Extra-hepatic portal vein aneurysm in a long-term liver transplant recipient

A 42-year-old female patient with a history of primary sclerosing cholangitis had been submitted to liver transplantation 32 years prior. The patient had been followed elsewhere and had no imaging examinations in her possession. A routine abdominal ultrasound was ordered by the referring physician.

Abdominal ultrasound was performed and revealed normal liver measurements and parenchymal echogenicity, without evidence of focal lesions or fatty infiltration. The pancreatic head and body were unremarkable.
The vascular structures of the liver pedicle were identified as well as its site of anastomosis. Downstream to the portal vein anastomosis, there was a focal outpouching with 25 x 21mm in size (Figure 1) and a pedicle with a wide neck, consistent with an extra-hepatic portal vein aneurysm.
Doppler ultrasound documented that the aneurysm lumen was completely permeable with swirling flow, showing the yin-yang sign (Figures 2-3).  Median velocities at the portal vein trunk downstream of the aneurysm as well as at the right and left branches were normal (Figure 4). The resistive index and peak systolic velocities of the proper hepatic artery and its main branches were also within normal limits.

Vascular complications of liver grafts develop in approximately 7,2-15% of adult patients and are the most feared complications with a high risk of graft rejection and mortality [1]. Arterial lesions account for 5-10%, followed by portal (1-3%) and caval (<2%) [1]. The most common complications are reportedly hepatic artery or portal vein thrombosis, and they should be treated aggressively [2].
Portal vein aneurysms (PVA) are rare focal dilations of the portal venous system and may be of congenital or acquired nature [3], although the pathophysiological mechanisms remain unclear. Congenital causes are associated with incomplete regression of the right primitive distal vitelline vein [4], and patients may complain of abdominal pain. Secondary causes include liver disorders, portal hypertension, trauma or surgery [5]. In cases of long term liver transplant, there are some possible explanations for the portal vein aneurysm: stenosis of anastomosis, weakening of the vessel wall, changes in liver and portal vein over time, portal vein thrombosis, among others.
Most common locations include the portal vein trunk and splenomesenteric venous confluence for extra-hepatic PVAs [6] and portal vein bifurcations in the intra-hepatic system [7]. Although uncommon, PVAs may complicate with rupture, development of portosystemic shunts, rupture or compression of adjacent structures such as the biliary tree [8]. Portal vein thrombosis is seen in 20-30% of patients and is always associated with symptoms [7,9].
This case reports a post-liver transplantation extra-hepatic portal vein aneurysm that has only been previously described once in an adult [5] and in a child [8], according to our knowledge. The patient stated that a portal vein anomaly had been previously reported, but she had no documentation for comparison. Also, contrast-enhanced computed tomography (CT) could not be performed due to advanced chronic renal insufficiency.
Ultrasound is helpful to evaluate portal vein patency and blood flow inside the aneurysm [4]. Findings are similar to those found in a pseudoaneurysm which usually shows an anechoic ovoid structure with swirling flow and bidirectional flow in the lumen [10].
Contrast-enhanced CT and/or magnetic resonance imaging may be performed for size evaluation, neck dimensions, location and end-circulation, all of which are determinant features for treatment planning between minimally invasive procedures (embolization w/out stent placement) and surgery [10].
Management of portal vein aneurysms is still not well established [4] and is considered mainly in case of complication [9]. In asymptomatic patients, close follow up of aneurysm diameter and/or conservative treatment is recommended [4]. Medical therapy includes anticoagulation (to prevent thrombosis) and beta-blockers (to reduce venous pressure) [11].