FIG 4. Case 4: Aplasia of the left ICA.

A, Frontal view from a right CCA arteriogram shows collateral flow to the left ACA across a patent ACOM (arrow).

B, Frontal view from a left vertebral arteriogram displays collateral flow to the left MCA (arrow) via forward flow through a patent PCOM (arrowhead).

C, Axial CT scan through the skull base reveals a diminutive left carotid canal (arrow).