How can a abdominal aortic aneurysm (AAA) cause hematuria?

This is rare, but here's how hematuria can occur ...

AAA ruptures into the inferior vena cava or one of the iliac veins producing an aortocaval or aortoiliac fistula. This causes hematuria secondary to intravesicular venous hypertension. Patients with this type of fistula may also present with lower extremity edema, high-output congestive heart failure, and a continuous abdominal bruit.


Source

Townsend: Sabiston Textbook of Surgery, 18th ed.