Triangular anastomosis enhances early patency of small middle hepatic vein tributaries in right lobe living donor liver transplantation

Abstract

Background

In right-lobe living donor liver transplantation (LDLT) without middle hepatic vein (MHV) inclusion, conventional anastomosis results in poor early patency of MHV tributaries ≤ 5 mm, which may cause graft congestion and dysfunction, especially in recipients with marginal graft-to-recipient weight ratio (GRWR). This study evaluated the safety and efficacy of a novel triangular anastomosis for small MHV tributary reconstruction.

Methods

A single-center, two-period comparative study enrolled 42 adult LDLT recipients (May 2019–December 2025). Period 1 (2019–2023) comprised 24 patients undergoing conventional anastomosis; Period 2 (2023–2025) included 18 patients receiving triangular anastomosis for MHV tributaries ≤ 5 mm (standard reconstruction for > 5 mm). Primary endpoint was 7-day patency of ≤ 5 mm tributaries; secondary endpoints included graft function, complications, and 1-year survival. Patency was analyzed by generalized estimating equations (GEE), and survival by Kaplan–Meier method.

Results

Baseline and intraoperative characteristics were well balanced. The 7-day patency of ≤ 5 mm tributaries was significantly higher in Period 2 (75.0% vs. 26.7%, GEE-adjusted P = 0.032), with no significant 30-day patency difference. Time to total bilirubin normalization was shorter (7.10 ± 3.28 vs. 11.17 ± 3.24 days, P = 0.009). Complication and 1-year survival rates were comparable between groups (both P > 0.05).

Conclusions

Within the limitations of this small single-center cohort, triangular anastomosis improves early patency of small MHV tributaries and may contribute to earlier graft functional recovery without additional risks. It is a safe and feasible option for high-risk small venous reconstruction in MHV-excluded right-lobe LDLT with marginal GRWR. However, these findings are preliminary, and larger studies with longer follow-up are needed to confirm long-term efficacy.

Introduction

Living donor liver transplantation (LDLT) is a cornerstone therapy for end-stage liver disease, particularly in regions with few deceased donor organs [1, 2]. Right-lobe LDLT without MHV is widely performed in adults. The right liver graft (RLG) procured in this procedure balances donor safety and the recipient’s need for sufficient liver volume [3]. However, inadequate drainage of the MHV branches (primarily V5 and V8) during this procedure can easily lead to congestion in the right anterior lobe (segments S5 and S8) [4]. If the effective graft-to-recipient weight ratio (GRWR) is marginal or inadequate, such congestion further reduces the functional graft volume, increases the risk of small-for-size syndrome (SFSS), and adversely affects transplant outcomes [5, 6].

Reconstruction of hepatic venous outflow is therefore crucial for improving graft perfusion and functional recovery [4, 5, 7]. Current mainstream practice recommends routine reconstruction of major MHV tributaries > 5 mm in diameter, while tributaries ≤ 5 mm are often not reconstructed due to technical difficulty and historically poor patency rates (20%–30%) [7–9]. Nevertheless, in selected cases, preoperative imaging indicated a predicted GRWR below the safe threshold (e.g., < 0.8%). If these small tributaries are omitted, the inadequate reconstruction may exacerbate functional volume loss due to congestion, rendering an already marginal graft volume insufficient [8, 9]. At our center, preoperative contrast-enhanced multidetector CT with three-dimensional reconstruction enables precise volumetric assessment of the graft and drainage territories of individual MHV tributaries (V5 and V8), providing an objective basis for reconstruction decisions. Despite such planning, conventional anastomotic techniques for tributaries ≤ 5 mm are associated with very low early patency rates and a high risk of thrombosis, failing to relieve segmental congestion reliably.

To address these limitations, we developed a novel triangular anastomosis technique designed to enlarge the anastomotic orifice, optimize hemodynamics, and reduce flow resistance. This single-center two-period study compared triangular anastomosis with conventional techniques, focusing on early patency and clinical outcomes, to validate its utility for reconstructing ≤ 5 mm MHV tributaries in MHV-excluded LDLT.

Materials and methods

Study design and patient cohort

This was a single-center, two-period, retrospective cohort study of patients who underwent RLG without MHV inclusion at our institution between May 2019 and December 2025. Patients were divided chronologically by the anastomotic technique used for MHV tributary reconstruction. In Period 1 (May 2019 to July 2023), conventional anastomosis was used for MHV tributaries, and 24 patients were retrospectively enrolled. During Period 2 (August 2023–December 2025), a triangular anastomosis technique was adopted for MHV tributaries ≤ 5 mm in diameter, and 18 patients were prospectively included.

