critical appraisal for our monthly journal club.

1. Dr. Yasser Asiri , R2

2. WHY ARE WE LOOKING AT THIS
PROTOCOL?
• Introduction:
• hydrocephalus results from a diverse group of disorders that have in
common an abnormality of formation, flow, or absorption of CSF.
• large number of disorders producing hydrocephalus result in its ranking
among the most common chronic neurosurgical conditions
• Ventriculoperitoneal shunt placement, the primary treatment of
hydrocephalus, is one of the most commonly performed neurosurgical
operation.
• the role of radiologists in the evaluation of shunt malfunction is often to
evaluate ventricular size, usually with head CT

3. • Extensive interest exists among the general public and radiologists regarding
how best to minimize radiation dose
• Several recent studies have also described a novel method for performing low-
dose head CT with associated dose reductions in the range of 30– 70%.
• The objective of this study was to evaluate whether use of a limited three-slice
head CT protocol could consistently provide adequate information for the
diagnosis of shunt malfunction with a substantial decrease in effective dose.

4. CRITICAL APPRAISAL
• Are the results of the study valid? (Validity)
• What are the results? (Importance)
• Will the results help in caring for patients? (Applicability)

5. IS THE STUDY VALID?
• Was there a clear question for the study to address?
• In this case yes, the study asked:
“whether a limited three-slice CT protocol would consistently provide adequate
information for the diagnosis of shunt malfunction with a decrease in effective
dose?”
• This information can usually be found in the abstract or the introduction to the
study

7. IS THE STUDY VALID?
SCREENING
• Is there comparison with an appropriate (gold) reference standard for diagnosing
the disorder under assessment?
• In this case yes, the study stated that:
“Comparison images, which were available for every examination, were provided to the reviewing
neuroradiologists during both sessions as complete CT examinations. Results of the limited and complete
examinations were compared. The complete CT examination served as the reference standard against which the
limited study was judged.”
• As the answer is yes to both of our initial screening questions, we should continue with
our analysis of the diagnostic test study

8. IS THE STUDY VALID?
POPULATION
• Did the study include people with all the common presentations of the target
disorder?
• Yes, the study states that:
“Two hundred thirty-one CT studies were included, performed on 128 patients (59 male, 69
female; age range, 10 months–82 years; mean, 31.1 years). Fifty-one pediatric patients were
included and stratified as follows: younger than 1 year (five patients), 1 year to younger than
5 years (20 patients), 5 years to younger than 10 years (13 patients), and 10–18 years (13
patients). Multiple studies were included for a single patient as follows: 20 patients had two
studies included, seven had three studies included, four had five studies included, four had
six studies included, one had nine, studies included, one had 11 studies included, and one
had 13 studies included..”

9. IS THE STUDY VALID?
BLINDING
• Were the people assessing the results of the index diagnostic test blinded to the results of
the reference standard?
• Yes, while the study does not explicitly state blinding, it is very specific that each CT examinations
were analysed randomly. :
• “Two review sessions were conducted. In the first session, the examinations were presented in the
limited-slice format, consisting of the lateral topogram and the three preselected slices. In the
second review session, the complete examination, all imaging slices included, was reviewed after a
2-week delay from the first session, and images were presented randomly”
• “All 231 scans were reviewed successfully during two sessions, first as a limited-slice scan and
during a second session as a complete examination. Neither radiologist reported difficulty selecting
the slices for the limited protocol..”
• “A total of 231 axial CT examinations of patients with ventricular catheters were reviewed in two
sessions by one of two board-certified fellowship-trained neuroradiologists with at least 2 years of
subspecialty neuroradiology practice. To create the theoretic limited slice examinations, the lateral
topographic image was retrospectively reviewed”

10. IS THE STUDY VALID? TESTING
• Was the reference standard applied regardless of the index test result?
• No , “CT examinations performed in the immediately postoperative period (0–7 days
after surgery) were excluded from the study, as were all CT studies without a
previous study for comparison.”
• Was the diagnostic test validated in a second independent group of patients?
• No , “our study was a preliminary retrospective study with findings that must be
validated in a prospective study. Although we theorize that findings not seen with the
limited protocol would not affect clinical management, a prospective study is needed
for confirmation. In addition, a prospective study would take into account inadequate
and repeat images needed because of patient movement from the time of scout
image acquisition to acquisition of the three slices, possibly increasing patient dose.
This is an especially important consideration in the elderly and children”.

