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Introduction
Collardeau-Frachon and Scoazec [1] summarized a role of communications between the left and right vitelline veins in development of the extrahepatic portal vein: (1) the inferior intervitelline anastomosis, (2) the middle intervitelline anastomosis, and (3) the superior or subhepatic anastomosis. To explain anomalous portal vein courses, many researchers postulated diagrams showing fetal communications between the left and right vitelline veins especially of the chronological changes [23]. All diagrams seemed to be considered on an assumption that the bilateral vitelline veins pass through the final hepatoduodenal ligament since the topographical relation with the common bile duct and hepatic artery were usually included in the diagrams. However, the present anomaly would suggest that a fate of the left vitelline vein is still obscure and it may be out of the final hepatoduodenal ligament (Fig. 1) [4].
Case Report
Materials and methods
The study was performed in accordance with the provisions of the Declaration of Helsinki 1995 (as revised in Edinburgh 2000). In the large collection kept at the Embryology Institute, Universidad Complutense, Madrid, we described a portal vein anomaly using a series of serial sagittal sections stained with hematoxylin and eosin (5 µm in thickness) of a fetus on week 9 (crown-rump length, 36 mm). The specimens in the collection were products of miscarriages and ectopic pregnancies managed at the Department of Obstetrics at the University. The study protocol was approved by the University Ethics Committee (No. B08/374).
Results
The most striking feature of the specimen was found in a thick vein crossing the lesser sac from a site near the celiac arterial origin to merge with the upper part of the ductus venosus (Fig. 2). Since a major tributary of this anomalous vein was the superior mesenteric vein, we regarded it as a portal vein anomaly. Notably, the anomalous portal vein separated and far distant from the hepatoduodenal ligament, stomach and duodenum by the large liver caudate lobe (Spiegel's lobe). The caudate lobe protruded leftward and occupied in the lesser sac.
During the course across the lesser sac (Fig. 2A-D), the vein provided a deep notch on the inferior aspect of the liver caudate lobe. In spite of the notch, the inferior vena cava was covered from the dorsal side by the liver parenchyma of the caudate lobe (Fig. 2H). The anomalous vein issued a branch when it took off the upper margin of the pancreatic body. The hepatoduodenal ligament contained (1) the hepatic artery, (2) the common bile duct and, at the right posterior margin of the ligament, and (3) a branch of the anomalous portal vein which communicated with the right branch of the portal vein at the hepatic hilum. Herein, the right branch of the portal vein was identified as a part from which the anterior and posterior sectorial trunks originated because the hilar bifurcation was absent. After merging with the branch, the right branch of the portal vein received a thin vein from the pancreatic head. The umbilical portion of the portal vein appeared normal and it received the umbilical vein and gave off the ductus venosus. We did not find any anomalies in the intrahepatic vascular configuration as well as the extrahepatic course of the bile duct. We were able to identify three major hepatic veins as well as segmental portal vein branches. The cardiac anatomy including the great vessels to and from the heart was also normal.
Discussion
In spite of no hilar bifurcation of the portal vein, we hypothesized the site of the usual bifurcation according to anatomy of the portal vein branches. Thus, the present anomalous portal vein was connected with not only the ductus venosus but also the right branch of the portal vein. The both connections seemed to be remnants of the left vitelline vein due to the venous course between the retropancreatic area and the left end of the hepatic hilum. Conversely, we considered that, in the usual development, the left vitelline vein is not included in the hepatoduodenal ligament but regresses to disappear. Yi et al. [5] and Dighe and Vaidya [6] reported double portal veins running through the hepatoduodenal ligament: one of the duplicated portal veins might correspond to the present anomalous portal vein or a remnant of the left vitelline vein. However, the peritoneal attachment to the vein or the configuration of gastric mesenteries were unclear in the reports.
In contrast to the adult morphology, the liver caudate lobe (Spiegel's lobe) was located closely to the abdominal esophagus. This was consistent with our previous description about the fetal liver caudate lobe extending into the lesser sac [7]. A deep notch (the so-called caudate notch) is often seen on the inferior surface of the adult caudate lobe [89]. The notch seems to be sculptured by the common hepatic artery or a hepatic artery variant coming from the left gastric artery [7]. However, the present anomaly suggested a rare possibility that an anomalous portal vein is likely to make a deep notch of the caudate lobe. The artery-derived notch is unlikely to correspond to a border between the left and right portal vein territories in the caudate lobe. Although the pathogenesis involves the portal vein development, the branching pattern seemed to be normal in the present anomaly (Fig. 3). Therefore, at any situation for providing the caudate notch, the left/right border in the caudate lobe is unlikely to correspond to the notch.
Consequently, in contrast to the usual diagram (Fig. 1), the present anomaly exhibited a possibility that the left vitelline vein does not accompany the hepatic artery and bile duct in the hepatoduodenal ligament but it is likely to run outside of the ligament. A re-examination of the portal vein development seemed to be needed especially for describing the topographical relation to mesenteries.
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