What Is a Liver Shunt in Humans? Causes & Symptoms

A liver shunt, known medically as a portosystemic shunt, is an abnormal blood vessel or pathway that diverts blood around the liver instead of through it. Normally, blood from your intestines flows into the liver via the portal vein so the liver can filter out toxins, metabolize nutrients, and process drugs before that blood reaches the rest of your body. When a shunt exists, some or all of that blood skips the liver entirely, allowing unfiltered substances like ammonia to circulate freely and accumulate in the brain and other organs. The term might be more familiar from veterinary medicine, where certain dog breeds are prone to congenital shunts, but liver shunts absolutely occur in people and can be congenital, acquired through disease, or even deliberately created as a medical procedure.

How a Liver Shunt Disrupts Normal Blood Flow

Your liver sits between two massive circulatory networks. The portal vein collects blood from your stomach, intestines, spleen, and pancreas and routes it through the liver’s filtering system. That blood then exits via the hepatic veins into the inferior vena cava, which carries it to the heart. A portosystemic shunt creates a shortcut between the portal vein system and the general (systemic) circulation, letting blood bypass the liver’s filtering and detoxification functions altogether.¹

The consequences of this bypass depend on how much blood avoids the liver. A small shunt might cause no noticeable symptoms for years. A large one can flood your bloodstream with ammonia and other waste products that normally get broken down during their first pass through the liver. This is where symptoms like confusion, fatigue, and personality changes come from, and why liver shunts can be surprisingly difficult to diagnose if nobody is looking for one.

Congenital Liver Shunts

Some people are born with a liver shunt. These congenital portosystemic shunts form during fetal development when the complex network of embryonic veins that eventually becomes the portal system and inferior vena cava fails to develop normally. In the embryo, there are temporary connections between the vitelline veins (which form the portal system) and the cardinal veins (which become the vena cava). These connections are supposed to close off as the fetus grows. When they persist, blood has a permanent detour around the liver from birth.²

The most dramatic version is the Abernethy malformation, where the portal vein either never forms at all or forms but has a large side branch draining directly into the vena cava. In the most severe form, all portal blood bypasses the liver completely, and the liver itself develops abnormally because it is deprived of the portal blood flow it needs. In less severe forms, the portal vein exists but an abnormal branch siphons off a portion of its flow. These congenital shunts are rare and sometimes go undetected until adulthood, particularly the smaller ones that cause only subtle symptoms.

Acquired Shunts From Liver Disease

Far more common than congenital shunts are the ones that develop as a consequence of chronic liver disease, especially cirrhosis. When the liver becomes scarred and stiff, blood has a harder time flowing through it. Pressure builds up in the portal vein, a condition called portal hypertension. As that pressure rises, the body responds the way water responds to a blocked pipe: it finds alternate routes. Existing tiny venous connections between the portal and systemic circulations, which normally carry negligible flow, get forced open and enlarge into significant shunt vessels.³

These acquired shunts can form in several locations. Some develop around the esophagus and stomach, which is why people with advanced liver disease sometimes develop esophageal varices (swollen veins in the esophagus that can bleed dangerously). Others form around the spleen, in the abdominal wall, or even within the liver tissue itself. Portal vein thrombosis, where a blood clot blocks the portal vein, can also trigger shunt formation even in people without cirrhosis. The body is resourceful at rerouting blood, but every new shunt means more unfiltered blood reaching the brain and other organs.

TIPS and Other Deliberately Created Shunts

Sometimes doctors create a liver shunt on purpose. The most common example is a transjugular intrahepatic portosystemic shunt, or TIPS. First described in 1969, the TIPS procedure uses a catheter threaded through the jugular vein in the neck and down to the liver, where a radiologist places a small metal stent connecting the portal vein to a hepatic vein inside the liver itself. This artificially created channel relieves the dangerous pressure buildup from portal hypertension.⁴

TIPS is primarily used when someone with cirrhosis develops life-threatening complications that don’t respond to medications: variceal bleeding that keeps recurring despite treatment, or refractory ascites (fluid buildup in the abdomen that won’t go away with diuretics).⁵ By lowering portal pressure, TIPS reduces the forces driving fluid into the abdomen and takes pressure off the swollen veins that cause bleeding. The trade-off is real, though: because a TIPS is literally a shunt, it carries the same risk of letting unfiltered blood reach the brain. Hepatic encephalopathy after TIPS placement is a recognized and fairly common complication.

