The ductus venosus (DV) is an embryonic vascular structure. In utero, DV connects the umbilical vein to IVC, allowing a portion of the oxygenated umbilical vein blood to bypass the liver and return to the heart, and spontaneous closure begins immediately after birth and complete functional closure usually occurs by about 18 days of age[6, 7]. However, closure of DV may not happen after birth because of poorly developed intrahepatic portal system and lead to PDV. PDV is more common in boys[4, 9], with a male to female ratio of 7:2 in this study. PDV was classified as a type of intrahepatic portosystemic shunt (PSS). PSS leads to portal venous blood bypassing the liver and directly entering the systemic circulation, resulting in decreased hepatic blood flow, increasing blood volume and toxic substances in the systemic circulation.
1. Clinical symptoms and laboratory tests
The clinical presentations of PDV were highly diverse[10-13]. In this study, the initial symptoms and signs were varied, but jaundice and respiratory symptoms were the most common. In the younger patients, jaundice was often the initial presentation, while in the older patients, repeated pulmonary inflammation was more common. Previous reports suggest PDV is a very rare cause of cholestatic jaundice. Symptoms of patients with PDV can appear at different ages, which can be severe in infancy or initially asymptomatic and develop slowly with age. The severity of symptoms is related to PDV diameter, but it does not correspond to PDV diameter, and depends on the individual.
Hepatic dysfunction secondary to PDV has been reported previously[14,15]. This study showed that 89% (8/9) of the cases had hepatic dysfunction. Hepatic dysfunction was an important initial presentation of PDV and may be secondary to reduction of blood flow in portal vein which deprives hepatocytes of nutrients and cause hepatic dysfunction including protein synthesis. Hyperammonemia can be caused by hepatocellular insufficiency or abnormal shunting of portal blood from the intestine directly into the systemic circulation, and hepatic encephalopathy occurred with hyperammonemia. The incidence of hyperammonemia in patients with PDV has been reported to be high. In a study involving 8 patients with PDV, the incidence of hyperammonemia was 100%. Hyperammonemia was detected in only 2(22%) cases in this study, and the serum ammonia concentrations of 4 cases with hepatic encephalopathy were within the normal range. Hypoxemia, hyperbilirubinemia and coagulation dysfunction associated with PDV have been reported previously[4,9,17]. In this study, the incidence of hypoxemia was 56%, hyperbilirubinemia was 78%, and coagulation dysfunction was 67%. Few reports of myocardial enzyme abnormalities and renal dysfunction secondary to PDV have been reported. In this study, significant abnormalities in myocardial enzymes were detected in 4(44%) cases. All of these 4 cases had a relatively larger PDV diameter(7.0mm-14.5mm), we believed that PDV significantly increased the blood volume returning to heart, increased the ventricular load and led to myocardial damage. Renal dysfunction was detected in case 1, case2 and case7. The imaging findings of case1 and case2 were abnormal, while case7 were normal. Contrast-enhanced CT showed the MPV, splenic vein and superior mesenteric vein were small and renal enhancement was significantly reduced in case 1. Therefore, we suggested that renal dysfunction may be secondary to PDV.
