Ultrasound G.E.L. – Intussusception

Originally published on Ultrasound G.E.L. on 4/11/22 – Visit HERE to listen to accompanying PODCAST! Reposted with permission.

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Diagnostic Accuracy of Point-of-Care Ultrasound for Intussusception: A Multicenter, Noninferiority Study of Paired Diagnostic Tests

Take Home Points

  1. The diagnostic accuracy of POCUS for the detection of clinically important intussusception is noninferior to that of RADUS when performed by expert sonologists.
  2. Interrater reliability for POCUS studies was high. Agreement between POCUS and RADUS for secondary sonographic findings was high.
  3. Further studies are needed to compare expert PEM sonologists with PEM trained physicians in making this diagnosis with POCUS.

Background

‌Intussusception is the most common cause of bowel obstruction in children less than 6 years old. Delayed diagnosis can lead to impaired efficacy of air enema reduction and intestinal ischemia. Ultrasound is the diagnostic test of choice prior to reduction of ileocolic intussusception by radiology or surgery. Recent studies have demonstrated that a small percentage of ileocolic intussusceptions reduce spontaneously, however the vast majority require procedural reduction. In contrast, ileoileal intussusception is often transient and reduces spontaneously without intervention. The current standard of care is radiology-performed diagnostic ultrasound (RADUS), but recently published studies using POCUS demonstrate similar accuracy in diagnosis.
 ‌
This isn’t the first time we have talked about this! Another interesting study on the topic – Intussussception Feb 2018.

Questions

 ‌1. Is the diagnostic accuracy of POCUS performed by ultrasound-trained pediatric emergency medicine sonologists noninferior to that of RADUS for the detection of clinically important intussusception?
2. What is the agreement between POCUS and RADUS for identification of secondary sonographic findings?

Population

Children aged 3 months to 6 years presenting with clinical suspicion for intussusception and RADUS orders were eligible for inclusion. Children with imaging results from referring facilities for whom the sonologist was aware of those results were excluded.
Patients were enrolled when a study sonologist was available to perform the POCUS scan. Children were screened for enrollment by a member of the study team.

Design

Multicenter, prospective, noninferiority study of paired diagnostic tests – RADUS vs. POCUS

17 tertiary care pediatric EDs in North America, Central American, Europe, and Australia

  • 12 university-based academic medical centers with affiliated children’s hospitals
  • 4 large community children’s hospitals
  • 1 large urban academic center with a dedicated pediatric ED
  • 12 sites with 24/7 radiology capabilities
  • 5 sites with radiology ultrasound services available only during daytime hours with technicians called at night and offsite radiology read
Study conducted between October 2018 – December 2020

If the POCUS study would cause a delay in care, it was performed immediately after RADUS with the study sonologist remaining blinded to RADUS results

If fewer than requested images were obtained, study group used what was obtained for analysis

Deidentified images were shared with the principal investigator

Study sonologists recorded the start and end times of POCUS scanning AND a confidence rating of their POCUS interpretation (positive or negative) as follows: not at all, somewhat, moderately, very, or completely.
POCUS studies were considered positive for intussusception if at least ONE of the following criteria occurred:
  1. Presence of a target-shaped mass >/= 2.0 cm in transverse axis diameter
  2. Sonologist’s clinical judgment that the intussusception would require intervention (i.e. ileocolic)
If an intussusception was identified, it was classified as/with:
  1. Ileoileal or ileocolic
  2. Presence of absence of trapped free fluid
  3. Presence or absence of color Doppler signal
  4. Presence or absence of echogenic foci
The POCUS study was NEGATIVE if:
  1. Absence of a target sign in all four quadrants
  2. Sonologist judgment that an intussusception was not present
*** 2 cm chosen as a cutoff because this value lies about 1-2 standard deviations above mean for ileoileal intussusceptions and 1-2 standard deviations below the mean for ileocolic intussusceptions
For RADUS studies, the impression of the attending radiologist was the final determination of a positive or negative study
Primary Outcome = whether POCUS and RADUS correctly detected clinically important intussusception (defined as an intussusception that required radiographic or surgical reduction during or within 7 days of the ED visit)
Secondary Outcomes = a) agreement between POCUS and RADUS for identification of secondary sonographic findings (maximal diameter measurement, presence of trapped free fluid, decreased Doppler signal, echogenic foci) b) Frequency of serious complications, defines as peritonitis, bowel perforation, intestinal obstruction, shock, or death
Inter-rater reliability for POCUS image clips was evaluated with Cohen’s kappa => two investigators interpreted a random sample of POCUS studies (20% of goal)
Noninferiority study resources

Who did the ultrasounds?

35 sonologists, PEM physicians
  • All had completed either a) an ultrasound fellowship, b) Registered Diagnostic Medical Sonographer designation (RDSM), or c) had previously completed at least 20 abdominal POCUS exams with at least 1 positive intussusception study
  • All study sonologists required to watch a standardized training video that covered study procedures and scanning protocol (technique, image acquisition/storage, measurements, secondary findings)

The Scan

Long Linear

PROTOCOL

  • Patient supine
  • Move transducer superiorly from the RLQ to the hepatic flexure, right to left to the splenic flexure, and then inferiorly to the left lower quadrant
  • At least 2 still images or video clips were obtained in transverse and longitudinal planes in each quadrant (total of 8 images/clips)
  • If an intussusception was identified, the sonologist captured at least 1 still image in the short axis plane of the intussusception (with caliper measurement of the maximal intussusception diameter), 1 still image in longitudinal plane, and 1 still image with color Doppler over the intussusception

