Tentorium Cerebelli

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Tentorium Cerebelli

• A portion of the dura mater that covers the
  cerebellum.
• An opening within the tentorium at the junction
  of the midbrain and the cerebrum is called the
  tentorium incisura.

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Tentorium Incisura

• The incisura is the weakest point of the cranial
  covering.
• The brain stem is directly below, and the third
  cranial nerves pass through the incisura.

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Great, Why Do We Care???

• If the tentorium incisura herniates due to
  increased intracranial pressure, then the third
  cranial nerve will be compressed.
• Further inferior herniation will will compress
  the tenth cranial nerve.

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Third Cranial Nerve Compression
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Tenth Cranial Nerve Compression
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Cerebral Blood Flow

• Cerebral blood flow is remarkably constant
  despite changes in blood pressure.
• However, it begins to decrease when the mean
  arterial pressure drops below 60mmHg.

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Mean Arterial Pressure

• MAP diastolic pressure 1/3 pulse pressure
• Pulse pressure systolic - diastolic
• B/P 120/80, MAP 80 1/3(40)
• MAP 93mmHg

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Cerebral Perfusion Pressure

• The residual pressure that supplies and
  distributes blood flow in the brain (CPP).

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What's Your Point???

• CPP MAP - ICP
• As ICP increases, than the CPP drops.
• As MAP decreases, than the CPP drops.

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Our Goal

• To maintain adequate MAP and decrease ICP to
  maintain an adequate CPP.

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Intracranial Pressure

• The pressure within the cranial vault.

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Intracranial Pressure

• Any time that pressure is increased in an
  enclosed vessel, the pressure is transmitted
  equally throughout the internal surface of the
  enclosed vessel. (Pascals Principle).
• Matter that is moved with pressure, will move in
  the path of least resistance.

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Causes of Increased ICP

• Cerebral Edema (swelling).
• Cerebral Hemmorhage.

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The bodys reaction

• As ICP increases CPP decreases, and the brain is
  forced into anerobic metabolism due to hypoxia.
• The initial response is to activate the
  cardiovascular system to increase blood pressure
  and increase blood flow.
• Respiration's increase in order to keep up with
  increased blood flow.

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The bodys reaction

• If ICP continues to rise then the brain will have
  no choice except to herniate through the
  tentorium or the foramen magnum, or both (path of
  least resistance).

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