Fig 4.

A 34-year-old man with headache. Sagittal early-phase postcontrast T1WI reveals an arachnoid cyst at the septum pellicidum (A). Early-phase postcontrast T1WI shows passage of the intrathecally administered contrast to the fourth ventricle (arrow) and basal cisterns, whereas there is no contrast in the arachnoid cyst (A). Coronal (B) and axial (C) late-phase postcontrast images show passage of the contrast to the lateral ventricles (arrow in B), but not to the arachnoid cyst. Imaging findings are consistent with a non-communicating arachnoid cyst.