Chapter_16_Disorders_of_Brain_FunctionCopyright__2019_Wolters

Chapter 16: Disorders of Brain Function

Common Pathways of Brain Damage

The effects of ischemia

Excitatory amino acid injury

Cerebral edema

Injury due to increased intracranial pressure (ICP)

Conditions Causing Injury to the Brain

Trauma

Tumors

Stroke

Metabolic derangements

Degenerative disorders

Manifestations of Global Brain Injury

Alterations in sensory and motor function

Changes in the level of consciousness

Rostral-to-caudal stepwise progression

As the diencephalon, midbrain, pons, and medulla are affected, additional respiratory, pupillary, and eye movement reflexes and motor signs become evident.

Classifications of Skull Fractures

Simple or Linear

A break in the continuity of bone

Comminuted

A splintered or multiple fracture line.

Depressed

When bone fragments are embedded into the brain tissue, the fracture is said to be depressed.

Basilar

A fracture of the bones that form the base of the skull

Levels of Consciousness

Confusion

Delirium

Obtundation

Stupor

Coma

Injury from Excitatory Amino Acids

Definition

Injury to neurons caused by overstimulation of receptors for specific amino acids that act as excitatory neurotransmitters

Causes

Stroke

Hypoglycemic injury

Trauma to chronic degenerative disorders such as Huntington disease and Alzheimer dementia

Signs of Diminution in Level of Consciousness

Earliest Signs

Inattention, mild confusion, disorientation, and blunted responsiveness

With further deterioration

The person becomes markedly inattentive and variably lethargic or agitated.

The person may progress to become obtunded and may respond only to vigorous or noxious stimuli.

Medical Documentation of Brain Death

Cause and irreversibility of the condition

Absence of brain stem reflexes and motor responses to pain

Absence of respiration with a PCO2 of 60 mm Hg or more

The justification for use of confirmatory tests and their results

Criteria for Diagnosis of Vegetative State #1

Absence of awareness of self and environment

An inability to interact with others

Absence of sustained or reproducible voluntary behavioral responses

Lack of language comprehension

Hypothalamic and brain stem function to maintain life

Criteria for Diagnosis of Vegetative State #2

Bowel and bladder incontinence.

Variably preserved cranial nerve and spinal cord reflexes.

The condition has continued for at least 1 month.

Hypoxia and Ischemia

Hypoxia

A deprivation of oxygen with maintained blood flow

Ischemia

Reduced or interrupted blood flow

Focal cerebral ischemia—stroke

Global cerebral ischemia—MI

Question #1

Which of the following is not a common cause of neural injury?

Recreational drug use

Ischemia

Excitatory amino acids

Cerebral edema

Increased intracranial pressure (ICP)

Answer #1

A. Recreational drug use

Rationale: Recreational drug use can cause damage, but it is not a common cause.

Intracranial Pressure

Increased ICP is a common pathway for brain injury.

Can obstruct cerebral blood flow, destroy brain cells, displace brain tissue, and damage delicate brain structures

Cranial cavity

10% blood, 80% brain tissue, 10% CSF

Normal ICP 0 to 15 mm Hg

Monro-Kellie hypothesis of normalization of ICP

Brain Herniation #1

Cingulate

Involves cerebral artery

Clinical sign: leg weakness

Central Transtentorial

Involves the reticular activating system and corticospinal tract

Clinical signs: altered level of consciousness, decorticate posturing, rostral–caudal deterioration

Brain Herniation #2

Uncal

Involves the cerebral peduncle, oculomotor nerve, posterior cerebral artery, cerebellar tonsil, respiratory center

Clinical signs: hemiparesis, pupil dilation, visual field loss, respiratory arrest

Hydrocephalus

Definition

An abnormal increase in CSF volume in any part or all of the ventricular system

Enlargement of the CSF compartment occurs.

