A portosystemic shunt is an abnormal connection that routes blood around the liver instead of through it, dumping it directly into the body’s general circulation. The portal vein normally collects blood from the gut, spleen, and pancreas and delivers it to the liver for filtering and processing. When a shunt exists, some or all of that blood skips the liver entirely, which means toxins like ammonia build up in the bloodstream and the liver itself may not develop or function properly. These shunts can be present from birth or develop later in life, most commonly as a consequence of severe liver disease, and their treatment ranges from daily medication to catheter-based closure to organ transplantation.
How the Portal System Normally Works
The portal vein is the central vessel of the portal venous system, carrying blood from the gastrointestinal tract, gallbladder, pancreas, and spleen into the liver.1PubMed Central. All about portal vein: a pictorial display to anatomy, variants and physiopathology Once inside the liver, this blood passes through a vast network of tiny vessels called sinusoids, where liver cells extract nutrients, metabolize drugs, clear bacteria, and detoxify waste products like ammonia. The cleaned blood then drains into the hepatic veins and from there into the heart. This first-pass filtering is one of the liver’s most important jobs. A portosystemic shunt short-circuits that arrangement: blood flows from the portal system straight into a systemic vein without ever touching liver tissue. The consequences ripple outward to the brain, lungs, and heart.
Congenital Shunts
Some people are born with portosystemic shunts. These congenital shunts form during fetal development when the veins of the abdomen are still taking shape, and they are rare enough that many clinicians will see only a handful of cases in a career. The best-known variety is the Abernethy malformation, in which portomesenteric blood bypasses the liver and drains into a systemic vein through a partial or complete shunt.2PubMed Central. Abernethy malformation: A comprehensive review Abernethy malformations are classified into two types based on the anatomy of the connection.
In type 1, the portal vein essentially does not connect to the liver at all. All portal blood diverts into the systemic circulation through an end-to-side connection, and the liver receives no portal flow. This type is associated with other congenital abnormalities and has historically been recognized predominantly in girls. In type 2, some portal blood still reaches the liver through a side-to-side connection, so the liver retains partial portal supply. Type 2 shunts are rarer still and have been reported more often in boys.3Journal of Pediatric Surgery. Congenital extrahepatic portocaval shunts—The Abernethy Malformation The distinction between these two types matters enormously for treatment, as we will see.
Another congenital variant is a patent ductus venosus. During fetal life, the ductus venosus is a normal channel that shunts oxygenated blood from the umbilical vein past the liver and into the heart. It usually closes within the first days or weeks after birth. When it fails to close, portal blood continues to bypass the liver. In a case series of nine children with patent ductus venosus, most had evidence of liver dysfunction, abnormal clotting, and elevated bilirubin, and five had low blood oxygen levels.4PubMed Central. Clinical findings, diagnosis and therapy of patent ductus venosus in children: a case series These shunts can be subtle and sometimes go undiagnosed until laboratory screening catches high ammonia or bile acid levels in a newborn.
Congenital portosystemic shunts are rare developmental anomalies that carry a higher risk of benign and malignant liver tumors and, if untreated, can result in complications including encephalopathy and pulmonary hypertension.5PubMed Central. Congenital portosystemic venous shunt Some children with congenital shunts also have genetic syndromes. One reported case involved a newborn with 22q11.2 deletion syndrome whose shunt was discovered after newborn screening flagged high ammonia, bile acids, and galactose levels.6PubMed Central. Congenital portosystemic venous shunt associated with 22q11.2 deletion syndrome: a case report
Acquired Shunts and Cirrhosis
Far more common than congenital shunts are the ones that develop in adults with liver cirrhosis. When the liver becomes scarred and stiff, blood has trouble flowing through it, creating a traffic jam known as portal hypertension. The body responds by opening up alternative pathways, rerouting portal blood through smaller collateral veins that connect the portal system to the systemic circulation. These are called spontaneous portosystemic shunts, and they grow more prevalent as liver function deteriorates.7PubMed Central. Spontaneous porto-systemic shunts in liver cirrhosis: Clinical and therapeutical aspects
The common varieties include splenorenal shunts (connecting the splenic vein to the left renal vein), gastrorenal shunts (routing blood through dilated gastric veins to the renal vein), and dilated paraumbilical veins (reopened remnants of fetal vessels along the abdominal wall). These shunts are the body’s attempt to relieve pressure, but they come with their own problems. Diverting portal blood into the systemic circulation leads to what is called portosystemic shunt syndrome.8PubMed. Relevance of Spontaneous Portosystemic Shunts Detected with CT in Patients with Cirrhosis The shunts do not actually protect against the complications of cirrhosis; they just create additional ones.
