ICP and Herniation Syndromes Flashcards Preview

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Flashcards in ICP and Herniation Syndromes Deck (11)
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1

Monroe Kellie Doctrine

States that the total volume of intracranial contents is constant.

In adults, this is about 1700cc. VBrain + Vcsf + Vblood + Vmass = constant

As Vmass increases, body compensates by lowering Vcsf and Vblood (esp venous blood) - increased CSF absorption at arachnoid villae

2

Normal ICP

5-20cm measured by ventriculostomy

3

Rate of CSF formation

500cc/day in choroid plexus

4

4 causes of increased ICP

1) Increased intracranial volume (cerebral or extracerebral) - mass or hemorrhage

2) Acute generalized brain swelling - anoxia, hepatic encephalopathy, Reyes, hypertensive encephalopathy

3) CSF flow obstruction or impaired absorption - obstructive hydrocephalus

4) Increased CSF production - choroid plexus papilloma

5

General symptoms of increased ICP

HA, nausea, vomit, lethargy, visual changes

Papilledema** (all patients with increased ICP) - blurring of optic disc margins

Specific - related to anatomic consequence (types of herniation)

6

Subfalcine herniation

When ipsilateral cingulate gyrus is pushed under the falx cerebri to contralateral side.

This causes compression of contralateral frontal lobe and bilateral anterior cerebral arteries

This can lead to bilateral ACA infarcts presenting as leg weakness, incontinence, and mental status changes

7

Uncal herniation

When the uncus (medial projection of parahippocampal gyrus on basal surface of cerebellum) herniates under the tentorial notch

This causes compression of the ipsilateral posterior cerebral artery and the adjacent oculomotor nerve - causes ipsilateral mydriasis

As syndrome progresses, PCA infarcts (ipsilateral or bilateral) occur as well as complete ipsilateral oculomotor palsy

Interestingly, this syndrome can lead to an ipsilateral hemiparesis by compressing the contralateral cerebral peduncle against the tentorium at the so-called Kernohan's notch. This is a false localizing sign as the culprit lesion causes a hemiparesis on the ipsilateral side of the body by compressing contralateral structures

8

Cerebellar tonsilar herniation

When increased ICP causes the cerebellar tonsils to displace inferiorly through the foramen magnum, causing medullary compression. This leads to respiratory depression and is usually a fatal event.

9

Treatment of elevated ICP

Through decreasing volume of intracranial contents and by increasing cerebral blood floow

1) Elevate head of bed to 30deg. This assists in CSF flow and absorption

2) Administer osmotic agent like mannitol which works immediately by increasing plasma volume, thereby increasing MAP and CBF. It also acts as osmotic diuretic drawing fluid from the cranial circulation as it does not cross the BBB. Dose related tox is renal failure.

3) Hyperventilation in intubated patient will cause immediate drop in ICP by vasoconstriction of cerebral small vessels. These vessels are exquisitely sensitive to local pH and constrict in the presence of a high pH, as in the case of decreased pCO2. Downside is that in long run, it will decrease CBF and is therefore only used in acute, emergent setting

4) Barbs - no longer routinely recommended

5) Hypothermia - maybe

6) Steroids - not used for routine reduction of ICP. They are useful only when there is a component of vasogenic edema usually in setting of a mass (tumor or abscess)

10

Cerebral blood flow

AKA Cerebral Perfusion Pressure

MAP minus ICP

The higher the ICP the lower the CBF

11

Brain elastance

Ratio of change in ICP to change in CSF volume. In normal brain, infusion of 1cc of CSF causes rise in ICP by 0-2mmHg, resulting in elastance of 1mmHg/mL

In a swollen brain that has already employed its compensatory mechanisms, the elastance can be 10-20