The inclusion criteria were as follows: (1) recipients of right-lobe LDLT without MHV trunk inclusion; (2) adult age (> 18 years); and (3) complete clinical and follow-up data. Exclusion criteria were as follows: (1) history of multi-organ transplantation; (2) preoperative severe infection, coagulopathy, or multi-organ failure; and (3) follow-up < 3 months. All research complied with the 2013 Declaration of Helsinki and 2018 Declaration of Istanbul. The study protocol was approved by the Institutional Review Board of Tianjin First Central Hospital (approval number: KELUNSHEN2026-39), which covered the retrospective analysis of Period 1 data and prospective approval for Period 2. For the retrospective cohort (Period 1), the requirement for written informed consent was waived due to the use of anonymized data. For the prospective cohort (Period 2) and for the use of surgical imaging, written informed consent was obtained from all recipients and donors.

Surgical technique

All procedures in both study periods were performed by the same core surgical team (led by two senior transplant surgeons with > 15 years of LDLT experience) to minimize variability in technical skill and perioperative management. The triangular technique was introduced after a standardized team training protocol including bench simulation.

All donors underwent contrast-enhanced CT with a 3D reconstruction software to precisely measure the total liver volume, RLG volume, remnant liver volume, and diameters of the V5/V8 tributaries (Fig. 1). The anticipated congestive volume (total volume of V5/V8 territories if not reconstructed) was also quantified. The “non-congested GRWR” was calculated as (RLG volume – anticipated congestive volume) / recipient body weight. When the non-congested GRWR was < 0.8%, MHV tributaries ≤ 5 mm were reconstructed, regardless of their small caliber. The donor inclusion criteria were as follows: (1) age 18–60 years; (2) normal liver function, hepatic steatosis < 10%; (3) remnant liver volume ≥ 30% of the total liver volume; (4) absence of major anatomical variants; and (5) no underlying liver disease or history of malignancy.

Fig. 1.

Schematic diagram of preoperative 3D-CT evaluation and non-congested GRWR calculation. Legend: Preoperative assessment of liver volume and hepatic vein anatomy was performed using enhanced CT combined with 3D-CT reconstruction software (UNITED IMAGING) to guide the decision-making of MHV tributary reconstruction. a 3D-CT reconstruction of the whole liver, with color-coded segmentation (right hemi-liver graft = orange, MHV and its V5/V8 tributaries = green/yellow). The software precisely measures total liver volume (TLV = 905.5 mL), right hemi-liver graft volume (RLGV = 534.2 mL), and left residual liver volume (371.3 mL, accounting for 41.0% of TLV), ensuring donor safety. b Magnified view of V5/V8 tributaries and their drainage areas. V5 (green) has a diameter of 5.8 mm and a drainage volume of 55.25 mL; V8 (yellow) has a diameter of 3.9 mm and a drainage volume of 48.7 mL. The non-congested GRWR is defined as (RLGV - drainage volume of unreconstructed ≤ 5 mm MHV tributaries)/recipient weight. For the representative recipient (65 kg), if V8 is not reconstructed, non-congested GRWR = (534.2–48.7)/65 = 0.75% (< 0.8%), indicating the necessity of V8 reconstruction. Note: Volume measurements were conducted by two independent radiologists; discrepancies were resolved by consensus

The RLG was donated according to the standard technique following Couinaud segmentation. The ischemic line was marked after temporary clamping of the right portal vein and hepatic artery. Parenchymal transection was performed along the ischemic line using the Cavitron Ultrasonic Surgical Aspirator guided by the MHV course. The MHV trunk was preserved on the donor side to maintain venous drainage from the remnant liver. The V5 and V8 tributaries were carefully dissected and preserved, without iatrogenic injury. Back table preparation was performed under cold preservation (4 °C HTK solution): ligatures on V5/V8 tributaries were gently released to allow adequate flush; planned tributaries underwent pressure testing to confirm patency and integrity; and diameter, length, and flow direction were recorded for subsequent reconstruction.

Conventional Anastomosis (Period 1): MHV tributaries were anastomosed to interposition grafts (cryopreserved allogeneic iliac veins procured from deceased donors through our institutional tissue bank, which operates under national regulatory standards and with approval from the relevant ethics committee; cryopreserved in 10% DMSO solution and stored in vapor-phase liquid nitrogen at -196 °C; mean storage time 18.4 ± 6.7 months, range 12–32 months) using an end-to-end or oblique end-to-end technique. All grafts underwent rigorous screening for infectious diseases and viability testing prior to release. For size mismatch, the interposition graft orifice was partially narrowed with sutures to match the tributary diameter. Anastomoses were performed with continuous or interrupted 7–0 or 8–0 Prolene sutures (Ethicon, Somerville, NJ, USA) to avoid torsion and ensure an unimpeded flow direction. The choice of suture technique (continuous vs. interrupted) was at the operating surgeon’s discretion, based on intraoperative assessment of vessel wall quality, diameter mismatch, and local tension.

