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Embryology · Nervous system and senses

Ventricles and cerebrospinal fluid !

  • Embryonic structure

The ventricles are what is left of the hollow neural tube; the choroid plexuses inside them make the fluid that bathes the brain and cord.

Updated 2026-11-01

See it in 3D: Lateral ventricles · Third ventricle · Cerebral aqueduct · Fourth ventricle · Choroid plexus

What it is

The ventricular system is the lumen of the neural tube that persists inside the brain. Each brain vesicle contributes one cavity, and choroid plexuses form in the roof of some of them and secrete cerebrospinal fluid (CSF). If CSF cannot flow or be absorbed, the ventricles dilate: hydrocephalus.

Key facts

  • Lateral ventricles (telencephalon) → interventricular foramina of Monro → third ventricle (diencephalon).
  • Third ventricle → cerebral aqueduct (midbrain) → fourth ventricle (hindbrain).
  • Fourth ventricle → median (Magendie) and lateral (Luschka) apertures → subarachnoid space.
  • Choroid plexuses are modified ependyma plus vascular pia, in the ventricular roofs.
  • CSF is absorbed into venous blood through arachnoid villi and granulations.
  • The aqueduct is the narrowest segment: the classic site of congenital obstruction.

Structure

  • Ependymal lining derived from the neuroepithelium of the neural tube.
  • Choroid plexuses in the lateral ventricles, the roof of the third and the roof of the fourth.
  • The roof of the fourth ventricle is a thin sheet (the hindbrain roof plate) where its outlets open.

What it becomes

  • Lumen of the telencephalon: lateral ventricles.
  • Lumen of the diencephalon: third ventricle.
  • Lumen of the mesencephalon: cerebral aqueduct (of Sylvius).
  • Lumen of the rhombencephalon: fourth ventricle.
  • Lumen of the cord: central canal.

Step by step

  1. Choroid plexuses secrete CSF into the lateral ventricles.
  2. CSF passes through the foramina of Monro into the third ventricle.
  3. It runs down the aqueduct into the fourth ventricle.
  4. It leaves through the foramina of Magendie and Luschka into the subarachnoid space.
  5. It is absorbed through arachnoid granulations into the venous sinuses.

Clinical notes

  • Obstruction at the aqueduct: lateral and third ventricles dilate, the fourth stays normal (aqueductal stenosis).
  • Obstruction of the fourth-ventricle outlets: all four ventricles dilate (Dandy–Walker pattern).
  • Fetal ventriculomegaly is found on ultrasound and prompts a search for a cause (infection, Chiari II, genetic).

Test yourself

Think of the answer, then tap the question to see it.

The cerebral aqueduct is the lumen of which embryonic vesicle?

The mesencephalon, which does not subdivide and whose cavity narrows.

Through which openings does CSF leave the fourth ventricle?

The median aperture (Magendie) and the two lateral apertures (Luschka), into the subarachnoid space.

Which ventricles dilate in aqueductal stenosis?

The lateral and third ventricles; the fourth, downstream of the block, does not.

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See it in 3D

The structures of Durgical's 3D anatomy where it is found.

← All of embryology

Educational content on embryonic development; not a guide to prenatal diagnosis or to medicines in pregnancy and no substitute for a health professional's advice. No doses are given.

Sources: 13.1 The Embryologic Perspective - Anatomy and Physiology 2e (OpenStax, 2022); Hydrocephalus (National Institute of Neurological Disorders and Stroke, 2024); Langman's Medical Embryology, 13th ed., ch. 18: Central Nervous System (Wolters Kluwer, 2015).

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