Arachnoid granulations are small outgrowths of the arachnoid mater that push through the dura into the dural venous sinuses, mainly the superior sagittal sinus. They act as one-way valves through which cerebrospinal fluid drains into the venous blood. With age they enlarge and can cause small pits in the inner skull.
| Location | Mainly along the superior sagittal sinus and its lateral lacunae, also in the transverse sinuses and other dural sinuses |
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| Connections |
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| Blood Supply | Not applicable (avascular arachnoid outgrowths bathed in venous sinus blood) |
Return cerebrospinal fluid from the subarachnoid space to the venous circulation, driven by the pressure difference between CSF and venous blood.
Scarring of the arachnoid granulations after meningitis or subarachnoid haemorrhage reduces CSF absorption and causes communicating hydrocephalus. Large granulations in the transverse sinus can be mistaken for a clot or tumour on imaging. Raised venous sinus pressure, as in sinus thrombosis, also reduces CSF absorption and raises intracranial pressure.
Ventricular enlargement from impaired CSF absorption at the arachnoid granulations, often after haemorrhage or infection.
An enlarged granulation in a venous sinus, usually harmless, that can mimic thrombosis on scans.
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