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Moderate tetra-ventricular dilatation is noted showing no periventricular CSF permeation. The mamillopontine distance (7.4 mm).
The dilated fourth ventricle is seen freely communicating with infracerebellar posterior fossa cyst. A choroid plexus seen at the lower portion of the fourth ventricle and stretched along the anterior aspect of the cyst. The cerebellar vermis is upward displaced with no hypoplasia.
CSF flow dynamic study with Ultra-thin 3D sagittal T2 weighted images & Phase contrast sequence revealed:
- preserved T2 hypointense signal void flow at aqueduct showing normal bidirectional flow with mild increase in CSF velocity (6.85 cm/sec) and absolute stroke volume (68 microliter)
- normal bidirectional flow of CSF at the craniocervical junction and cervical subarachnoid spaces. Weak flow seen to the cyst