How Ammonia Buildup Causes Symptoms

The single most important consequence of any liver shunt is what happens when ammonia and other gut-derived toxins reach the brain without being neutralized first. Under normal circumstances, your liver converts ammonia (produced by gut bacteria breaking down proteins) into urea, which your kidneys then excrete harmlessly. When a shunt lets ammonia bypass the liver, blood ammonia levels rise. The brain and muscles have a backup mechanism: an enzyme called glutamine synthetase that can convert ammonia to glutamine. The kidneys can then extract ammonia from glutamine and dump it into urine. But in chronic or severe cases, this backup system gets overwhelmed and cannot keep pace.⁶

The result is hepatic encephalopathy, a spectrum of brain dysfunction ranging from barely detectable cognitive slowing to full coma. In its mildest form, you might not even realize anything is wrong. In more advanced stages, the symptoms become impossible to miss.

Recognizing the Symptoms

Liver shunt symptoms tend to fall into a few categories. The most prominent are neurological and psychiatric, driven by ammonia toxicity to the brain. But shunts can also affect the lungs, the heart, and the liver tissue itself.

Neurological and cognitive symptoms include:

Confusion and disorientation: difficulty following conversations, getting lost in familiar places, or being unable to perform routine tasks
Daytime drowsiness: excessive sleepiness during the day even with adequate nighttime sleep, sometimes alternating with insomnia at night
Personality changes: irritability, apathy, or disinhibition that family members often notice before the patient does
Motor problems: a characteristic flapping tremor of the hands (called asterixis), slowed movements, slurred speech, or unsteady walking
Severe episodes: stupor or coma in advanced hepatic encephalopathy

A case report of a 75-year-old man illustrates how insidious these symptoms can be: he presented with five weeks of confusion, daytime sleepiness, and fatigue before imaging revealed an intrahepatic portosystemic shunt as the cause of his encephalopathy.⁷ Five weeks of vague symptoms before anyone found the underlying problem is not unusual, particularly in older adults where confusion has many potential explanations.

Beyond the brain, shunts can also affect the lungs. Hepatopulmonary syndrome occurs when abnormal blood vessel dilation in the lungs causes poor oxygen exchange, leading to shortness of breath that characteristically worsens when sitting or standing up. This has been reported in roughly a quarter of patients with chronic liver disease when thorough testing is performed, though estimates range widely.⁸ Heart failure and pulmonary hypertension are also possible downstream effects, though they tend to develop in more advanced or long-standing cases.

Liver Nodules and Tumor Risk

A less well-known consequence of portosystemic shunts is their effect on the liver tissue itself. When portal blood flow to the liver drops because it is being diverted elsewhere, the liver compensates by increasing its arterial blood supply. This shift in blood flow patterns can trigger the growth of abnormal nodules in the liver, ranging from benign focal nodular hyperplasia to hepatic adenomas and, in rare cases, hepatocellular carcinoma.⁹

The connection between increased arterial flow and liver nodule formation has been documented for decades. In one early report, a 13-year-old boy with a spontaneous intrahepatic shunt developed multiple liver cell adenomas containing areas of focal nodular hyperplasia, strongly suggesting that arterial overgrowth drove the nodule development.¹⁰ Some of these nodules, particularly a subtype of hepatic adenoma known as beta-catenin-activated adenoma, carry a real risk of transforming into liver cancer, which means patients with known congenital shunts need ongoing monitoring.¹¹

