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4th ventricular

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I now have comprehensive information to give a thorough anatomical overview of the 4th ventricle. Here is the full answer:

Fourth Ventricle - Anatomy & Structure

Overview

The fourth ventricle is a rhomboid (diamond)-shaped CSF-filled space in the posterior fossa. It is the mature derivative of the cavity of the rhombencephalon (hindbrain), as the ventricular system as a whole derives from the embryonic neural tube cavity.

Boundaries

WallStructures
Floor (anterior/ventral)Pons (upper part) and medulla oblongata (lower part) - together forming the rhomboid fossa
Roof (posterior/dorsal)Cerebellum - the tented apex of the roof is called the fastigium
SuperolateralSuperior cerebellar peduncles + superior medullary velum
InferolateralInferior cerebellar peduncles + inferior medullary velum

Connections

  • Superiorly: communicates with the cerebral aqueduct (of Sylvius), which traverses the midbrain and connects to the 3rd ventricle
  • Inferiorly: tapers to the obex, which marks the entry into the central canal of the spinal cord (typically obliterated/closed in adults)
  • CSF outflow via three foramina:
    • Foramen of Magendie (median aperture) - single, midline, in the inferior roof
    • Foramina of Luschka (lateral apertures) - paired, one on each side, through which CSF exits into the cerebellopontine angle cisterns

The Floor (Rhomboid Fossa) - Key Landmarks

The floor is clinically important because cranial nerve nuclei bulge into it from below:
LandmarkCranial Nerve / Structure
Facial colliculusAbducens nucleus (CN VI) + looping fibers of facial nerve (CN VII)
Hypoglossal trigoneHypoglossal nucleus (CN XII)
Vagal trigoneDorsal motor nucleus of vagus (CN X)
Sulcus limitansLandmark groove separating motor (medial/basal plate) from sensory (lateral/alar plate) columns
Striae medullaresTransverse fibers crossing the floor (arcuate fibers of CN VIII)
Locus coeruleusNoradrenergic nucleus, visible as a bluish spot superiorly

Choroid Plexus

The fourth ventricular choroid plexus extends laterally into both foramina of Luschka, often projecting out into the subarachnoid space. Its blood supply comes from branches of the PICA (posterior inferior cerebellar artery), AICA (anterior inferior cerebellar artery), and SCA (superior cerebellar artery).

Embryological Origin

The fourth ventricle derives from the rhombencephalon. The floor is formed by the myelencephalon/metencephalon, where the alar plate (sensory) and basal plate (motor) are separated by the sulcus limitans. The rhombic lip - the thickened alar plate margin - gives rise to the cerebellum and several brainstem nuclei (including the inferior olivary nucleus and pontine nuclei).
Embryological development showing the alar and basal plates of the 4th ventricle floor, with rhombic lip, choroid plexus, and cranial nerve nuclear columns
Development of the 4th ventricular floor - Langman's Medical Embryology

Imaging Appearance

On MRI/CT (Grainger & Allison's), the 4th ventricle is well visualized in multiple planes:
  • Sagittal T2: shows the fastigium (tented apex) and foramen of Magendie clearly
  • Coronal: reveals the characteristic rhomboid/diamond shape, with lateral recesses funneling into the foramina of Luschka
  • Axial: demonstrates both foramina of Luschka laterally and the foramen of Magendie posteriorly
MRI and CT images of the 4th ventricle: (A) sagittal showing fastigium and Magendie, (B) coronal showing rhomboid shape and lateral recesses, (C) axial showing Magendie and Luschka foramina, (D) CT showing calcified choroid plexus tufts projecting through foramina of Luschka
Fig. 53.14 - Grainger & Allison's Diagnostic Radiology

Summary of CSF Pathway Through the 4th Ventricle

Lateral ventricles → Foramina of Monro → 3rd ventricle → Cerebral aqueduct of Sylvius → 4th ventricle → Foramina of Luschka (lateral) + Foramen of Magendie (midline) → Subarachnoid space (cisterna magna and cerebellopontine cisterns)
Sources:
  • Grainger & Allison's Diagnostic Radiology (Ventricular System and Subarachnoid Space)
  • Neuroanatomy through Clinical Cases, 3rd Ed. (Brainstem surface anatomy, p. 525)
  • Langman's Medical Embryology (Myelencephalon and Cerebellum chapters)
  • Bailey and Love's Short Practice of Surgery, 28th Ed.
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