Symptoms and Complications
The most recognizable complication of portosystemic shunting is hepatic encephalopathy, a brain disorder caused by the buildup of toxins, especially ammonia, that the liver would normally clear. The spectrum ranges widely. Some people have no obvious symptoms but perform poorly on specialized cognitive tests. Others experience confusion, personality changes, disorientation, slurred speech, and sleep-wake cycle disruption. In severe cases, encephalopathy can progress to coma. Portosystemic shunt syndrome encompasses everything from asymptomatic portal hypertension to recurrent and refractory hepatic encephalopathy, potentially progressing to hepatic failure in patients with cirrhosis and large shunts.9PubMed Central. Portosystemic shunts and refractory hepatic encephalopathy: patient selection and current options
Variceal bleeding is another serious consequence. As portal pressure rises, the collateral vessels that form, particularly in the esophagus and stomach, can become dangerously dilated. These varices have thin walls and high flow, making them vulnerable to rupture. Gastrorenal shunts, for example, are frequently found alongside dilated gastric varices and carry a significant risk of variceal bleeding.10Journal of Clinical and Translational Hepatology. Non-variceal Extrahepatic Portosystemic Shunts: A Review of Pathogenesis, Diagnosis, and Treatment
The lungs can suffer too. Portal hypertension is associated with two distinct pulmonary complications. Hepatopulmonary syndrome results from abnormal widening of tiny blood vessels in the lungs, which impairs oxygen exchange and causes breathlessness and low blood oxygen levels. Portopulmonary hypertension is the opposite problem in a sense: vasoconstriction and remodeling of the pulmonary arteries drive up pressure in the lung’s blood vessels, straining the right side of the heart.11PubMed Central. Hepatopulmonary Syndrome and Portopulmonary Hypertension: Current Status and Implications for Liver Transplantation Both conditions stem from vasoactive substances produced in the gut that the liver would normally clear but that reach the lungs unchecked when shunts are present.12PubMed Central. Portopulmonary hypertension and hepatopulmonary syndrome
Congenital shunts add another wrinkle: liver tumors. Because the liver does not receive its normal portal blood supply, it may develop abnormal nodules over time. These can range from benign growths like focal nodular hyperplasia and adenomas to hepatocellular carcinoma.13Journal of Clinical and Translational Hepatology. Congenital Portosystemic Shunts: A Review In the early literature on type 1 Abernethy malformations, five of the first thirteen reported cases had developed liver tumors.3Journal of Pediatric Surgery. Congenital extrahepatic portocaval shunts—The Abernethy Malformation That high rate underscores why even asymptomatic congenital shunts often need to be addressed.
How Shunts Are Diagnosed
Portosystemic shunts are often found incidentally during imaging for something else, or they are sought out when symptoms like unexplained encephalopathy or abnormal blood tests point toward the diagnosis. Ultrasound with Doppler is usually the first step because it can show the direction and speed of blood flow in the portal system without any radiation. In newborns and infants, ultrasound is particularly valuable because congenital shunts can appear as an obvious abnormal vessel connecting the portal vein to a systemic vein.
Contrast-enhanced CT scanning provides far more anatomical detail. CT angiography, performed with a delayed portal-phase image acquisition, can map the full course of collateral vessels and varices without needing a separate injection of contrast. Three-dimensional reconstruction of these scans enhances perception of the relationships between shunts and surrounding structures, which helps surgeons plan interventions.14PubMed. Three-dimensional CT angiography of spontaneous portosystemic shunts CT portography, which combines CT with arterial contrast injection, has proven more sensitive than conventional angiography for detecting portal vein anatomy, thrombosis, and subtle evidence of reversed portal flow.15PubMed. Hemodynamics of portal blood flow shown by CT portography. Work in progress
MRI is another option, especially in children and in patients who need repeated imaging, since it avoids radiation. Both CT and MRI can reliably distinguish type 1 from type 2 congenital shunts by showing whether any portal blood reaches the liver at all.16PubMed Central. Congenital Extrahepatic Portosystemic Shunts: Spectrum of Findings on Ultrasound, Computed Tomography, and Magnetic Resonance Imaging This classification drives treatment decisions. Catheter-based angiography, where a thin tube is threaded into the blood vessels and contrast is injected directly, remains the gold standard for detailed hemodynamic assessment and is often performed immediately before an interventional procedure.
