study was reviewed and results correlated the finding on the magnetic resonance angiograms.

Continuous variables were analyzed through a Student t-test. Nominal variables were analyzed with a χ2 test. Statistical significance was determined to be p ≤ 0.05.

RESULTS

Between January 1, 2013 and December 31, 2016, a total of 591 adult patients received a triple MRI/MRA study of the head and neck simultaneously. Overall, only 15 patients in this cohort (2.5%) had an intervention within 90 days of the examinations. This rate of intervention was substantially lower than our hypothesized 10% rate of intervention.

In our cohort of patients who underwent intervention, the median number of days between the triple study and intervention was 51 days (interquartile range, 2.5-56.5 days). There were 303 women and 288 men, with an average age ± SD of 63.7 ± 15.9 years. The average age of the women (62.7 ± 17.4 years) was not significantly different from that of the men (64.8 ± 14.0 years) (Student t-test, p > 0.05).

As shown in Table 1, 162 patients (27.4%) were found to have moderate or severe stenosis based on MRI studies, while 429 patients (72.6%) did not demonstrate any stenosis on MRI studies. The average ± SD age was 68.1 ± 15.3 years for patients with stenosis and 62.1 ± 15.8 years for the group without stenosis (Table 2). This age difference was statistically significant (Student t-test, p < 0.001). Among those patients with stenosis, there were 77 women and 85 men; among those without a major stenosis, there were 226 women and 203 men, which was not significantly different (χ2 test, p > 0.05) (Table 2).

Table 1. Comparison of patients determined to have had or not had a stroke by magnetic resonance imaging

  Total (n = 591) No stroke (n = 384) Acute stroke (n = 207)
No stenosis 429 (72.6) 322 (83.9) 107 (51.7)
Stenosis 162 (27.4) 62 (16.1) 100 (48.3)
 Intracranial 58 (35.5) 21 (33.9) 37 (37.0)
 Extracranial 95 (64.5) 39 (62.9) 56 (56.0)
 Both 9 (1.5) 2 (3.2) 7 (7.0)
No intervention 571 (96.6) 378 (98.4) 193 (93.2)
Intervention 20 (3.2) 6 (1.6) 14 (6.8)

Values are presented as n (%).

Table 2. Comparison of the sexes and average ages of patients who did or did not have a stenosis

  No stenosis (n = 429) Stenosis (n = 162)
Age, y 62.1 ± 15.8 68.1 ± 15.3
Sex    
 Men 203 (47.3) 85 (52.5)
 Women 226 (52.7) 77 (47.5)

Values are presented as averages ± SD or n (%).

As shown in Figure 1, 207 (35.0%) of the 591 patients who underwent the triple study had an acute stroke as determined by MRI. Of the patients who had a stroke, 100 (48.3%) also had some major stenosis. Only 62 patients (16.1%) who did not have a stroke had a major stenosis. Patients who had a stroke were significantly more likely to have a stenosis (χ2 test, p < 0.001). Of the patients who had a stroke, 37 (37.0%) presented with intracranial stenosis only, 56 (56.0%) presented with extracranial stenosis only, and 7 (7.0%) presented with both (Table 1). Of the patients who did not have a stroke, 21 stenoses (33.9%) were intracranial, 39 (62.9%) were extracranial, and 2 (3.2%) presented with both (Table 1). There was no significant difference in the distribution of intracranial versus extracranial stenoses among patients who did or did not have a stroke (χ2 test, p > 0.05).

tpj20214 pdf1

Figure 1. A flow chart description of triple-study patients who did or did not have an acute stroke, did or did not have a major stenosis, and did or did not have an intervention and how long the intervention took.

None of the patients in this cohort who presented with intracranial stenosis underwent a percutaneous endovascular or open surgical procedure. Of 63 patients with a major extracranial stenosis who also had an acute stroke, 9 (14.2%) underwent surgical intervention within 90 days. The remaining 54 patients (85.7%) did not undergo surgical intervention within 90 days. There were 41 patients with a major extracranial stenosis who did not have an acute stroke, 5 of whom (12.2%) underwent surgical intervention within 90 days. The remaining 36 patients (87.8%) did not undergo surgical intervention. Intervention rates between patients with a major cervical stenosis were not significantly different (χ2 test, p > 0.05) between patients who did or did not have an acute stroke.

