Despite technical advances in LDLT, including the adoption of surgical loupes and operative microscopes [5], HA anastomosis remains challenging due to its small caliber (2-3 mm) and susceptibility to complications such as thrombosis, stenosis, and dissection [6,7].

It has been shown that high-frequency (8-12-MHz) IOS, with superb resolution visualizing reverberation echo from each of anastomotic stitches, is capable of assessing the HA anastomosis as it is [3] (Fig. 1). There may be a technical difficulty in case of vascular tortuosity and small size of the vessels.

To detect HA stenosis, the diameter of HA anastomosis is first measured, followed by color and spectral Doppler US of the graft HA to identify abnormal Doppler parameters indicative of HA insufficiency, as follows: (1) peak systolic velocity <30 cm/s, resistive index <0.5, and systolic acceleration time >0.08 seconds [3] (Fig. 2).

The IOS evaluation of HA should include not only the anastomosis but also the perianastomotic graft and recipient HA to identify thrombus, intimal flap, or mural thickening suggestive of HA dissection.

HA thrombosis after LDLT occurs with an incidence of 1.4% [8]. Its relatively low prevalence compared to cadaveric donor liver transplantation (LT) is expected, given that LDLT offers the advantage of significantly reduced graft preservation time, often to less than a few hours. On sonographic evaluation, thrombus typically appears as echogenic filling defect within the arterial lumen. Lack of flow within the intrahepatic arterial branches can be documented by IOS (Fig. 3) [4].

HA dissection is an uncommon complication after LT. Several authors have suggested that this condition may be attributed to a honeycomb-like intimal deformity of the recipient’s HA in chronic liver disease [9]. Intimal dissection of HA can extend both to the graft HA or to the proximal common hepatic artery of the recipients. IOS may demonstrate double lumen of HA, intimal flap, and no color flow signal in the false lumen, with or without significant compromise of intrahepatic arterial flow distal to the dissection (Fig. 4). Significant compromise of intrahepatic arterial flow in HA dissection is suspected when a combination of resistive index <0.5 and systolic acceleration time >0.08 seconds are present, or when no detectable flow is present at graft HA [10].

In uncomplicated cases, IOS evaluation of the PV anastomosis, straight and large enough, is relatively easy. Significant PV stenosis is suspected, when there are (1) a PV diameter of ≤2.5 mm, (2) Doppler abnormality of an acceleration of flow at the stricture or a poststenotic jet of PV flow, or (3) both [11]. There may be size discrepancy between the donor and recipient PVs at the anastomotic site, producing considerable velocity increase across the anastomosis, without significant stenosis (Fig. 5). It has been shown that there is no significant relationship between the graft PV velocity and anastomotic stenosis [12]. Flow velocity at the graft PV may vary depending on factors such as flow modulation or the degree of preexisting portal hypertension [13].

PV complication may be an issue in recipients with chronic partial thrombosis, wall calcification, and luminal narrowing of PV, which can be managed by simple thrombectomy, an eversion technique and/or incision technique, intraoperative metallic stent insertion via the inferior mesenteric vein, or a total portal removal including the thrombus with graft interposition [14]. In these cases, unexpectedly, thromboembolus may occlude intrahepatic PV branch, hence IOS need a thorough review of not only PV anastomosis but intrahepatic PV branches. Similarly, thromboembolus of PV may be found in patients with portosystemic collateral embolization [15] or splenectomy. IOS show intraluminal filling defect in case of PV thromboembolus (Fig. 6).

In small-for-size grafts (defined as GRWR <0.8%), excessive portal flow may cause graft damage, which has been a topic of much debate recently. Some investigators advocate portal inflow modulation might be required in order to improve the early postoperative outcome when PV pressure exceeds 25 mmHg [16]. IOS is a noninvasive and effective technique for quantification of PV flow [17]. Software accommodated in the ultrasonography machine automatically calculates PV flow based on the diameter, and maximal and minimal velocity which we enter; Flow volume=Area×Mean velocity×60 (mL/min) [18]. Excessive portal inflow for small grafts may be characterized by portal flow exceeding 250-260 mL/min per 100 g of graft weight based on previous studies [16].

A hallmark that differentiates LDLT with a right lobe graft from cadaveric whole-liver transplantation is the presence of multiple hepatic venous outflows. Although the right HV (RHV) typically serves as the primary drainage route for the right-lobe graft, a substantial portion of right anterior sector drains into the middle HV (MHV). However, because the MHV is usually preserved in the donor for safety reasons, the right anterior sector is prone to congestion unless the corresponding HV tributaries are reconstructed using an interposed venous conduit. Similarly, a considerable portion of the right posterior sector may drain into the inferior RHV (IRHV). Therefore, without anastomosis of IRHV to inferior vena cava, the right posterior sector may also become congested. Nonetheless, the indication for reconstruction of these venous tributaries remains subject of debate, as the development of intrahepatic veno-venous collaterals may save these areas from congestion [4].

When the MHV tributaries of the anterior sector are large enough (>5 mm caliber), they are reconstructed via interposition vein graft (autologous [recipient’s great saphenous vein, external iliac vein, umbilical collateral vein], cryopreserved cadaveric cavo-iliac vein, or polytetrafluoroethylene grafts) into the recipient’s MHV and/or left HVs or inferior vena cava) in our institution. Similarly, inferior RHVs are directly anastomosed to the inferior vena cava, if large enough (>5 mm caliber). All of these HVs, together with RHV, are confidently evaluated by IOS (Fig. 7).

HV complications are relatively common in LDLT with modified right-lobe graft. IOS visualize anastomotic site directly and hemodynamic effect by changes in flow velocity and waveform [19]. Pathologic state that compromises the HVs produce a dampening of the Doppler tracing, with loss of various component of the normal triphasic pattern (Fig. 8). There has been controversy regarding as the relationship between the HV velocity within the graft and anastomotic stenosis [12,20]. Particularly in MHV tributaries and interposition vein graft, there are tendency of very rapid thrombus formation with flow stasis. Thrombus may appear as echogenic filling defect within the lumen in IOS (Fig. 9) [21].