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FIG 2. Case 2: Agenesis of the left ICA.
A, Source image from a 3D time-of-flight MR angiogram reveals absence of flow-related signal within the left petrous ICA (arrow).
B, Compressed view from the MR angiogram displays absence of flow-related signal intensity within the left ICA with collateral supply to the left hemisphere through a patent ACOM. Normal flow is present within the right ICA (arrowhead). Focal loss of flow-related signal intensity within the A1 segment of the right ACA (arrow) represents a clinically insignificant stenosis.
C, Axial CT scan of the skull base shows absence of the left carotid canal and a normally developed right carotid canal (arrow).
D, Collateral supply to the left cerebral hemisphere is provided through a patent ACOM, as demonstrated on the frontal view from the right carotid arteriogram. Stenosis of the A1 segment of the right ACA is revealed again (arrow).
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