Comparing diagnostic accuracy of transperineal ultrasound using microconvex probe versus conventional linear probe to predict rectal histoendoscopic activity in ulcerative colitis: a paired prospective, head-to-head comparative study

BACKGROUND AND AIMS: Prior studies have reported variable diagnostic accuracy of transperineal ultrasound (TPUS) in ulcerative colitis (UC) using linear and/or microconvex probes. This study directly compared these probes for predicting rectal histoendoscopic activity. METHODS: Adults with UC prospectively underwent transabdominal ultrasound (TAS) with TPUS using linear followed by microconvex probes by blinded operators. Rectal total wall thickness (TWT), vascularity (Modified Limberg score [MLS]), and Milan ultrasound criteria (MUC) were recorded. Receiver operating characteristic analysis determined area under the curve (AUC) for endoscopic (Ulcerative Colitis Endoscopic Index of Severity >1) and histologic (Nancy Index >1) activity, with paired AUC comparisons. RESULTS: Ninety-seven patients (32% female; age 18-70 years) were included. For endoscopic activity, TPUS outperformed TAS. Microconvex TPUS showed numerically higher AUCs for selected parameters (TWT: 0.77; vascularity: 0.78; MUC: 0.81) compared with linear TPUS (TWT: 0.75; vascularity: 0.71; MUC: 0.77), although head-to-head differences were not consistently statistically significant. For histologic activity, microconvex and linear TPUS demonstrated comparable performance (AUC range 0.66-0.80). Axial-plane posterior wall thickness assessment with the microconvex probe showed favorable trends over longitudinal measurements (endoscopic: ΔAUC -0.071, P = .074; histologic: ΔAUC 0.081, P = .08). Vascularity-based metrics were consistently superior on TPUS compared with TAS, irrespective of probe type. CONCLUSION: TPUS provides clinically relevant, noninvasive assessment of rectal inflammation in UC. While microconvex TPUS offers technical advantages-particularly axial-plane assessment of posterior wall thickness with favorable diagnostic trends-no single probe demonstrated uniform superiority. These findings highlight the complementary roles of linear and microconvex probes and support ongoing standardization of TPUS.