SRS392 - Qualitative and quantitative assessment of smooth muscle fibres in the common bile duct

Abstract Introduction Classically, the common bile duct (CBD) is believed to have a variable presence of scattered smooth muscle within the muscularis mucosae. The prevalence and organisation of these fibres remain poorly defined. This study aimed to qualitatively and quantitatively assess smooth muscle in CBD resections from patients with biliary obstruction and examine correlations with peak preoperative bilirubin levels. Methods CBD specimens from 81 surgeries, between January 2019 and January 2025, were retrieved from Queen’s Medical Centre, Nottingham, and stained for desmin, smooth muscle actin (SMA), and calretinin. Qualitative analysis classified smooth muscle banding around the lumen. Quantitative analysis was conducted using QuPath, employing a semi-automated approach, with manual annotation where required. Independent reviewers resolved discrepancies >10% by consensus. Additionally, bilirubin concentrations were correlated with quantitative smooth muscle measurements. Results Smooth muscle was present in all samples. Interrupted muscle bands were observed in 74.07% of cases, focal muscle fibres in 23.46%, and concentric bands in only 2.47%. Quantitative analysis of samples demonstrated mean tissue staining of 2.54% ± 2.44 (0.26–17.30) for Desmin, 32.86% ± 12.58 (3.74–66.25) for SMA and 2.27% ± 2.25 (0.27–18.24) for Calretinin. A weak positive correlation was observed between SMA expression and peak bilirubin (ρ = 0.241, P = 0.0312); correlations with desmin and calretinin were not significant. Conclusions This study introduces a novel semi-automated method for assessing smooth muscle in the CBD. The consistent presence of smooth muscle across all specimens challenges traditional assumptions and may have implications for understanding biliary physiology, pathology, and surgical planning.