2. Imaging findings
Imaging examinations can make an accurate diagnosis based on the specific anatomic position of PDV. The direct imaging sign of PDV was a vascular structure from the anterior inferior to the posterior connecting LPV to IVC, running in the depth of the Arantius sulcus. PDV can be mistaken for hepatic veins if PDV diameter was close to that of hepatic veins on CT images, however, PDV communicates with LPV and in the early stage of portal vein, its density was higher than that of hepatic vein, which can be distinguished. It is important to evaluate the secondary imaging changes caused by PDV. PDV can lead to an increase of blood volume returning to right heart and then into the pulmonary artery, causing dilation of the right heart and pulmonary artery. All our cases had dilatation of right atrium, right ventricle and pulmonary artery. These signs were not specific for the diagnosis of PDV, but may be the first to be detected, since the initial presentation of patients with PDV were often respiratory symptoms and the chest imaging examination is performed first. In fact, in several cases of this study, the dilatation of pulmonary artery was first observed, followed by further examinations to confirm PDV. Case7 was admitted for several times for cough, and chest CT revealed obvious dilatation of right heart and pulmonary artery for unknown reasons, but abdominal examination was not performed, leading to missed diagnosis for many times. So PDV should be considered as a possible cause in the presence of unexplained dilatation of right heart and pulmonary artery. PDV was previously reported to coexist with hypoplasia of the intrahepatic portal venous system[4,14]. Dilated LPV and atrophic RPV were shown in all cases in this study. We speculated that PDV increased the blood flow of LPV, while decreased of RPV, leading to the dilatation of LPV and the dysplasia of RPV. This sign was rare observed in other types of portosystemic shunt, and it was a relatively characteristic indirect manifestation of PDV, which was of great value in suggesting PDV. Dysplasia of RPV may result in decreased blood flow to the right lobe of the liver, as manifested by decreased perfusion on CTA images. Hypoperfusion in the right lobe of the liver was observed in 3 cases at the portal phase in this study. In addition, enlargement of the liver and spleen was common, and the enlargement of the liver may be manifested as whole liver or left lobe.
3. Complications and coexistent malformations
Complications of portosystemic shunt depends on shunt ratio and on aging. When the shunt ratio is small, there may be asymptomatic, while the shunt ratio is large, it can lead to multiple systemic symptoms, such as pulmonary hypertension, hepatopulmonary syndrome, high-discharge heart failure, gastrointestinal bleeding, membranous proliferative glomerulonephritis, and hepatic encephalopathy [10,18,19]. Hepatic encephalopathy due to cerebral effects of circulating toxins, which normally undergo first pass metabolism in the liver, is a critical problem in patients with PDV. The age of onset of encephalopathy is variable and partially related to the volume and duration of the shunt. In the previous reports, when the shunt ratio is less than 30%, symptoms associated with portosystemic shunt may not develop throughout the lifetime of the individual. When the shunt ratio exceeds 30%, hepatic encephalopathy could develop at any time. When the shunt ratio exceeds 60%, the risk of hepatic encephalopathy is increased. In this study, 4 cases were confirmed with hepatic encephalopathy by brain MRI. Unfortunately, the shunt ratio was not measured, but we found that the diameter of PDV was larger in these 4 cases, with the smallest diameter of 9.5mm, at the same time, the 4 cases were more older, with the minimum age being 1.6 years. It is important to note that although hepatic encephalopathy is present, there may be no neurological symptoms or mild symptoms. 2 patients in this study had no neurological symptoms, although brain MRI suggested hepatic encephalopathy. Therefore, when the diameter of PDV is larger and the patients are older, regardless of whether they have neurological symptoms, we suggested that brain MRI should be performed to detect hepatic encephalopathy. In order to prevent these complications, shunts should be closed using endovascular or surgical methods, although spontaneous closure of portosystemic shunt including PDV may be expected to occur after 1‐2 years.
Patients with PDV may be accompanied by other deformities . In this study, 78% (7/9) of the cases were combined with other malformations involved multiple systems, including congenital heart disease (CHD), vascular abnormalities, genital deformity and schizencephaly. The most common coexistent malformations were CHD and vascular abnormalities, with 5 and 6 cases respectively in this study. Of the 5 cases combined CHD, 4 cases were from the younger age group(16d-1.6y).The most common types of CHD associated with PDV were ASD and PDA. There is a recognized association between extrahepatic shunts and CHD . We believed that PDV is also associated with CHD. A review of the literatures showed that up to 25% of patients with PDV had CHD. All of the cases in this study had dilation of the right atrium and right ventricle, so we speculated that PDV increased the blood volume returning to right heart, increased the pressure of right heart and pulmonary artery, thereby delayed or impeded the closure of ASD and PDA.
In conclusion, PDV was a rare vascular malformation that can lead to multi-system lesions. The clinical symptoms, signs and laboratory findings were diverse. The diagnosis of PDV mainly depends on imaging examinations, and it is important to evaluate the secondary imaging changes. Complications and coexistent malformations were common, so we need to prevent omissions during the imaging evaluations.