Triangular Anastomosis (Period 2, for tributaries ≤ 5 mm) (Fig. 2): After backtable perfusion with a 4 °C HTK solution, the stump of the ≤ 5 mm MHV tributary was gently dilated with vascular forceps to ensure luminal patency. A longitudinal incision parallel to the right hepatic vein (RHV) orifice was made on the tributary stump, and the incision length was standardized to 0.5× the vessel circumference to form a triangular orifice with three distinct vertices. The interposition graft was trimmed to a matching triangular shape (base length equal to tributary incision length), with continuous 8–0 Prolene suturing (Ethicon) following the “apex-to-apex, base-to-base” principle. A continuous suturing technique was mandated for the triangular anastomosis to ensure precise, symmetrical apposition along the geometrically defined edges, to distribute tension evenly across the three vertices, and to standardize the technical approach across all cases in Period 2. Interrupted sutures were avoided as they risk uneven tension distribution and geometric distortion at the apexes. The first suture was placed at the apex of the tributary orifice, followed by symmetric sutures along the two sides and a final suture at the base. Tension-free apposition was confirmed intraoperatively using Doppler ultrasound (flow velocity > 10 cm/s; considered adequate). The key steps of triangular anastomosis are comprehensively illustrated in Figs. 2 and 3 with detailed annotations.

Fig. 2.

Triangular anastomosis technique for small MHV tributaries and combined outflow tract reconstruction in MHV-devoid right liver grafts. a Preparation of donor MHV tributaries and interposition vein graft (IVG). Legend: Donor MHV-devoid right liver graft, with identified MHV tributaries (V5, V8, diameter ≤ 5 mm) and isolated IVG. b Triangular opening creation. Legend: Triangular incisions on V5 stump (donor) and IVG end; magnified view shows matched triangular structures. c Triangular anastomosis of V5 and IVG. Legend: Completed triangular anastomosis between V5 and IVG (7–0/8–0 Prolene suture); magnified view displays tight coaptation. d Combined outflow tract reconstruction. Legend: IVG anastomosed to RHV to form a single wide outflow tract; magnified view shows the IVG-RHV anastomosis

Fig. 3.

Intraoperative key steps of MHV tributary reconstruction and postoperative patency confirmation. a Perfusion of MHV V5/V8 tributaries with 4 °C HTK solution; intraoperative re-measurement of tributary diameter, length, and blood flow direction. b Conventional end-to-end anastomosis of V5 (> 5 mm) with cryopreserved allogeneic iliac vein (interposition vessel) using 7–0 Prolene suture. c Creation of a triangular orifice on V8 (≤ 5 mm) via a longitudinal incision (parallel to RHV orifice, length ≈ half vessel circumference). d Triangular anastomosis between V8 and interposition vessel (matching triangular trimming, “apex-to-apex, base-to-base” continuous suture with 7–0 Prolene). e Alignment check: interposition vessels parallel to RHV orifice, no torsion at V5/V8 anastomotic sites. f Triangular splicing anastomosis of reconstructed MHV tributaries with RHV orifice to form a common wide outflow tract. g Modified piggyback implantation: anastomosis of graft common outflow tract to recipient IVC orifice. h Postoperative 2-week enhanced CT: contrast filling in reconstructed MHV tributaries confirms patency. Note: All intraoperative images were sterilely acquired; postoperative CT used 64-slice spiral scanner with 1.0 mm slice thickness

In both periods, a “combined anastomosis” technique was used to create a single wide outflow orifice. On the back table, the interposition grafts of the reconstructed MHV tributaries were sutured to the RHV orifice in a triangular fashion, forming a single common outflow orifice. In recipients, a modified piggyback technique was used: the recipient hepatic vein stump was trimmed, and the inferior vena cava (IVC) was longitudinally incised to match the graft outflow. End-to-side anastomosis between the common orifice of the graft and recipient IVC was performed to establish a wide, physiologically oriented outflow, minimizing the risk of kinking or obstruction due to graft regeneration and rotation.

Perioperative management

The donors were routinely monitored for liver function, coagulation, and abdominal drainage. Recipient management included immunosuppression with basiliximab induction, followed by maintenance with tacrolimus, mycophenolate mofetil, and corticosteroids. Anticoagulation followed a standardized protocol: early low-molecular-weight heparin, then oral anticoagulants, adjusted according to activated partial thromboplastin time (aPTT) or international normalized ratio (INR). Liver support included hepatoprotective and choleretic agents, and fluid and electrolyte balance. Vascular patency surveillance comprised daily Doppler ultrasound during the first postoperative week and twice weekly in weeks 2–4. Computed tomography angiography (CTA) was performed at 2 weeks to confirm patency and assess right anterior sector regeneration.

Study endpoints and data collection

The primary endpoint was patency of the reconstructed MHV tributaries on postoperative days 7 and 30. Patency was defined as a detectable intraluminal flow on Doppler ultrasonography. Postoperative patency was assessed qualitatively (patent/occluded) by Doppler ultrasound; quantitative hemodynamic parameters were not systematically recorded in the database used for this analysis.

Secondary endpoints included early graft function (peak ALT, AST, and total bilirubin within 30 days; time to bilirubin normalization), incidence of PNF, DGF, SFSS, outflow obstruction, AKI, intra-abdominal bleeding, abdominal infection, and acute rejection, patient mortality within 30 days; and 1-year survival.

