Discussion
Liver transplantation is the only effective treatment for patients suffering from terminal stages of liver disease. Postoperative arterial complications are the most important factors affecting the success of the transplant (5,6). The most common hepatic artery complications are hepatic artery stenosis, embolization, hepatic artery dissection and HAP (7–10). HAP is the rarest and most dangerous complication with an incidence rate of 0.5–2.6% (11,12). HAP may lead to mortality due to rupture and hemorrhage. The mortality rate, after liver transplantation, due to HAP is extremely high (2.7%). Timely detection, diagnosis and treatment can effectively reduce the mortality rate (1,13).
The preferred method of blood flow monitoring after liver transplantation is the common ultrasound (14), CTA, MRI and DSA. Other large equipment cannot be used for POCT, and are often applied as supplementary examination and qualitative diagnosis. CT, MRI and DSA are not routine examinations, and are usually applied prior to hospital discharge or in the event of a possible vascular complication following ultrasonic examination. In this study, we used CEUS as a postoperative routine imaging examination method. CEUS, has been widely used for the differential diagnosis of abdominal organs with space-occupying lesion (15,16), and it has also been applied for the diagnosis of vascular complications following liver transplantation (17–19). Ultrasound contrast agent, which also served as a blood pool tracer, can be used in real-time ultrasound contrast imaging to identify large blood vessels and the micro-vascular system (20).
HAP mostly occurs in the anastomotic site, and is often linked to infection, bile leakage or multiple TACE treatment prior to transplantation. Certain technical difficulties are involved in the detection of arterial anastomosis with common ultrasound. HAP, which is located near the hilar, possessing disrupted artery blood fow, was lined with the artery, and common ultrasound was able to make a diagnosis (21), as in the 3 cases of HAP diagnosed using common ultrasound in the study. Detection of anastomosis is difficult when located far from the hilar. This is due to the interference caused by gas, intestine and omentum. In this study, 3 cases of HAP that were far from the hilar, demonstrated abnormal hemodynamic parameters in the common ultrasound examination. CEUS successfully diagnosed 2 of the cases, while the other one was diagnosed by CTA. In the HAP cases, during examination with CEUS, we observed a circular contrast agent perfusion area around the artery after the perfusion of contrast agent.
In one case of HAP, the diagnosed primary diseases were liver cirrhosis and hepatocellular carcinoma. TACE was performed 6 times prior to operation and postoperative clinical manifestations were two occasions of biliary tract hemorrhage. In the first biliary tract hemorrhage, common ultrasound showed no abnormalities while in the second one, grayscale ultrasound identified a hilar hypoechoic mass. Color Doppler ultrasound did not identify any sign of blood flow in lumps. CEUS showed that, in the arterial phase, contrast agent was sprayed into the tumor with arterial pulse in the low echoic block. Emergency laparotomy was carried out and tumor resection and arterial ligation were conducted under the guidance of ultrasound. During the operation, we detected a large tumor with high probability to rupture and cause hemorrhage.
If the surgery had been delayed the patient would have faced a life-threatening condition. The case was analyzed to determine the reason for the failure of color Doppler ultrasound to detect any blood flow signal in the tumor leading to missed diagnosis. We hypothesized that the failure was due to the presence of a smaller fistula orifice between the HAP and hepatic artery that retarded the blood flow.
Ultrasound contrast agents belong to the blood pool tracers and mimic the blood flow. Contrast agent perfusion also occurs, and thus ultrasound has a function of diagnosis. It was reported that multiple TACE prior to liver transplantation in liver cancer cases may increase the risk of HAP following liver transplantation (22). Therefore, for liver transplantation recipients with multiple TACE treatment, any of the following symptoms suggest a high risk for occurrence of HAP: i) Biliary tract bleeding; ii) bile leakage; and iii) abdominal bleeding. In these cases, the best course of action would be performing ultrasound angiography, CTA or DSA as early as possible to avoid missed diagnosis.
CTA, MRI and DSA were not used as routine examination methods of vascular complications after liver transplantation. Therefore when postoperative common ultrasound detects any of these conditions, CEUS or other vascular imaging should be conducted to verify: i) Arterial hemodynamic abnormalities; ii) follicular block; and iii) low echoic lump in hilar. The treatment of HAP should be proactive, whenever possible, and arterial revascularization treatment should be immediately carried out to avoid tumor rupture. In the present study, only 1 of 8 cases of HAP succumbed, and this may be attributed to the timely diagnosis of CEUS and timely surgical intervention.
In summary, CEUS was identified as a convenient and effective diagnostic method for HAP cases following liver transplantation. This is a superior method of diagnosis compared with CTA, as it can be realized in real-time and is considered more convenient. Poor grayscale image display affected the display effect of CEUS. For HAP located far from the hilar, there was a high probability of missed diagnosis. CEUS made up for the deficiencies associated with enhanced CT, DSA and other large equipment, and was crucial in the diagnosis of vascular complications subsequent to liver transplantation.