The Rex Block, also known as the Meso-Rex Shunt or Meso-Rex Bypass, is a specialized surgical procedure. It is designed to correct blocked blood flow to the liver by creating a new pathway to bypass an obstruction. While the technique can be applied to adults, it is primarily used in pediatric patients with circulatory issues. The goal is to restore physiological blood flow, which alleviates the high blood pressure that develops in the abdominal veins.
The Underlying Condition Requiring the Procedure
The Rex Block procedure is most frequently used to treat Extrahepatic Portal Vein Obstruction (EHPVO). EHPVO is the most common cause of non-cirrhotic portal hypertension in children. The portal vein system carries nutrient-rich blood from the intestines, stomach, and spleen directly to the liver for processing. When the main trunk of the portal vein outside the liver becomes obstructed, usually by a blood clot (thrombosis), this normal flow is blocked.
This blockage creates abnormally high pressure within the portal system, known as portal hypertension. The body attempts to cope by developing a network of small collateral veins around the obstruction, sometimes called a cavernoma, but these are inefficient. This pressure causes the formation of enlarged, fragile veins, known as varices, particularly in the esophagus and stomach. These varices are prone to rupture, leading to severe gastrointestinal bleeding, which often prompts the need for surgical intervention.
How the Rex Shunt Works
The Meso-Rex Shunt re-establishes the normal, forward flow of blood directly into the liver, rather than just diverting pressure away. The procedure bypasses the clotted main portal vein by creating a new channel connecting the Superior Mesenteric Vein (SMV) to the intrahepatic left portal vein. The SMV is a large vein carrying blood from the intestines, making it the ideal inflow vessel for the new pathway.
The surgeon uses a vascular graft, often a segment of the patient’s own internal jugular vein, to bridge the gap. This graft connects the SMV, typically located behind the pancreas, to a specific channel within the liver called the Rex Recess. Routing the blood directly into the liver’s circulation normalizes the portal pressure. This restoration of proper blood flow, known as hepatopetal flow, reverses the effects of portal hypertension and allows varices to shrink.
The Surgical Procedure and Immediate Recovery
Preparation involves extensive pre-operative imaging, such as magnetic resonance angiography (MRA) and specialized ultrasounds, to confirm the precise anatomy. The surgery typically requires several hours and involves two primary sites. The first site is the abdomen for vascular reconstruction, and the second is usually the neck, used to harvest the patient’s own vein graft.
Once the shunt is constructed, the surgical team uses intraoperative Doppler ultrasound to confirm immediate patency and proper blood flow. Patients are then transferred to a pediatric intensive care unit (ICU) for close monitoring during the initial 24 to 48 hours. This time focuses on ensuring the shunt remains open and managing pain. The median postoperative length of stay is around 7 days, allowing for monitoring and transition to oral pain medication before discharge.
Long-Term Monitoring and Success Rates
The Meso-Rex Shunt is considered an effective treatment for EHPVO when performed in specialized centers. Long-term success rates, defined by the shunt remaining open and functional, can approach 90%. The restoration of normal blood flow into the liver typically results in significant improvement in the patient’s overall health, including the resolution of varices and associated gastrointestinal bleeding.
Lifelong follow-up is necessary to monitor shunt function, primarily through routine ultrasound examinations to check for patency. The most frequent long-term concern is delayed shunt thrombosis, or clotting, which can occur months or years after surgery. Patients may receive anti-coagulation therapy to help maintain the graft’s patency. Successful shunting eliminates the risk of variceal bleeding and can reverse related issues like an enlarged spleen and low platelet counts, improving quality of life for children.