Chapter 23 – Central Nervous System
Edema, Herniation, and Hydrocephalus
Cerebral Edema
Cerebral edema is the accumulation of excess fluid within the brain parenchyma. There are
two types:
Vasogenic edema
o Integrity of the normal blood-brain barrier is disrupted
o Vascular compartment extracellular spaces
Cytotoxic edema
o Increase in intracellular fluid
o Hypoxic or ischemic insult or exposure to certain toxic.
The edematous brain is softer than normal and often appears to ‘overfill’ the cranial vault.
The gyri are flattened, the intervening sulci are narrowed, and the ventricular cavities are
compressed.
Hydrocephalus
Hydrocephalus refers to an increase in the volume of the CFS within the ventricular system.
This disorder most often is a consequence of impaired flow or decreased resorption of CSF.
If hydrocephalus develops in infancy before closure of cranial sutures, the head enlarges.
Once the sutures fuse, hydrocephalus causes ventricular expansion and increased
intracranial pressure.
Herniation
Herniation is the displacement of brain tissue from one compartment to another in response
to increased intracranial pressure. If the pressure is sufficiently high, portions of the brain
are displaced across these rigid structures. Three are three main types of herniation:
Subfalcine (cingulate) herniation
o Unilateral or asymmetric expansion displaces cingulate gyrus under the edge
of the falx
o Compression of anterior cerebral artery
Trans-tentorial (uncinate) herniation
o Medial aspect of the temporal lobe is compressed against the free margin of
the tentorium
o Comprising of third cranial nerve pupillary dilation and impaired ocular
movements
Tonsillar herniation
o Displacement of the cerebellar tonsils through the foramen magnum
o Brain stem compression and comprises vital respiratory and cardiac centers
Congenital Malformations and Perinatal Brain Injury
Malformations
Neural Tube Defects
Partial failure or reversal of neural tube closure may lead to several malformations, each
characterized by abnormalities involving neural tissue, meninges, and overlying bone or soft
, tissues. Most frequent type of CNS malformations. Neural tube defects include the
following:
Posterior end of the neural tube
o Spina bifida flat, disorganized segment of spinal cord associated with an
overlying meningeal outpunching.
Myelomeningocele
o Extension of CNS tissue through a defect in vertebral column
o Motor and sensory deficits in lower extremities and problems with bowel and
bladder control
Anencephaly
o Anterior end of the neural tube that leads to the absence of the forebrain and
top of the skull
Encephalocele
o Diverticulum of malformed CNS tissue extending through a defect in the
cranium
Forebrain Malformations
Microencephaly describes the group of malformations in which the volume of the brain is
too small. It has a wide range of associations, including chromosome abnormalities, fetal
alcohol syndrome, HIV and Zika virus. The unifying feature is decreased generation of
neurons destined for the cerebral cortex.
Megalocephaly, excessive brain volume that is always associated with a large head, is far less
common and is mostly associated with rare genetic disorders.
Posterior Fossa Anomalies
The most common malformations in this region of the brain result in misplacement or
absence of portions of the cerebellum:
Arnold-Chiari malformation (type II)
o Combines a small posterior fossa with a misshapen midline cerebellum and
downward extension of the vermis through the foramen magnum
Chiari Type I malformation
o Low-lying cerebellar tonsils that extend through the foramen magnum
o Results in partial obstruction of CNS flow and compression of medulla
o Symptoms of headache or cranial nerve deficits
Dandy-Walker malformation
o Enlarged posterior fossa, absence of cerebellar vermis and large midline cyst
Perinatal Brain Injury
The two major types of injury that occur in the perinatal period are hemorrhage and infarcts.
Increased risk for intraparenchymal hemorrhage within the germinal matrix. Hemorrhages
may extend into the ventricular system and from there to the subarachnoid spaces,
sometimes causing hydrocephalus.
