Neurologic Diseases (Exam III)-Mordekai Flashcards
What factors affect cerebral blood flow?
- CMR (cerebral metabolic rate)
- CPP (cerebral perfusion pressure. MAP - ICP)
- ICP
- PaCO₂
- PaO₂
- Various drug and intracranial pathologies
What vessels provide the blood flow to the brain?
- 80% via the carotid arteries
- 20% via the vertebral arteries
What is the average cerebral blood blow?
50ml/100g/min
* Approx - 750mL/min total
What percent of cardiac output goes to cerebral blood flow?
15%
What structures are contained in the intracranial and spinal vault?
What 2 structures enclose these vaults?
- Neural tissue (brain and spinal cord)
- blood
- CSF
- Dura mater
- Bone
Under normal conditions, what is the combined volume of brain tissue, intracranial CSF, and intracranial blood?
1200-1500mL
What is the Monroe Kellie Doctrine?
Any increase in one component of the intracranial space (blood, brain tissue, CSF) must be offset with an equivalent decrease in another component to prevent an elevated ICP.
Name the three components of the brain that form the Monroe-Kellie Doctrine.
- Brain 80%
- Blood 12%
- CSF 8%
What mengial barriers seperate the brain contents?
- Falx cerebri - a reflection of dura that seperates the 2 cerebral hemispheres.
- Tentorium cereblli - a reflection of the dura that lies rostral to the cerebellum and marks the border between the supratentorial and infratentorial spaces.
What happens when you hvae an increase in the contents of one region of the brain?
- This will cause regional increases in ICP, and in extreme cases, the contents will herniate into different compartments of the brain.
What are herniation syndromes categorized by?
The region of the brain affected.
What is subfalcine herniation?
Herniation of hemispheric contents under the falx cerebri, typically compressing branches of the anterior cerebral artery.
What range is normal for ICP?
5 - 15 mmHg
What is transtentorial herniation?
- Herniation of the supratentorial contents past the tentorium cerebelli, causing brain stem compression in a rostral to caudal direction.
What are the S/S of transtentorial herniation?
- AMS
- Defects in gaze and ocular reflexes
- hemodynamic and respiratory compromise
- Eventual death
What is Uncal herniation?
- A subtype of transtentorial herniation, where the uncus (medial portion of the temporal lobe) herniates over the tentorium cerebelli.
- This results in ipsilateral oculomotor nerve dysfunction.
What are the signs and symptoms of uncal herniation?
- pupillary dilation
- ptosis
- lateral deviation of the affected eye.
- brain stem compression
- eventual death
Why do the pupils become fixed and dilated with uncal herniation?
CN-3 (oculomotor) crosses near tentorium and is compressed by the herniation.
What is herniation of the cerebellar tonsils?
- Occurs due to elevated infratentorial pressure, causing the cerebellar structures to herniate through the foramen magnum.
What are the S/S of herniation of the cerebellar tonsils?
- Medullary dysfunction
- cardiorespiratory instability
- subsequently death
What is the most common site of brain herniation?
Uncal
↑ICP forces temporal uncus into the infratentorial space (see 3 on the figure below).
Label the sites of brain herniation
- Subfalcine
- Transtentorial
- Herniation of Cerebellar tonsils
- Traumatic event causing herniation out of cranial cavity
What are causes of increased ICP?
- Tumors (directly because of their size, indirectly by causing edema in surrounding brain tissue, and by obstructing CSF flow as seen with tumors involving the 3rd ventricle)
- Intracranial hematomas (Cause increasedd ICP similar to mass lesions)
- Blood in the CSF (as seen in subarachnoid hemorrhage, which may lead to obstruction of CSF reabsorption, and granulations can further exacerbate increased ICP)
- Infections (such as meningitis or encephalitis can lead to edema or obstruction of CSF reabsorption)
- Aqueductal stenosis
What symptoms are seen with abnormally high ICP?
- Headache
- N/V
- Papilledema
- ↓LOC