Medical Management
When a portosystemic shunt is causing hepatic encephalopathy, medication is the front line. The two mainstays are lactulose and rifaximin. Lactulose is a synthetic sugar that passes undigested into the colon, where bacteria ferment it. This acidifies the colon’s contents, trapping ammonia and promoting its excretion in stool. It also acts as a laxative, which helps move ammonia out of the body faster.
Rifaximin is an antibiotic that works almost entirely in the gut, with minimal absorption into the bloodstream. It reduces the population of ammonia-producing bacteria. In a pivotal trial, rifaximin cut the risk of a hepatic encephalopathy episode by more than half over six months compared to placebo, with breakthrough episodes occurring in roughly 22% of the rifaximin group versus about 46% of the placebo group. Hospitalizations related to encephalopathy were also halved. Over 90% of patients in that trial were already taking lactulose.17PubMed. Rifaximin treatment in hepatic encephalopathy Current evidence supports both lactulose alone and the combination of lactulose plus rifaximin for long-term prevention of recurrent encephalopathy, with the combination providing added benefit.18PubMed Central. Long-term management of hepatic encephalopathy with lactulose and/or rifaximin: a review of the evidence
Medication also plays a role after TIPS placement, a therapeutic shunt discussed below. A meta-analysis found that giving prophylactic medication after TIPS significantly reduced the incidence of new hepatic encephalopathy, with rifaximin in particular lowering the risk, while lactulose alone did not reach a significant preventive effect in that specific post-TIPS context.19PubMed Central. Incidence and efficacy of strategies for preventing hepatic encephalopathy following transjugular intrahepatic portosystemic shunt: A meta-analysis Dietary changes also matter: moderating protein intake and avoiding constipation help keep ammonia levels in check, though severe protein restriction has fallen out of favor because malnutrition worsens liver disease.
Interventional and Catheter-Based Treatments
For congenital shunts and certain acquired shunts that are not responding to medication, interventional radiologists can close the abnormal connection from the inside. Using catheters threaded through the veins, they deploy devices like vascular plugs, coils, or occluders to block the shunt. One case report described a child whose congenital extrahepatic shunt was first managed by creating a temporary TIPS to reroute blood into the liver, then occluding the original shunt with an atrial septal defect occluder. In a second procedure, the temporary TIPS was embolized with a flow-reductor stent and a vascular plug. At one year, the patient’s liver nodules had shrunk and the shunt was closed.20PubMed Central. Multistage closure of a congenital extrahepatic portosystemic shunt Another case demonstrated coil embolization of a congenital shunt using twelve coils, after which ammonia and bile acid levels dropped and the patient remained symptom-free.21Journal of Clinical Imaging Science. Long-term follow-up and transcatheter embolization of extrahepatic congenital portosystemic shunt with shifting hemodynamics
These procedures require careful planning. Clinicians must confirm that the liver can handle the increased blood flow before shutting the shunt down. If the liver has never received portal blood (as in a type 1 Abernethy malformation), suddenly forcing blood through it could dangerously raise portal pressure. That is why trial occlusion, where the shunt is temporarily blocked while portal pressures are measured in real time, is often performed first.
TIPS as a Therapeutic Shunt
It may seem contradictory that shunts cause problems while a TIPS procedure deliberately creates one, but context is everything. A transjugular intrahepatic portosystemic shunt is an artificial channel made inside the liver by connecting the portal vein to a hepatic vein using a metal stent. Its purpose is to decompress dangerously high portal pressures in cirrhosis, preventing life-threatening variceal bleeding and managing refractory ascites. The technique has been refined over more than three decades since its serendipitous discovery in animal studies and has become one of the most important advances in the treatment of portal hypertension.22PubMed Central. The History of the Transjugular Intrahepatic Portosystemic Shunt
TIPS is not without trade-offs. By diverting portal blood through the stent, it reduces the liver’s blood supply, and studies have documented a decrease in total liver volume and an increase in disease severity scores in the months following the procedure. The main portal vein itself tends to dilate after TIPS placement. If the hepatic vein used for the shunt develops a clot, liver function scores can worsen more sharply than in patients whose hepatic vein remains open.23ScienceDirect (Clinical Imaging). Long term impact of transjugular intrahepatic portosystemic shunt (TIPS) creation on hepatic morphology The most common complication is new or worsened hepatic encephalopathy, which is why prophylactic rifaximin is increasingly considered after the procedure.
