In vascular imaging, an intimal flap is best described as?

• A. Flap of intima that divides the true and false lumen in arterial dissection
• B. Atherosclerotic plaque
• C. Intraluminal clot
• D. Perforation in the vessel wall

Answer: (B)

The intimal flap is a flap of the tunica intima that tears away and forms the boundary between the true lumen and a false lumen in arterial dissection. Blood enters the vessel wall through a tear in the intima, creating a parallel channel (the false lumen) alongside the original channel (the true lumen). The flap itself is this loose sheet of intimal tissue that can move with pulsatile flow and may be seen as a linear, membrane-like structure separating two lumens on imaging.

On ultrasound, you may see two lumens with a mobile, echogenic membrane between them and different flow patterns in each lumen. On CT or MR angiography, a double lumen can be seen with a thin linear flap delineating the true and false channels.

This is distinct from an atherosclerotic plaque, which is a thickening and buildup within the intimal layer that narrows the lumen rather than creating two separate channels. A thrombus is a clot within the lumen, not a separating membrane, and perforation is a hole through the vessel wall causing outflow or extravascular leakage, not a dissection flap.