Structure: reading the section from the midline
A coronal section through the thalamus and brainstem is read from the midline outwards and from top to bottom.
- Longitudinal fissure: the deep midline cleft between the hemispheres, holding the falx cerebri.
- Corpus callosum: the white bridge at the bottom of the fissure, forming the roof of both lateral ventricles.
- Lateral ventricles: the two bodies lie under the corpus callosum, separated by the thin septum pellucidum.
- Fornix: the body of the fornix lies at the lower edge of the septum, over the third ventricle.
- Third ventricle: a narrow midline slit between the two thalami.
- Lateral fissure: the deep cleft on the outer side, with the insula in its depth.
| From medial to lateral at thalamic level | Type |
|---|---|
| Third ventricle | CSF space |
| Thalamus | Grey matter |
| Posterior limb of internal capsule | White matter |
| Lentiform nucleus: globus pallidus, then putamen | Grey matter |
| External capsule | White matter |
| Claustrum | Grey matter (thin sheet) |
| Extreme capsule | White matter |
| Insular cortex | Grey matter |
The body of the caudate nucleus lies higher, in the lateral wall of the lateral ventricle, above the thalamus. Below, the section passes through the midbrain, with the interpeduncular cistern between the cerebral peduncles, then the pons with its middle cerebellar peduncles, and the medulla.
White matter: capsules and corona radiata
The white matter on the section carries three kinds of fibres: projection fibres to and from lower centres, commissural fibres between the hemispheres, and association fibres within one hemisphere.
- Corona radiata: projection fibres fanning out between the cortex and the internal capsule.
- Internal capsule: a compact band of projection fibres between the thalamus and caudate medially and the lentiform nucleus laterally. Its anterior limb lies between the head of the caudate and the lentiform nucleus; the genu carries corticobulbar fibres; the posterior limb, between thalamus and lentiform, carries corticospinal fibres and the sensory radiation from the thalamus.
- External capsule: a thin layer between the putamen and claustrum.
- Extreme capsule: a thin layer between the claustrum and the insular cortex.
- Corpus callosum: the largest commissure.
Below the internal capsule, the same descending fibres continue into the cerebral peduncle, the basilar pons and the medullary pyramids.
Deep grey matter and ventricles
The deep grey nuclei on this section are the basal ganglia and the thalamus.
- Caudate nucleus: a C-shaped nucleus that follows the lateral ventricle, with its body in the ventricle's lateral wall and floor.
- Lentiform nucleus: the outer putamen and inner globus pallidus. The caudate and putamen together form the striatum, part of the circuits that control movement.
- Claustrum: a thin sheet of grey matter of uncertain function, lying between the external and extreme capsules.
- Thalamus: an egg-shaped mass forming the lateral wall of the third ventricle. It relays sensory, motor and limbic information to the cortex.
CSF is made by the choroid plexus, found in the bodies and inferior horns of the lateral ventricles and in the roofs of the third and fourth ventricles. It is produced at roughly 500 mL a day. It flows from each lateral ventricle through the interventricular foramen to the third ventricle, then through the cerebral aqueduct to the fourth ventricle, and out through its median and lateral apertures into the subarachnoid space and cisterns. The interpeduncular cistern lies between the cerebral peduncles and contains the oculomotor nerves and the termination of the basilar artery.
Blood supply
The deep structures on the section are supplied by small perforating end arteries, which is why small strokes here cause large deficits.
| Artery | Parent | Supplies |
|---|---|---|
| Lenticulostriate (lateral striate) arteries | Middle cerebral | Putamen, much of the caudate, upper internal capsule |
| Recurrent artery (of Heubner) | Anterior cerebral | Head of caudate, anterior limb of internal capsule |
| Anterior choroidal artery | Internal carotid | Lower posterior limb of internal capsule, choroid plexus of inferior horn, part of globus pallidus |
| Thalamoperforating and thalamogeniculate arteries | Posterior cerebral and posterior communicating | Thalamus |
Clinical relevance
The deep structures on a coronal section are common sites of stroke, haemorrhage and degeneration.
- Internal capsule infarct: because the fibres are packed tightly, a small lacunar infarct can cause a dense weakness of the opposite face, arm and leg equally.
- Hypertensive haemorrhage: most often arises in the putamen from a ruptured lenticulostriate artery, spreading into the internal capsule.
- Hydrocephalus: blockage at the interventricular foramen or cerebral aqueduct enlarges the ventricles upstream.
- Huntington's disease: atrophy of the caudate flattens the lateral wall of the lateral ventricle.
- Thalamic stroke: contralateral sensory loss, sometimes followed by severe central pain.
On the specimen
Orient the section by finding the ventricles first, then work outwards.
- Caudate or thalamus: the caudate body is small and sits high in the lateral wall of the lateral ventricle; the thalamus is larger and lower, on either side of the third ventricle.
- Internal or external capsule: the internal capsule is the thick white band medial to the lentiform nucleus; the external capsule is the thin white line lateral to it.
- Claustrum: the thin grey ribbon between the external capsule and the white matter under the insula (the extreme capsule).
- Fornix or corpus callosum: the corpus callosum forms the roof of the lateral ventricles; the fornix is a smaller white bundle under the septum pellucidum.
- Choroid plexus: dark, tufted tissue in the floor of the lateral ventricle and the roof of the third.
- Pons or medulla: the pons is the broad bulge joined to the cerebellum by the middle cerebellar peduncles; the medulla is narrower, below it.