In this consecutive MRCP cohort, older age groups had a lower prevalence of gallbladder stones and a higher prevalence of CBD stones, larger CBD caliber, and more frequent IHBD dilatation. This distribution is best described as an age-associated cross-sectional imaging pattern rather than a temporal change within the same patients. Gallstone disease becomes more common with age, but the balance between gallbladder and ductal findings is not uniform across age groups [11,12,13,14]. The present study adds an MRCP-based description from routine radiology practice, in which gallbladder morphology, duct caliber, and additional anatomical findings were evaluated together. This distinction is important because a referred MRCP cohort is enriched for symptomatic and diagnostically complex cases and should not be interpreted as a population prevalence sample.

The strongest result was the association between CBD diameter and CBD stones. CBD diameter increased across age strata, differed markedly between CBD-positive and CBD-negative patients, correlated with maximum CBD stone size among positive cases, and remained the strongest imaging correlate in the adjusted model. The age coefficient was no longer significant after CBD diameter was included. Because the study was cross-sectional, this attenuation should be interpreted as overlap in the statistical information carried by age and duct caliber. It does not demonstrate that CBD dilatation mediates an effect of age or establishes the temporal order of these findings. The finding nevertheless narrows the interpretation as follows: within this dataset, duct caliber carried more adjusted information about CBD stone status than chronological age alone.

These findings should be considered alongside published age-dependent reference limits for CBD diameter. Ultrasound and MRCP studies in asymptomatic populations have shown gradual widening of the CBD with age [8,9,10,15,16]. Such reference values are useful for avoiding overdiagnosis of obstruction in older individuals. However, a reference-range interpretation and a disease-oriented interpretation address different questions. In patients referred for biliary symptoms or suspected obstruction, a widened CBD remains relevant when it is accompanied by IHBD dilatation, a filling defect, or an abnormal distal duct. The present data therefore support contextual interpretation rather than reliance on a single universal diameter cutoff. The same measured diameter may therefore have different significance depending on symptoms, prior cholecystectomy, laboratory abnormalities, and associated ductal signs.

This point is clinically relevant because current guidelines recommend MRCP or EUS for patients with an intermediate likelihood of choledocholithiasis and reserve ERCP mainly for therapy [17,18,19,20,21,22,23]. MRCP is highly specific for ductal stones, although very small stones, sludge, and impacted ampullary calculi may remain difficult to identify [20,21,22]. In that setting, CBD caliber can serve as an indirect imaging clue that prompts careful review of the source images, distal CBD, ampullary region, and adjacent pancreaticoduodenal structures, where uncommon lesions may create diagnostic ambiguity because of their close relationship to the Vater papilla, pancreatic duct, and bile duct [24]. It should not, however, be used as a stand-alone diagnosis of choledocholithiasis, particularly in older or previously operated patients in whom duct caliber may be increased for other reasons. When MRCP remains equivocal despite persistent clinical suspicion, EUS is an important complementary test because it can identify small distal stones that may be inconspicuous on MRCP [17,18,19,20,21,22].

The ROC findings further illustrate this distinction. CBD diameter alone showed good discrimination for the consensus MRCP-defined outcome (AUC 0.853), while the parsimonious Model 2 achieved an apparent AUC of 0.896 and an optimism-corrected AUC of 0.884. These values describe separation within the present dataset and should not be interpreted as diagnostic accuracy against ERCP or surgery. The approximately 8.3 mm Youden threshold provided a balance between sensitivity and specificity, whereas 6.0 mm favored sensitivity and 10.0 mm favored specificity. All of these thresholds are exploratory and require external validation before clinical use. The high negative predictive values at lower thresholds may be useful descriptively, but predictive values are prevalence-dependent and cannot be transferred directly to populations with different referral patterns.

Gallbladder stone morphology provided additional, but smaller, information. Multiple GB stones and greater GB maximum stone size were inversely associated with CBD stones in the adjusted model. This finding is compatible with reports suggesting that smaller stones may pass more readily through the cystic duct [25,26,27,28]. Nevertheless, the present study did not document stone migration over time, previous spontaneous passage, or complete surgical history. In addition, GB maximum stone size was coded as 0 in stone-negative patients to retain the full cohort, so its coefficient combines information on stone absence or presence with increasing size. The association should therefore be considered hypothesis-generating rather than a direct estimate of migration risk. The inverse association may also reflect previous passage as follows: patients presenting with a CBD stone may have fewer or smaller residual GB stones at the time of MRCP. This possibility cannot be separated from stone morphology in a single cross-sectional examination.

The expanded dataset also allowed assessment of cystic duct anatomy and CBD stone location. Cystic duct diameter and insertion distance differed between CBD-positive and CBD-negative groups. These variables were not retained in the parsimonious primary model because the number of candidate predictors was large relative to the 65 CBD-stone events; their independent contribution should be assessed in a larger cohort. Distal, impacted ampullary, and multisegment stones accounted for most positive examinations. This distribution supports systematic inspection of the distal duct and periampullary region, particularly when the CBD is enlarged or upstream dilatation is present. The cystic duct is the anatomical route for secondary stone migration, so its caliber and insertion may be relevant even when they do not enter a stable multivariable model. Measurement reproducibility and anatomical variation should be evaluated before these parameters are proposed for routine risk assessment.

