Duplication of the portal vein (DPV) is an extremely rare anatomical variation, with
only a few documented cases.[1] Understanding potential variations in portal venous anatomy is crucial for the early
detection of developmental anomalies, particularly during assessments for liver transplantation,
hepatic resection, and before catheter-based endovascular procedures. This knowledge
aids in treatment planning and helps minimize iatrogenic complications. We present
a case of incidentally discovered DPV.
A 42-year-old gentleman was being evaluated as a potential liver donor for his brother
who was suffering from end-stage liver disease. Physical examination and laboratory
tests were unremarkable. As part of the workup, he underwent a multiphasic contrast-enhanced
computed tomographic (CT) scan of the abdomen. The portal venous phase images showed
differential enhancement of the right and left lobes of the liver with two portal
veins (PVs) entering the porta along the hepatoduodenal ligament ([Fig. 1]). One of the PVs was seen as continuation of the superior mesenteric vein (SMV)
and coursed between the duodenum and pancreas to ascend to the porta hepatis and supply
predominantly the right lobe of the liver (referred to as “mesenteric PV” later in
the article). Another anastomotic branch originated from the SMV immediately caudal
to the uncinate process to join the splenic vein (SV) posterior to the neck of the
pancreas to form the other PV, which then coursed posterior to the pancreas and duodenum
to ascend to the porta and supply predominantly the left lobe of the liver (referred
to as “splenic PV” later). At least two separate anastomoses were also seen between
the two PVs within the liver parenchyma. Keeping in mind the complex portal venous
reconstruction that might be required during donor hepatectomy and graft implantation,
a multidisciplinary board decided against proceeding with transplant and another donor
was identified for workup.
Fig. 1 Coronal-oblique maximum intensity projection (MIP) computed tomography (CT) image
(A) demonstrating the “mesenteric portal vein” (solid arrow) and “splenic portal vein”
(dashed arrow) along with the splenic vein (arrowhead). Axial CT image (B) showing the differential enhancement of the left lobe of the liver supplied by the
splenic portal vein (asterisk).
The vitelline veins give rise to the portal venous system during liver development
between the 4th and 12th weeks of gestation.[2] The left and right vitelline veins pass through the septum transversum and enter
the sinus venosus, running cranially alongside the foregut. As this occurs, the liver
buds begin to form within the septum transversum, with the hepatic cords growing between
the vitelline circulation. This process divides the vitelline veins into three segments:
the proximal section becomes the hepatic vein, the intermediate section remains as
the liver's sinusoids, and the distal section ultimately forms the PV ([Fig. 2]).
Fig. 2 Schematic diagram of the crucial steps in the development of normal portal vein (I,
IIA, IIIA) and the likely deviations in our case (IIB, IIIB).
Subsequently, the distal portions of the right and left vitelline veins form three
transverse anastomoses around the foregut: the cranial ventral anastomosis, which
lies within the liver, and the middle dorsal and caudal ventral anastomoses ([Fig. 2I]). These anastomoses together create a caudal and cranial anastomotic ring around
the foregut. Meanwhile, the developing SMV and SV independently join the left vitelline
vein below the dorsal anastomosis ([Fig. 2IIA]). The right limb of the caudal ring, the caudal ventral anastomosis, and the left
limb of the cranial ring all undergo selective involution ([Fig. 2IIIA]). The PV stem forms from the persistence of a small segment of the left vitelline
vein, situated between the middle anastomosis and the entry points of the SMV and
SV, the middle dorsal anastomosis, and the right vitelline vein, which lies between
the cranial ventral and middle dorsal anastomoses.
In our case, DPV can be attributed to the persistence of the left vitelline vein cranial
to the dorsal anastomosis, with the SV joining at the usual point to form the “splenic
PV,” while the SMV joins the right vitelline vein to form the “mesenteric PV” ([Fig. 2IIB]). The splenic PV follows the typical postpancreatic, postduodenal course, whereas
the mesenteric PV follows the prepancreatic, postduodenal course. The caudal ventral
anastomosis is involuted, as evidenced by the absence of the preduodenal PV. The middle
dorsal anastomosis remained as the inferior extrahepatic anastomosis, located just
below the uncinate process, while the cranial ventral anastomosis persisted as the
superior intrahepatic anastomosis connecting the two PVs ([Fig. 2IIIB]). Notably, in the portal venous phase of the CT scan, there was differential enhancement
of the two portal systems and the two lobes of hepatic parenchyma, likely due to the
faster blood flow in the splenic PV, as suggested by Garnett et al.[3]
To the best of our knowledge, 14 cases of DPV have been reported.[4] Out of these, 11 cases can be classified as true DPV, where both PVs enter the liver
through the porta hepatis. In the remaining three cases, one PV entered via the porta
hepatis, while the other directly entered the hepatic parenchyma. In most cases, including
ours, the splenic PV followed the typical postpancreatic, postduodenal course. However,
the mesenteric PV followed either a preduodenal or a prepancreatic, postduodenal course,
with our case falling into the latter category.
DPV can be asymptomatic or associated with a range of complications, including abdominal
pain, dyspepsia, portal hypertension, and obstructive biliopathy.[4] Three reported cases of DPV observed differential geographical fatty infiltration
of the liver parenchyma, where the area spared from fat accumulation primarily received
blood flow from the mesenteric PV. Two of these cases developed portal hypertension,
one of which resulted in fatal gastrointestinal hemorrhage. The presumed cause in
these instances was stenosis of the anastomotic segments connecting the two PVs and
their abnormal course. In another case, compression of the common bile duct by the
venous fenestration of one of the PVs led to bile duct stenosis and biliary stones.[4]
Even when detected incidentally, as in our case, DPV has significant clinical implications
for both the surgeon and the interventional radiologist.[5] Due to the multiple intrahepatic connections between the two PVs, donor hepatectomy
involving either lobe could be challenging and may necessitate multiple porto-portal
anastomoses between the donor and the graft. For patients undergoing endovascular
hepatic procedures, a thorough understanding of the portal venous anatomy is essential
for the interventional radiologist to ensure the best possible outcome.