Why Liver Shunts Are Frequently Misdiagnosed

One of the most striking things about liver shunts, particularly congenital ones in people without obvious liver disease, is how often they get misdiagnosed as psychiatric or neurological conditions. A person who shows up at a clinic with progressive confusion, personality changes, or psychotic episodes is far more likely to be evaluated for dementia, depression, or a primary psychiatric disorder than for an abnormal blood vessel near their liver. In one review, researchers reported patients with portosystemic shunts who had been diagnosed with Parkinsonism, organic psychosis, recurrent delirium, and cognitive decline before anyone thought to check for a shunt.¹²

Some patients have been hospitalized in psychiatric institutions or geriatric care facilities for what turned out to be treatable encephalopathy from an unrecognized shunt.¹³ One patient with congenital intrahepatic shunts was initially misdiagnosed with a psychiatric disorder; imaging eventually revealed the true cause.¹⁴ The key red flag that should prompt a search for a shunt is unexplained encephalopathy in someone without an obvious cause, particularly when there is elevated blood ammonia. If you or a family member has persistent unexplained confusion and a blood ammonia test comes back high, a portosystemic shunt should be on the list of possibilities even in the absence of known liver disease.

How Liver Shunts Are Diagnosed

Finding a liver shunt usually involves imaging. Ultrasound with Doppler is often the first test because it is noninvasive and readily available. It can show the direction and speed of blood flow in the portal vein and sometimes directly visualize the abnormal vessel. However, ultrasound has limitations: it is highly operator-dependent and can miss smaller shunts or those in hard-to-see locations.

CT and MRI are both better at detecting spontaneous shunts and varices. In one comparison, CT and MRI each detected spontaneous shunts about 75% of the time, while ultrasound detected them only about 13% of the time. On the other hand, ultrasound and MRI were more sensitive than CT for determining which direction blood was flowing in the portal vein.¹⁵ In practice, doctors often use a combination: ultrasound for initial screening, followed by CT or MRI for a more detailed look. For monitoring shunts that have already been treated, CT angiography has shown strong accuracy in detecting structural abnormalities, correctly identifying about 97% of morphologic problems in one study.¹⁶

Beyond imaging, a blood ammonia level is a critical part of the workup. Elevated ammonia in the setting of neurological symptoms, with no other clear explanation, is often what first raises suspicion of a shunt. Conventional liver function tests may be normal, especially in congenital shunts where the liver tissue itself is healthy but underperfused.

Treatment Options

Treatment depends on whether the shunt is congenital, acquired from cirrhosis, or deliberately created. The approaches are quite different.

For congenital shunts, the goal is to close the abnormal vessel and restore normal portal blood flow to the liver. This can be done either surgically (tying off the shunt) or through minimally invasive catheter-based embolization, where a radiologist threads a catheter to the shunt and blocks it with coils or plugs. Endovascular techniques are generally considered the first choice because they involve shorter procedure times, less blood loss, and favorable outcomes. A study comparing the two approaches in patients with congenital extrahepatic shunts found that both surgical ligation and embolization were effective, with ammonia levels normalizing in all patients within six to twelve months. Embolization showed advantages in procedure time and blood loss, while surgery remained a better option for patients with short, wide shunts or high portal pressures.¹⁷

There are practical trade-offs between the two approaches. Catheter-based embolization using metal coils carries a small risk of coil migration, reported at roughly 0.3% to 6% in adults, and patients need follow-up imaging (usually annual abdominal X-rays) to monitor coil position. Surgical ligation avoids those concerns entirely but is a more invasive procedure.¹⁸

For acquired shunts associated with cirrhosis, the picture is more complicated because the underlying liver disease is the root problem. When large spontaneous shunts are causing recurrent hepatic encephalopathy that does not respond to medication, embolizing the shunt can make a real difference. A meta-analysis found that shunt embolization significantly reduced encephalopathy recurrence in patients with cirrhosis-related portosystemic shunts, cutting the odds by roughly 75%.¹⁹ However, this only works when a dominant shunt can be identified and safely blocked. In many patients with cirrhosis, multiple small collateral vessels exist, and blocking one may simply redirect flow to another.

