Which condition is characterized by the abnormal connection between arteries and veins without intervening capillaries?

The condition characterized by an abnormal connection between arteries and veins without intervening capillaries is an arteriovenous malformation (AVM). AVMs are congenital vascular anomalies where arterial blood flows directly into the venous system, bypassing the capillary network. This direct connection can lead to various complications, including increased blood flow and pressure in the veins, which can cause venous hypertrophy and potentially serious health issues.

In contrast, a fistula typically refers to an artificially created connection for medical purposes, often used in dialysis, between an artery and a vein, and is not necessarily congenital. An aneurysm involves the abnormal enlargement of a blood vessel due to weakness in the vessel wall and does not describe a direct connection between arteries and veins. Thrombosis refers to the formation of a blood clot within a blood vessel, which obstructs blood flow, but again does not imply an abnormal connection between arterial and venous systems. Therefore, arteriovenous malformation is the most accurate choice for this description.