A young pt with recurrent episodes of TIA advised MR Angiography of neck along with Brain.
Non contrast 2D TOF MRA performed, a MIP image of neck demonstrating of left carotid bifurcation and a row axial image at the level of the ICA origin.
A focal notching in ICA at its origin appears to be:
2. External compression.
Answer: it’s an artifact, due to turbulence of flow at the bifurcation as axial sections of contrast enhanced CT Angiography of same patient at the same level are normal.
RE CIRCULATION FLOW ARTIFACT on 2 D TOF Non contrast MRA
Carotid bulb is a normal focal expansion of cervical ICA at its origin is patent and relatively prominent in young patient. Again due to vigorous flow there is formation of an eddy circulation in bulb with reversal of flow. This reversed flow leads to diminished signal on 2D TOF MRA because of the linked saturation band that suppresses all caudal flow, regardless of its nature.
This problem can be obviated by use of contrast during MR Angiography as in contrast enhanced MRA study, flow related signal by contrast is insensitive to direction of flow and demonstrates the normal contour of the carotid bulb.
Reference: Practical MR Physics and case file of MR artifacts and pitfalls, Alexander C. Mamourian, MD