In one dramatic long-term case, a patient developed severe, disabling encephalopathy twenty years after a surgical shunt had been placed for portal vein thrombosis. Closing that shunt restored portal blood flow to the liver via collateral veins, cleared the encephalopathy, and allowed a return to near-normal protein tolerance.²⁰

Managing Symptoms With Medication and Diet

Whether or not a shunt can be closed, controlling ammonia levels is central to managing symptoms. The first-line medication for hepatic encephalopathy has been lactulose for over fifty years. Lactulose works in a surprisingly elegant way: it acidifies the gut, converting ammonia into a form (ammonium) that cannot be reabsorbed through the intestinal wall. It also acts as a prebiotic, encouraging the growth of beneficial gut bacteria that do not produce ammonia, and its laxative effect physically removes nitrogenous compounds from the intestine before they can be absorbed.²¹

Rifaximin, a gut-targeted antibiotic that barely enters the bloodstream, is typically added on top of lactulose. It works by reshaping the gut microbiome, reducing the populations of bacteria that produce ammonia, and has been shown to reduce encephalopathy hospitalizations. Together, lactulose and rifaximin form the backbone of medical management.

Diet matters more than many patients realize. Current guidelines recommend a high-energy, high-protein diet with about 1.2 to 1.5 grams of protein per kilogram of body weight daily, distributed across small meals throughout the day with a late-night snack of complex carbohydrates. The old advice of restricting protein in hepatic encephalopathy has been largely abandoned, since protein restriction accelerates muscle wasting, which actually makes encephalopathy worse (muscle is one of the body’s backup systems for clearing ammonia). Shifting toward more vegetable-based protein can help, as vegetable protein diets increase dietary fiber, speed intestinal transit, and boost ammonia excretion in stool.

The Burden on Daily Life

Hepatic encephalopathy from portosystemic shunting takes a toll that extends well beyond the medical symptoms. In a study comparing patients with cirrhosis who had experienced hepatic encephalopathy to those who had not, the differences in daily functioning were stark. Among those with a history of encephalopathy, unemployment was dramatically higher (about 88% versus 19%), and financial difficulties were more prevalent as well. Caregiver burden also rose significantly: family members of encephalopathy patients reported higher stress and more disruption to their own lives.²²

Even in its milder forms, hepatic encephalopathy can impair driving ability, workplace performance, and the capacity to manage finances or medications independently. Patients often do not recognize the extent of their own impairment, which places an enormous responsibility on family members and caregivers both to notice changes and to help manage the daily regimen of medications, dietary adjustments, and medical appointments. The practical reality of living with a portosystemic shunt, especially one that cannot be fully corrected, involves not just treating acute episodes of confusion but restructuring daily life around prevention.

When Children Have Liver Shunts

Congenital portosystemic shunts in children present unique challenges. A shunt present from birth means the child’s liver has never received its full portal blood flow, which can affect liver development and function from the start. Children with congenital shunts sometimes come to attention through newborn screening (elevated galactosemia levels can be a clue), unexplained high ammonia in infancy, or the incidental discovery of liver nodules on imaging done for other reasons.

In pediatric patients, the decision of when and how to close a shunt is complicated by ongoing growth. Some small congenital shunts close spontaneously during the first years of life. For those that persist, the choice between catheter embolization and surgery must account for the fact that the child’s blood vessels will continue to grow, potentially altering the relationship between any implanted device and the surrounding anatomy. Monitoring after coil embolization is especially important in children, since there are essentially no long-term data on how coils behave as pediatric vascular structures mature over years and decades. Despite these uncertainties, early treatment is generally preferred to prevent the cumulative effects of ammonia toxicity on brain development, and both approaches have shown good results in normalizing ammonia and resolving symptoms.