Dilatation of an artery characterized by a focal outpouching of one arterial wall, most often caused by trauma or infection is called

• A. Saccular
• B. Fusiform
• C. Mycotic Aneurysm
• D. Pseudoaneurysm

Answer: (A)

A focal outpouching of one arterial wall is a saccular aneurysm. This shape is a true aneurysm where a localized segment of the vessel wall balloons out on one side, creating an opening or neck. It contrasts with a fusiform dilation, which enlarges the entire circumference of the vessel in a spindle-shaped way. The description also helps distinguish from a pseudoaneurysm, which is not a true aneurysm: it results from a breach in the vessel wall with blood contained by surrounding tissue, forming a hematoma that communicates with the artery rather than an outpouching of the wall itself. Mycotic aneurysm refers to an infection-driven true aneurysm and can be saccular in shape, but the hallmark descriptor here is the focal, pouch-like bulge of a single wall.