Anomalies of the PV branches at the hepatic hilum are not so common compared with those of the hepatic arteries, hepatic veins, and biliary ducts [8, 9]. APB is a rare anomaly, first reported by Couinaud [10, 11]. The adult PV develops from the vitelline (future main PV) and umbilical veins (future vertical segment of the left PV) during the 4th to 10th weeks of gestation. The absence of the horizontal part of the LPV or APB can be due to failure of the anastomosis between the caudal portion of the right vitelline and left umbilical veins [1, 2].

Regarding the anatomy of the bile ducts in patients with APB, Terasaki et al. [12] reported two patients with different bile duct characteristics, in whom the left hepatic duct ran either inside the liver along the PV or separately down into the common hepatic duct. The differences in running patterns between the PV and the bile duct can be explained from an embryological perspective. In our patient, an ordinary left bile duct was present, and IHBD stones were identified in the dilated B2 and B4. It is noteworthy that on routine preoperative plain CT images, the APB anomaly was not detected owing to the limitation of the images in outlining the detailed anatomy of the liver vasculature. However, the anomaly was detected on the preoperative enhanced CT images, which allowed us to reconstruct 3D images and view the detailed anatomy of the liver vasculature from different positions (neutral and left anterior oblique positions), as shown in Fig. 3.

Focusing on hemihepatectomy (right or left hepatectomy), this anomaly should be recognized before surgery to assess and determine the PV blood flow. Until now, there have been several reports of right hepatectomy by preserving the main and left PVs in patients with APB [5, 6, 13]. Among them, two patients experienced PV thrombosis after surgery, and one patient died of liver failure [5, 13]. When considering surgical treatment for patients with APB, surgeons must examine the precise arterial, biliary, and PV anatomy and consider the risks associated with right hepatectomy preoperatively. In contrast, left hepatectomy can be safely performed because surgeons do not have to identify the left PV at the perihilar area, and the right PV can easily be preserved.

It is difficult to determine the demarcation line when performing left hepatectomy in patients with APB. In this situation, the only option is to split the liver parenchyma along the Rex–Cantlie line and separate the PV from the anterior section. Besides our limited experience with this technique, we initially attempted PV puncture by injecting indigo carmine (10 mg) into the LPV above the MHV under US guidance to visualize the demarcation line. However, only a temporary demarcation line appeared (Fig. 4a). The hepatic parenchyma was transected along this temporary demarcation line, and the LPV was dissected and encircled. We then injected ICG (2.5 mg) into the peripheral vein, and after clamping the LPV, we could precisely see the well-established demarcation line (Fig. 4c) using ICG fluorescence real-time imaging and completed the left hepatectomy. However, owing to the complexity of liver resection, the hepatic cut surface was not smooth. This could have promoted the formation of abscesses at the cut margins and eventually lead to a postoperative intraabdominal abscess, for which the patient was successfully treated with CT-guided drainage and antibiotics.

ICG fluorescence imaging has been used for intraoperative identification of hepatic tumors and segmental boundaries during laparoscopic hepatectomy, particularly for anatomical resection [14, 15]. Recently, this technique has become common during laparoscopic hepatectomies because fluorescence images can allow surgeons to identify the segmental boundaries of the hepatic parenchyma with or without blood perfusion and thus guide surgeons to complete anatomic resections laparoscopically [16]. Although the histopathological report revealed this case as a benign disease, ICG fluorescence real-time imaging was used preoperatively, and we planned to perform a laparoscopic anatomical liver resection based on a strong suspicion of intrahepatic cholangiocarcinoma due to the impacted IHBD stones. Therefore, this real-time intraoperative imaging technique might be useful for patients with APB requiring hepatectomy by facilitating the visualization of the demarcation line and consequently aiding in liver parenchyma resection. Although the assessment of hepatic perfusion by fluorescence imaging following the intravenous injection of ICG cannot be used repeatedly, this modality can allow surgeons to perform safe and accurate laparoscopic hepatectomies.