Introduction
The liver is anatomically divided into eight independent segments, each supplied by its own portal and hepatic venous systems (1). Segment I (the caudate lobe) is located between the ligamentum venosum and the inferior vena cava. The middle hepatic vein separates the remaining portion of the liver into right and left lobes. The right lobe comprises segments V, VI, VII and VIII, while the left lobe includes segments II, III and IV. The left lobe is further subdivided by the umbilical fissure and falciform ligament into lateral (segments II and III) and medial (IV, the quadrate lobe) segments (2).
The hepatobiliary tree consists of both intrahepatic ducts (IHDs) and extrahepatic ducts (EHDs). The intrahepatic biliary system is formed by the right hepatic duct (RHD) and left hepatic duct (LHD). The RHD arises from the confluence of the right posterior duct (RPD), which drains segments VI and VII, and the right anterior duct (RAD), which drains segments V and VIII. Typically, the RPD follows a relatively horizontal course, whereas the RAD is more vertically oriented. The LHD is formed by the biliary ducts of segments II, III and IV. The RHD and LHD join to form the common hepatic duct (CHD), which is then joined by the cystic duct (CD) from the gallbladder. The CD most commonly inserts into the middle third of the CHD on its right-lateral side, forming the common bile duct (CBD). The CBD empties the main pancreatic duct into the major duodenal papilla in the second part of the duodenum (2-4). This conventional biliary anatomy is present in 55-65% of the general population worldwide (3-5).
Although anatomical variations of the IHD and CD have been well described in other populations, such as Asian, European and American, their prevalence within Middle Eastern populations, as well as their interrelationship and clinical significance with biliary conditions, such as gallstone disease, cholecystitis and obstructive jaundice, remain insufficiently explored. Importantly, previous studies (6-12) have evaluated IHD and CD variations separately, with limited data addressing their combined occurrence and impact on biliary pathology. A thorough understanding of biliary anatomy is crucial for anatomists, radiologists and surgeons, as unrecognized variations can increase the risk of postoperative complications, such as bile duct injury, biliary peritonitis, jaundice and sepsis (2,5,13-17). Therefore, the present study aimed to investigate the coexistence of IHD and CD variations and evaluate their effect on biliary pathology in a Middle Eastern population using magnetic resonance cholangiopancreatography (MRCP).
Discussion
The present study investigated the prevalence and clinical associations of biliary ductal anatomical variations in a Jordanian population using MRCP. Conventional IHD anatomy (type 1) was observed in 61.4% of cases, whereas 38.6% exhibited variant branching patterns. Consistently, the right-lateral CD insertion (type 1) was present in 63.3% of patients, while medial insertions accounted for 36.7%. A significant association between IHD and CD variations was identified, thus indicating a potentially coordinated developmental association. Compared with the majority of previous studies (6-12) that had evaluated these anatomical systems independently, in the present study a combined analysis of IHD and CD variations was performed, which demonstrated a statistically significant interrelationship. Furthermore, variant CD insertions were associated with a higher prevalence of biliary lithiasis and cholecystitis, highlighting their clinical relevance. These findings extended prior work, such as that by Renzulli et al (19) by confirming the coexistence of IHD and CD variations and further highlighting the clinical relevance of CD variations. Whereas Renzulli et al focused primarily on IHD anatomy with EHD as a secondary aim, the present study specifically characterized CD insertion variants as the primary outcome and their independent clinical predictors using multivariable analysis. In addition, the present study is the first to evaluate these associations in a Middle Eastern population, directly addressing the limitation acknowledged by Renzulli et al regarding the generalizability of their findings beyond an almost exclusively European series from a single Italian center. A comprehensive understanding of biliary anatomy is essential for accurate preoperative planning and for minimizing complications during hepatobiliary procedures (2,20). It has been reported that anatomical variations can increase the risk of bile duct injury during laparoscopic cholecystectomy, with an incidence of 0.5-1.7% as reported across multiple international studies (14,15,21), thus resulting in severe complications, including jaundice, biliary peritonitis, sepsis and secondary biliary cirrhosis (16,17). Certain IHD variations carry important surgical implications. The trifurcation pattern (type 2), in which the RPD, RAD and LHD share a common confluence point, is considered a contraindication for safe right hepatectomy in living donor liver transplantation, as it necessitates additional biliary anastomoses in the recipient, increasing the risk of postoperative biliary complications (22). The type 3a IHD variant, in which the RPD drains into the LHD, are important, as they can complicate liver transplantation and increase donor risk (22). Unrecognized type 3a anatomy during left hepatectomy can also result in bile leakage, biliary stasis, recurrent infections or cirrhosis due to RPD transection or ligation (9). A previous study demonstrated that in percutaneous transhepatic drainage, obstruction of the LHD could lead to cholestasis in the right posterior lobe (7). Therefore, particular variants, such as types 2 and 3a, are considered relative contraindications for liver donation in some centers (22,23).
