Section Editor: Sandy Cheng-Yu Chen, M.D.
Taipei Medical University Hospital, Taipei, Taiwan
Figure Caption
An arachnoid granulation (AG) is an arachnoid protrusion into venous sinuses through dural defects. AG is often seen at the parasagittal locations, over the parietal regions and posterior fossa. On MRI, AG often presents as an impression on the inner table in a typical location, with signal intensity parallel to CSF (arrows in A and B). Giant AGs (those greater than 1 cm) are uncommon anatomic variants, and may cause expansion of the diploic spaces (arrows in C). It can be misdiagnosed as an osteolytic neoplasm. Fat-saturated T1WI with contrast injection is indicated when the diagnosis is doubtful.