Types

Communicating

Decreased absorption of CSF

Noncommunicating

Overproduction of CSF

Cerebral Edema

Vasogenic Edema

Occurs with conditions that impair the function of the blood–brain barrier and that allow transfer of water and protein from the vascular into the interstitial space

Cytotoxic Edema

Involves an increase in intracellular fluid

Interstitial Cerebral Edema

Edema of the central white matter as in hydrocephalus affecting the brain

Types of Brain Injuries

Primary or Direct Injuries

Damage is caused by an impact.

Include diffuse axonal injury and the focal lesions of laceration, contusion, and hemorrhage

Secondary Injuries

Damage results from the subsequent brain swelling, infection, and cerebral hypoxia.

Often diffuse or multifocal, including concussion, infection, and hypoxic brain injury

Types of Hematomas

Brain injuries can be categorized as traumatic (i.e., epidural hematoma, subdural hematoma, concussion, contusion, or diffuse axonal injury) or nontraumatic brain injury (i.e., stroke, infection, tumor, or seizure).

Epidural hematomas, subdural hematoma, and traumatic intracerebral hematomas

Focal and Diffuse Brain Injuries

Primary brain injuries include focal (e.g., contusion, laceration, hemorrhage) and diffuse (e.g., concussion, diffuse axonal injury) injuries.

Secondary brain injuries are often diffuse or multifocal, including edema, infection, and hypoxic brain damage.

Coup–Contrecoup

The brain floats freely in the CSF; blunt force to the head accelerates the brain within the skull, and then the brain decelerates abruptly on hitting the inner skull surfaces.

Coup—direct contusion of the brain at the site of external force

Contrecoup—rebound injury on the opposite side of the brain

Question #2

Rotational acceleration of the head may result in which type of injury?

Coup

Contrecoup

Answer #2

B. Contrecoup

Rationale: Contrecoup is the rebound injury on the opposite side of the brain.

Postconcussion Syndrome

Concussion refers to “an immediate and transient loss of consciousness accompanied by a brief period of amnesia after a blow to the head.”

Recovery usually takes place in 24 hours.

Mild symptoms may persist for months:

Headache

Irritability

Insomnia

Poor concentration and memory

Types of Hematomas #1

Epidural Hematoma

Usually caused by head injury in which the skull is fractured

Develops between the inner table of the bones of the skull and the dura

Subdural Hematoma

Usually is the result of a tear in the small bridging veins that connect veins on the surface of the cortex to dural sinuses

Develops in the area between the dura and the arachnoid (subdural space)

Types of Hematomas #2

Traumatic Intracerebral Hematomas

May be single or multiple

Occur in any lobe of the brain but are most common in the frontal or temporal lobes

Structures Supplying Blood Flow to the Brain

Two internal carotid arteries anteriorly

Ophthalmic, posterior communicating, anterior choroidal, anterior cerebral, and middle cerebral

Vertebral arteries posteriorly

Internal carotid and vertebral arteries communicate at the base of the brain through the circle of Willis.

Cerebral Blood Flow

Autoregulation

Sympathetic stimulation

Metabolic factors

Carbon dioxide

Hydrogen ion

Oxygen concentration

Risk Factors and Deficits of Stroke

Age, sex, race

Family history

Hypertension

Smoking

Diabetes mellitus

Asymptomatic carotid stenosis

Sickle cell disease

Hyperlipidemia

Atrial fibrillation

Stroke-Related Deficits

Motor deficits

Dysarthria and aphasia

Cognitive and other deficits

Two Main Types of Strokes (Brain Attack)

Ischemic Strokes

Caused by an interruption of blood flow in a cerebral vessel and are the most common type of strokes, accounting for 70% to 80% of all strokes.

Hemorrhagic Strokes

Caused by bleeding into brain tissue usually from a blood vessel rupture caused by hypertension, aneurysms, arteriovenous malformations, head injury, or blood dyscrasias

Warning Signs and Danger Zones

Ischemic penumbra in evolving stroke

Transient ischemic stroke

Brain angina

Watershed zone

Signs and Symptoms of Cerebral Aneurysms

Most small aneurysms are asymptomatic.

