Images from MR Angiography (MRA) with Time of Flight (ToF) source sequence on the left and reconstructed Maximum Intensity Projection (MIP) showing stenoses in the Internal Carotid Artery (ICA). This patient has a stent in the distal carotid artery that beginns in petrous and ends in cavernous segment. Presence of the stent can influence images of this ToF a non-contrast MRA. You can see stenosis (arrow). In such case I would recommend CTA. I would like to use this case for a short reminder of the terminology concerning ICA segments.
It is easier in CTA since we have reference anatomy points but just in case of the above MIP the typical curves can help. Here are the names of the Internal Carotid Artery Segments:
C1 = cervical
C2 = petrous
C3 = lacerum
C4 = cavernous
C5 = clinoidal
C6 = ophthalmic
C7 = communicating
Location of the markers corresponds with beginning of the segments (except for C1).
As we see our patient has stenosis in the C3 and C4 segments. Also note that there is hypoplastic A1 segment on the right (origin marked with arrowhead) as anatomic variant.
However when reporting the locations of stenosis I also like to give their descriptive names, not only numbers.
See also interesting publication from Medscape
Aneurysms of the Petrous Internal Carotid Artery: Anatomy
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