Lateral Ventricles

Overview

The lateral ventricles are paired C-shaped cavities found in each cerebral hemisphere, which contain approximately 7 – 10 mL of CSF.

Structure & Relations

Frontal Horn

Extends anterior from the interventricular foramina (of Monro) and communicates with the body of the lateral ventricles posteriorly

• Anterior wall and roof: are formed by the genu of the corpus callosum
• Floor: is formed by the thalamus and rostrum of corpus callosum
• Lateral wall: Head of the caudate nucleus
• Medial wall: columns of the fornix and septum pellucidum

Body

Communicates with the atrium posteriorly, from the foramina of Monro to the corpus callosum and psalterium of the fornix

• Roof: Body of corpus callosum
• Floor: Thalamus
• Superomedial wall: Septum pellucidum
• Inferomedial wall: Body of fornix
• Lateral wall: Caudate nucleus and thalamus
• In the groove between the caudate nucleus and thalamus along the lateral wall sits the stria terminalis – a main outlet pathway of the amygdala and the location of the thalamostriate vein

Atrium

A triangular cavity that communicates with the body, temporal horn, and occipital horn

• Roof: The body and splenium of the corpus callosum
  • The tapetum, which is a sheet-like bundle of decussating fibers in the splenium of the corpus callosum, arches over the atrium and forms the roof.
• Lateral wall: The tapetum continues laterally and comprises the lateral wall and the caudate nucleus.
• Floor: Collateral trigone – a continuation of the collateral eminence formed by the collateral sulcus.
• Medial wall: The contour of the medial wall is formed by the calcar avis and bulb of the corpus callosum, which is a bulging created by the forceps major
• The calcar avis was previously known as the hippocampus minor and represents an indentation formed by the calcarine fissure. When prominent, the calcar avis can mimic hemorrhage on cranial sonography.

Temporal Horn

The longest and largest horn, extends anteriorly from the atrium below the thalamus and terminating at the amygdala

• Floor: the collateral eminence and hippocampus form the floor, which is separated from the hippocampus by a thin layer of white matter called the alveus.
• Roof: Thalamus, tail of the caudate nucleus, and tapetum.
• The striothalamic sulcus separates the caudate tail and thalamus. The tapetum also runs inferiorly to comprise the lateral wall and separates the lateral wall from the optic radiations. The choroidal fissure runs along the medial wall.

Occipital Horn

The occipital horn curves posteriorly and medially from the atrium and varies in size.

• Roof: Tapetum of the corpus callosum
• Lateral wall: Tapetum of the corpus callosum
• Floor: Collateral trigone f
• Medial: The bulb of the corpus callosum and calcar avis

Development

• After the closure of the neural tube during the fourth week of gestation, the lateral ventricles begin forming from the 2 outpouchings of the telencephalon

Variants

• Coarctation – apposition or fusion of 2 ventricular walls, resulting in partial or complete obliteration of the lumen. This can isolate a portion of the ventricle, creating multiple ‘connatal cysts’. More commonly seen in the occipital horns.
• Asymmetric size and morphology (5 – 12%)
• Cavum Septi Pellucidi, Cavum Vergae, and Cavum Veli Interpositi
• Choroid plexus cyst (acquired or congenital) – may be referred to as xanthogranulomas if thought to be acquired.