Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Abdominal aortic aneurysm ?
    ### Response:
    Abdominal aortic aneurysms (AAAs) are aneurysms that occur in the part of the aorta that passes through the abdomen. They may occur at any age, but are most common in men between 50 and 80 years of age. Many people with an AAA have no symptoms, but some people have a pulsing sensation in the abdomen and/or pain in the back.
    