11. IS THE STUDY VALID?
METHODS
• radiologists were asked to evaluate the bodies of the lateral ventricles, temporal horns of the lateral
ventricle, and the fourth ventricle individually (total of three ventricular areas) and to categorize them
as follows: a, not imaged; b, normal in appearance; c, abnormal size or morphologic features but
stable in appearance; d, abnormal with evidence of shunt failure; e, abnormal with evidence of
overshunting. Reviewing radiologists were also asked to record whether the ventricular catheter tip
was visualized. Any additional findings were also noted
• Methods for calculating or comparing measures of diagnostic accuracy and statistical
uncertainty (95% CI)
• The sensitivity of three-slice CT for identifying the ventricular system (bodies of the lateral ventricles,
temporal horns, and fourth ventricle) was 91.6% (95% CI, 87.3–94.7%) and for identifying the
ventricular catheter tip was 93.5% (95% CI, 91.4–97.5%)..
• Now that we have established that the study is valid, we should consider the results

13. RESULTS
•Do the results include estimates of diagnostic test accuracy and statistical
uncertainty (95% CI(?
•Yes the study includes 95% CI for all comparisons made:

16. RESULTS
• Do the results include cross tabulation of the index test results by the reference standard
results? Or enough information to generate this table?
• No table was written in the article , Although the study includes sensitivity, specificity, and cofienence
intervals (CI)

17. DOES THIS DIAGNOSTIC TEST APPLY TO
YOUR SPECIFIC PATIENT?
•Is the diagnostic test available, and if so, is applicable?
•To answer this question you would need to check availability, and also how current the
research is at the time of assessment
•Will the test change the way the patient is managed?
•The test will not change the management entirely , but it will lead to similar result with
substantial reduction in radiation exposure.

18. • There were limitations to our study. Images were selected from the lateral CT topographic
images by a radiologist, not a technologist. Widespread implementation of this protocol will
require investment of time training CT technologists to select appropriate images. Real-time
evaluation of the adequacy of each limited-slice examination before the patient leaves the
scanner would also be ideal to minimize the need for additional imaging. Although this
requires a dedication of resources, we believe that the benefit to patients provided by the
reduction in radiation dose would validate additional effort on the part of even small
institutions to train either technologists or physicians to supervise limited scans.

19. • Another limitation was that comparisons were between limited three-slice CT and complete
head CT. We realize that if widespread implementation of our limited protocol is achieved,
patients will have only limited-slice studies to compare with each other. If the comparison
study is performed with a three-slice protocol, differences in slice position may make it more
difficult to definitively compare ventricular caliber. It will be important to educate clinicians that
an occasional full CT examination should be performed to image the entire ventricular system.
In addition, all of our three-slice studies had a comparison study. Although patients often do
not have a comparison study in clinical practice, we do not believe it was a serious
disadvantage to our study to exclude this scenario, because the limited protocol should never
serve as a baseline study.

20. • our study was a preliminary retrospective study with findings that must be validated in a
prospective study. Although we theorize that findings not seen with the limited protocol would
not affect clinical management, a prospective study is needed for confirmation. In addition, a
prospective study would take into account inadequate and repeat images needed because of
patient movement from the time of scout image acquisition to acquisition of the three slices,
possibly increasing patient dose. This is an especially important consideration in the elderly
and children.

21. IN CONCLUSION
• This study seems to be valid with no major methodological flaws
• In patients with suspected ventriculoperitoneal shunt failure, a limited three-
slice CT protocol produces radiologic results comparable to those of a
standard protocol and offers a potential screening alternative with a
potential substantial reduction in radiation exposure.
• The study population does in this case match our patients, so
we can be reasonably comfortable in the knowledge that if the
protocol was implemented , the result will most likely be
accurate, Provided that the radiologist , technologist and the
physic ion were well educated about it.