Hepatic vascular malformations are increasingly recognized thanks to the improvement of imaging, especially prenatal diagnosis. They are divided into two main categories: veno-venous connections commonly congenital portosystemic shunts (CPSS) on the one hand and arterio-venous connections mostly arterio-portal shunts on the other hand. They should not be misdiagnosed as hepatic infantile or congenital haemangioma which is a liver tumour with endothelial proliferation.
How frequent are hepatic vascular abnormalities in children?
Congenital hepatic vascular malformations are rare. Their exact frequency is unknown. Congenital porto-systemic shunts are reported to happen in about 1/30,000. However, a large Chinese prenatal series reports an incidence of 1/6,000 foetuses with mostly porto-hepatic shunts. Congenital arterio-portal shunts are very exceptional with very few reports in the literature.
Which are the main pathologic entities an IR can encounter in children?
Congenital portosystemic shunts are the most common malformations that will be referred to the IR for evaluation and treatment. Those malformations create a direct communication between the portal and the systemic circulation causing a partial or complete diversion of the portal blood to the systemic vein with, on one hand, the decrease or absence of the first hepatic pass of the mesenteric venous blood, and, on the other hand, a more or less severe functional hypoplasia of the portal veins downstream the abnormal connection. The absence of first hepatic pass can lead to complications at any age such as abnormal liver or coagulation tests, hepatic encephalopathy, benign and malignant liver tumours, porto-hepatic or hepato-pulmonary syndrome.
Congenital portosystemic shunts have various anatomic types according to the position of the abnormal porto-systemic connection. The most frequent type is the porto-hepatic shunt (a direct connection between one or several intrahepatic portal veins and one or several hepatic veins). Spontaneous closure of those porto-hepatic shunts is expected in most cases during the first months of life. Congenital portosystemic shunts can consist in a communication between the main portal vein (MPV) and the inferior vena cava either at the beginning or at the end part of the MPV.
Another form is the persistence of a malformative ductus venosus between the left portal vein and the left hepatic vein. Finally, congenital portosystemic shunts can consist of communications between any afferent vein to the MPV (mesenteric, splenic veins…) and any afferent vein to the IVC (renal, iliac veins…) leading to complete or partial functional hypoplasia of the MPV. Those are usually called in the literature Abernethy malformations or even congenital absence of the MPV. Closure of congenital portosystemic shunts allows the restoration of the portal flow to the liver and the correction and prevention of most complications. The main fear when performing closure of the CPSS is the occurrence of portal hypertension, especially in forms with extreme hypoplasia of the MPV and/or in association with severe cardiac disorders or pulmonary hypertension.
Angiographic preoperative evaluation with direct portography and occlusion test of the CPSS is of utmost importance: firstly to evaluate the exact anatomy of the portal system, especially the visualization of hypoplastic veins that can be missed by non-invasive imaging technics, and secondly to measure the portal pressure during occlusion in order to evaluate the feasibility of closure and the potential need for multiple steps closure when the portal pressure is too high during the occlusion-test.
Depending on anatomy, the portal pressure gradient during the occlusion test, and the local IR and surgical resources, closure of the congenital portosystemic shunts will be performed in one or two steps, surgically or with endovascular techniques. Multiple types of devices and techniques can be used for endovascular closure. Per- and post-operative anticoagulation is very important to prevent thrombosis of the portal system before the effective restoration of the portal flow to the liver the following days after partial or complete closure of the malformation.