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Institute of Clinical Medicine, University of Tsukuba, Tsukuba 305-8575, Japan
Sheporaitis and Freeny report unusual hepatic and portal veins located just beneath, and protruding from, the hepatic capsule [1]. They state that these veins are anatomic variants because most patients have no clinical or laboratory evidence of liver disease and no morphologic abnormalities of the liver on CT except four patients with liver cirrhosis. These unusual surface veins are not necessarily anatomic variants. The authors partly misinterpret their images and data, and neglect to cite some important papers.
First, the appearance of a widened, tortuous, protruding portal vein (fig. 3 of their paper) in the posterior segment of a cirrhotic patient is the same as the second most common intrahepatic portosystemic venous shunt described by Mori et al. and others [2, 3, 4]. I presume that this portal vein communicates with the inferior vena cava since I have never seen such a widened and tortuous intrahepat-ic portal vein in cases other than the intrahepatic portosystemic shunt described in the original article (Fig. 1) and in liver segment IV (Couinaud's segmental anatomy [5]). In segment IV, the paraumbilical vein, the most common location of an intrahepatic portosystemic shunt, emerges from the anteromedial portion of the liver near the falciform ligament [4]. Paraumbilical veins (recanalized umbilical vein is a myth) are located in the liver parenchyma (mostly segment IV), the fissure for the ligamentum teres hepatis, or both [4].
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Second, the authors also describe five patients with both hepatic and portal surface veins, whose diameters are described differently in their tables 1 and 2. Why do they divide shunt vessels into the portal vein and the hepatic vein? In the past, portohepatic venous shunts were reported in the normal liver (as well as in cirrhotic liver) and were almost always associated with aneurysmal dilatation [3]. With the introduction of color Doppler sonography, portohepatic venous shunts are more frequently encountered, and shunt vessels often show a curved tubular structure rather than focal aneurysmal dilatation.
Third, "protruding from" the hepatic capsule is one of the characteristics of "a new anatomic variant" vein, but how often and in what degree is this finding noted? On the other hand, focal dilatation is seen in one case with the hepatic surface vein (fig. 5 in [1]). How often is this finding along with tortuous vessels noted in the series of Sheporaitis and Freeny?
Fourth, indentation of the hepatic capsule is definitely or equivocally noted in the normal liver cases (figs. 4C and 2A in [1] respectively). The hepatic vessel may be seen in the peripheral or subcapsular location in the right lobe if the peripheral part of the parenchyma is collapsed [6]. Neither normal liver function nor clinical history can deny the focal collapse of the liver parenchyma of the old, insidious episode. Finally, although the difference in incidence between the cirrhosis group and the healthy group was statistically highly significant (p << 0.001), the authors drew a reverse conclusion on the basis of the number of incidences.
In conclusion, I congratulate the authors on the new description of the subcapsular location of the hepatic and portal vein depicted by CT; however, I hope that, on the basis of their current findings, the authors do not conclude that all such veins are normal variants. (At least patients with liver cirrhosis should be excluded.)
References
University of Washington School of Medicine, Seattle, WA 98195
We describe not portosystemic collaterals or shunts but an anatomic variant in the course of hepatic and portal veins [1]. This variant takes the veins to the surface of the liver on their way to their normal drainage or to their distribution within the various hepatic segments. Whether the case illustrated in figure 3 [1] also represents a shunt is not the subject of our paper; we are illustrating the surface location of the vein. As best we could determine, there was no portosystemic connection. In addition, some of the veins coursed to the liver surface via a fissure that has not been previously described (fig. 2, [1]). Thus, we believe that this is also a previously unrecognized anatomic variant. The papers referenced by Itai all refer to portosystemic collaterals, not to hepatic or portal vein location on the liver surface.
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