Transabdominal intestinal ultrasound versus transmural histopathological findings in severe ulcerative colitis requiring colectomy.

Background: Transabdominal intestinal ultrasound (IUS) is a promising, non-invasive tool for monitoring ulcerative colitis (UC). This modality has the advantage of assessing intestinal inflammation transmurally, suggesting that UC can be considered a transmural disease. Determining what transabdominal IUS findings indicate in terms of histopathology would improve its value in assessing disease activity. However, associations between sonographic and histopathological findings have not yet been established for active UC. To address this gap, we investigated patients with active UC who underwent colectomy following IUS examination. Methods: Patients who underwent total colectomy for severe active UC within 1 week of undergoing transabdominal IUS at our facility between December 2020 and March 2023 were consecutively included in this study. Sonographic and histopathological findings were compared for each colonic segment in these patients. Results: Four patients underwent IUS 3-6 days before colectomy, which was performed due to insufficient response to medical treatment. IUS findings, particularly loss of bowel stratification and increased color Doppler signals, were associated with severe inflammation and vascular proliferation in the transmural colon, including the subserosa. Thickened muscularis propria was also observed in inflamed colonic segments; this may have contributed to the increased bowel wall thickness according to IUS. Conclusions: This is the first report comparing IUS findings and transmural pathological features in active UC. It provides an imaging atlas and clinical insights into the role of IUS in determining transmural histopathological inflammatory status in patients with active UC.