The objectives of this evidence based review are:
- i) To determine the effectiveness of computed tomography (CT) and magnetic resonance imaging (MRI) scans in the evaluation of persons with a chronic headache and a normal neurological examination.
- ii) To determine the comparative effectiveness of CT and MRI scans for detecting significant intracranial abnormalities in persons with chronic headache and a normal neurological exam.
- iii) To determine the budget impact of CT and MRI scans for persons with a chronic headache and a normal neurological exam.
Clinical Need: Condition and Target Population
Headaches disorders are generally classified as either primary or secondary with further sub-classifications into specific headache types. Primary headaches are those not caused by a disease or medical condition and include i) tension-type headache, ii) migraine, iii) cluster headache and, iv) other primary headaches, such as hemicrania continua and new daily persistent headache. Secondary headaches include those headaches caused by an underlying medical condition. While primary headaches disorders are far more frequent than secondary headache disorders, there is an urge to carry out neuroimaging studies (CT and/or MRI scans) out of fear of missing uncommon secondary causes and often to relieve patient anxiety.
Tension type headaches are the most common primary headache disorder and migraines are the most common severe primary headache disorder. Cluster headaches are a type of trigeminal autonomic cephalalgia and are less common than migraines and tension type headaches. Chronic headaches are defined as headaches present for at least 3 months and lasting greater than or equal to 15 days per month. The International Classification of Headache Disorders states that for most secondary headaches the characteristics of the headache are poorly described in the literature and for those headache disorders where it is well described there are few diagnostically important features.
The global prevalence of headache in general in the adult population is estimated at 46%, for tension-type headache it is 42% and 11% for migraine headache. The estimated prevalence of cluster headaches is 0.1% or 1 in 1000 persons. The prevalence of chronic daily headache is estimated at 3%.
Computed tomography (CT) is a medical imaging technique used to aid diagnosis and to guide interventional and therapeutic procedures. It allows rapid acquisition of high-resolution three-dimensional images, providing radiologists and other physicians with cross-sectional views of a person’s anatomy. CT scanning poses risk of radiation exposure. The radiation exposure from a conventional CT scanner may emit effective doses of 2-4mSv for a typical head CT.
Magnetic Resonance Imaging
Magnetic resonance imaging (MRI) is a medical imaging technique used to aid diagnosis but unlike CT it does not use ionizing radiation. Instead, it uses a strong magnetic field to image a person’s anatomy. Compared to CT, MRI can provide increased contrast between the soft tissues of the body. Because of the persistent magnetic field, extra care is required in the magnetic resonance environment to ensure that injury or harm does not come to any personnel while in the environment.
- What is the effectiveness of CT and MRI scanning in the evaluation of persons with a chronic headache and a normal neurological examination?
- What is the comparative effectiveness of CT and MRI scanning for detecting significant intracranial abnormality in persons with chronic headache and a normal neurological exam?
- What is the budget impact of CT and MRI scans for persons with a chronic headache and a normal neurological exam.
A literature search was performed on February 18, 2010 using OVID MEDLINE, MEDLINE In-Process and Other Non-Indexed Citations, EMBASE, the Cumulative Index to Nursing & Allied Health Literature (CINAHL), the Cochrane Library, and the International Agency for Health Technology Assessment (INAHTA) for studies published from January, 2005 to February, 2010. Abstracts were reviewed by a single reviewer and, for those studies meeting the eligibility criteria full-text articles were obtained. Reference lists were also examined for any additional relevant studies not identified through the search. Articles with an unknown eligibility were reviewed with a second clinical epidemiologist and then a group of epidemiologists until consensus was established.
- Systematic reviews, randomized controlled trials, observational studies
- Outpatient adult population with chronic headache and normal neurological exam
- Studies reporting likelihood ratio of clinical variables for a significant intracranial abnormality
- English language studies
- Studies which report outcomes for persons with seizures, focal symptoms, recent/new onset headache, change in presentation, thunderclap headache, and headache due to trauma
- Persons with abnormal neurological examination
- Case reports
Outcomes of Interest
- Probability for intracranial abnormality
- Patient relief from anxiety
- System service use
- System costs
- Detection rates for significant abnormalities in MRI and CT scans
Summary of Findings
One systematic review, 1 small RCT, and 1 observational study met the inclusion and exclusion criteria. The systematic review completed by Detsky, et al. reported the likelihood ratios of specific clinical variables to predict significant intracranial abnormalities. The RCT completed by Howard et al., evaluated whether neuroimaging persons with chronic headache increased or reduced patient anxiety. The prospective observational study by Sempere et al., provided evidence for the pre-test probability of intracranial abnormalities in persons with chronic headache as well as minimal data on the comparative effectiveness of CT and MRI to detect intracranial abnormalities.