Infections of the Nervous System
Infectious agents may reach the nervous system through the several routes:
Hematogenous spread
o Arterial blood supply
Edema, Herniation, and Hydrocephalus
Cerebral Edema
Cerebral edema is the accumulation of excess fluid within the brain parenchyma. There are
two types:
Vasogenic edema
o Integrity of the normal blood-brain barrier is disrupted
o Vascular compartment extracellular spaces
Cytotoxic edema
o Increase in intracellular fluid
o Hypoxic or ischemic insult or exposure to certain toxic.
The edematous brain is softer than normal and often appears to ‘overfill’ the cranial vault.
The gyri are flattened, the intervening sulci are narrowed, and the ventricular cavities are
compressed.
Hydrocephalus
Hydrocephalus refers to an increase in the volume of the CFS within the ventricular system.
This disorder most often is a consequence of impaired flow or decreased resorption of CSF.
If hydrocephalus develops in infancy before closure of cranial sutures, the head enlarges.
Once the sutures fuse, hydrocephalus causes ventricular expansion and increased
intracranial pressure.
Herniation
Herniation is the displacement of brain tissue from one compartment to another in response
to increased intracranial pressure. If the pressure is sufficiently high, portions of the brain
are displaced across these rigid structures. Three are three main types of herniation:
Subfalcine (cingulate) herniation
o Unilateral or asymmetric expansion displaces cingulate gyrus under the edge
of the falx
o Compression of anterior cerebral artery
Trans-tentorial (uncinate) herniation
o Medial aspect of the temporal lobe is compressed against the free margin of
the tentorium
o Comprising of third cranial nerve pupillary dilation and impaired ocular
movements
Tonsillar herniation
o Displacement of the cerebellar tonsils through the foramen magnum
o Brain stem compression and comprises vital respiratory and cardiac centers
Congenital Malformations and Perinatal Brain Injury
Malformations
Neural Tube Defects
Partial failure or reversal of neural tube closure may lead to several malformations, each
characterized by abnormalities involving neural tissue, meninges, and overlying bone or soft
, tissues. Most frequent type of CNS malformations. Neural tube defects include the
following:
Posterior end of the neural tube
o Spina bifida flat, disorganized segment of spinal cord associated with an
overlying meningeal outpunching.
Myelomeningocele
o Extension of CNS tissue through a defect in vertebral column
o Motor and sensory deficits in lower extremities and problems with bowel and
bladder control
Anencephaly
o Anterior end of the neural tube that leads to the absence of the forebrain and
top of the skull
Encephalocele
o Diverticulum of malformed CNS tissue extending through a defect in the
cranium
Forebrain Malformations
Microencephaly describes the group of malformations in which the volume of the brain is
too small. It has a wide range of associations, including chromosome abnormalities, fetal
alcohol syndrome, HIV and Zika virus. The unifying feature is decreased generation of
neurons destined for the cerebral cortex.
Megalocephaly, excessive brain volume that is always associated with a large head, is far less
common and is mostly associated with rare genetic disorders.
Posterior Fossa Anomalies
The most common malformations in this region of the brain result in misplacement or
absence of portions of the cerebellum:
Arnold-Chiari malformation (type II)
o Combines a small posterior fossa with a misshapen midline cerebellum and
downward extension of the vermis through the foramen magnum
Chiari Type I malformation
o Low-lying cerebellar tonsils that extend through the foramen magnum
o Results in partial obstruction of CNS flow and compression of medulla
o Symptoms of headache or cranial nerve deficits
Dandy-Walker malformation
o Enlarged posterior fossa, absence of cerebellar vermis and large midline cyst
Perinatal Brain Injury
The two major types of injury that occur in the perinatal period are hemorrhage and infarcts.
Increased risk for intraparenchymal hemorrhage within the germinal matrix. Hemorrhages
may extend into the ventricular system and from there to the subarachnoid spaces,
sometimes causing hydrocephalus.
Infections of the Nervous System
Infectious agents may reach the nervous system through the several routes:
Hematogenous spread
o Arterial blood supply
