Giant arachnoid granulation

Case Discussion

Arachnoid granulations are incidentally discovered cystic structures within the cranial venous sinuses. The transverse sinus is a common location. They appear as a filling defect in dural venous sinuses following CSF signals, which can be mistaken for dural venous thrombosis. A sinus thrombus typically displays a bright T1 signal rather than a low T1 fluid signal and will lack the smooth cystic outlines of arachnoid granulation.

Arachnoid granulations larger than 10 mm are called giant arachnoid granulation and can sometimes show atypical signal intensity like brighter T1 signal and incomplete suppression on FLAIR.