In cerebral angiography, the dye is injected through –

On MRI, diagnostic confusion occasionally arises between arachnoid cysts and epidermoid cysts. The two masses may have similar characteristics on T1-weighted and T2-weighted images, and neither shows enhancement with gadolinium. However, arachnoid cysts follow CSF signals on all sequences, in particular on FLAIR sequence, in contradistinction to epidermoid cyst. Diffusion-weighted images (DWIs) allow easier differentiation of the two masses.