Giant arachnoid granulation

Case contributed by Mahmoud Yacout Alabd


Blurring of vision. MRI is done for assessment of possible cause.

Patient Data

Age: 35 years
Gender: Male

Incidentally discovered a large smooth cystic structure seen within the left transverse sinus with smooth attenuation of the sinus lumen. It reflects a high T2 and low T1 signal with no contrast enhancement. Contrast-enhanced MRV confirmed the intraluminal origin and cystic non-enhancing nature of this lesion and ruled out venous sinus thrombus. 

Bilateral maxillary retention cysts are incidentally noted.

The rest of the study is otherwise unremarkable.

Case Discussion

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.

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