An endoleak is a complication that occurs after an Endovascular Aneurysm Repair (EVAR). EVAR uses a stent graft—a fabric-covered metal tube—to create a new pathway for blood flow within the aorta. The graft is positioned to bypass the weakened, ballooning section of the artery, called an aneurysm, isolating it from high-pressure circulation. An endoleak is the persistence or recurrence of blood flow into this supposedly isolated aneurysm sac, outside the intended channel of the stent graft. This indicates the repair has not fully excluded the aneurysm from circulation. Endoleaks are classified based on the source of the persistent blood flow, which determines the potential danger and the appropriate course of action.
Why Endoleaks Require Attention
The main objective of EVAR is to depressurize the aneurysm sac to prevent its continued enlargement and eventual rupture. A successful repair causes the pressure within the sac to drop significantly, allowing the aneurysm to stabilize or shrink. An endoleak defeats this purpose by reintroducing blood flow and pressure into the isolated sac. This sac pressurization means the aneurysm wall is once again subjected to arterial pressure. Sustained pressure can lead to the continued growth of the aneurysm, retaining the initial risk of rupture that EVAR was meant to eliminate. The risk associated with an endoleak is directly related to the volume and pressure of the blood re-entering the sac.
The Five Categories of Endoleaks
Endoleaks are categorized into five types based on the origin of the blood flow, which helps determine the urgency of intervention. The most concerning types involve a direct connection to the main arterial pressure, leading to high-flow, high-pressure situations.
Type I Endoleak
A Type I endoleak occurs when the seal fails at the attachment site between the stent graft and the artery wall. This failure can happen at the upper (proximal) or lower (distal) ends of the graft, allowing blood to flow around the device and into the aneurysm sac. Since the leak comes directly from the aorta, the blood flow is at full systemic arterial pressure. Type I endoleaks are serious and require prompt re-intervention to prevent aneurysm expansion and rupture.
Type II Endoleak
Type II endoleaks are the most frequently observed category. They are caused by blood flowing backward into the sac from small side vessels, such as lumbar or inferior mesenteric arteries, which branched off the aorta but were not covered by the stent graft. This retrograde flow fills the aneurysm sac, but the blood is usually at a lower pressure compared to a Type I leak. Many Type II endoleaks resolve spontaneously and are often managed with observation if the aneurysm sac remains stable in size.
Type III Endoleak
A Type III endoleak involves a defect in the stent graft itself, allowing blood to flow directly through the device and into the sac. The defect may be a tear in the fabric or a separation where two modular components of the graft overlap. Similar to Type I, this leak reintroduces blood at high pressure into the aneurysm sac. The failure of the device’s integrity makes this a high-risk complication requiring urgent repair.
Type IV Endoleak
Type IV endoleaks are rare and relate to the porosity of the graft material. They represent blood seeping through the fabric of the stent graft, typically occurring immediately after the procedure. This type is often associated with a temporary condition, such as when a patient is fully anticoagulated during surgery. Modern graft materials have made this leak less common, and it often resolves once the patient’s blood clotting ability returns to normal.
Type V Endoleak
A Type V endoleak is a diagnosis of exclusion, often referred to as endotension. This occurs when the aneurysm sac continues to expand over time, yet no identifiable leak source can be found using standard imaging techniques. It is theorized that expansion is due to persistent, unmeasurable pressure transmission through the device or the thrombus within the sac. The continued growth of the aneurysm sac indicates a failure of the repair and warrants consideration for re-intervention.
Detection and Management
Regular monitoring is a lifelong necessity for all patients who have undergone EVAR to detect endoleaks early, often before symptoms develop. The standard post-procedure surveillance protocol involves using imaging tools to visualize the stent graft and the surrounding aneurysm sac.
Detection Methods
The primary diagnostic method is Computed Tomography Angiography (CTA), which uses contrast dye to highlight blood flow within the aorta and the sac. CTA is effective at identifying the presence and type of endoleak, as well as tracking changes in aneurysm sac size. Duplex Ultrasound is another non-invasive tool frequently used. It can detect blood flow within the sac and avoids the use of radiation and contrast agents in follow-up.
Management Strategies
The management strategy for an endoleak is determined by its type and the behavior of the aneurysm sac. Low-risk leaks, most commonly Type II, may be treated with surveillance if the aneurysm sac size is not increasing. The medical team watches the leak over several months to see if it seals off spontaneously, as many Type II leaks do.
If the aneurysm sac continues to expand, or if a high-risk leak (Type I or III) is detected, intervention is necessary. Minimally invasive methods, such as embolization, are often the first line of treatment. Embolization uses a catheter to deliver materials like coils or glue to block the source of the blood flow. For Type I or III leaks, secondary endovascular procedures may involve placing extension cuffs or balloons to reinforce the seal or repair the graft defect. If endovascular techniques fail or are unsuitable, the patient may require conversion to open surgical repair.