Data were extracted from electronic medical records, including baseline characteristics, operative parameters, and postoperative laboratory/imaging findings.

Statistical analysis

Statistical analyses were performed using SPSS 22.0 (IBM Corp., Armonk, NY, USA) and R 4.2.1 (R Foundation for Statistical Computing). Continuous variables are presented as mean ± SD and compared using an independent-samples t-test (normal distribution) or Mann-Whitney U test (non-normal distribution). Categorical variables are expressed as n(%) and compared via χ² test or Fisher’s exact test. Generalized Estimating Equations (GEE) were used to compare patency rates between periods, adjusting for potential confounders, including tributary diameter, drainage territory volume, and cold ischemia time (variables selected based on clinical relevance and univariate analysis, P < 0.10). The working correlation matrix was set to exchangeable, and robust standard errors were used to account for clustering of multiple tributaries per patient. Survival rates were estimated via Kaplan-Meier and compared via log-rank test. Two-tailed P < 0.05 was statistically significant.

Results

Baseline and donor characteristics

The baseline characteristics of the recipients and donors during the two study periods are summarized in Table 1. A total of 24 patients were enrolled in Period 1 and 18 in Period 2. No significant differences were observed between groups in sex, age, BMI, liver disease etiology (predominantly hepatitis B virus), or hepatocellular carcinoma prevalence (all P > 0.05). Regarding the etiology of liver disease, hepatitis B virus infection was the predominant cause in both groups, followed by hepatitis C virus infection, alcoholic liver disease, and other causes. The distribution was comparable between the two periods (P > 0.05). The proportion of patients with concomitant hepatocellular carcinoma did not differ significantly between groups (P > 0.05). Among donor-related parameters, the model for end-stage liver disease (MELD) score, graft volume, volumes of V5/V8 drainage territories, diameters of V5/V8 tributaries, GRWR, and non-congested GRWR values were all comparable between the two periods (all P > 0.05). These findings indicate well-balanced baseline characteristics between the two study cohorts.

Table 1.

Comparison of baseline characteristics and donor-related indicators between the two periods

	Period 1 (n = 24)	Period 2 (n = 18)	Test statistic	P value
Gender (Male/Female, n)	16/8	12/6	χ²=0.685	0.408
Age (years, x ± s)	54.92 ± 8.04	56.28 ± 7.47	t = 0.559	0.6579
BMI (kg/m², x ± s)	23.30 ± 1.70	23.05 ± 1.59	t = 0.477	0.636
Etiology (n, %)			χ²=1.724	0.631
HBV	16 (66.7)	10 (55.6)
HCV	2 (8.3)	0 (0)
Alcohol	4 (16.7)	4 (22.2)
Others	2 (8.3)	4 (22.2)
Accompanying HCC (n, %)	8 (33.3)	7 (38.9)	χ²=0.138	0.710
MELD Score (points, Median, IQR)	12.00 (9.00-15.25)	11.50 (9.25-15.00)	U = 214	0.969
Donor Graft Volume (mL, Median, IQR)	610.00 (564.75-680.75)	618.50 (563.25-681.25)	U = 210	0.888
V5 Drainage Area Volume(mL, Median, IQR)	139.00 (128.57-152.38)	140.15 (126.97-151.75)	U = 216	1.000
V5 diameter (mm, Median, IQR)	6.35 (4.97–8.92)	7.85 (5.00-10.20)	U = 191	0.541
V8 Drainage Area Volume (mL, Median, IQR)	62.60 (51.98–80.85)	60.90 (51.78–71.65)	U = 227	0.779
V8 diameter (mm, Median, IQR)	5.00 (3.72–5.70)	4.90 (3.62–6.25)	U = 214	0.979
GRWR (%, x ± s)	1.00 ± 0.14	1.00 ± 0.13	t = 0.055	0.956
non-congested GRWR (Median, IQR)	0.79 (0.73–1.04)	0.79 (0.73–0.95)	U = 219	0.939

Continuous variables with normal distribution were presented as mean ± standard deviation (x ± s) and compared using independent-samples t-test. Non-normally distributed continuous variables were presented as median (interquartile range, IQR) and compared using Mann–Whitney U test. Categorical variables were presented as number and percentage (n, %) and compared using Pearson χ² test. A two-sided P < 0.05 was considered statistically significant

Abbreviation: BMI, body mass index; MELD, model for end-stage liver disease; HBV, hepatitis B virus; HCV, hepatitis C virus; HCC, hepatocellular carcinoma; GRWR, graft recipient weight ratio; IQR, interquartile range

Intraoperative variables

Table 2 lists perioperative parameters. Total operation time, intraoperative blood loss, cold ischemia time, anhepatic phase duration, and anastomosis time per MHV tributary did not differ significantly (all P > 0.05). In Period 1, 43 MHV tributaries were reconstructed, including 28 with diameters > 5 mm and 15 with diameters ≤ 5 mm. In Period 2, 33 tributaries were reconstructed, including 21 with diameters > 5 mm and 12 with diameters ≤ 5 mm. The distributions of large (> 5 mm) and small (≤ 5 mm) tributaries did not differ significantly between the two periods (P > 0.05). These results suggest a comparable surgical burden and vascular reconstruction load between the two groups, thereby minimizing the potential confounding effects of operative factors on postoperative patency outcomes.

