A 44 year-old woman presented with headaches, worst when lying down.  Her neurologic examination was normal.

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). This amount of ventricular dilatation is mild, and likely represents a chronic compensated state. Note that the frontal horns are enlarged - they extend beyond the head of the caudate nucleus and form somewhat of a "mickey mouse" ears.

Revised 04/21/06.
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