Herniation

Question 1

What are the components of the blood brain barrier?

Answer 1

astrocyte endfeet, pericytes, capillaries with tight junctions

Question 2

What are the areas devoid of blood brain barrier?

Answer 2

posterior pituitary (for vasopressin and oxytocin)
area postrema (vomiting center)
pineal gland (melatonin and neuropeptides to regulate daytime and nighttime)
subfonical organ
medial eminence.

Question 3

How much CSF is made per day, and what is its distribution?

Answer 3

500 cc/day
150 around the brain at a time
2/3 in intracranial compartment; 1/3 in spinal cord

Question 4

What are the 2 kinds of edema and what are their sources?

Answer 4

vasogenic: intravascular fluid becomes extracellular due to a failure of the blood brain barrier
cytogenic: intracellular fluid compartment expands due to a failure of cell homeostasis

Question 5

4 locations of herniation?

Answer 5

1. transtentorial: usually uncal; sometimes central/diencephalic. may lead to duret hemorrhages
2. subfalcine herniation: cingulate gyrus
3. tonsillar/foramen magnum herniation
4. extracranial/calvarial herniation

Question 6

What are the 2 most clinically relevant herniations?

Answer 6

those involving tentorial notch- transtentorial, uncal, tentorial, parahippocampus and foramen magnum.
clinically relevant because the medial temporal lobe or cerebellar tonsil impinges on vital centers in the midbrain (tentorial) and medulla (foramen magnum)

Question 7

What are clinical signs of supratentorial transtentorial herniation?

Answer 7

1. ipsilateral pupillary dilation- interference with CNIII, which is responsible for contraction
2. ipisilateral hemiparesis due to compression of the contralateral cerebral peduncle/crus cerebri (Kernohan’s notch)
3. contralateral hemiparesis due to compression of the ipsilateral peducle (against the clivus)
4. visual field defects from compression of ipsilateral posterior cerebral artery
5. alternations in consiousness, abnormal breathing, coma, or death from distortion of midbrain reticular activating system

Question 8

What are some signs of chronic tonsillar herniation/

Answer 8

paresthesias, head tilt, stiff neck, arching of the neck

Question 9

What is a characteristic sign on autopsy of transtentorial herniation?

Answer 9

multiple, linear, midline hemorrhages in the midbrain and upper pons- hemorrhages of Duret

Question 10

What is hydrocephalus ex vacuo?

Answer 10

CSF fills intracranial ares left empty following loss of brain tissue from atrophy or infarction– example is in the huge ventricles seen in advanced cerebral atrophy

Question 11

When might you see communicating hydrocephalus?

Answer 11

sequelae of damage to arachnoid granulations following meningitis or subarachnoid hemorrhage
or, after thrombosis of superior saggital sinus, as in post-partum period/with hypercoaguable states

Question 12

Treatment for chronic hydrocephalus

Answer 12

permatent ventriculo-peritoneal shunt

Question 13

4 causes of coma- general

Answer 13

supratentorial mass lesions, infratentorial mass lesions, metabolic encephalopathy, psychogenicW

Question 14

What may 6th nerve palsies suggest in the context of herniation?

Answer 14

false localizing sings in pts with diffusely elevated pressure

Question 15

What is the first treatment for all cases of incr. intracranial pressure?

Answer 15

raise the head and neck to promote venous drainage

Question 16

What is mannitol?

Answer 16

osmotic diuretic that decreases brain water and body water to increased intracranial pressure.

Question 17

When should you give dexamethasone?

Answer 17

stabilize vascular membranes and prevent vasogenic edema within 24 hrs. good for tumors or abscesses

Question 18

How does barbiturate coma help with increased intracranial pressure?

Answer 18

reduces metabolic rate of the cerebrum- decreased blood flow and intracranial pressure