Variants Of Intrahepatic Biliary Radicals in Nepali Population

Anatomy of the biliary tree is intricate, with numerous intrahepatic and extrahepatic variations and cystic duct variations that are crucial to recognize to avoid complications in surgical or interventional procedures (1,2). Detailed anatomical knowledge is essential as bile duct surgeries, liver resections, and transplants become increasingly sophisticated (1). Magnetic Resonance Cholangiopancreatography (MRCP) is a preferred non-invasive imaging technique that safely and accurately maps both the bile and cystic duct anatomy without radiation exposure, ideal for patients with contrast allergies (2). Intrahepatic bile ducts follow the portal veins, with the right hepatic duct draining segments 5, 6, 7, and 8 and the left hepatic duct draining segments 2, 3, and 4. The right and left hepatic ducts merge at the hilum to form the CHD. With standard branching patterns occurring in roughly 50-60% of cases, knowledge of these frequent variants is critical for safe and effective surgical planning (4).

The classification of the right hepatic duct (RHD) by Huang et al. (2) includes five types: Type A1 (classic, RPD and RAD form RHD), Type A2 (trifurcation, all ducts converge), Type A3 (RPD drains into LHD), Type A4 (RAD drains into CHD), and Type A5 (absent RHD). Karakas et al. similarly classify the RHD into five types, mirroring Huang's types with slight variations in naming conventions. The left hepatic duct (LHD) classification by Cho A et al. (2) consists of four types: Type I (classic, LHD drains into RHD), Type II (accessory duct from the left lateral segment), Type III (segmental ducts join RHD or CHD separately), and Type IV (no unified LHD formation). These classifications are essential for understanding anatomical variations relevant to hepatobiliary surgeries and MRCP imaging.

Typically, the cystic duct is 2-4 cm long and 1-5 mm in diameter, joining the gallbladder neck to the common hepatic duct (CHD) to form the common bile duct (CBD), usually entering the CHD from the right lateral side (4). Variations in the cystic duct's insertion, length, and course-including low or high insertion points, parallel courses with the CHD, spiral orientations, and occasionally absent ducts-are documented and clinically significant (4).

There are few studies of similar kind done in Nepali population. Sharma et al(1)studied the prevalences of different variants of right hepatic duct as per classification of choi et al in 90 patients. In their study, 47.8% of patients were classified as having Type 1/normal intrahepatic bile duct (IHBD) variations (n=43). Type 2 was observed in 20% of the cases (n=18), while Type 3A accounted for 3.3% (n=3) and Type 3B for 5.6%. Type 5A was present in 5 patients (n=5), and Type 5B in 7.8% (n=7), with Type 6 seen in 3.3% (n=3) and Type 7 in 6.7% (n=6). No cases of Type 3C or Type 4 variations were identified. Among the Type 1 patients, 67.44% (n=29) were female, while the remainder were male. Sarawagi R(2) et al conducted a study similar to ours and obtained the prevalences of variants of right hepatic duct as per classification by Huang et al. The right posterior sectoral duct (RPSD) draining into the left hepatic duct (LHD) was the most common variant, observed in 27.6% of subjects. A trifurcation pattern was noted in 9.3% of cases, while 4% of subjects had the RPSD draining into the common hepatic duct (CHD) and 0.8% into the cystic duct. Other variants were seen in 2.6% of subjects, and an accessory duct was present in 4.9% of cases. The most frequent branching pattern of the LHD was a common trunk formed by the segment 2 and 3 ducts joining the segment 4 duct, seen in 67.8% of subjects. In 23.2% of subjects, the segment 2 duct united with the common trunk of segments 3 and 4, while 3.4% had all three segments (2, 3, and 4) merging to form the LHD. Other less common branching patterns were observed in 4.9% of subjects.K.C et al(3) studied about variants of cystic duct in Nepali population in 252 patients. The most frequently observed type was the right lateral insertion, found in 120 patients (47.62%), while the remaining patients exhibited other anatomical variants. The posterior insertion was the second most common variant, seen in 36 patients (14.29%), followed by high insertion in 25 patients (9.92%). The right posterior sectoral hepatic duct draining into the cystic duct was the least common variant. Sarawagi et al(4) also studied about variants of cystic duct in MRCP in Indian population. Normal lateral insertion of the cystic duct (CD) at the middle third of the common hepatic duct was found in 51% of cases. Medial insertion was seen in 16% (4% low medial), while low insertion occurred in 9%. A parallel course of the CD was present in 7.5%, high insertion in 6%, and a short CD in 1%. In one case, the CD drained into the right hepatic duct, and another case exhibited congenital cystic dilation consistent with a type IV choledochal cyst.

The four studies collectively highlight the diversity and prevalence of anatomical variations in the biliary system across different populations. Variations in the right hepatic duct were common, with normal intrahepatic bile duct patterns (Type 1) being the most prevalent, seen in 47.8% of cases in Sharma et al.'s study, while Sarawagi et al. noted that the right posterior sectoral duct (RPSD) draining into the left hepatic duct was the most frequent variant (27.6%). Trifurcation patterns and accessory ducts were also observed but were less common. Regarding cystic duct variants, both K.C. et al. and Sarawagi et al. found that the lateral insertion into the common hepatic duct was the most prevalent pattern, seen in 47.62% and 51% of cases, respectively. Other common variations included posterior and high insertions of the cystic duct, while rare cases such as RPSD draining into the cystic duct and congenital cystic dilation were also documented. These findings underscore the significance of understanding these variations for clinical and surgical applications.