The dura is the most outer layer of the meninges of the brain. The dura consists of two layers the periosteal layer and inner meningeal artery. These two layers are fused together except where the dural venous sinuses are located.
Under no circumstances should there be a space between the inner table of the table of the skull and the periosteal layer of the dura. Any pathology will be known as extra-dural or epidural. It does not always signify a haematoma, but could also be an abscess!
Sheet like septa envelope the brain, and divide the brain into compartments. The aim of these compartments to prevent displacement of the brain upon head movements. The four dural infoldings include:
- Falx Cerebri
- Tentorium Cerebelli
- Falx Cerebelli
- Diaphragma Sella
The falx cerebri is a longitudental dural infold that seperates the two hemispheres. It is clinically relevant as it is the most midline structure in the brain and contains the superior saggital sinus! The falx cerebri attaches to the frontal bone/crista gali of the ethmoid bone and posteriorly to the occipital protuberance where it becomes continuous with the tentorium cerebelli.
The tentorium divides the brain into supra-tentorial and infra-tentorial compartments. It attaches rostrally to the anterior clinoid process, rostrolaterally to the petrous temporal bone and posteriorly to the occipital bone. The rostromedial edge of the tentorium is free called the tentorial notch, where the brainstem runs. This is important. In Uncal Herniation caused by a lateral supra-tentorial mass this compresses the midbrain of which the 3rd nerve nucleus.
The falx cerebelli divides cerebellum into their relevant hemispheres.
The diaphragma sella is a small dural infolding that attaches to the clinoid process forming a roof over the hypophysial fossa (pituitary fossa).
The key note of the blood supply to the dura is via the middle meningeal artery. This is a branch of the maxillary artery (terminal branch of the external carotid artery). It enters the floor of the middle cranial fossa via the foramen spinosum and at the sphenoid bone it divides into anterior and posterior branch. Note the anterior branch of the middle meningeal artery supplies the Pterion, this vessel is ruptured in an extra-dural. Whilst performing a pterional cranitomy this vessel is encountered after removal of the bone flap, and can often be found squirting in your face!!! It needs bipolar diathermy
They are innervated by the trigeminal nerve