Which of the following is NOT one of the four aneurysm types?

• A. Fusiform
• B. Saccular
• C. Dissection
• D. True aneurysm

Answer: (D)

Understanding how aneurysms are categorized usually relies on two ideas: what the wall is doing and what the shape looks like. In many exam frameworks, the four commonly listed categories are fusiform, saccular, dissecting, and pseudoaneurysm. Fusiform and saccular describe shapes of aneurysms that involve all three layers of the vessel wall (true aneurysms). A pseudoaneurysm, or false aneurysm, is a contained rupture with surrounding tissue forming the sac. A dissecting aneurysm is a tear in the wall that creates a separate false lumen. Because true aneurysm is a description of wall involvement rather than a distinct shape category, it isn’t counted as one of the four types. That’s why true aneurysm is not considered a separate type in this context.