Table 2.

Comparison of surgery-related indicators between the two periods

Variables	Period 1 (n = 24)	Period 2 (n = 18)	Test statistic	P value
Total Operation Time (min, x ± s)	657.25 ± 55.57	675.50 ± 46.81	t = 1.125	0.267
Intraoperative Blood Loss (mL, Median, IQR)	800.00 (642.50–930.00)	810.00 (685.00-937.50)	U = 204	0.770
Cold Ischemia Time (min, x ± s)	85.75 ± 19.75	86.56 ± 16.87	t = 0.139	0.890
Anhepatic Phase Time (min, x ± s)	52.27 ± 7.52	53.91 ± 6.51	t = 0.740	0.463
MHV Tributary Anastomosis Time (min, x ± s)	22.54 ± 4.71	23.56 ± 4.40	t = 0.710	0.482
Total Number of Reconstructed MHV Tributaries (n)	43	33	-	-
Diameter > 5 mm (n, %)	28 (65.1)	21 (63.6)	χ²=0.021	0.884
Diameter ≤ 5 mm (n, %)	15 (34.9)	12 (36.4)	-	-

Continuous variables were expressed as mean ± standard deviation (x ± s) or median (interquartile range, IQR). Independent-samples t-test, Mann-Whitney U test and Chi-square test were used accordingly. A two-sided P < 0.05 was considered statistically significant

Abbreviation: MHV, middle hepatic vein; IQR, interquartile range

Primary endpoint: patency of reconstructed MHV tributaries

For small tributaries (≤ 5 mm), 7‑day patency was significantly higher in Period 2 (75.0%, 9/12) than Period 1 (26.7%, 4/15) (GEE-adjusted P = 0.032). At 30 days, patency declined to 41.7% (5/12) and 20.0% (3/15), respectively, with no significant difference (GEE-adjusted P = 0.185). For large tributaries (> 5 mm), 7-day and 30-day patency did not differ (GEE-adjusted P = 0.592 and P = 0.578). For all tributaries, 7-day patency was higher in Period 2 (81.8%, 27/33) than Period 1 (67.4%, 29/43) (P = 0.084), with no significant 30-day difference (P = 0.608) (Table 3).

Table 3.

Comparison of postoperative patency rates of MHV tributaries with different diameters between the two groups (n, %)

Vessel diameter	Period	Total reconstructed	7-day postoperative patency	P value	30-day postoperative patency	P value
≤ 5 mm	Period 1	15	4 (26.7%)	0.032	3 (20.0%)	0.185
	Period 2	12	9 (75.0%)		5 (41.7%)
> 5 mm	Period 1	28	25 (89.3%)	0.592	24 (85.7%)	0.578
	Period 2	21	18 (85.7%)		17 (81.0%)
Overall	Period 1	43	29 (67.4%)	0.084	27 (62.8%)	0.608
	Period 2	33	27 (81.8%)		22 (66.7%)

All P-values were computed using generalized estimating equations (GEE) with an exchangeable working correlation matrix, adjusted for the clustering effect of multiple hepatic vein tributaries within the same patient. A two-sided P value less than 0.05 was considered statistically significant

Abbreviation: MHV, middle hepatic vein. Categorical data were expressed as number and percentage (n, %)

A post‑hoc review of operative notes for the 15 ≤ 5 mm tributaries in Period 1 showed that 9 were anastomosed with continuous suture and 6 with interrupted suture. However, due to the small sample size and the absence of a standardized suture protocol in Period 1, no statistical comparison of patency by suture technique was performed, and these data are presented only for descriptive purposes.

The intraoperative feasibility and postoperative patency of triangular anastomosis are shown in Fig. 3. Figure 3a illustrates graft preparation with perfusion and measurement; Fig. 3b demonstrates conventional anastomosis for comparison. The triangular anastomosis procedure strictly followed the sequence of “triangular orifice creation → triangular anastomosis → common outflow orifice formation → modified piggyback implantation” (Fig. 3c‑g). No intraoperative complications such as vascular injury or anastomotic leakage were observed. The 2-week contrast-enhanced CT demonstrated clear contrast filling of reconstructed V5/V8 tributaries (Fig. 3h).

Learning curve analysis

To evaluate whether the observed improvement in patency was attributable to a learning curve effect, we performed a predefined subgroup analysis of Period 2 cases. The 18 patients in Period 2 were chronologically divided into two equal halves (first 9 cases vs. last 9 cases). Among the ≤ 5 mm tributaries reconstructed with the triangular technique, the 7-day patency rates were 66.7% (4/6 tributaries) in the first half and 83.3% (5/6 tributaries) in the second half (P = 1.000, Fisher’s exact test). Furthermore, key operative parameters including anastomosis time per tributary (23.78 ± 4.52 min vs. 23.33 ± 4.38 min, P = 0.854) and total operation time (672.33 ± 48.76 min vs. 678.67 ± 45.92 min, P = 0.791) showed no significant difference between the two halves. These findings suggest that the technical proficiency required for triangular anastomosis was achieved early after standardized team training, and the observed improvement in early patency is unlikely to be solely attributable to a general surgical learning curve over the study period.

