Three lines are drawn between the supraclinoid ICA and intracavernous ICA on coronal MRI imaging.
- medial tangent
- intercarotid line
- lateral tangent
These lines are used to define 4 grades of tumour invasion:
- grade 0 = medial to medial tangent
- grade 1 = tumour extends to space between the medial tangent and the intercarotid line
- grade 2 = tumour extends to space between the intercarotid line and the lateral tangent
- grade 3 = tumour extends lateral to the lateral tangent
- 3A = above the intracavernous ICA into the superior cavernous sinus compartment
- 3B = below the intracavernous ICA into the inferior cavernous sinus compartment
- grade 4 = complete encasement of intracavernous ICA