Topic 36 - Cerebral edema, hydrocephalus, malformations of the brain

What is cerebral edema? What are the 3 different types?

What

• accumulation of excess fluid within the brain parenchyma

Types

• vasogenic

• cytotoxic

• interstitial

What causes vasogenic cerebral edema (3)? How does it develop? What are 2 types? What does the edema fluid contain?

Cause

• inflammation

• ischemia

• tumor

How

• BBB is damaged → allows fluid to shift from the intravascular compartment into the extracellular compartment of the brain

Types

• localized

• generalized

Contains

• proteins

What characterizes cytotoxic cerebral edema? What causes it?

Characteristic

• an increase in intracellular fluid of the cells in the CNS

Cause

• metabolic disorder → ischemia or toxins (e.g. uremia) → dysfunction of Na+/K+ ATPase

What leads to interstitial edema? How does it differ from vasogenic edema?

What

• disruption of CSF-brain barrier → CSF enters the brain interstitium

How

• contains almost no proteins

What is the appearance of the brain in case of generalized edema (3)?

Flattened gyri

Narrowed sulci

Compressed ventricular cavities

What are 4 categories of causes of increased intracranial pressure? What are examples? (name some)

Mass in the brain

• tumor

• edema

• abscess

Generalized edema

• trauma

• ischemia

• uremia

Decreased reabsorption of CSF

• obstructive hydrocephalus

• meningitis

Increase in intracerebral blood volume

• hypercapnia

• venous sinus thrombosis

• venous congestion

What are 5 consequences of increased intracranial pressure?

• Headache

• Papilloedema - swelling of the optic disc

• Altered consciousness

• Decerebration - quadriplegia with all extremities extended

• Cerebral herniation

What are the 3 types of cerebral herniation?

• Subfalcine herniation

• Transtentorial herniation

• Foraminal herniation

When does subfalcine herniation occur? What is a possible consequence? What is another name for the condition?

When

• unilateral or asymmetric expansion of a cerebral hemisphere herniates the cingulate gyrus medially, under the edge of the falx cerebri

Consequence

• compression of the anterior cerebral artery

Name

• cingulate herniation

When does transtentorial herniation occur? What are possible consequences (2)? What is another name for the condition?

When

• medial aspect of the temporal lobe is compressed against the free margin of the tentorium cerebelli, which allows it to herniate inferiorly along the brain stem

Consequences

• compression of the oculomotor nerve → ptosis, mydriasis and ophthalmoplegia (drooping of eyelid, dilated pupil, and weakness of one or more extraocular muscles)

• rupture of arteries and veins in the pons → Duret bleeding

Name

• uncinate herniation

When does foraminal herniations occur? What is a consequence? What is another name for the condition?

When

• cerebellar tonsils herniate through the foramen magnum

Consequence

• compression of vital respiratory and cardiac centers in the medulla oblongata

Name

• tonsillar herniation

What is the most serious form of herniation?

Foraminal/tonsillar herniation

What is hydrocephalus? What are the most common causes (2)? What are the 3 major types?

What

• increased amount of CSF in the ventricular system

Most common

• impaired flow

• obstruction

Types

• communicating type

• non-communicating type

• hydrocephalus ex vacuo

When does non-communicating hydrocephalus occur? What does it lead to?

When

• there is an obstruction of CSF flow within the ventricles - most commonly at the site of the foramina of Monro or at the site of the cerebral aqueduct

Result

• dilation of parts of the ventricular system

When does communicating hydrocephalus occur? What are 4 examples of causes?

When

• there is an obstruction of CSF flow outside the ventricles, or when there is a reduction in CSF absorption

Causes

• tumor

• congenital malformations

• chronic meningitis

• subarachnoid hemorrhage

What is normal pressure hydrocephalus?

A form of communicating hydrocephalus where there is a classic triad of symptoms - dementia, gait disturbance and incontinence

What is hydrocephalus ex vacuo? When does it occur?