Secondary endpoints

With respect to early graft function, the peak levels of AST, ALT, and total bilirubin within the first 30 days were comparable between the two groups (U = 198.0, P = 0.717; U = 189.5, P = 0.668; U = 176.5, P = 0.307). However, time to bilirubin normalization was significantly shorter in Period 2 (7.10 ± 3.28 days) than Period 1 (11.17 ± 3.24 days, P = 0.009).

The postoperative complications are summarized in Table 4. The incidence of SFSS was 20.8% (5/24) in Period 1 and 11.1% (2/18) in Period 2, and this difference was not statistically significant (Fisher’s exact test, P = 0.487). The rates of DGF, biliary leakage, AKI, refractory ascites, and other complications did not differ (all P > 0.05).

Table 4.

Postoperative complications and prognosis after liver transplantation between the two periods

Variables	Period 1 (n = 24)	Period 2 (n = 18)	Test statistic	P value
Early Graft Function
AST Peak (U/L, Median, IQR)	415.0 (343.0, 865.0)	698.2 (513.5,883.5)	U = 198.0	0.717
ALT Peak (U/L, Median, IQR)	435.0 (302.0, 594.0)	570.0 (388.0,752.0)	U = 189.5	0.668
TB Peak (µmol/L, Median, IQR)	83.4 (66.8, 92.5)	76.9 (70.1, 82.0)	U = 176.5	0.307
Time to TB Normalization (days, x ± s)	11.17 ± 3.24	7.10 ± 3.28	t = 4.23	0.009
Postoperative Complications
Small-for-Size Syndrome (n, %)	5 (20.8)	2 (11.1)	Fisher’s exact = 0.432	0.487
PNF (n, %)	0 (0.0)	0 (0.0)	-	-
DGF (n, %)	3 (12.5)	2 (11.1)	χ²=0.015	0.903
Biliary Leak (n, %)	1 (4.2)	0 (0.0)	Fisher’s exact = 0.472	1.000
Acute Kidney Injury (n, %)	3 (12.5)	2 (11.1)	χ²=0.015	0.903
Refractory Ascites (n, %)	3 (12.5)	1 (5.6)	Fisher’s exact = 0.402	0.605
Abdominal Bleeding (n, %)	0 (0)	1 (5.6)	Fisher’s exact = 0.472	0.472
Abdominal Infection (n, %)	2 (8.3)	3 (16.7)	Fisher’s exact = 0.345	0.635
Acute Rejection (n, %)	1 (4.2)	1 (5.6)	Fisher’s exact = 0.472	1.000
Prognosis
30-Day Postoperative Mortality (n, %)	1 (4.2)	1 (5.6)	Fisher’s exact = 0.928	1.000
1-Year Survival Rate (%)	87.5	94.4	Log-rank χ²=0.826	0.363

Continuous variables were presented as median (interquartile range, IQR) or mean ± standard deviation (x ± s), and compared using Mann-Whitney U test or independent-samples t test, respectively. Categorical variables were presented as number and percentage (n, %) and compared using Chi-square test or Fisher’s exact test (for n < 5). Survival outcomes were compared using the Log-rank test. A two-sided P < 0.05 was considered statistically significant

Abbreviations: AST, aspartate aminotransferase; ALT, alanine aminotransferase; TB, total bilirubin; PNF, primary nonfunction; DGF, delayed graft function; IQR, interquartile range

Regarding patient prognosis, the 30‑day mortality was 4.2% (1/24) in Period 1 and 5.6% (1/18) in Period 2 (P = 1.000). The 1‑year survival rates were 87.5% and 94.4%, respectively (log-rank χ²=0.826, P = 0.363).

Discussion

In this two-period comparative study of 42 recipients who underwent RLG transplantation without MHV inclusion, we evaluated the efficacy of a novel triangular anastomosis technique for reconstructing small MHV tributaries ≤ 5 mm in diameter. Results showed this technique significantly improved 7-day patency of small tributaries (26.7% to 75.0%, GEE-adjusted P = 0.032) and shortened bilirubin normalization time (7.10 ± 3.28 vs. 11.17 ± 3.24 days, P = 0.009), without increasing operative risk or complications. These findings provide a new technical option for reconstructing high-risk small MHV tributaries in the setting of suboptimal GRWR. A recent study by Lin et al. further demonstrated that combined reconstruction of middle hepatic vein tributaries and the RHV in right lobe split liver transplantation significantly improved the 30-day complete patency rate of reconstructed middle hepatic vein, reduced warm ischemia time, and shortened ICU stay compared with separate reconstruction [10].

