Coronal T2 MRI of the brain

1. A Temporal horn of right lateral ventricle.

2. B Third ventricle.

3. C Left hippocampus.

4. D Right cochlea.

5. E Left parotid gland.

The lateral ventricles drain cerebrospinal fluid into the third ventricle via the right and left interventricular foramen (foramen of Munro). The third ventricle drains into the fourth ventricle via the cerebral aqueduct (aqueduct of Sylvius). The fourth ventricle drains via a central foramen of Magendie and two lateral foramina of Luschka.

The hippocampus is a key part of the limbic system and is seen as a curved prominence on the inferior horn of the lateral ventricle. It is a grey-matter structure with a thin covering of white matter, which is known as the alveus.

For more information and a flow diagram of the ventricular system see Question 4.2.

Coronal T1 MRI of the brain

1. A Right sylvian fissure.

2. B Right caudate nucleus.

3. C Septum pellucidum.

4. D Left putamen.

5. E Right lateral mass of C1.

The septum pellucidum is a thin membrane separating the anterior horns of the lateral ventricles. It consists of two layers of both white and grey matter, called the laminae septi pellucidi. During foetal development there is a space between these two laminae called the cavum septum pellucidum. This is fused in 85% of individuals by six months of age but can persist into adulthood as a normal variant.