Interventricular Foramen

foramen interventriculare

The interventricular foramina, or foramina of Monro, are the two small openings that connect each lateral ventricle to the third ventricle. They are bounded in front by the fornix and behind by the front of the thalamus. Cerebrospinal fluid and the choroid plexus pass through them.

Anatomical Data

Structure & Connections

Location	Between the column of the fornix and the anterior tubercle of the thalamus, at the front of each lateral ventricle's body and the upper front corner of the third ventricle
Parts	Anterior boundary (column of the fornix) Posterior boundary (anterior tubercle of the thalamus) Choroid plexus passing through
Connections	Lateral ventricles Third ventricle Thalamostriate and septal veins (joining to form the internal cerebral veins at its margin)
Blood Supply	Anterior and medial posterior choroidal artery branches in its choroid plexus

Biomechanics

Function & Actions

Allows cerebrospinal fluid made in the lateral ventricles to drain into the third ventricle.

Clinical Relevance

Clinical Notes

A colloid cyst at the foramen of Monro can suddenly block both foramina and cause acute hydrocephalus, sometimes with sudden death. Subependymal giant cell astrocytoma in tuberous sclerosis also arises here. Neurosurgeons use the foramen of Monro as the gateway for endoscopic access to the third ventricle.

Pathology

Common Injuries & Conditions

Colloid Cyst Obstruction

A benign cyst at the foramen of Monro causing positional headache and acute hydrocephalus of both lateral ventricles.

Subependymal Giant Cell Astrocytoma

A slow-growing tumour near the foramen of Monro in tuberous sclerosis that may block CSF flow.

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