Reconstruction of MHV tributaries is a critical strategy for resolving anterior sector congestion. The current consensus recommends routine reconstruction of major MHV tributaries > 5 mm in diameter, given their substantial contribution to venous drainage of the anterior sector. However, the management of small tributaries measuring ≤ 5 mm remains controversial. Most centers avoid their reconstruction due to technical difficulty, injury risk, poor patency, and lack of proven benefit. Some studies have also suggested that intrahepatic collateral circulation may gradually compensate for venous drainage in non-reconstructed areas postoperatively [11, 12]. Nevertheless, when the non-congested GRWR is inadequate (< 0.8%), omitting the reconstruction of these small MHV tributaries exacerbates the functional volume loss due to congestion, thereby increasing the risk of SFSS [7, 8, 13]. This clinical dilemma necessitates the development of innovative techniques to improve venous patency outcomes in small-tributary reconstructions.

Currently, preoperative evaluation using 3D-CT allows precise quantification of graft volume, volumes of V5/V8 drainage territories, and diameters of V5/V8 tributaries, providing an objective basis for individualized decision-making regarding small tributary reconstruction [14, 15]. At our center, when the “non-congested GRWR” was < 0.8%, reconstruction of V5/V8 tributaries was performed regardless of whether the diameter was ≤ 5 mm. This center-specific strategy is based on the concept of “functional graft volume”–when the non-congested GRWR, calculated as (RLG volume–anticipated congestive volume of unreconstructed tributaries) / recipient body weight, falls below 0.8%, the risk of SFSS increases significantly, and any additional volume loss from congestion becomes clinically critical. We acknowledge that this is an individualized approach aimed at maximizing functional graft volume in high-risk scenarios, and it requires further validation in prospective multicenter studies.

In Period 1 of this study, the 7-day patency rate for ≤ 5 mm MHV tributaries reconstructed with conventional anastomosis was only 26.7%, consistent with the low patency rates reported in the literature [7, 9]. Several factors may account for this poor outcome: (1) in small tributaries measuring ≤ 5 mm, the high local blood flow velocity and shear stress after anastomosis can damage the vascular endothelium and trigger platelet aggregation, leading to early thrombosis; (2) conventional end-to-end or oblique end-to-end anastomoses often fail to achieve optimal size matching, and partial closure of the interposition graft orifice to adjust for diameter mismatch further reduces the effective luminal area, exacerbating flow stasis [16]; (3) the thin vascular walls of small tributaries are susceptible to iatrogenic injury during dissection and anastomosis, which may lead to anastomotic intimal hyperplasia and stenosis, ultimately resulting in occlusion [17].

To address these technical challenges, we developed and applied the “triangular anastomosis” technique. This technique has several advantages. First, creating triangular incisions on both the graft MHV tributary stump and end of the interposition graft substantially increased the effective anastomotic circumference. This reduces the local blood flow velocity and shear stress, creates a more favorable hemodynamic environment, and minimizes endothelial injury and early thrombosis. Second, the “apex-to-apex, base-to-base” suture technique ensures precise vessel wall apposition, avoids anastomotic tension and angulation, thereby preventing mechanical obstruction, and maintains smooth blood flow—a principle consistent with the emphasis on “wide, non-angulated anastomosis” to ensure venous outflow patency in LDLT [16, 18]. Third, triangular anastomosis provides superior structural stability at the anastomotic site itself, effectively resisting anastomotic stenosis or kinking caused by graft regeneration and rotation, thereby lowering the risk of late outflow obstruction [19]. In the present study, triangular anastomosis significantly increased the 7-day patency rate for ≤ 5 mm MHV tributaries to 75.0%, and this difference remained statistically significant after GEE adjustment (P = 0.032). Furthermore, there were no significant differences between Periods 2 and 1 in total operation time, vascular reconstruction time, intraoperative blood loss, or complication rates, indicating that triangular anastomosis does not increase ischemic time or operative risk and is technically feasible.

As presented in the Results section, the predefined learning curve analysis showed no significant difference in 7-day patency of ≤ 5 mm tributaries between the first and second halves of Period 2 (66.7% vs. 83.3%, P = 1.000), nor in operative parameters. This supports that the observed improvement in patency is attributable to the technique itself rather than accumulated surgical experience over time. All procedures were performed by the same senior surgical team, further minimizing the influence of surgical skill variation.

In addition to improving vascular patency, triangular anastomosis confers additional clinical benefits. The time required for serum total bilirubin to normalize was significantly shorter in Period 2 than in Period 1 (7.10 ± 3.28 days vs. 11.17 ± 3.24 days, P = 0.009), suggesting that effective venous drainage reduced congestion-related graft injury and promoted early recovery of liver function. This finding aligns with recent studies demonstrating that the patency of reconstructed MHV tributaries directly influences graft functional recovery [20–22].

