The present study demonstrates that cholecystectomy is associated with a measurable, anatomically significant enlargement of the CBD that progresses gradually over time and with advancing age. In our cohort, patients in the post-cholecystectomy group exhibited significantly wider CBD diameters compared with controls (6.61 vs. 4.56 mm; p < 0.001), consistent with the concept of compensatory ductal remodelling following gallbladder removal [14].

From an anatomical perspective, the bile duct wall contains smooth muscle and connective tissue, allowing gradual structural adaptation [15]. The loss of the gallbladder’s reservoir function alters biliary dynamics by conversion of the biliary system into a single-outlet pathway for bile flow into the duodenum [16]. This anatomical and functional reconfiguration may also influence sphincter of Oddi activity, with reported increases in basal pressure, disordered or retrograde contractions, and loss of the normal inhibitory response to cholecystokinin [3]. As a result, mild postoperative CBD dilatation is often a physiological adaptive change, whereas marked or progressive dilatation, or dilatation accompanied by symptoms or abnormal liver tests, is more suggestive of underlying pathology [17,18].

The observed mean difference of approximately 2.0 mm in CBD diameter between post-cholecystectomy patients and controls in our study aligns well with ranges reported in previous investigations [14]. Analysis of CBD diameters according to clinically relevant thresholds revealed marked differences between the study groups. In the control group, most patients remained within the expected physiological range, with 77.0% showing CBD diameters ≤5 mm and 94.6% remaining <7 mm. After cholecystectomy, this proportion decreased substantially, with values ≥7 mm becoming more common. Although dilatation exceeding 10 mm was uncommon overall, it occurred more frequently in post-cholecystectomy patients (8.8% vs. 1.4%). These findings support prior reports indicating that while 7 mm is generally considered the upper limit of normal, diameters up to 10 mm may still represent physiological adaptation in elderly or post-cholecystectomy individuals [6,9].

Previous studies have reported wider bile duct diameters in patients with prior cholecystectomy. At the same time, larger population-based MRCP studies have further refined reference values, indicating that CBD diameters of up to 8 mm in individuals younger than 65 years and up to 11 mm in those aged 65 years or older can be considered physiological [19,20]. Our findings are entirely consistent with these observations. Nonetheless, some studies have not observed postoperative CBD dilatation, suggesting that the biliary response after cholecystectomy is variable and that ductal enlargement does not occur uniformly in all patients [21,22].

In everyday clinical practice, the important question is not simply that the bile duct may be wider after cholecystectomy, but how this should be interpreted in patients who have no clinical or biochemical signs of cholestasis. Such findings are often detected incidentally on imaging performed for unrelated reasons and, in many cases, represent a benign postoperative change [23]. Recognising this helps avoid unnecessary concern and limits additional invasive or costly investigations.

In our multivariable analysis, prior cholecystectomy emerged as the strongest independent determinant of CBD dilatation ≥7 mm, indicating a markedly increased likelihood of ductal widening. When a fixed cutoff was applied, advancing age was associated with lower odds of crossing the ≥7 mm threshold, despite a gradual increase in absolute CBD diameter with age. This apparent discrepancy likely reflects a threshold and distribution effect, in which age-related ductal widening often falls below commonly used dilation cutoffs. In contrast, sex and body mass index did not significantly influence CBD diameter, consistent with previous reports [9,24].

Linear regression analysis further supported a time-dependent widening of the CBD following surgery, with an average increase of approximately 0.12 mm per postoperative year. Although the proportion of explained variance was moderate (R² = 12.3%), this finding suggests that progressive ductal enlargement represents a gradual physiological remodelling process. A similar linear association was observed between age and CBD diameter in the overall cohort, with older age predicting wider ducts at approximately 0.04 mm per year.

These observations highlight the importance of anatomical literacy in everyday clinical practice. An accurate understanding of normal postoperative anatomy is essential, as isolated CBD widening should be interpreted in the context of age and time since surgery rather than immediately attributed to biliary obstruction [23]. Misclassification of postoperative CBD dilatation can also have important consequences. If physiological enlargement is mistaken for pathological, patients may undergo unnecessary MRCP or ERCP, with accompanying risks and healthcare costs [6]. Conversely, assuming that marked dilatation is physiological may delay the diagnosis of clinically relevant obstruction. Different diameter thresholds reported in the literature add to this uncertainty, since the same CBD value can be interpreted in different ways [4]. Therefore, postoperative CBD dilatation should always be evaluated in conjunction with symptoms, laboratory results, and the overall clinical context.

Limitations

This study has several limitations. First, it was conducted at a single centre with a moderate sample size, which may limit generalizability. Second, despite a standardised ultrasound protocol, measurement of the CBD may be influenced by operator dependence and technical factors such as bowel gas or patient positioning. Third, biochemical parameters and longer postoperative follow-up were not systematically analysed, which could have provided additional insight into the functional aspects of biliary adaptation. Finally, the cross-sectional nature of the study precludes longitudinal assessment of intra-individual ductal changes.