Interventricular foramina

In the brain, the interventricular foramina (or foramina of Monro) are channels that connect the paired lateral ventricles with the third ventricle at the midline of the brain. As channels, they allow cerebrospinal fluid (CSF) produced in the lateral ventricles to reach the third ventricle and then the rest of the brain's ventricular system. They also contain choroid plexus, a specialized CSF-producing structure, that is continuous with that of the lateral and third ventricles.


The crescent-shaped interventricular foramina are located on the medial and inferior aspect of the lateral ventricles. Each foramen is bounded by the fornix and thalamus. The lumens of the foramina have a diameter of several millimeters.

Clinical relevance

Inflammation, tumor, or other conditions that may occlude the foramina may lead to internal hydrocephalus.


The foramina were named after the Scottish physician Alexander Monro, who first described the structures in his 1783 publication, Observations on the Structure and Functions of the Nervous System. They had previously been identified by the 17th century anatomist Raymond Vieussens.

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