The Anatomical Landscape of Living Donor Livers: A 101-Case Retrospective Single-Center Study in Indonesia From 2010 to 2025

Introduction

Liver transplantation is a life-saving therapy for end-stage liver disease and selected hepatic malignancies, offering not only improved survival and quality of life but also renewed hope for patients [1]. While deceased donor liver transplantation (DDLT) is widely implemented in many countries, Indonesia continues to face significant barriers, including underdeveloped donation systems, limited infrastructure, and persistent sociocultural resistance to post-mortem organ donation [2,3]. Consequently, living donor liver transplantation (LDLT) has emerged as the predominant modality, addressing the growing demand amidst a shortage of deceased donors.

In LDLT, a comprehensive evaluation of hepatobiliary and hepatic vascular anatomy is essential for surgical safety and success. These anatomical structures exhibit substantial variability, which can complicate donor hepatectomy, affect vascular and biliary reconstruction, and increase the risk of intraoperative and postoperative complications [4,5]. As such, precise preoperative planning is vital for anticipating technical challenges and tailoring operative strategies [6–8]. Several widely recognized classification systems are used to describe these anatomical variations. The Michel classification system categorizes hepatic arterial variations into 10 types, crucial for arterial reconstruction in liver transplantation [9]. The Nakamura classification system describes 4 main types of portal vein branching, aiding in portal vein reconstruction during surgery [10]. The Huang classification system classifies intrahepatic bile duct patterns into 3 types and is important for preventing biliary complications [11].

Despite the growing number of LDLT procedures in Indonesia, population-specific anatomical data remain limited [3]. In many cases, anatomical challenges are encountered intraoperatively, limiting the ability to anticipate and mitigate surgical risks [4,5]. A clearer understanding of local anatomical patterns is essential to improve preoperative assessment and enhance donor and recipient outcomes.

Therefore, this retrospective study aimed to evaluate hepatic artery, portal vein, hepatic vein, and intrahepatic bile duct anatomy in 101 living liver donors at a single center in Indonesia from 2010 to 2025. Specifically, we sought to identify the predominant anatomical variations and assess their implications for liver transplantation. By characterizing these variations, this study aims to support safer surgical planning and contribute valuable insights to the global anatomical database.

Material and Methods

ETHICS STATEMENT:

All procedures in this study were performed in accordance with the ethics standards of the institutional and/or national research committee and with the 1964 Declaration of Helsinki and the Declaration of Istanbul on Organ Trafficking and Transplant Tourism, as amended. The study protocol was reviewed and approved by the Ethics Committee of the Faculty of Medicine, Universitas Indonesia, Dr. Cipto Mangunkusumo National General Hospital (Approval No. KET-/76/UNZ.F1/ETIK/PPM.00.02/2024). Written informed consent was obtained from all participants prior to inclusion.

STUDY POPULATION:

This study included 72 subjects from a total of 101 liver donors who underwent donor evaluation at Dr. Cipto Mangunkusumo National General Hospital (CMNGH) between December 2010 and July 2025. All subjects had undergone computed tomography angiography (CTA), but only 96 had complete CTA records. In contrast, magnetic resonance imaging (MRI) data were available for 72 subjects, as incomplete documentation was present in the other cases. Demographic and clinical data, including age, sex, body mass index (BMI), and operative time, were obtained from medical records. Donors with incomplete imaging were excluded from analyses specific to the missing modality.

ANATOMICAL CLASSIFICATIONS:

Anatomical variations were categorized using established classification systems. The hepatic arteries were classified according to the Michel classification system, which classifies variations in the origin and branching patterns of the hepatic arteries into 10 distinct types. The portal vein branching was described using the Nakamura classification system, which categorizes the portal venous anatomy into 4 main types based on the number and branching patterns of the portal vein. This classification system was applied to evaluate the variations in portal vein anatomy, which is crucial for portal vein reconstruction during liver transplantation.

The intrahepatic bile duct patterns were assessed according to the Huang classification system, which classifies bile duct anatomy into 3 types based on the number and configuration of bile ducts within the liver to identify variations in the biliary system that can reduce the risk of biliary complications during surgery.

STATISTICAL ANALYSIS:

The baseline characteristics of donors were summarised and analyzed using descriptive statistics. Logistic regression analysis was used to estimate the adjusted odds ratios (aOR) with 95% confidence interval (CI) of having any form of variant anatomy as opposed to canonical anatomy while controlling for age, BMI, and sex. To the extent permitted by sample size, multinomial regression analysis was performed to assess possible relationships with anatomical classes. Predictors of operative time, such as age, BMI, sex, and anatomical variation, were assessed using linear regression. The Hosmer–Lemeshow test (logistic models) and residual plots (linear models) were used to evaluate model fit. To prevent quasi-complete separation, rare categories with an incidence of fewer than 5 were collapsed. All analyses were performed using IBM SPSS Statistics, version 29.0.2.0 (IBM Corp., Armonk, NY, USA), with a 2-tailed P value of less than 0.05 regarded as statistically significant.

