Ventricles Axial – Concepts

Transverse or Axial Projection – Concepts

Ashley Davidoff MD

Introduction

The Bacward and Downward Facing ‘C’s” of the Brain in the Axial Plane

Ventricular System (light blue) in Central Position

The anchoring concept of the brain in the axial plane is two cerebral hemispheres with a series of structures reminiscent of backward and downward facing “C’s” symettrically positioned around the center.

The Innermost Layer – The Ventricular System

The most central, backward and downpointing ‘C” is the ventricular system (teal)

The Transverse Plane

The axis of the brain in the sagittal view consists of an anteroposterior or relatively horozontal vector and a relatively vertical, craniocaudal vector. The ventricular system folows these vectors and consists of a paired horizontal system and a single vertical system

The Lateral Ventricles

The lateral ventricles are the first components of the ventricular system to appear as the planes advance from the top of the brain caudally. They are almost H shaped as they start to appear and retain a semblance of this shape for a number of cuts.

Form – Two Anterior Horns and Two Posterior Horns

The anterior and posterior aspect of the lateral ventricle diverge from the body to form structures reminiscent of horns and hence the name anterior or frontal horns and posterior or occipital horns.

The Lateral Ventricles

This T2 weighted image is taken in the transverse or axial plane when the superior aspect of the lateral ventricles are first clearly seen as the scan advances in the forebrain region from superior to inferior. The H shape is characteristic at this level, and the ventricles are most voluminous at this level in the axial plane

The Third Ventricle

The 3rd ventricle in the axial projection is shown as a slit like structure posterior to the frontal horns. It is very narrow heing longer in the A-P dimension than it is in the transverse direction creating a a shape reminiscent of a sausage. It is deceptively large in its craniocaudad span. It is seen in a variety of shapes including a narrow oblong, narrow diamond, and sometimes even as keyhole shaped structure.

3rd Ventricle

The 3rd ventricle in the axial projection is very narroe and is linger than it is narrow, but is deceptively large in its craniocaudad span. Its shape varies from a narrow oblong, to a narrow diamond, to a keyhole shaped structure.

Aqueduct of Sylvius – Cerebral Aqueduct

The aqueduct of Sylvius is the next structure to come into focus as we proceed inferiorly It is a tiny rounded structure that is located in the posterior aspect of the midbrain.It is barely visible on most imaging studies and it lies posterior and inferior to the third ventricle.

Aqueduct of Sylvius

Cerebral Aqueduct in the Midbrain

The axial T2 weighted MRI image through the midbrain shows the small but all important aqueduct of Sylvius (cerebral aqueduct) as it passes through the midbrain (Mickey Mouse appearance).

The 4th Ventricle

The 4th ventricle is the last landmark of the ventricular system seen as we proceed inferiorly. It is seen as a puffed crown or the pontifs hat (mitre), which lies posterior to the pons (ponntiff /pons) inferior to the aqueduct of Sylvius and anterior to the cerebellum. It lies within the hinbrain.

The 4th Ventricle

The T2 weighted axial image through the 4th ventricle is chatracterised by the “puffed crown” or pontiffs hat of the pons of this ventricle. Identifying the 4th ventricle allows localisation of the cut to the hindbrain. The 4th ventricle is anterior to the cerebellum and posterior to the pons.

The Distribution of the ventricles in the Brain

Forebrain (green) Midbrain (orange) and hindbrain (salmon)

This diagram shows the positioning of each of the components of the ventriclar system . The lateral ventricles and third ventricle lie in the forebrain (green), the aqueduct of Sylvius (orange) lies in the midbrain, and the 4th ventricle (salmon) lies in the hinbrain.

Axial T2 weighted Image

The horizontal limbsreviewed in the sagittal section are reflected as two parallelvectors that include parrt of the frontal horns and occipital components, while the teal green limb in the middle represents the conglomerate vertical limb that includes the third ventricle, the aqueduct of Sylvius and the fourth ventricle.