FIG 1. Case 1: Hypoplasia of the left ICA.

A, Source image from a 3D time-of-flight MR angiogram shows diminished flow-related signal intensity within the petrous portions of the left ICA (arrow).

B, Compressed image from the MR angiogram shows a tortuous, enlarged PCOM (arrow) extending forward to supply the left MCA. The left ACA is supplied via a patent ACOM (arrowhead). There is no perceivable flow-related signal intensity within the supraclinoid left ICA on the compressed image.

C, Axial image from a CT angiogram at the level of the petrous ICA shows hypoplasia of the left carotid canal (arrowhead).