Results

Anatomical Variations

HEPATIC ARTERY VARIATIONS: Among 96 donors with complete computed tomography angiography (CTA), Michel Type I (normal anatomy) predominated (70.8%). Variants were present in 29.2% of donors, most frequently Type II (12.5%) and Type IX (4.2%). No Type VII or X variants were observed. The overall distribution is illustrated in Table 1, with representative CTA images of selected variants shown in Figure 1.

PORTAL VEIN VARIATIONS: Nakamura Type I (standard bifurcation) was the predominant pattern (71.9%). Variants were observed in 28.1% of donors, most commonly Type III (13.5%) and Type II trifurcation (10.4%), with rare forms including Types IV, III+IV, and V (<3% each). The overall distribution is presented in Table 2, and representative CTA images of a Type II trifurcation are shown in Figure 2.

HEPATIC VEIN ANATOMY: Regarding hepatic venous drainage, the right hepatic vein (RHV) was the main drainage channel in all donors. In 58 donors (71.6%), a single dominant RHV drained directly into the inferior vena cava (IVC). An accessory inferior right hepatic vein (accessory IRHV) was identified in 22 donors (27.2%), resulting in a double-vein configuration (dominant RHV with accessory IRHV). Only 1 donor (1.2%) exhibited an additional small inferior RHV, producing a triple-drainage pattern (Table 3). For the left hepatic system, a common trunk of the left and middle hepatic veins draining together into the IVC was observed in 53 donors (65.4%), whereas separate drainage of the left and middle hepatic veins occurred in 28 donors (34.6%).

INTRAHEPATIC BILE DUCT VARIATIONS: In 72 donors evaluated with MRCP, Huang Type A1 was most frequent (59.7%). More complex variants accounted for 40.3% of donors, with A2 and A3 each observed in 13.8%, A4 in 11.1%, and A5 in 1.4% (Table 4).

SEX AND ANATOMICAL VARIATIONS:

In most structures, anatomical variations were more prevalent across both male and female donors; however, females were more likely to have anatomical variations in the vascular and biliary systems.

MICHEL HEPATIC ARTERY:

Type I was the most common pattern present across both sexes; however, it was more common in males, at 78.4% for males and 66.1%for females. Females had more variants, with 33.9% as opposed to males at 21.6%. Type II, “replaced LHA from LGA”, was more common in females.

NAKAMURA PORTAL VEIN:

Type I bifurcation was more common in males (75.7% for males and 69.5% for females. However, the variant forms such as trifurcation and early right posterior were more common in females (30.5% for females and 24.3% for males.

HUANG INTRAHEPATIC BILE DUCTS:

Type A1 was the most common of all configurations and was present in both males and females. Males had more A1 and A3, and females had A1, A2, A3, and A4, which means females had a more biliary configurations. Taken together, although females had a greater frequency of both vascular and biliary variants, the overall distribution patterns were similar, and canonical anatomy predominated.

ETHNICITY AND ANATOMICAL VARIATIONS:

Analysis of ethnic subgroups showed differences in the vascular and biliary anatomy of Indonesian living liver donors among subgroups.

HEPATIC ARTERY (MICHEL):

Among Javanese donors (N=32), Michel Type I (canonical anatomy) predominated, observed in 90.6% (n=29), with variants identified in 9.4% (n=3). In contrast, Sumatran donors (N=13) demonstrated a lower prevalence of Type I anatomy (53.3%, n=7) and a higher frequency of variants (46.7%, n=6), most commonly Michel Type II (26.7%, n=4). Donors from Sulawesi (N=4) exhibited mixed patterns, with both Type I and Type III anatomies observed. Kalimantan donors (N=2) showed both Type I and Type III variants. All donors from Maluku (N=1) and Chinese Indonesian donors (N=1) exhibited Michel Type I anatomy exclusively. Interpretations for these smaller subgroups should be made cautiously due to the limited sample size.

PORTAL VEIN (NAKAMURA):

Nakamura Type I was the most common portal vein configuration across ethnic groups, occurring in 84.4% of Javanese donors (n=27/32) and 60.0% of Sumatran donors (n=6/10). Among Sumatran donors, portal vein variants – including Type II trifurcation and Type III early right posterior branching – were more frequently observed than in Javanese donors. In Sulawesi donors (N=3 with evaluable CTA), Type III anatomy predominated (66.7%, n=2), whereas Kalimantan (N=2), Maluku (N=1), and Chinese Indonesian (N=1) donors primarily had Type I anatomy. The small number of donors in these subgroups limits definitive conclusions.

