Lateral Ventricles

The lateral ventricles are a pair of large, C-shaped cavities located within each cerebral hemisphere. They are the largest components of the ventricular system and serve as reservoirs for cerebrospinal fluid (CSF). Each lateral ventricle communicates with the third ventricle via an interventricular foramen (foramen of Monro). They play a key role in CSF production, circulation, and spatial orientation within neuroanatomy.

Location

The lateral ventricles are situated deep within the cerebral hemispheres and extend into the frontal, parietal, occipital, and temporal lobes. They are separated from each other medially by the septum pellucidum and curve around the thalamus, following the shape of the cerebral hemisphere.

Parts of the Lateral Ventricle

Each lateral ventricle is divided into five parts:

• Anterior horn (frontal horn): Located in the frontal lobe anterior to the interventricular foramen. It is bounded:
  • Medially by the septum pellucidum
  • Laterally by the head of the caudate nucleus
  • Superiorly by the corpus callosum (genu)
• Body (central part): Located in the parietal lobe, posterior to the interventricular foramen and above the thalamus. The floor is formed by:
  • Thalamus
  • Body of the caudate nucleus
  • Fornix
• Posterior horn (occipital horn): Extends into the occipital lobe. Its walls are formed by:
  • Medially by the calcar avis (an elevation due to the calcarine sulcus)
  • Laterally by the tapetum of the corpus callosum
• Inferior horn (temporal horn): Extends into the temporal lobe. The roof is formed by the tapetum, and the floor includes:
  • Hippocampus
  • Fimbria of the hippocampus
  • Collateral eminence
• Atrium (trigone): The enlarged junctional area between the body, posterior horn, and inferior horn. Contains the glomus of the choroid plexus (a large tuft of choroidal tissue).

Choroid Plexus and CSF Production

The choroid plexus is a vascular structure within the lateral ventricles that produces cerebrospinal fluid. It is located in the floor of the body and extends into the atrium and inferior horn. The choroid plexus consists of a layer of ependymal cells covering fenestrated capillaries and secretes CSF into the ventricular space.

Communication with the Third Ventricle

The lateral ventricles communicate with the third ventricle via the interventricular foramina (foramina of Monro), located at the anterior portion of the ventricular body, near the midline. CSF flows from each lateral ventricle through the foramen into the third ventricle, continuing through the cerebral aqueduct to the fourth ventricle and subarachnoid space.

Relations

• Caudate nucleus: Follows the curvature of the lateral ventricle and forms part of its lateral wall.
• Corpus callosum: Forms the roof of most portions of the lateral ventricle.
• Thalamus: Forms the floor of the body of the lateral ventricle.
• Hippocampus: Forms the floor of the inferior horn in the temporal lobe.

Development

The lateral ventricles develop from the cavities of the paired telencephalic vesicles in the embryonic forebrain. As the cerebral hemispheres expand and grow posteriorly, inferiorly, and laterally, the lateral ventricles assume their characteristic C-shape. The choroid plexus begins to form during early fetal development, contributing to CSF production before birth.

Clinical Significance

• Hydrocephalus: Enlargement of the lateral ventricles may occur due to obstruction of CSF flow, overproduction, or impaired absorption. It can result in increased intracranial pressure, especially in infants (causing macrocephaly).
• Colloid cyst: A benign lesion near the foramen of Monro may block CSF flow, leading to acute hydrocephalus and requiring surgical removal.
• Intraventricular hemorrhage: Common in premature infants; blood may accumulate within the lateral ventricles, potentially obstructing CSF flow.
• Ventriculomegaly: Enlargement of the lateral ventricles seen in various conditions, including normal pressure hydrocephalus, brain atrophy, or congenital anomalies.
• Ventricular catheter placement: Ventriculostomy or shunt placement often involves accessing the frontal horn of the lateral ventricle.

Imaging

CT and MRI are commonly used to assess the lateral ventricles. Enlargement or asymmetry may indicate hydrocephalus, mass effect, or brain atrophy. MRI provides high-resolution views of the ventricular walls, choroid plexus, and adjacent brain structures. Ultrasonography through the anterior fontanelle is used in neonates to evaluate ventricular size and hemorrhage.