For patients who are candidates for liver transplantation, TIPS can serve as a bridge. Evidence suggests that TIPS placement does not worsen the surgical aspects of transplantation in terms of intraoperative bleeding, postoperative complications, or intensive care stay. It may actually improve a patient’s clinical condition before transplant and help preserve the technical feasibility of the surgery itself.24PubMed Central. Role of Transjugular Intrahepatic Portosystemic Shunt in the Liver Transplant Setting
Surgical Options
When catheter-based closure is not feasible or when a shunt is too large for devices alone, surgery enters the picture. For type 2 congenital shunts in children, surgical ligation (tying off the abnormal vessel) has shown good results. In a series of twelve children with type 2 Abernethy malformations, six underwent single-stage ligation, five needed a two-stage approach, and one had a partial ligation. Portal pressure rose after surgery in all cases, which is expected and actually desired, since it means blood is now being redirected through the liver.25PubMed. Surgical ligation of a portosystemic shunt for the treatment of type II Abernethy malformation in 12 children The staged approach allows the liver time to adjust to increasing blood flow, reducing the risk of acute portal hypertension.
For type 1 congenital shunts, where the portal vein does not connect to the liver at all, ligation is not an option because there is nowhere for the blood to go. In these patients, liver transplantation is the only definitive treatment. Transplantation replaces the diseased liver with one that has a normal vascular architecture, allowing portal blood to flow through the organ as it should.26Radiographics. Clinical and radiologic manifestations of congenital extrahepatic portosystemic shunts: a comprehensive review Surgical mesocaval shunts, where the surgeon creates a direct connection between the superior mesenteric vein and the inferior vena cava, are occasionally used in patients with refractory variceal bleeding who cannot receive a TIPS, as this approach can reduce portal pressures.27PubMed Central. Could there be light at the end of the tunnel? Mesocaval shunting for refractory esophageal varices in patients with contraindications to transjugular intrahepatic portosystemic shunt
Why Early Diagnosis Matters in Children
Congenital portosystemic shunts in children can be deceptively quiet. A child may grow normally for years while ammonia slowly damages the brain, or liver nodules develop silently. Newborn metabolic screening has become an unexpected ally in catching these shunts early: elevated galactose, ammonia, or bile acids on a routine heel-prick test can be the first clue. One infant with 22q11.2 deletion syndrome was flagged by newborn screening for high galactose and ammonia, leading to the discovery of an abnormal vessel running from the splenic vein to the left renal vein. After cardiac surgery at age one and transcatheter shunt occlusion at age two, the child’s laboratory values promptly normalized.6PubMed Central. Congenital portosystemic venous shunt associated with 22q11.2 deletion syndrome: a case report
The stakes of delayed diagnosis are real. Children with untreated congenital shunts face a growing risk of hepatic encephalopathy, pulmonary hypertension, and liver tumors as they age into adulthood.5PubMed Central. Congenital portosystemic venous shunt Some shunts close spontaneously in infancy, so a period of watchful waiting with serial imaging is reasonable in small, asymptomatic shunts. But if ammonia levels remain elevated, imaging shows the shunt persisting, or liver nodules begin to appear, intervention is warranted. The window for catheter-based closure or surgical ligation is best when the liver still has the capacity to regenerate and accept redirected portal flow, making early identification and regular monitoring the practical priorities for pediatric patients.
Living with a Portosystemic Shunt
For adults with cirrhosis-related shunts, management is usually lifelong unless a liver transplant removes the underlying disease. That means ongoing medication, regular blood work to track ammonia and liver function, and periodic imaging to check shunt size and look for new varices. Diet plays a supporting role: adequate protein to prevent muscle wasting, enough fiber and fluids to prevent constipation (which worsens ammonia absorption), and strict avoidance of alcohol if cirrhosis is the cause. Sedatives and certain pain medications that are metabolized by the liver often need to be avoided or used at reduced doses because the liver’s impaired filtering can allow drug levels to climb unpredictably.
Patients with successfully closed congenital shunts generally do well once the liver adapts to receiving portal blood. Liver nodules that developed before closure often shrink or stabilize after the shunt is closed, though they need ongoing surveillance. For those who undergo transplantation, the post-operative course follows the usual transplant pathway of lifelong immunosuppression and monitoring, with the shunt itself no longer a concern once the new liver is in place. Regardless of the shunt type, the pattern is the same: early recognition, precise imaging to classify the anatomy, and a treatment plan tailored to whether the liver can accept portal flow or needs to be replaced entirely.