Abernethy malformation, also known as congenital extrahepatic portosystemic shunt, is an extremely rare syndrome. The majority of affected patients described to date were under the age of 18 [2-4]. Type I malformations have complete portosystemic shunts that do not perfuse the liver and are predominantly found in females [5-7]. Type II malformations have a hypoplastic portal vein leading to liver perfusion.
As shown in our cases, Abernethy malformations have a wide spectrum of symptoms including hematochezia, cyanosis, fatigue, hematuria, and others. Other relevant symptoms recorded in studies include nausea, vomiting, epigastric pain, asthenia, anorexia, jaundice, and dyspnea . The symptoms may be mild and non-specific, with some patients being asymptomatic [8, 9]. Pulmonary hypertension is a frequent initial clinical manifestation of the disease and hyperammonemia is a common manifestation. In our group, 50% (7/14) patients presented with unexplained pulmonary hypertension, and 71.4% (10/14) had hyperammonemia. Severe elevation of blood ammonia can lead to hepatic encephalopathy but only one of our 14 cases had this manifestation.
Abernethy malformation is frequently associated with cardiovascular abnormalities, including atrial septal defect (ASD), patent foramen ovale (PFO), ventricular septal defect (VSD), patent ductus arteriosus (PDA), tetralogy of Fallot (TOF) and dextrocardia [1,5,6,10,11]. In our 14 cases, 42.9% (6/14) cases had a history of congenital heart disease, and included ASD, VSD, PDA, PAPVC, and polysplenia syndrome (one patient with type I and five patients with type II). Some studies have indicated that type I Abernethy malformation occurs more frequently in girls and is associated with other congenital anomalies, while type II Abernethy shunts are rarely seen with these malformations [9, 12, 13]. Two of three cases of type I Abernethy malformation were female patients. However, in our eleven cases of type II, five cases had congenital heart disease. Nodular liver lesions were observed in almost half of the reported cases, and attributed to the absence of portal blood flow and compensatory increased hepatic arterial blood flow. The most frequently observed lesion is focal nodular hyperplasia, while others include nodular regenerated hyperplasia, hepatoblastoma, hepatic adenoma, hepatocellular carcinoma, and cirrhosis . Only 21.4% of our cases (3/14) showed nodular liver lesions but were not confirmed by pathology.
When a portosystemic shunt carries an increased risk of hepatic encephalopathy or is associated with the development of liver tumors, it requires treatment . Early diagnosis is important. Many image modalities can be used for diagnosing Abernethy malformation, including ultrasound, CT, DSA, and MRI.
Ultrasound is a non-invasive method of examination. Eight of the fourteen cases underwent US in our study, and all eight cases were able to confirm Abernethy malformation by showing the exact position of the shunt. However, compared with MSCT, US did not clearly show the development of the intrahepatic portal vein. Hypoplastic portal veins were found in only two cases using US. It would appear that confirmation of the type of Abernethy malformation by US is less efficient compared with MSCT.
MSCT is a non-invasive imaging technique with high spatial resolution and the ability to rapidly test for the diagnosis of Abernethy malformation. We have a low-dose CT protocol (100-120 kVp, 50 mA) for children since the procedure involves ionizing radiation. In our 14 cases, MSCT was able to show the exact location of the portacaval shunt (Fig.4) in all cases. Through post-processing technology (MPR, MIP, VR), CT can visually display the location of shunt and its relationship with surrounding tissues. Among these imaging examinations, MSCT is a relatively efficient method. The major advantages of CTA are rapid examination and easy availability, with a very short scanning time . First of all, it is a non-invasive and rapid method of imaging examination. Secondly, CT can accurately display the relationship between the location of shunt and the surrounding tissues. MSCT can give accurate classification of Abernethy malformation (Type II) especially in cases where the intrahepatic portal vein can be accurately demonstrated. Therefore, MSCT can accurately follow up these patients without using DSA each time.
Radiation dose is the main concern in imaging pediatric patients. The organ doses delivered from a traditional CT examination result in a potentially increased risk of radiation-induced carcinogenesis, particularly for children . Of our 14 cases, three cases used 64-slice high definition CT scanner. The DLP, CTDI and calculated ED for cases using the 64-slice high definition CT scanner were significantly lower than those using 16-row CT scanner. However, advances in CT technology can reduce the radiation dose to patients on the premise of ensuring image quality. GE Healthcare developed a novel iterative reconstruction technique, ASiR-V, that uses almost full iterative reconstruction system with the potential for significant radiation dose reduction and superior image quality than conventional ASiR and a shorter imaging processing time than the model-based iterative reconstruction . The use of wide detector technology and the acceleration of scanning speed also help to reduce the radiation dose of children's CT examination .
The conventional original non-contrast MRA techniques such as time of fight and phase contrast MR angiography produce static images with prolonged acquisition time and cannot detect small vessels. Several non-contrast and contrast enhanced MR angiography (MRA) techniques have been developed . New developments of non-contrast MRA include cardiac-gated 3D fast-spin-echo, arterial spin labeling, and balanced steady-state free-precession. These techniques have better image quality and shorter examination time, but they may be associated with flow artifacts. Due to problems such as sedation, lower spatial resolution, and long examination time, none of our cases underwent MRI examination. For young children, longer examination time means deeper levels of sedation. The number of procedures requiring anesthesia and or sedation in these children is growing and the cumulative effect of these repeated exposures on the developing brain is unknown . The possible side effects of sedatives on children, especially newborns, cannot be ignored. Recent several vivo studies have shown that early use of anesthetics and sedatives can lead to permanent structural and functional changes of central nervous system (CNS) . Compared with MRI, CT has a very fast scanning speed. Wide-detector CT makes CT scanning with lighter to no sedation possible due to the advancement of CT technology . It is believed that with the advancement of technology, the acceleration of scanning speed and the optimization of image quality, MRA will play an increasingly important role in the diagnosis of small vessel diseases in children.
However, some patients with Abernethy type II have extremely hypoplastic portal veins distal to the shunt that are sometimes difficult to visualize with CT angiography scan. In these patients, DSA is still essential for studying the anatomy of the shunt. Among our fourteen cases, two cases of type II Abernethy malformation were misdiagnosed as type Ib Abernethy malformation using MSCT. As shown in Fig.5, MSCT was not able to show the tiny intrahepatic portal veins, which could be seen in the DSA image. Because of portosystemic shunt, the pressure of intrahepatic portal vein is higher than that of systemic vein. Contrast agents are more likely to enter the systemic vein through communicating branches. During DSA examination, after balloon occlusion in the shunt, the contrast agents failed to enter the systemic vein, which increased the pressure of the small portal vein branches in the liver . Therefore, DSA images can show small portal vein branches in the liver which not able to be shown in CT images.
DSA remains the gold standard for the diagnosis of the disease, although it is an invasive imaging examination. However, it is especially useful for cases where the development of intrahepatic portal vein cannot be accurately demonstrated in MSCT, and consequently DSA is a necessary diagnostic regimen. Another important point is that some cases of Abernethy Malformation can be treated using DSA.
The treatment of Abernethy malformation is dictated by the classification. Type I malformations are definitively treated by liver transplantation due to complete absence of intrahepatic portal veins . Type II malformations can be treated with either surgical ligation or endovascular shunt occlusion. When the shunt is not amenable to surgical closure, the only alternative is liver transplantation .