Several classification systems have described IHD variations (24). In the present study, the Huang classification (18) was adopted due to its simplicity and clinical applicability. The prevalence of conventional anatomy varies across populations, with higher rates reported in Asian populations (~65%) compared with European and American ones (~60%) (25). Consistent with prior studies (7,9,18,19,22,24,26-28), in the present study no significant sex-based differences were observed, although certain reports suggested a higher prevalence of IHD variants among women (25,29).
The proportion of conventional IHD anatomy in the current study (61.4%) lied within the range reported in the literature (41.0-87.0%) (5-9,11,12,19,20,25-27,29-42). The most common variation was type 2 trifurcation (22.0%), although its prevalence varied widely in previous studies (3.0-44.0%) (5,19,25,27,30,37,40,42). Types 3a and 3b occurred in 7.7 and 8.5% of cases, respectively, which were also within previously reported ranges (2.2-27.8% and 1.5-10%, respectively) (5-9,11,12,19,20,25-27,29-42). A rare variant involving draining of two separate LHDs into the CHD was identified in one case (0.4%), which was consistent with prior reports of low prevalence of this variant (0.2-2.4%) (7,20,27,30,40). Other rare variations, such as drainage of the RPD or RHD into the CD, or the presence of accessory hepatic ducts, which have been reported in previous studies (5-8,20,26,27,30-32,34,37,40), were not observed in the present study.
A key finding of the present study was the strong association between CD insertion patterns and IHD variations, an observation that has been previously noted (19). For example, type 2 CD insertion was most commonly associated with type 2 IHD, while type 3 CD frequently co-occurred with type 3a IHD. Preoperative identification of EHD anatomy could therefore help anticipate corresponding variations in IHD. The aforementioned association could likely reflect a shared embryologic origin from the hepatic diverticulum, where the pars hepatica forms the IHD, while the pars cystica gives rise to the CD, CBD and gallbladder (43). Disruptions in this developmental process could account for the concurrent occurrence of variations in both systems (19,43,44).
By contrast, CD anatomy lacks a standardized classification system (10). Existing studies have described CD variants using descriptive anatomical classifications and imaging-based approaches that categorize variations by insertion site, course and morphology (6,10,11,23,45,46). These descriptive and imaging-based strategies collectively highlight the heterogeneity in the characterization of CD variations. Therefore, the present study employed a simplified MRCP-based classification system focusing on insertion patterns and course, as these features are consistently identifiable and clinically relevant. The distinction between conventional lateral insertion and medial spiral insertions represents a well-reported and clinically important pattern across MRCP-based studies (6,10,11,46-48). In contrast to existing systems that variably emphasize insertion level, duct length or complex morphological configurations, the present classification focused on parameters consistently visualized on MRCP and directly applicable to surgical planning and radiological reporting. Specifically, classification according to CD insertion pattern and course enables consistent identification and reporting of anatomical variants on MRCP. For example, recognition of anterior or posterior spiral CD insertion can be explicitly communicated in radiological reports and considered during preoperative assessment, thereby improving awareness of atypical biliary anatomy and facilitating surgical planning for hepatobiliary procedures. Accordingly, the current classification was intended as a pragmatic and reproducible reporting framework aligned with routine MRCP practice, rather than as a substitute for more comprehensive anatomical classification systems.
CD variations are considered to arise from embryologic malrotation during duodenal development, resulting in anterior or posterior spiral courses around the CHD (49). In the present study, conventional CD anatomy was observed in 63.3% of cases, slightly lower than rates reported in previous studies (76.1-89%) (6,10,11,46). These variants can increase the risk of bile duct injury and intraoperative bile leakage during laparoscopic cholecystectomy (50).