Periampullary diverticulum, CBD tortuosity, microlithiasis, cystic duct stones, pericholecystic fluid, and MRI signs of pancreatitis were not strong independent correlates in the primary analysis. Their absence from the final predictor set should not be read as evidence of no clinical relevance. Previous studies have linked periampullary diverticula, duct diameter, and duct angulation with biliary stasis or recurrent ductal stones [29,30,31,32,33,34,35]. In the present cohort, these variables were less frequent or showed smaller associations than CBD diameter. They are therefore better regarded as contextual MRCP findings that may become more informative in selected clinical subgroups or longitudinal studies. Their associations may also be more relevant to recurrence after duct clearance than to the presence of a stone at one MRCP examination. Longitudinal cohorts would be better suited to evaluate that question.

From a reporting perspective, the results support systematic documentation of CBD diameter, stone number and location, IHBD dilatation, and relevant cystic duct or periampullary findings. A structured description can improve communication among radiologists, gastroenterologists, and surgeons and can make the basis of an imaging impression more transparent. The clinical decision to proceed to EUS, ERCP, surgery, or follow-up should still integrate symptoms, laboratory findings, prior procedures, and pre-test probability. The present study did not evaluate management changes or patient outcomes and therefore cannot determine whether use of the proposed imaging pattern improves care. This approach avoids reducing interpretation to a binary stone-present or stone-absent statement and records the anatomical context that may explain equivocal findings or guide further evaluation.

Overall, the study identifies an age-associated pattern of greater ductal involvement and confirms CBD diameter as the strongest imaging correlate of CBD stones in this cohort. The results do not establish within-patient progression or a causal sequence. Future multicenter studies should combine standardized MRCP review with liver function tests, ERCP or surgical confirmation where appropriate, cholecystectomy history, and longitudinal outcomes. Such studies could determine whether age-specific reference limits, CBD caliber, and stone morphology improve prediction beyond established clinical pathways. Prospective follow-up would also help distinguish retained, recurrent, and spontaneously passed stones and would clarify whether the observed age-associated distribution has prognostic value.

The study has several strengths. It included a consecutive radiology-service cohort, applied predefined eligibility and imaging criteria, and evaluated a broad set of gallbladder, CBD, cystic duct, and periampullary variables. Ordered trend analyses, group comparisons, a parsimonious adjusted model, calibration assessment, and bootstrap internal validation provided complementary statistical checks. Review by two experienced radiologists with consensus resolution also ensured a consistent imaging classification across the cohort.

Several limitations should be acknowledged. The retrospective, single-center, cross-sectional design limits external validity and does not permit assessment of temporal sequence. Referral patterns and local MRCP protocols may also influence the observed prevalence of stones and associated anatomical findings. Consequently, the age-associated differences cannot be interpreted as progression within individual patients or as evidence of causation. The very young and very old strata were relatively small, so estimates at the extremes of age are less precise than those for the middle groups.

CBD stone status was determined by consensus MRCP interpretation rather than systematic ERCP, EUS, surgical, or longitudinal confirmation. These data were available only for subsets of patients and could not be used as a uniform independent reference standard. The study therefore evaluated associations with MRCP-defined CBD stones and did not estimate sensitivity, specificity, or diagnostic accuracy against endoscopic or operative findings. Small stones or sludge may be missed on MRCP, while equivocal signal defects may be overcalled; without a uniform reference, the direction and magnitude of any misclassification cannot be quantified.

Same-day liver function tests, including bilirubin, alkaline phosphatase, gamma-glutamyl transferase, and transaminases, were not consistently available in the retrospective radiology dataset and were not analyzed. Clinical symptom severity, inflammatory markers, treatment decisions, and longitudinal outcomes were also unavailable for the full cohort. These omissions limit comparison with established clinical prediction algorithms and prevent assessment of the incremental value of imaging over laboratory data. In particular, bilirubin and cholestatic enzymes could have added clinically important information to the imaging model and may alter the apparent contribution of CBD diameter.

The examinations were assessed by consensus, and formal interobserver agreement was not quantified. The reproducibility of ordinal variables such as IHBD dilatation, CBD tortuosity, image quality, and stone-location classification therefore remains uncertain. Future studies should include blinded independent readings and agreement statistics, particularly for variables intended for structured reporting or predictive modeling. Consensus reading can improve internal consistency but may overstate reproducibility compared with independent reporting in routine practice.

Some variables also require cautious interpretation. Several ancillary findings were infrequent, reducing power to detect smaller associations. Multiple comparisons were performed without formal adjustment, so p-values close to 0.05 should be regarded as exploratory. CBD stone-size variables were analyzed only in positive cases, while GB maximum stone size was coded as 0 in stone-negative patients; the latter coefficient is therefore a composite measure rather than a purely within-stone size effect. The subgroup analyses of stone size were also based on fewer observations than the full-cohort comparisons, which widens uncertainty around those estimates.

Finally, the original candidate set was too large for 65 CBD-stone events. The primary adjusted analysis was therefore reduced to six predictor parameters, yielding an events-per-variable ratio of 10.8. Bootstrap correction indicated limited optimism in model discrimination, but internal validation does not replace external validation. The model and the data-derived CBD diameter thresholds should be tested in larger independent cohorts with laboratory, endoscopic, surgical, and outcome data before they are used for clinical prediction. Penalized regression and prospective sample-size planning should be considered in subsequent model-development studies.