A biliary stricture is a narrowing of the bile ducts with upstream dilatation. Since most cases are malignant, histological diagnosis is essential. ESGE guidelines recommend an integrated diagnostic approach that combines multiple techniques to improve diagnostic accuracy. In this setting, Endoscopic ultrasound (EUS) tissue acquisition (TA) has demonstrated good sensitivity (83%) being the preferred diagnostic modality for both imaging and TA, even in absence of abnormal laboratory test. The introduction of ancillary techniques as DFI (Detective Flow Imaging), which enables the detection of low-velocity blood flow without the use of contrast media, represents a potential useful addition in the diagnostic algorithm. The aim of this study is to assess the feasibility of performing the novel DFI-EUS technique in the setting of biliary stricture and its capability to evaluate the presence and type of stricture microvascularization.

Single-centre retrospective study on the role of EUS-DFI in characterizing unexplained biliary strictures and CBD dilatation. We included consecutive patients with unexplained biliary strictures/CBD dilatation who underwent biliopancreatic EUS between January 2024 and October 2025 at the Digestive Diseases Unit of Sant’Andrea University Hospital, Rome. A convex echoendoscope (EG-740UT; Fujifilm) and an ultrasound system (ARIETTA 850; FUJIFILM Medical Co., Ltd., Tokyo, Japan) were used. During EUS for biliary stricture evaluation (lesions or thickening of CBD wall), DFI was performed and if microvascularization was observed, vascular pattern was classified as regular or irregular. Results were compared with the final diagnosis, defined by histopathology obtained with EUS-TA or ERCP-based sampling and/or ≥6 months clinical follow-up as gold standard. TA was performed with EUS-FNB (fine needle biopsy) and/or ERCP (Endoscopic Retrograde Cholangiopancreatography) intraductal biopsies/brushing.

Nineteen patients included (12(63%) male; median age 75). All underwent MRI/ Contrast-Enhanced CT as first line imaging: 4(21.1%) had a perihilar stricture, 14 (73.7%) a medio-distal, 1(5.3%) had “in toto” CBD thickening. Among all, EUS identified 16 (84%) lesions (mean diameter 17 mm) and 3 (15.8%) CBD wall thickening. Eighteen (94%) strictures were hypoechoic, 1 (6%) isoechoic. EUS-TA was performed in all patients, revealing 12(63%) malignancies (8 cholangiocarcinomas, 4 PDAC), 3 (16%) dysplasias, 4 (21%) fibroinflammatory strictures. In 6 cases (31.6%) a second look TA < 6 months was needed to obtain the final diagnosis. In all pts DFI-EUS was feasible. Microvascularization was detected in 17 cases (89%), with an irregular pattern observed in 14(73.7%) patients. Among these, 8(57%) cholangiocarcinoma, 3(14.3%) PDAC, 2(14.3%) dysplasia, 1(7.1%) inflammatory disease. A regular pattern was detected in 3 (15.8%; all benign strictures). Hypovascularization was shown in 2(10.5%) cases (1 PDAC; 1 dysplasia).

In a small cohort of patients with indeterminate biliary strictures, the novel DFI-EUS technique proved to be feasible for assessing microvascularization in CBD stenosis and revealed characteristic irregular patterns or hypovascularization in malignant lesions and dysplasia. Further prospective studies with larger population are needed to confirm these preliminary findings.