Where is the largest collection of blood located? In what compartment is it?
The largest collection is located deep to the parietal bone on the left and in an extradural / epidural location.
By what are extradural haematomas bounded, and how does this limit their spread?
Extradural haematomas are best thought of as subperiosteal haematomas, located on the inside of the skull. Dura mater is composed of two layers which are fused everywhere except the dural venous sinuses. The outer (parietal) layer is continuous with the periosteum of the skull bones and as such passes into the sutures. As a result extradural haematomas do not cross suture lines (but they are able to elevate dural venous sinuses, when not overlying sutures).
What other collections of blood are evident?
Scalp haematoma, subdural haematomas, cerebral haemorrhagic contusion.
Non-contrast CT demonstrates a moderate left lateral convexity epidural haematoma, measuring 18 mm in maximal depth, associated an undisplaced left temporoparietal fracture. Thin smear subdural haematomas are seen overlying the left and right temporal lobes, with further blood seen layering on the tentorium cerebelli on the right. 18 mm haemorrhagic contusion involving the left middle/superior temporal gyrus.
Mild mass effect principally from the left epidural haematoma causes local sulcal effacement and approximately 4 mm of midline shift to the right. No hydrocephalus. Basal cisterns are within normal limits.
The left parietal bone fracture extends through the region of the pterion into the squamous temporal bone and along the floor of the middle cranial fossa, passing through the foramen spinosum and stopping just short of the internal carotid canal.
A fracture through the anterior maxillary wall and floor of the left orbit is also seen, involving the inferior orbital rim and inferior orbital canal. It extends through the lateral orbital wall with probable diastasis of both the sphenozygomatic and frontozygomatic sutures.