A total of 68 patients (11.5%) also received follow-up imaging within 30 days (±1 week) of the simultaneous triple study. Of these, 52 patients received an ultrasound of the carotid arteries (76.5%). One patient underwent a cerebral angiography (1.5%) and the remaining patients received either MRA or CTA.

Twelve patients (17.7%) had a substantial difference in their imaging findings in follow-up studies compared to the original triple study. Of these, no patients underwent intervention. Eleven of the 12 patients showed no major stenosis on carotid ultrasound compared to the original neck MRA findings at the time of the triple study because the stenosis was not substantial enough to meet criteria for major stenosis on an ultrasound. One patient showed a stenosis in the high neck that was not seen on the carotid ultrasound. However, this patient also had prior catheter angiography performed 5 years earlier, which demonstrated the same high-grade stenosis of the extracranial right internal carotid artery above the region imaged by ultrasound.

Of the 15 patients who underwent surgical intervention within 90 days of examination, 4 patients had an intervention within a week. One of these patients underwent carotid endarterectomy the day after examination, for the patient’s convenience. One of the patients underwent urgent carotid endarterectomy for crescendo transient ischemic attack and another underwent urgent carotid endarterectomy for continued symptoms 2 days after acute stroke. The fourth patient underwent carotid endarterectomy within a week of imaging because of ongoing drug abuse, which the operating surgeon felt made the patient to be unreliable for discharge without surgical intervention.

Of the remaining 11 patients, surgical intervention occurred more than a week after the triple study. In addition, 3 patients had an intervention that occurred more than 90 days after their triple study. These patients were not included in our analysis because of the long time interval between the surgical intervention and their triple study.

During 2013, 120 triple studies were completed. In 2014, there were 129 triple studies. This number increased in 2015 to 163 triple studies. Finally, in 2016, 187 of these triple studies were completed. This high utilization continues in our HMO, as the data from 2019 demonstrated 119 such triple studies in patients with suspected acute stroke in just the first 6 months.

DISCUSSION

Each year, more than 795,000 people experience a stroke and more than 130,000 people die from stroke in the US.4,5 To assess strokes, brain MRI, intracranial MRA, and neck MRA are frequently used because of their high sensitivity in the detection of acute stroke and stenoses.1-3 The American College of Radiology appropriateness criteria currently state that for patients with suspected stroke with symptoms lasting longer than 6 hours, “Further evaluation is ideally performed with a contrast-enhanced brain MRI along with TOF-MRA of the circle of Willis and CE-MRA of the cervical vessels.”6 This may be one reason why many physicians in our HMO are ordering a simultaneous triple study of brain MRI, head MRA, and neck MRA when patients experience stroke-like symptoms. However, we could find no studies published in the medical literature that demonstrate a substantial improvement in clinical outcomes for patients who undergo simultaneous imaging of the brain with intracranial and neck MRA compared to those who do not. Our study found that the number of simultaneous triple studies increased from 120 to 187, annually, from 2013 to 2016. During this period, membership within the HMO increased by less than 2%, marking an approximate 50% increase in the number of these studies.

Medicare reimbursement is often used as a marker of imaging cost.7,8 According to Medicare Part B, the global fees in our region are $250.10 for brain MRI, $277.46 for head MRA without dye, and $278.70 for neck MRA.9 Thus, the average Medicare reimbursement of this triple study is approximately $806.26. In addition, ultrasound imaging is used as indication for surgery and has a reimbursement of $227.43, which brings the total fees to $1033.69. At a time when there is increasing scrutiny of health expenditures, this is an expensive combination of studies.

Furthermore, even within our HMO, many of our patients have substantial copayment requirements. Depending on their health care copayment requirements, some patients may be required to pay up to $300 per imaging study. In a time when health care costs are an increasing burden and leading cause of bankruptcy, it is important to consider the financial burden of all procedures.10 Finally, there are considerable wait times for MRI studies within our HMO because of the high demand for all MRI studies. We undertook this investigation because we suspected that there were very few urgent surgical interventions associated with these triple MRI studies, which also require increased setup and imaging times for our radiology technologists and therefore limit the availability of these magnets for other imaging studies.

For patients presenting within 3 to 4.5 hours of stroke onset, intravenous alteplase may be used to dissolve clots and improve blood flow.11,12 Such patients can also undergo an endovascular procedure to remove clots if presenting within 6 hours of symptom onset.11,12 These patients were not included in this study, as our acute stroke protocol dictates that such patients undergo emergent computed tomography of the head with CTA of the neck and brain rather than MRI.