INTRAHEPATIC BILE DUCTS (HUANG):

Huang Type A1 was the most common biliary pattern overall. Among Javanese donors (N=24 with MRCP), Type A1 was observed in 75.0% (n=18). All Kalimantan donors (N=2) demonstrated Type A1 anatomy. In contrast, all Sumatran donors who underwent MRCP (N=5) exhibited Huang Type A3 anatomy (100%), suggesting greater biliary complexity in this subgroup. However, this finding should be interpreted with caution given the limited sample size. Overall, anatomical variants – particularly of the hepatic artery, portal vein, and bile ducts – were more frequently observed among Sumatran donors compared with Javanese and Kalimantan donors, reflecting the anatomical diversity within Indonesia’s multiethnic population.

HEPATIC ARTERY (MICHELS):

Age was significantly associated with the presence of arterial variation (aOR per year=1.08, 95% CI 1.00–1.16, P=0.046). BMI (aOR=0.99, p=0.897) and sex (aOR male vs female=1.74, P=0.256) were not significant predictors.

PORTAL VEIN (NAKAMURA):

The multinomial logistic regression model was significant overall (χ²=28.06, P=0.021). BMI showed an effect across subtypes (P=0.006), with higher BMI tending to increase the likelihood of certain variants (eg, Type IV: B=1.30, P=0.053). However, estimates were unstable due to small numbers in rare subgroups, and results should be interpreted cautiously. Age (P=0.178) and sex (P=0.185) were not significant.

INTRAHEPATIC BILE DUCT (HUANG):

None of the predictors was associated with biliary variation. Age (aOR=0.98, P=0.795), BMI (aOR=1.16, P=0.349), and sex (aOR=1.43, P=0.698) were all non-significant.

OPERATIVE TIME PREDICTORS:

Linear regression analysis showed that age (B=0.01, P=0.999), BMI (B=−15.6, P=0.319), and sex (B=−136.7 minutes for males vs females, P=0.122) were not significant predictors of operative time. Likewise, the presence of anatomical variation in the hepatic artery (P=0.947), portal vein (P=0.401), or bile duct (P=0.666) did not significantly influence operative time. The overall model was not statistically significant (P=0.763, R²=0.16).

Discussion

STRENGTHS AND LIMITATIONS:

Our study represents the largest single-center experience in Indonesia, encompassing 101 living liver donors evaluated over a 15-year period. Key strengths include the systematic application of validated anatomical classification systems and the use of regression modeling to explore potential demographic predictors of vascular and biliary variation.

Several limitations should be acknowledged. First, the retrospective single-center design limits generalizability to other institutions and populations. Second, incomplete availability of MRCP imaging prior to 2015 reduced the number of donors included in the biliary anatomy analysis. Third, although regression analyses were performed to assess predictors of anatomical variation, rare portal vein subtypes were represented by very small numbers, resulting in unstable coefficient estimates and wide confidence intervals. Consequently, the observed associations – particularly for infrequent Nakamura variants – should be interpreted with caution, and the regression models should be regarded as exploratory rather than confirmatory for these subgroups. The limited event-per-variable ratio further constrained statistical power and precluded robust inference for rare anatomical patterns.

Finally, postoperative outcomes were not evaluated, preventing correlation of donor anatomical variation with recipient complications or graft survival. Future directions include multicenter collaboration and the development of a national living donor registry to improve sample size, representation, and statistical robustness. Prospective studies with standardized imaging protocols could enable more stable multivariable modeling and clarify the clinical relevance of rare vascular and biliary variants. Incorporation of three-dimensional reconstruction, virtual surgical planning, and patient-specific liver modeling may further enhance operative precision, particularly in donors with complex anatomy. Participation in international anatomical variation databases would also allow Indonesian data to contribute to global reference standards and improve cross-population applicability.

Conclusions

This study provides a comprehensive analysis of hepatic vascular and biliary anatomy in Indonesian living liver donors. Canonical anatomical patterns predominated across all systems, with subtle ethnic differences observed, particularly among Sumatran donors, who showed higher rates of vascular and biliary variants. Regression analysis identified age as a predictor of hepatic artery variation and BMI as a factor influencing portal vein subtypes, while biliary anatomy remained unaffected by demographic variables. Notably, anatomical variations did not significantly prolong operative time, showing that with meticulous preoperative imaging and planning, complex anatomy can be safely managed without affecting donor hepatectomy duration. This study underscores the importance of preoperative imaging and standardized classification systems for optimal donor selection and surgical planning, while also providing valuable insights into the anatomical diversity within Indonesia’s multiethnic population.