Results

262 patients enrolled, n = 256 in primary analysis
  • Median age = 21.1 months
  • Most presented with concerns for abdominal pain (82.8%) or fussiness (80.5%)
  • POCUS occurred prior to RADUS in 248 children (96.9%)
58 (22.7%) children had cases of clinically important intussusception
  • 55 (21.5%) treated with radiographic reductions
  • 16 (6.3%) required surgical reduction
POCUS identified 60 (23.4%) cases as positive => 4 false positives, 2 false negatives
Primary Outcome
Diagnostic accuracy of POCUS 97.7% (95% CI 94.9% to 99%) vs. RADUS 99.3% (95% CI 96.8% to 99.9%)
  • Excluding the site with high rate of positive scans, as well as higher proportion of transfers and bloody stools: diagnostic accuracy of POCUS 97.5%, sensitivity 92.9%, specificity 97.9%
Secondary Outcomes
96.9% agreement between POCUS and RADUS with respect to clinically important intussusception (Cohen’s kappa 0.911 [95% CI 0.852 to 0.972])
Median POCUS scanning time was 6 minutes vs. median time to RADUS results was 65 minutes
Agreement between POCUS and RADUS for:
  1. Presence of trapped free fluid – 83.3% (95% CI 70.4% to 91.3%; n = 40/48)
  2. Decreased color Doppler signal – 95.7% (95% CI 78.1% to 99.9%; n = 22/23)
  3. Presence of echogenic foci – 80% (95% CI 44.4% to 97.5%; n = 8/10)
Telephone follow up data was available for 190 children (74.2%)
  • 14 children (7.4%) had an ED return visit within 7 days of discharge
  • 5 children (2.0%) had serious complications, but all were correctly identified by POCUS at the index visit
Interrater reliability was high between the two study sonologists (Cohen’s kappa of 0.835 [95% CI 0.615 to 1.000] for binary interpretation of findings)

Strengths

  • Multicenter and international
  • Largest prospective study to date
  • Appropriate reference standard
  • Had follow up on patients
  • High agreement between POCUS and RADUS for most secondary sonographic findings
  • Probably best evidence on POCUS accuracy for intussusception

Limitations

  • Convenience sampling based on availability of sonologists
  • Sample size below target so study slightly underpowered
  • Differences between sites – some sites with much higher positivity rate, referrals, use of RADUS
  • Sonologists may have completed the POCUS scan after taking the history and performing a physical exam which may have influenced how diligently they evaluated for intussusception (but not sure this is really a limitation…)
  • Using expert sonologists is ideal for testing the accuracy for POCUS, but is not as generalizable to different sites as most PEMs do not have this level of POCUS training
 ‌

Discussion

This was the largest prospective study to date comparing POCUS to RADUS for diagnosing intussusception which is awesome. Accuracy of POCUS was impressive with 96% accuracy for clinically important intussusception, and only 4 false positive and 2 false negative cases. There have been multiple prior studies looking at the test characteristics of POCUS in intussusception, most were retrospective but with decent accuracy in diagnosis. Prospective studies were limited by small case numbers. Additionally, essentially all prior studies included scanners reflecting all levels of POCUS skill, as opposed to only experts as seen in this study. The authors chose to focus on expert sonologists so as to prove POCUS non-inferiority as compared to RADUS, and more accurately represent how POCUS is used in the PEM world.
One interesting thing these authors did was investigate accuracy by PEM sonologists in identifying secondary signs of clinically important intussusception. As I like to tell my PEM fellows, secondary signs are often primary signs when it comes to abdominal POCUS… such findings are known to aid diagnosis by sonologists and radiologists alike. There was good agreement (>80%) between POCUS and RADUS, with the exception of significantly smaller measurements of the intussusception by POCUS.
At many tertiary PEDs, there is access to radiology ultrasound 24/7. But what about general EDs or satellite/rural PEDs where there are no pediatric sonographers available overnight? POCUS users who can accurately risk stratify clinically important intussusception will in theory speed up a necessary transfer of patient, or prevent an unnecessary one. Additionally, as PEM providers across the board improve their POCUS skills, we can in theory expect even higher accuracy in delineating ileoileal vs. ileocolic pathology. Lastly, as those who do this type of research know… clinical research on pediatric POCUS is difficult to pull off for various reasons (low incidence, convenience sampling, not enough skilled sonologists at site) so congrats to Bergmann et al. on your excellent study.

Summary

In this 18-center prospective observation study of 256 children being evaluated for intussusception, the accuracy of POCUS was not inferior to radiology ultrasound. POCUS had a sensitivity of 96.6% (95% CI 87.2 to 99.1) and specificity of 98% (95% CI 94.7 to 99.2) for intussusception requiring reduction ‌

Take Home Points

  1. The diagnostic accuracy of POCUS for the detection of clinically important intussusception is noninferior to that of RADUS when performed by expert sonologists.
  2. Interrater reliability for POCUS studies was high. Agreement between POCUS and RADUS for secondary sonographic findings was high.
  3. Further studies are needed to compare expert PEM sonologists with PEM trained physicians in making this diagnosis with POCUS.

More Great FOAMed on This Topic

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Cite this post as

Delia Gold. Intussusception: A Prospective Multi-center Study. Ultrasound G.E.L. Podcast Blog. Published on April 11, 2022. Accessed on June 10, 2022. Available at https://www.ultrasoundgel.org/123.

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