FIG 1. On axial (A) and coronal (B) T2-weighted images, hypoplasia of the right cerebellar hemisphere and absence of the inferior cerebellar vermis are present. Note that the abnormally dilated basilar artery with numerous small signal intensity void structures corresponds with the collateral networks at the prepontine cistern. On MR angiography (C, -D), both internal carotid arteries are not seen, and the distal portion of internal carotid arteries is reconstituted from the external carotid arteries.