Magnetic resonance imaging of the cerebral aqueduct.

1.5 Tesla MRI examinations were evaluated for aqueductal configuration, hydrocephalus and flow-related signal void in 70 patients with juxtaaqueductal pathology and in 20 normal controls. In the 70 cases with pathology, the aqueduct was obliterated or distorted in 34, dilated in 3, normal in 29 and not evaluable in 4. A definite flow-related signal void indicated CSF movement within the aqueduct in all normal examinations. Flow-related signal void was absent in some, but not all, patients with aqueductal obliteration and distortion. CSF turbulence can create an intra-aqueductal signal void in the dilated proximal aqueduct, despite more distal obstruction. Thus hydrocephalus related to aqueductal obstruction is frequently, but not always, associated with absence of signal void.