Best Evidence Topics

Review or meta-analysis

Robert F. McCormack, MD and Alan Hutson, PhD
Can Computed Tomography Angiography of the Brain Replace Lumbar Puncture in the Evaluation of Acute-onset Headache After a Negative Noncontrast Cranial Computed Tomography Scan?
Society for Academic Emergency Medicine
2010; 17:444-451
  • Submitted by:Stephanie Cunningham - Emergency Medicine Resident
  • Institution:Grand Rapids Medical Education Partners/ Michigan State University College of Human Medicine
  • Date submitted:11th April 2011
Before CA, i rated this paper: 5/10
1 Objectives and hypotheses
1.1 Are the objectives of the study clearly stated?
  Yes. The objective of the study as outlined by the authors is to evaluate the role of CT/CTA versus CT/LP in the diagnostic workup of acute-onset headache.
2 Design
2.1 Is the study design suitable for the objectives?
  Yes. A recent literature review is employed focusing on the prevalence of subarachnoid hemorrhage in ED patients with acute onset headache, the sensitivity of CT for subarachnoid hemorrhage, and the sensitivity and specificity of CTA for detection of aneurysms. A mathematical probability model is then employed to compare CT/LP versus CT/CTA in excluding aneurysmal or AVM subarachnoid hemorrhage.
2.2 Were the search methods used to locate relevant studies comprehensive?
  A MEDLINE search was undertaken with key words: subarachnoid hemorrhage, tomography x-ray computed, spinal puncture, angiography, angiography digital subtraction. The search was from 1996-present and included review of the article references. The most recent and relevant studies were selected, although the authors do not go into detail on their methods regarding this selection. A total of 15 articles were selected.
2.3 Was this the right sample to answer the objectives?
  Yes. The search included the prevalence of subarachnoid hemorrhage in ED patients with acute onset headache, the sensitivity of CT for subarachnoid hemorrhage, the sensitivity and specificity of LP or subarachnoid hemorrhage, and the sensitivity and specificity of CTA for detection of aneurysm.
2.4 Is the study large enough to achieve its objectives?
  It is unclear why the 15 listed articles were chosen except that they met the search terms and were recent and relevant. The mathematical model was employed because an equivalence study comparing CT/LP to CT/CTA would require 3,000 + subjects.
2.5 Were all the studies accounted for?
  No. Only selected studies were referenced in the article. There were five studies referenced regarding the prevalence of subarachnoid hemorrhage in ED headache patients, six studies referenced for sensitivity of CT for subarachnoid hemorrhage detection, and four studies referenced for sensitivity and specificity of CTA for detection of subarachnoid hemorrhage. One study was discussed briefly in the methods section regarding sensitivity and specificity of LP for subarachnoid hemorrhage.
2.6 Were all appropriate outcomes considered?
  Yes. The authors considered subarachnoid hemorrhage in the presence or absence of AVM or aneurysm.
2.7 Has ethical approval been obtained if appropriate?
  As this was a review article that then employed a mathematical probability model, no further ethical approval was needed.
3 Measurement and observation
3.1 Is it clear what was measured, how it was measured and what the outcomes were?
  In regards to the literature review and the chosen articles, only the outcomes of the articles that were relevant to the authors objectives were discussed. The specific articles were not reviewed in depth. In regards to the mathematical model that was employed, the methods and results were adequately discussed.
3.2 Were explicit methods used to determine which studies to include in the review?
  The search terms were outlined clearly, but the authors then selected the most recent and relevant articles to use. They did not outline their methods for determining which articles were most recent and relevant.
3.3 Was the selection of primary studies re-producible and free from bias?
  No. The authors explicitly state the search terms used, but then selected articles for being most recent or relevant.
3.4 Was the methodologic quality of the primary studies assessed?
  No. Only the results were reviewed.
3.5 Are the measurements valid?
  Unable to determine - authors did not outline their methods for determining which articles were most recent and relevant.
3.6 Are the measurements reliable?
  Reliability was not reported
3.7 Are the measurements reproducible?
  Description of mathematical model was clear and reproducuble
4 Presentation of results
4.1 Are the basic data adequately described?
  Three tables were used to compare the studies in each of the three reviewed areas: prevalence of subarachnoid hemorrhage, sensitivity of CT for subarachnoid hemorrhage, and sensitivity and specificity of CTA for aneurysm. These tables do review the basic data in the studies, but it is otherwise not discussed in depth in the text. For the mathematical model, the authors do thoroughly describe their process and data.
4.2 Were the differences between studies adequately described?
  No. The differences in the studies were not examined. Only the results were reviewed.
4.3 Are the results presented clearly, objectively and in sufficient detail to enable readers to make their own judgement?
  The results of the mathematical model are presented clearly in plain language. It would be difficult for readers to make their own judgments due to the complexity of the math and dependence on assumptions. These assumptions are based on the aforementioned literature review.
4.4 Are the results internally consistent, i.e. do the numbers add up properly?
5 Analysis
5.1 Were the results of primary studies combined appropriately?
  No. They were outlined in three tables, but were not combined.
5.2 Has a sensitivity analysis been performed?
5.3 Were all the important outcomes considered?
5.4 Are the data suitable for analysis?
5.5 Are the methods appropriate to the data?
5.6 Are any statistics correctly performed and interpreted?
  Yes, in regards to the mathematical probability study. No statistics were performed in the review of the literature.
6 Discussion
6.1 Are the results discussed in relation to existing knowledge on the subject and study objectives?
  Yes. Current knowledge on subarachnoid hemorrhage and the current standard of CT with LP to rule out is taken into account in the discussion.
6.2 Is the discussion biased?
  Yes. Although the discussion recognizes both the limitations and utility of this mathematical model, the initial literature review is biased.
7 Interpretation
7.1 Are the author's conclusions justified by the data?
  Yes. The author's use a mathematical probability model to predict that in an ED patient with headache of less than 48 hours and no increased risk of aneurysm that a CT/CTA would exclude subarachnoid hemorrhage due to aneurysm or AVM with 99% posttest probability.
7.2 What level of evidence has this paper presented?
  3b - homogeneity was not measured; analysis based on poor quality estimates of data, but including sensitivity analyses incorporating clinically sensible variations.
7.3 Does this paper help me to answer my problem?
  No. It identifies a new avenue for evaluation of acute headache in the ED. It does not definitively answer the question set out in the title : Can computed tomography angiography of the brain replace lumbar puncture in the evaluation of acute-onset headache after a negative noncontrast cranial computed tomography scan?
After CA, i rated this paper: 3/10
8 Implementation
8.1 Can any necessary change be implemented in practice?
  Not at this time. Further study is needed.
8.2 What aids to implementation exist?
  The invasive nature of the LP will likely continue to propel care providers towards an alternative. The high sensitivity of CT and CTA also lend credence to the CT/CTA route being a viable alternative to CT/LP.
8.3 What barriers to implementation exist?
  As the authors state at the start of the article, 3,000+ patients would be required for a CT/LP versus CT/CTA equivalence study. Difficulty with implementation may lie also in that the true prevalence of incidental aneurysm is unknown. A third point would be the increased radiation and IV contrast needed to perform the CTA.