Fenestration of the septum pellucidum is one of the findings in chronic obstructive hydrocephalus.

Obstructive hydrocephalus, also known as non-communicating hydrocephalus is simply hydrocephalus due to obstruction of CSF flow out of the ventricles.

Frequent causes of obstructive hydrocephalus include:
-aqueduct stenosis

Features of long standing obstructive hydrocephalus are:
-marked dilatation of the lateral and third ventricles
-thinned and elevated corpus callosum.
-depression of the fornices
-the floor of the 3rd ventricle is plastered to the skull base, obliterating the suprasellar cistern.
-rounding of the infundibular, optic and pineal recesses
-ballooning of the suprapineal recess
-fenestration of the septum pellucidum
Treatment options include:
-shunting, most commonly VP shunt
-third ventriculostomy

Reference: Primer of Diagnostic Imaging by Weissleder
Credit: Dr Frank Gaillard