Outcome 1: Pre-test Probability.
The pre-test probability is usually related to the prevalence of the disease and can be adjusted depending on the characteristics of the population. The study by Sempere et al. determined the pre-test probability (prevalence) of significant intracranial abnormalities in persons with chronic headaches defined as headache experienced for at least a 4 week duration with a normal neurological exam. There is a pre-test probability of 0.9% (95% CI 0.5, 1.4) in persons with chronic headache and normal neurological exam. The highest pre-test probability of 5 found in persons with cluster headaches. The second highest, that of 3.7, was reported in persons with indeterminate type headache. There was a 0.75% rate of incidental findings.
Likelihood ratios for detecting a significant abnormality
Clinical findings from the history and physical may be used as screening test to predict abnormalities on neuroimaging. The extent to which the clinical variable may be a good predictive variable can be captured by reporting its likelihood ratio. The likelihood ratio provides an estimate of how much a test result will change the odds of having a disease or condition. The positive likelihood ratio (LR+) tells you how much the odds of having the disease increases when a test is positive. The negative likelihood ratio (LR-) tells you how much the odds of having the disease decreases when the test is negative.
Detsky et al., determined the likelihood ratio for specific clinical variable from 11 studies. There were 4 clinical variables with both statistically significant positive and negative likelihood ratios. These included: abnormal neurological exam (LR+ 5.3, LR- 0.72), undefined headache (LR+ 3.8, LR- 0.66), headache aggravated by exertion or valsalva (LR+ 2.3, LR- 0.70), and headache with vomiting (LR+ 1.8, and LR- 0.47). There were two clinical variables with a statistically significant positive likelihood ratio and non significant negative likelihood ratio. These included: cluster-type headache (LR+ 11, LR- 0.95), and headache with aura (LR+ 12.9, LR- 0.52). Finally, there were 8 clinical variables with both statistically non significant positive and negative likelihood ratios. These included: headache with focal symptoms, new onset headache, quick onset headache, worsening headache, male gender, headache with nausea, increased headache severity, and migraine type headache.
Outcome 2: Relief from Anxiety
Howard et al. completed an RCT of 150 persons to determine if neuroimaging for headaches was anxiolytic or anxiogenic. Persons were randomized to receiving either an MRI scan or no scan for investigation of their headache. The study population was stratified into those persons with a Hospital Anxiety and Depression scale (HADS) > 11 (the high anxiety and depression group) and those < 11 (the low anxiety and depression) so that there were 4 groups:
Group 1: High anxiety and depression, no scan group
Group 2: High anxiety and depression, scan group
Group 3: Low anxiety and depression, no scan group
Group 4: Low anxiety and depression, scan group
There was no evidence for any overall reduction in anxiety at 1 year as measured by a visual analogue scale of ‘level of worry’ when analysed by whether the person received a scan or not. Similarly, there was no interaction between anxiety and depression status and whether a scan was offered or not on patient anxiety. Anxiety did not decrease at 1 year to any statistically significant degree in the high anxiety and depression group (HADS positive) compared with the low anxiety and depression group (HADS negative).
There are serious methodological limitations in this study design which may have contributed to these negative results. First, when considering the comparison of ‘scan’ vs. ‘no scan’ groups, 12 people (16%) in the ‘no scan group’ actually received a scan within the follow up year. If indeed scanning does reduce anxiety then this contamination of the ‘no scan’ group may have reduced the effect between the groups results resulting in a non significant difference in anxiety scores between the ‘scanned’ and the ‘no scan’ group. Second, there was an inadequate sample size at 1 year follow up in each of the 4 groups which may have contributed to a Type II statistical error (missing a difference when one may exist) when comparing scan vs. no scan by anxiety and depression status. Therefore, based on the results and study limitations it is inconclusive as to whether scanning reduces anxiety.
Outcome 3: System Services
Howard et al., considered services used and system costs a secondary outcome. These were determined by examining primary care case notes at 1 year for consultation rates, symptoms, further investigations, and contact with secondary and tertiary care.
