Charlie, a 26-year-old male, slipped and fell down a set of concrete steps. He hit his head and was rendered unconscious for around 15 seconds (reported by his friends). Six hours later the same day he lost consciousness and was taken to the emergency department. History and preliminary examination pointed toward an intracranial bleed.
a) Describe the meningeal layers, their arrangement/order
There are three meningeal layers. From superficial to deep are the:
- Dura – lines the inner surface of the cranium and is formed from 2 layers (periosteal and meningeal).
- Arachnoid – sits deep to the dura lining the inner surface of the meningeal dura.
- Pia – sits deep to the arachnoid lining the outer surface of the neural tissue,
b) Describe the location and purpose of the main dural formations.
The dural formations are double-layered folds of meningeal dura. The main ones are the:
- Falx cerebri – located in the sagittal plane between the left and right cerebral hemispheres
- Falx cerebelli – located in the sagittal plane between the left and right cerebellar hemispheres
- Tentorium cerebelli – located in an approximately axial plane between the inferior parts of the occipital and temporal lobes and the cerebellum
- Diaphragm sellae – Sits around the pituitary gland in the region of the sella turcica.
c) Name the spaces around the meninges and describe their location.
The epidural space sits superficial to the periosteal dura, between the dura and the skull.
The subdural space sits between the dura and arachnoid.
The subarachnoid space sits between the arachnoid and pia.
d) State the two most likely locations for Charlie’s bleed (ensure you explain where the blood is located), whether the blood is arterial or venous and the most likely vessel(s) for origin of the blood.
In a young patient with a blunt force head injury the bleed is either epidural (arterial blood from the meningeal arteries located outside of either the meningeal or periosteal layer of dura), or subdural (venous blood from the bridging veins located between the meningeal layer of dura and the arachnoid). In this case, given the short lucid period following the injury it is most likely that the bleed is arterial and is in an epidural location.
e) Explain what the pterion is, state its surface location and explain why a fracture at this location can lead to an intracranial bleed.
The pterion is a region on the temporal region of the cranium where 4 bones meet at suture joints (temporal, frontal, parietal and sphenoid), It sits ~4cm superior to the midpoint of the zygomatic arch (or within a 2cm diameter circle in this region). the anterior branch of the middle meningeal artery runs deep to the pterion so can be injured by a regional fracture.
f) Describe the main dural venous sinuses and explain their locations.
- Superior sagittal sinus (passes along the sagittal midline of the inner cranium at the root of the falx cerebri)
- Confluence of sinuses (formed from the superior sagittal sinus meeting the straight sinus to form the transverse sinuses)
- Transverse sinuses (pass around the attachment point of the tentorium cerebelli)
- Sigmoid sinus (snakes down from the anterior end of the transverse sinus to the internal jugular foramen.
- Cavernous sinus sits either side of the sella turcica (and pituitary)