Arachnoid granulations are incidentally discovered cystic structures within the cranial venous sinuses. It is important to be aware of these lesions to avoid mistaking them with venous sinus 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. The affected venous sinus is smoothly narrowed and pear otherwise normal. Arachnoid granulations larger than 10 mm are called giant arachnoid granulation and can sometimes show atypical signal intensity with brighter T1 signal and incomplete suppression on FLAIR.