Table 2. Summary of different types of endoleaks with respective definitions and treatment modalities when repair is indicated.

Type	Mechanism	Therapy
I	Sealing failure at one of the attachment sites of the graft to the vessel. Ia: proximal leak; Ib: distal leak	Endovascular repair
II	Retrograde flow through collateral vessels into the perigraft space	Observation vs. endovascular repair
III	Device failure due to dysfunction of the components of a modular graft (IIIa) or in the fabric of the graft (IIIb)	Endovascular repair (very rare)
IV	Passage of blood or fluid into the aneurysmal sac as a result of graft porosity	Endovascular repair (very rare)
V	Continued aneurysm sac expansion without a demonstrable leak by an imaging modality	Observation vs. endovascular repair