text: The exact pathogenesis of<unk>  is unknown. It has been proposed that chronic obstruction of submucosal veins coupled with the effect of aging, ultimately lead to the formation of small arterio-venous collaterals. Angiogenic factors have also been found to play a role in the development of<unk> .
option_0: Angiodysplasia pathophysiology
option_1: Angiodysplasia risk factors
option_2: Atherosclerosis pathophysiology
option_3: Varicose veins pathophysiology
option_4: Thrombosis pathophysiology
option_5: Gastrointestinal varices pathophysiology
option_6: Portal vein thrombosis pathophysiology
option_7: Lower gastrointestinal bleeding pathophysiology