Transperineal ultrasonography for treatment response evaluation in children with perianal Crohn's disease

Abstract

Purpose: This study assessed the performance of transperineal ultrasonography (TPUS) in evaluating the treatment response in children with perianal Crohn's disease (PACD) compared with pelvic magnetic resonance imaging (MRI).

Methods: This retrospective study was approved by the Institutional Review Board of our institution, which waived the requirement for informed consent. Twenty-nine patients (19 boys and 10 girls; median age, 14 years [range, 8 to 18 years]) with 56 fistulas were examined. Each fistula's thickness and abscess size were measured using both modalities, and treatment response was classified as positive or negative based on each modality. The concordance of the classifications was compared between TPUS and pelvic MRI. A receiver operating characteristic curve (ROC) was used to evaluate the performance of TPUS.

Results: TPUS found 80.4% (45/56) of the fistulas. On MRI, 39 fistulas (70%) were classified as having positive treatment responses, and the remaining 17 as having no response. The agreement of the classifications between TPUS and MRI was moderate (κ=0.486; P<0.001; Spearman ρ=0.573; P<0.001). Based on the ROC analysis with the MRI findings as a reference to distinguish positive from negative treatment responses, TPUS exhibited sensitivity, specificity, positive predictive value, negative predictive value, and accuracy of 63.3%, 93.3%, 95.0%, 56.0%, and 73.3%, respectively.

Conclusion: TPUS can be an appropriate adjuvant imaging modality for pelvic MRI to evaluate the treatment response of PACD in children when initial TPUS detects PACD with a location and imaging features comparable to those visualized on MRI.

Keywords: Abscess; Anal canal; Fistula; Ultrasonography.

Fig. 1.. Normal anal canal anatomy on transperineal ultrasonography.

A, B. Mid-sagittal and mid-coronal transperineal ultrasonographic images of the anal canal show a hypoechoic, internal anal sphincter (arrowhead) and a hyperechoic, external anal sphincter (arrow) on both sides of the anal canal (C). An ischioanal fossa (IAF) is located lateral and posterior to the external anal sphincter.

Fig. 2.. Diagrammatic schema of the Parks classification.

Fig. 3.. A 14-year-old boy with a positive treatment response (complete remission) on both transperineal ultrasonography (TPUS) and magnetic resonance imaging (MRI).

A, C. Sagittal TPUS and sagittal fatsuppressed T2-weighted images show a perianal fistula at the 12-o’clock location (arrow). B, D. On follow-up TPUS and MRI, the perianal fistula completely disappeared after steroid and methotrexate treatment.

Fig. 4.. A 17-year-old boy with a positive treatment response (partial remission) on both transperineal ultrasonography (TPUS) and magnetic resonance imaging (MRI).

A, C. Sagittal TPUS and sagittal fatsuppressed T2-weighted images demonstrate a perianal fistula (arrow) and abscess (arrowhead) at the 12-o’clock location. B, D. Follow-up TPUS and MRI reveal partial remission of the perianal fistula (arrow) and abscess (arrowhead) after infliximab, steroid, and methotrexate treatment.

Fig. 5.. A 12-year-old boy with discordant treatment response evaluations between transperineal ultrasonography (TPUS) and magnetic resonance imaging.

A, C, E. On baseline sagittal TPUS, sagittal and coronal fat-suppressed T2-weighted images, a perianal fistula (arrow) is noted at the 3-o’clock location. B. On follow-up TPUS after infliximab, steroid, and methotrexate treatment, the perianal fistula (arrow) appears to persist. D, F. Follow-up sagittal and coronal fat-suppressed T2-weighted images show complete remission of the perianal fistula (arrow).

Fig. 6.. A 14-year-old boy with two fistulas; one showed discordant treatment response between transperineal ultrasonography (TPUS) and magnetic resonance imaging (MRI), and the other was not detected with TPUS.

A. Sagittal TPUS shows a perianal fistula at the 12-o’clock location (arrow). B. Followup ultrasonography image after steroid and methotrexate treatment demonstrates no interval change in the fistula (arrow). C, E. On baseline MRI (sagittal and axial fat-suppressed T2-weighted images), the perianal fistula at 12 o’clock (arrow) corresponds with the TPUS finding. A second perianal fistula (arrowhead) is present at 6 o’clock, undetected using TPUS. Although both lesions are superficial, the 12-o’clock fistula is thicker than the 6-o’clock fistula. D, F. On follow-up sagittal and axial fatsuppressed T2-weighted images, the two perianal fistulas completely disappeared.