Which term refers to an aneurysm infected with bacteria?

• A. Berry aneurysm
• B. Mycotic aneurysm
• C. True aneurysm
• D. Fusiform aneurysm

Answer: (B)

An aneurysm that becomes infected is called a mycotic aneurysm. The word "mycotic" is historical and refers to infection rather than the organism itself, so these aneurysms are typically caused by bacteria (though fungi can rarely be involved). They often arise from septic emboli or bacteremia in settings like infective endocarditis, weakening the vessel wall and leading to dilation and possible rupture.

This differs from a berry aneurysm, which is a small, saccular outpouching of a cerebral artery at branch points (often in the circle of Willis) and is not defined by infection. A true aneurysm means dilation involving all three layers of the vessel wall (intima, media, and adventitia), whereas a fusiform aneurysm is a spindle-shaped dilation that encircles the entire circumference of a vessel segment, not a focal wall defect from infection.