Flashcards in Herniation Deck (18)
What are the components of the blood brain barrier?
astrocyte endfeet, pericytes, capillaries with tight junctions
What are the areas devoid of blood brain barrier?
posterior pituitary (for vasopressin and oxytocin)
area postrema (vomiting center)
pineal gland (melatonin and neuropeptides to regulate daytime and nighttime)
How much CSF is made per day, and what is its distribution?
150 around the brain at a time
2/3 in intracranial compartment; 1/3 in spinal cord
What are the 2 kinds of edema and what are their sources?
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
4 locations of herniation?
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
What are the 2 most clinically relevant herniations?
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)
What are clinical signs of supratentorial transtentorial herniation?
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
What are some signs of chronic tonsillar herniation/
paresthesias, head tilt, stiff neck, arching of the neck
What is a characteristic sign on autopsy of transtentorial herniation?
multiple, linear, midline hemorrhages in the midbrain and upper pons- hemorrhages of Duret
What is hydrocephalus ex vacuo?
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
When might you see communicating hydrocephalus?
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
Treatment for chronic hydrocephalus
permatent ventriculo-peritoneal shunt
4 causes of coma- general
supratentorial mass lesions, infratentorial mass lesions, metabolic encephalopathy, psychogenicW
What may 6th nerve palsies suggest in the context of herniation?
false localizing sings in pts with diffusely elevated pressure
What is the first treatment for all cases of incr. intracranial pressure?
raise the head and neck to promote venous drainage
What is mannitol?
osmotic diuretic that decreases brain water and body water to increased intracranial pressure.
When should you give dexamethasone?
stabilize vascular membranes and prevent vasogenic edema within 24 hrs. good for tumors or abscesses