A 47 year-old woman presented with confusion, headaches and gait imbalance. There was a history of meningitis as a child.

Axial CT scan - note the prominent enlargement of the lateral and third ventricles but with a normal size appearance of the 4^th ventricle.  This pattern is one of obstructive hydrocephalus, which occurs from impaired drainage through the cerebral aqueduct (connecting the third to the fourth ventricles).  Note also the relatively effaced (i.e. small) sulci, which excludes the possibility of large due to atrophy (i.e., hydrocephalus ex vacuo).

Revised 04/21/06.
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