What

• a compensatory increase in CSF volume due to atrophy of the brain parenchyma

When

• after degenerative diseases or infarcts

What percentage of the population have CNS malformations? What are the 4 categories of developmental malformations?

Percentage

• 1-2% - more common in people who have multiple birth defects

Categories

• neural tube defects / spinal dysraphisms

• forebrain anomalies

• posterior fossa anomalies

• spinal cord anomalies

What are 2 neural tube defects? What are 3 subtypes of one of them?

Anencephaly

Spina bifida

-spina bifida occulta

-meningocele

-meningomyelocele

What are 7 forebrain anomalies?

Holoprosencephaly

Microcephaly

Megalencephaly

Lissencephaly

Polymicrogyria

Corpus callosum agenesis

Cortical malformation

What are 2 posterior fossa anomalies?

Dandy-Walker malformation

Arnold-Chiari malformation

What are 2 spinal cord anomalies?

Hydromyelia

Syringomyelia

When does formation of the neural tube occur? What leads to neural tube defects? What is the most important cause? What are other causes (2)?

When

-early in the embryogenesis

What

-improper closure of the neural tube

Most important

-folate deficiency

Others

-genetic

-hyperthermia

What are the most important neural tube defects (4)? What is the problem in each?

Anencephaly

-absence of the brain and top of skull

Spina bifida occulta

-asymptomatic bone defects

Meningocele

-defect in the vertebral column containing dura and arachnoid maters

Myelomeningocele

-defects in the vertebral column containing dura and arachnoid maters and spinal cord

What is the most common congenital CNS malformation? What are common symptoms of this condition?

What

-spina bifida

Symptoms

-back pain

-paraplegia

-meningitis

What leads to development of forebrain anomalies? What is the most frequent result of it?

What

-abnormal proliferation and migration of subependymal progenitor cells

Result

-development of fewer mature neurons -> microcephaly - may also cause megalencephaly

What are anomalies of the forebrain associated with (4)?

Chromosome abnormalities

Fetal alcohol syndrome

HIV infection

DM in the mother

What are the 7 most important forebrain abnormalities?

Holoprosencephaly

Lissenhephaly/pachygyria

Microcephaly

Megalencephaly

Polymicrogyria

Corpus callosum agenesis

Cortical malformation

What is lissencephaly? What is microcephaly? What is megalencephaly? What is polymicrogyria? What is cortical malformation often associated with?

Lissencephaly

-decreased/absence of gyration - smooth-surfaced brain

Microcephaly

-smaller than average brain

Megalencephaly

-larger than average brain

Polymicrogyria

-increased, abnormal gyri - cobblestone-like surface

Cortical malformation

-epilepsy

What does holoprosencephaly involve? What occurs in mild forms? What occurs in severe forms? What is it associated with?

What

-abnormal fission and rotation of the forebrain - disrupts the normal midline-pattern of the brain

Mild

-only the olfactor bulbs and related structures are absent (potentially other things too)

Severe

-the brain may not be divided into hemispheres and lobes

Associated with

-facial midline defects - e.g. cyclopia

What do posterior fossa anomalies involve? What are the 2 most important ones?

What

-misplacement or absence of portions of the cerebellum

Most important

-Arnold-Chiary malformations

-Dandy-Walker malformations

How many types of Arnold-Chiari malformations are there? What may it involve (4)?

Types

-4 - I is the mildest

What

-tonsillar herniation

-lumbar meningomyelocele

-cerebellar hypoplasia

-syringomyelia

What does Dandy-Walker involve (4)?

An enlarged posterior fossa

Hypoplastic vermis

Cystic 4th ventricle

Non-communicating hydrocephalus

What do spinal cord anomalies involve? What are the 2 most important ones?

What

-abnormalities of the spinal cord that don't affect the spinal column or overlying skin

Types

-hydromyelia - dilated central canal

-syringomyelia - fluid-filled cyst in spinal cord