Although IHD variations were not directly associated with specific clinical conditions, they frequently co-occurred with atypical CD insertions. Spiral CD variants, particularly posterior types, were more commonly associated with biliary stones and inflammation, potentially due to impaired bile flow and stasis (10,51). Multivariable analysis revealed that both IHD variations and biliary stones independently predicted CD variants, while CD variants were strongly associated with IHD variations. These findings supported the interrelationship between intrahepatic and extrahepatic biliary anatomy and their combined contribution to disease pathology.
The observed association between CD variations, biliary lithiasis and cholecystitis further supports the clinical importance of recognizing biliary anatomical variants during preoperative evaluation. From a practical perspective, current evidence supports a selective rather than routine application of MRCP prior to cholecystectomy. The American Society for Gastrointestinal Endoscopy guidelines (52) advocate a risk-stratified approach, categorizing patients into low-, intermediate- and high-probability groups for CBD stones. To verify the diagnosis, the American Society for Gastrointestinal Endoscopy recommends that patients with an intermediate risk (10-50%) of choledocholithiasis should undergo endoscopic ultrasound or MRCP (53). A subsequent study further supported this strategy, suggesting that intermediate-risk classification could guide the use of additional imaging, including MRCP or endoscopic ultrasound, rather than performing routine imaging in all patients (53). Furthermore, the American Society for Gastrointestinal Endoscopy guidelines have been associated with a reduced number of unnecessary diagnostic endoscopic retrograde cholangiopancreatographies, thus minimizing procedure-related complications (52,53). Particularly, identification of CD variations or complex biliary anatomy is clinically important, as it can alert the surgeon to an increased risk of misidentification and warrant a more cautious dissection strategy. When anatomical variation is identified or suspected, a cautious operative approach is essential (54), involving careful dissection to achieve the critical view of safety; a method of target identification requiring: Clearance of the hepatocystic triangle of fat and fibrous tissue, separation of the lower third of the gallbladder from the cystic plate, and confirmation that only the CD and cystic artery remain attached to the gallbladder before clipping and division (54). When these criteria cannot be safely met, bail-out strategies such as subtotal fenestrating cholecystectomy should be employed, and intraoperative imaging considered when anatomy remains unclear, as part of a broader strategy to improve operative safety (54). Given that EHD and IHD variants may coexist, identification of any variation should prompt a systematic search for additional ductal variations (19). In this context, preoperative identification of complex biliary anatomy should be incorporated into patient counseling, informed consent and operative planning for possible intraoperative imaging or endoscopic procedures.
The present study has several limitations. Firstly, its retrospective, cross-sectional design limits inference of causal relationships between biliary anatomical variations and associated clinical conditions. In addition, several potential confounders, including body mass index, metabolic syndrome, diabetes, dyslipidemia and medication history, were not consistently available in the present retrospective imaging-based study and therefore could not be included in the multivariable analyses. Consequently, the aORs should be interpreted as associations adjusted for the available demographic, anatomical and radiological variables, rather than as fully adjusted causal estimates accounting for all metabolic or systemic clinical risk factors. Furthermore, the single-center design could limit the generalizability of the results, as the study population was derived from a tertiary referral center that typically manages more complex or symptomatic cases. This could introduce referral bias, potentially leading to an overrepresentation of patients with biliary pathology compared with the general population. Consistent with this possibility, the relatively high prevalence of biliary stones (40.9%) likely reflects selection bias, given that MRCP is more commonly performed in patients with suspected biliary disease rather than in asymptomatic individuals. Consequently, the observed associations between anatomical variations and biliary pathology could be overestimated and should therefore be interpreted with caution. Additionally, patients referred for MRCP may not accurately reflect the true distribution of biliary anatomical variations in the general population. Therefore, future multicenter prospective studies, including more representative populations, are needed to externally validate these findings. Lastly, although MRCP is a reliable, non-invasive imaging tool for evaluation of the biliary system, its spatial resolution can occasionally fail to identify rare anatomical variations.
In conclusion, IHD and CD variations are common and strongly associated, supporting a shared developmental origin. Their identification is of clinical importance for surgical planning and risk stratification, particularly given the association of CD variants with biliary lithiasis and inflammation. Identification of a variation in one component should prompt careful evaluation for concurrent variations in the other. Patients with such variations may also benefit from closer monitoring due to their potentially increased susceptibility to stone formation and cholecystitis.