The authors report that the use of neurologist and psychiatrist services was significantly higher for those persons not offered as scan, regardless of their anxiety and depression status (P<0.001 for neurologist, and P=0.033 for psychiatrist)
Outcome 4: System Costs
There was evidence of statistically significantly lower system costs if persons with high levels of anxiety and depression (Hospital Anxiety and Depression Scale score >11) were provided with a scan (P=0.03 including inpatient costs, and 0.047 excluding inpatient costs).
Comparative Effectiveness of CT and MRI Scans
One study reported the detection rate for significant intracranial abnormalities using CT and MRI. In a cohort of 1876 persons with a non acute headache defined as any type of headache that had begun at least 4 weeks before enrolment Sempere et al. reported that the detection rate was 19/1432 (1.3%) using CT and 4/444 (0.9%) using MRI. Of 119 normal CT scans 2 (1.7%) had significant intracranial abnormality on MRI. The 2 cases were a small meningioma, and an acoustic neurinoma.
The evidence presented can be summarized as follows:
Based on the results by Sempere et al., there is a low pre-test probability for intracranial abnormalities in persons with chronic headaches and a normal neurological exam (defined as headaches experiences for a minimum of 4 weeks). The Grade quality of evidence supporting this outcome is very low.
Based on the systematic review by Detsky et al., there is a statistically significant positive and negative likelihood ratio for the following clinical variables: abnormal neurological exam, undefined headache, headache aggravated by exertion or valsalva, headache with vomiting. Grade quality of evidence supporting this outcome is very low.
Based on the systematic review by Detsky et al. there is a statistically significant positive likelihood ratio but non statistically significant negative likelihood ratio for the following clinical variables: cluster headache and headache with aura. The Grade quality of evidence supporting this outcome is very low.
Based on the systematic review by Detsky et al., there is a non significant positive and negative likelihood ratio for the following clinical variables: headache with focal symptoms, new onset headache, quick onset headache, worsening headache, male gender, headache with nausea, increased headache severity, migraine type headache. The Grade quality of evidence supporting this outcome is very low.
Relief from Anxiety
Based on the RCT by Howard et al., it is inconclusive whether neuroimaging scans in persons with a chronic headache are anxiolytic. The Grade quality of evidence supporting this outcome is low.
Based on the RCT by Howard et al. scanning persons with chronic headache regardless of their anxiety and/or depression level reduces service use. The Grade quality of evidence is low.
Based on the RCT by Howard et al., scanning persons with a score greater than 11 on the High Anxiety and Depression Scale reduces system costs. The Grade quality of evidence is moderate.
Comparative Effectiveness of CT and MRI Scans
There is sparse evidence to determine the relative effectiveness of CT compared with MRI scanning for the detection of intracranial abnormalities. The Grade quality of evidence supporting this is very low.
Volumes for neuroimaging of the head i.e. CT and MRI scans, from the Ontario Health Insurance Plan (OHIP) data set were used to investigate trends in the province for Fiscal Years (FY) 2004-2009.
Assumptions were made in order to investigate neuroimaging of the head for the indication of headache. From the literature, 27% of all CT and 13% of all MRI scans for the head were assumed to include an indication of headache. From that same retrospective chart review and personal communication with the author 16% of CT scans and 4% of MRI scans for the head were for the sole indication of headache. From the Ministry of Health and Long-Term Care (MOHLTC) wait times data, 73% of all CT and 93% of all MRI scans in the province, irrespective of indication were outpatient procedures.
The expenditure for each FY reflects the volume for that year and since volumes have increased in the past 6 FYs, the expenditure has also increased with a pay-out reaching 3.0M and 2.8M for CT and MRI services of the head respectively for the indication of headache and a pay-out reaching 1.8M and 0.9M for CT and MRI services of the head respectively for the indication of headache only in FY 08/09.
Cost per Abnormal Finding
The yield of abnormal finding for a CT and MRI scan of the head for the indication of headache only is 2% and 5% respectively. Based on these yield a high-level estimate of the cost per abnormal finding with neuroimaging of the head for headache only can be calculated for each FY. In FY 08/09 there were 37,434 CT and 16,197 MRI scans of the head for headache only. These volumes would generate a yield of abnormal finding of 749 and 910 with a CT scan and MRI scan respectively. The expenditure for FY 08/09 was 1.8M and 0.9M for CT and MRI services respectively. Therefore the cost per abnormal finding would be $2,409 for CT and $957 for MRI. These cost per abnormal finding estimates were limited because they did not factor in comparators or the consequences associated with an abnormal reading or FNs. The estimates only consider the cost of the neuroimaging procedure and the yield of abnormal finding with the respective procedure.