47 yr old being investigated for extrapyramidal symptoms shows an appx 14 mm sized CSF signal intensity on loa sequences lesion in close proximity to left sigmoid sinus with no restricted diffusion/ blooming on SW suggesting Arachnoid granulation (pacchionian bodies)
Teaching points by Dr MGK Murthy, MRI Technologist: Mr Hari
1.Normal variants and can potentially produce CSF otorrhoea in a few cases and whether produce or occur as result of benign intracranial hypertension is debated . Possible internal stenosis of transverse sinus due to large arachnoid granulation playing a role in Idiopathic intracranial hypertension is a matter of scientific deliberations at present .
These increase in size , number with age and may calcify as well .
2. Are absent at birth and occur after fontanelle closure in areas of weaknesses of dura mater and hence could be regarded as developing form CSF pulsation at higher pressure through dural defects in to sinuses at lower pressure
3.Needs to be understood to avoid misinterpretation as extra axial/ parenchyma/ sinus diverticula/ calvarial(destructive) / dermoid cyst/ other aetiologies
4. Sizes are usually small, and can be unilateral, large ones referred to as Giant granulations
5. More common clustering the parasinusoidal blood lakes along side the Superior sagittal sinus
6. Are bulbous aggregates of fibro elastic tissue that are continuous with subarachnoid space. CSF circulates through these and enters venous system. Do increase in size and number with age.
Arachnoid granulations on MRI
4/ 5Oleh Habifa