Notably, the patency rate for ≤ 5 mm tributaries in Period 2 declined from 75.0% at 7 days to 41.7% at 30 days. Several factors may contribute to this late attrition. First, despite the improved hemodynamics of the triangular anastomosis, the small caliber of the native tributary (≤ 5 mm) inherently predisposes it to a higher risk of late stenosis or occlusion due to neointimal hyperplasia, a common challenge in microvascular surgery that is not fully overcome by anastomotic geometry alone. Second, graft regeneration and positional changes in the early postoperative period can exert mechanical stress or cause kinking of the interposition grafts, particularly affecting the smaller, more delicate reconstructions. Third, and perhaps most importantly, the establishment of intrahepatic venous collaterals between the MHV and RHV territories, which typically begins around postoperative day 7 and matures by 2–3 weeks, may lead to competitive flow and decreased flow through the reconstructed small tributaries, potentially contributing to their late occlusion [11, 12].

This phenomenon–whereby collateral circulation provides alternative drainage–may explain why the late patency drop does not translate into worse clinical outcomes. Importantly, the high early patency likely provided critical drainage during the most vulnerable phase (days 1–7), mitigating severe congestion and allowing time for collateral formation, which may explain the preserved clinical outcomes (favorable bilirubin recovery, comparable SFSS rates) despite the later patency drop. The reduction in SFSS rate (20.8% to 11.1%), while not statistically significant, shows a favorable trend that may reach significance in larger studies. The lack of statistical significance is likely due to the small sample size and the multifactorial nature of SFSS.

Importantly, not all small tributaries require reconstruction, and the decision to reconstruct should be based on the volume of the drainage territory. In this study, the smallest reconstructed tributary had a diameter of 2.7 mm and a liver territory volume of 65.8 mL.

This study had several limitations. First, the single-center, two-period non-randomized design may introduce selection bias and cannot fully exclude the influence of confounding factors, such as accumulated surgical experience and subtle changes in perioperative management over the 6-year study period. Multicenter randomized trials are needed to validate efficacy and generalizability. Second, the relatively small sample size (24 patients in Period 1 and 18 in Period 2), particularly the limited number of reconstructed ≤ 5 mm tributaries (15 in Period 1 and 12 in Period 2), may constrain the statistical power of our subgroup analysis. Larger cohort studies are required to confirm these findings and to robustly evaluate the long-term efficacy and safety of this technique. Third, this study focused primarily on short-term outcomes within the first postoperative year; extended follow-up is necessary to comprehensively evaluate the long-term results of triangular anastomosis. Fourth, the assessment of venous patency relied on a binary outcome (patent/occluded) from Doppler ultrasound; future studies should incorporate quantitative hemodynamic parameters (e.g., flow velocity, pulsatility index) and contrast-enhanced ultrasound or magnetic resonance venography to provide a more nuanced evaluation of outflow quality and early hemodynamic changes.

Conclusions

Within the limitations of a small single-center cohort, triangular anastomosis significantly improves early patency of ≤ 5 mm MHV tributaries and may accelerate graft functional recovery in MHV-excluded right lobe LDLT, without increasing operative or postoperative risks. Triangular anastomosis is recommended for reconstructing ≤ 5 mm MHV tributaries when the non-congested GRWR is calculated to be < 0.8%, indicating a marginal functional graft volume where salvaging congested territory is crucial. It is not recommended for routine use when GRWR is adequate (> 0.8%) or when tributaries are > 5 mm (where conventional techniques perform well). This technique offers a practical strategy to alleviate congestion in grafts with marginal GRWR. Owing to the non-randomized design and limited sample size, these results are preliminary. Future multi-center randomized controlled trials with long-term follow-up are required to validate the stability, safety, and generalizability of this anastomotic approach.

Author contributions

Wen-Tao Jiang was responsible for the research design and conception. Chi-Yi Chen and Qi-Ming Zheng was in charge of data collection. Chi-Yi Chen, Ji-San Sun, Yan Xie and Hong-Hai Wangwere responsible for data analysis, interpretation, and manuscript drafting. Wen-Tao Jiang, Li Zhang and Qing-Jun Guo were responsible for the critical revision of the manuscript.

Funding

This research was supported by the Key Project of Scientific Research Plan of Tianjin Municipal Education Commission (Grant No. 2023YXZX08), the Project of Tianjin Science and Technology Bureau Applied Basic Research (Grant No. 2023JCYBJC01800) and the Tianjin Key Medical Discipline Construction Project (Grant No. TJYXZDXK-3-006A).

Data availability

No datasets were generated or analysed during the current study.

Declarations

Competing interests

The authors declare no competing interests.

Ethical approval

This study has been approved by the Research Ethics Committee of Tianjin First Central Hospital (Approval No.: KELUNSHEN2026-39). The study was conducted in accordance with the Declaration of Helsinki (1964) and its subsequent amendments or similar ethical standards.

Research involving human participants/informed consent

For the retrospective component (Period 1), the requirement for written informed consent was waived by the ethics committee due to the use of anonymized retrospective data. For the prospective component (Period 2) and for publication of identifiable surgical images, written informed consent was obtained from all recipients and donors.