Dr. Yasser Asiri , R2

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

• 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.

CRITICAL APPRAISAL

• Are the results of the study valid? (Validity)

• What are the results? (Importance)

• Will the results help in caring for patients? (Applicability)

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

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

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..”

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”

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”.

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

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:

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)

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.

• 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.

• 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.

• 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.

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.