Most other patients who experience a stroke do not undergo surgical interventions. The standard treatment for patients who experience an acute stroke involves 4 preventative therapies: an antiplatelet agent, a statin, an angiotensin-converting enzyme inhibitor, and a diuretic.13

None of the 591 patients in this study had surgical intervention for intracranial stenosis. Some patients may benefit from imaging of their cervical arteries. This can be done with carotid ultrasound, CTA, or MRA depending on the clinical scenario. In our HMO, ultrasound is considered the standard imaging modality for suspected cervical carotid stenosis.

In our patient population, less than 3% of patients undergoing a triple study had a subsequent surgical intervention within 90 days; the majority of these patients did so more than a week later. Based on our data, 48.3% of patients with an acute stroke had a major stenosis. These patients may benefit from additional vascular imaging during their admission or shortly thereafter if they are candidates for intervention. Only 16.1% of patients who did not have an acute stroke had a major stenosis. Less than 2% of patients who had a stroke underwent intervention within 90 days. Therefore, the vast majority of these patients did not require immediate vascular imaging. The workup for these patients could have been performed at their convenience as clinically appropriate.

Only 4 patients out of the entire cohort had surgical intervention within a week of their triple study. One of these patients elected to have that intervention within that week for the patient’s own convenience. Two other patients had ongoing or worsening symptoms and therefore required urgent surgical intervention, which was performed 2 days after their triple study. The fourth patient was unreliable for follow-up and it was decided to perform the procedure before the patient was discharged.

Our study suggests that only patients with ongoing or worsening symptoms after admission may require urgent vascular imaging to determine whether surgical revascularization is necessary. Even these patients do not require simultaneous brain MRI and MRA at their initial presentation because they can and do undergo urgent imaging with carotid ultrasound, CTA, or MRA. Since they represent a very small proportion of our cohort (<1%), these studies would rarely be necessary on an emergent basis. In fact, 2 of the 3 patients in this study requiring urgent surgical revascularization also had a carotid ultrasound prior to their surgical intervention.

Limitations of this study include its retrospective nature, which precludes us from understanding why physicians simultaneously order these triple studies and why some patients underwent urgent revascularization without worsening symptoms while other patients’ surgeries were delayed 90 or more days. Review of the medical records at the time of admission for a small sample of the patients in this study revealed that very few had a recorded National Institutes of Health stroke scale score included in their admission history and physical examination. As a National Institutes of Health stroke scale score greater than 10 has been shown to be associated with a greater likelihood of large vessel occlusion, requiring a similar threshold to order a triple study in patients not eligible for acute thrombolytic therapy may reduce the number of these studies.14 Finally, the findings of our study should not be applied to those patients presenting with acute stroke who may be eligible for thrombolytic therapy. In our HMO, those patients undergo a different care pathway with emergent brain computed tomography with CTA and perfusion imaging.

In summary, only 3% of patients in our cohort underwent subsequent surgical intervention. Furthermore, approximately 1% of these patients underwent urgent revascularization within a week of their MRI studies. Even within this small group, only 2 patients had worsening or continued symptoms that required urgent intervention. Therefore, it is readily apparent that the intracranial MRA or neck MRA need not be performed concurrently with brain MRI in patients with stroke-like symptoms.

Conclusion

Physicians should not simultaneously order brain MRI, head MRA, and neck MRA for patients presenting with stroke-like symptoms and instead should order each study individually as clinically indicated.

Disclosure Statement

The author(s) have no conflicts of interest to disclose.

Acknowledgments

Kathleen Louden, ELS, of Louden Health Communications performed a primary copy edit.

Author Affiliations

Department of Diagnostic Imaging, Kaiser Permanente Moanalua Medical Center, Honolulu, HI

Corresponding Author

Alyssa Finger ()

Author Contributions

Mark Harris and Hyo-Chun Yoon, MD, PhD, participated in the study design, acquisition and analysis of data, and drafting of the final manuscript. Alyssa Finger participated in the critical review, drafting, and submission of the final manuscript. Emily Nishimura participated in the analysis of data and drafting of the final manuscript. Blake Watabe participated in the study design. All authors have given final approval to the manuscript.

Financial Support

No financial support was received for this work.

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Keywords: MRI, EMR, head MRA, neck MRA, radiology, stroke, utilization

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