Deck 14: The Skull, the Brain, the Meninges, and the Blood Supply of the Brain Relative to Trauma and Intracranial Hemorrhage

Question 1

A 36-year-old man was admitted to the emergency department unconscious. He had been hit on the side of the head by a taxi while crossing the road. On examina- tion, he was found to have a dough-like swelling over the right temporalis muscle. He also had the signs of rightsided hemiplegia. Later, a right-sided, fixed, dilated pupil developed. A lateral radiograph of the skull showed a linear fracture running downward and forward across the right pterion. His coma deepened, and he died 6 hours
after the accident. Using your knowledge of anatomy, make the diagnosis. Explain the clinical findings. How would you explain the homolateral hemiplegia?

Answer 1

The initial loss of consciousness was due to cerebral trauma. The swelling over the right temporalis muscle and the radiographic finding of a linear fracture over the anterior inferior angle of the right parietal bone (pterion) would suggest that the right middle meningeal artery had been damaged and an extradural hemorrhage had occurred. Blood had extravasated through the fracture line into the overlying temporalis muscle and soft tissue. The right homolateral hemiplegia was due to the compression of the left cerebral peduncle against the edge of the tentorial notch of the tentorium cerebelli. This is unusual. A left hemiplegia due to pressure on the right precentral gyrus is more common.
The right-sided, fixed, dilated pupil was due to the pressure on the right oculomotor nerve by the hippocampal gyrus, which had herniated through the tentorial notch.

Question 2

Severe injury to the soft structures within the skull may follow head trauma. What structures exist within the skull to limit damage to the cerebral hemispheres and other parts of the brain? Which blood vessels are damaged more commonly, the cerebral arteries or the cerebral veins? Which cranial nerves are likely to be damaged in head injuries? What is the reason for their susceptibility?

Answer 2

The meninges and the cerebrospinal fluid afford a remarkable degree of protection to the brain tissue. The dural partitions limit the extent of side-to-side, forward and backward, and rotation movements of the brain within the skull.
The thin-walled cerebral veins are liable to be damaged during excessive movements of the brain relative to the skull, especially at the point where the veins join the dural venous sinuses. The thick-walled cerebral arteries are rarely damaged.
The small-diameter cranial nerves of long length are particularly prone to damage during head injuries. The trochlear, abducent, and oculomotor nerves are commonly injured.

Question 3

A 51-year-old woman was examined in the emergency department complaining of a severe headache. She said that the headache had started about 1 hour after she had hit her head on the mantle piece of a fireplace after bending down to poke the fire. Four hours later it was noticed that she was becoming mentally confused and was developing a left-sided hemiplegia on the side opposite the head injury. Her deep reflexes were exaggerated, and she had a positive Babinski response on the left side. A CT scan demonstrated a right subdural hematoma. Explain in anatomic terms the development of a subdural hematoma.

Answer 3

A subdural hematoma is an accumulation of blood clot in the interval between the meningeal layer of dura and the arachnoid mater. It results from tearing of the supe-
rior cerebral veins at their point of entrance into the superior sagittal sinus. The cause is usually a blow to the front or the back of the head (which may be minor), resulting in excessive anteroposterior displacement of the brain within the skull.

Question 4

Which part of the base of the skull is most prone to fracture? Can you give an anatomic reason for this answer?

Question 5

It is not uncommon to read in newspapers of the survival of a baby that has fallen from a great height, such
as a third-floor window, and yet it is known that if an
adult falls from a similar height, it would be fatal. Can
you give an anatomic explanation, based on age, for this
difference in survival?

Question 6

Using your knowledge of the anatomic pathways along which the cerebrospinal fluid flows, name the sites at which pathologic blockage may occur.

Question 7

There are no anastomoses of clinical importance between the terminal end arteries within the brain substance, but there are many important anastomoses between the large arteries, both within and outside the skull, and these may play a major role in determining the extent of brain damage in cerebral vascular disease. Name the sites at which important arterial anastomoses take place.

Question 8

A 35-year-old man was seen in the emergency department with a history of sudden excruciating, generalized headache while gardening. Ten minutes later the patient collapsed to the ground in a state of unconsciousness. After being carried indoors and placed on a settee, he regained consciousness but appeared confused. He complained of a severe headache and a stiff neck. Physical examination revealed some rigidity of the neck but nothing further. A careful neurologic examination 4 days later revealed some loss of tone of the muscles of the left leg. Using your knowledge of anatomy, make a diagnosis. What caused the neck rigidity?