Exclusion of the aneurysm sac is the main goal of the stent-graft treatment, and clinical success is defined by the "total exclusion" of the aneurysm. However, at times, failure of the stent-graft to totally exclude blood flow to the aneurysm sac may occur. As a matter of fact, endoleak is the major cause of complications, and thus failure in endoluminal treatment of AAA. When an endoleak occurs, it causes continued pressurization of the aneurysm sac and may leave the patient at risk of an AAA rupture.
Endoleak is defined as a persistent blood flow outside the lumen of the endoluminal graft but within an aneurysm sac or adjacent vascular segment being treated by the device. Endoleaks are due to incomplete sealing, or exclusion of the aneurysm sac, and thus cause reflux of blood flow into the sac. Four types of endoleaks are currently known and labeled.
Type I endoleak: blood flow into the aneurysm sac due to incomplete seal or ineffective seal at the end of the graft. This type of endoleak usually occurs in the early course of treatment, but may also occur later.
Type II endoleak: blood flow into the aneurysm sac due to opposing blood flow from collateral vessels. In some circumstance when there are two or more patent vessels a situation of inflow and outflow develops creating an actively blood flow within channel created within the aneurysm sac.
Type III endoleak: blood flow into the aneurysm sac due to inadequate or ineffective sealing of overlapping graft joints or rupture of the graft fabric. Again, this endoleak usually occur early after treatment, due to technical problems, or later due to device breakdown.
Type IV endoleak: blood flow into the aneurysm sac due to the porosity of the graft fabric, causing blood to pass through from the graft and into the aneurysm sac.
For the present, as a result of the major complications that endoleaks cause, one may conclude that endovascular treatment of AAA is still an evolving field. It is to be hoped in the future that better patient selection and improved devices will result from proper recording and appropriate analysis of clinical data.