Sagittal T1 MRI of the brain

1. A Mammillary body.

2. B Fourth ventricle.

3. C Tectum of the midbrain.

4. D Tentorium cerebelli.

5. E Cerebellar tonsil.

The mammillary bodies are a pair of rounded prominences at the anterior arches of the fornix. They are part of the limbic system. They can be damaged as a result of thiamine deficiency (Wernicke–Korsakoff syndrome). The fourth ventricle is the most inferior of the ventricular spaces and is diamond-shaped in cross section. It connects to the third ventricle via the aqueduct of Sylvius, and drains via the foramen of Luschka (two lateral tracts) and the foramen of Magendie (single midline tract). The tectum is located at the dorsal region of the midbrain and consists of superior (visual) and inferior (auditory) colliculi. There is a cerebellar tonsil on the undersurface of each cerebellar hemisphere in continuity with the uvula of the cerebellar vermis. It is helpful to assess these on sagittal section to look for elongation and descent of the cerebellar tonsils into the foramen magnum, which can be associated with raised intracranial pressure or congenital malformations (Chiari malformations).

Axial T2 FLAIR MRI of the brain

1. A Right external capsule.

2. B Choroid plexus in the right lateral ventricle.

3. C Splenium of the corpus callosum.

4. D Left caudate nucleus (head).

5. E Left lentiform nucleus.