Giant Arachnoid granulation

CT Brain with MR Brain and MR Venogram of Brain

Axial non contrast CT Brain

MRI Brain Axial FLAIR, T2 and T1

Non contrast 2D TOF MR Venogram of Brain

These CT and MR images of Brain shows a nodular lesion iso dense on CT, T2 hyper intense on MRI, hypo intense on FLAIR due to complete signal suppression.
A filling defect noted on MR venogram in right lateral sinus in corresponding region.
This is a Gaint Arachnoid Granulation, to be mentioned as an incidental finding.

Discussion

Normal drainage of CSF occurs from subarachnoid space into venous system via microscopic Arachnoid villi, measure a few millimetres, are growths of arachnoid membrane into the dural sinuses. When these villi are distended and visible to the naked eye are termed as Giant Arachnoid granulations, are noted and passed off as an incidental finding.

Occur anywhere along course of dural venous sinus but more common in transverse sinus near sigmoid sulcus. Seen as round to ovoid filling defect in the region of sinus, On CT isodense to csf and on MR isointense to csf on all pulse sequence.


Differential diagnosis includes thrombosed sinus. Thrombus or clot in the sinus is linear and along the course sinus, does not follow same sequences as that of csf on all pulse sequences.

Although noted as an incidental finding, giant arachnoid granulations can be a rare cause of sinus obstruction resulting in venous hypertension. Dural sinus pressure measurement, normal pressure and absence of pressure gradient across the lesion are used to exclude the lesion as the cause of the patient’s symptoms.