Large aneurysms may cause chronic headache, neurologic deficits, or both.

Other manifestations include signs of meningeal irritation, cranial nerve deficits, stroke syndrome, cerebral edema and increased ICP, and pituitary dysfunction.

Hypertension and cardiac dysrhythmias result from massive release of catecholamines triggered by the subarachnoid hemorrhage.

Aneurysmal Subarachnoid Hemorrhage

Bleeding into the subarachnoid space

Causes

Congenital defect

Acute increases in ICP

Cigarette smoking

Hypertension

Excessive alcohol intake

Hemodynamic Effects of Arteriovenous Malformations

First, blood is shunted from the high-pressure arterial system to the low-pressure venous system without the buffering advantage of the capillary network.

The draining venous channels are exposed to high levels of pressure, predisposing them to rupture and hemorrhage.

Second, the elevated arterial and venous pressures divert blood away from the surrounding tissue, impairing tissue perfusion.

Question #3

Which type of stroke is the result of a ruptured blood vessel?

Ischemic

TIA

Arteriovenous malformation

Hemorrhagic

Answer #3

D. Hemorrhagic

Rationale: Hemorrhagic strokes are caused by the rupturing of a major vessel in the brain.

Typical Problems Arising from Stroke

Motor deficits are most common, followed by deficits of language, sensation, and cognition.

Classifications of Infections of the CNS Type of Invading Organism

By structure

Meninges: meningitis

Brain parenchyma: encephalitis

Spinal cord, myelitis

Brain and spinal cord: encephalomyelitis

By type of invading organism

Bacterial, viral, or other

Meningitis

Inflammation of the pia mater, the arachnoid, and the CSF-filled subarachnoid space

Fever and chills; headache; stiff neck; back, abdominal, and extremity pains; and nausea and vomiting

Acute lymphocytic meningitis

Acute purulent meningitis

Bacterial meningitis

Pneumococcus

Meningococcus

Viral meningitis

Encephalitis

Infection of the parenchyma of the brain or spinal cord

Local necrotizing hemorrhage

Progressive degeneration of nerve cell bodies

Prominent edema

Transmission

Ingestion

Mosquito

Rabid animal

Types

Viral

Herpes simplex virus, West Nile virus

Bacteria

Fungi

Classification of Brain Tumors

Primary intracranial tumors of neuroepithelial tissue

Neurons, neuroglia

Primary intracranial tumors that originate in the skull cavity but are not derived from the brain tissue itself

Meninges, pituitary gland, pineal gland, primary CNS lymphoma

Metastatic tumors

Benign versus malignant

Types and Symptoms of Brain Tumors

Ependymomas

Meningiomas

Primary CNS lymphomas

Increased ICP

Focal disturbances in brain function

Edema

Disturbances in blood flow

Tumor infiltration

Brain compression

Treatment and Evaluation Methods for Brain Tumors

Surgery

Irradiation

Chemotherapy

MRI

CT scans

Electroencephalogram

Visual field and funduscopic examination

Include physical and neurologic examinations

Epilepsy

Syndromes of associated seizure types

EEG patterns

Exam findings

Hereditary patterns

Precipitating factors

Seizures and Convulsions

Seizure

The abnormal behavior caused by an electrical discharge from neurons in the cerebral cortex

A discrete clinical event with associated signs and symptoms that vary according to the site of neuronal discharge in the brain

Manifestations generally include sensory, motor, autonomic, or psychic phenomenon

Convulsion

Specific seizure type of a motor seizure involving the entire body

Causes of Epilepsy #1

Seizures may be caused by alterations in cell membrane permeability or distribution of ions across the neuronal cell membranes.

Another cause may be decreased inhibition of cortical or thalamic neuronal activity or structural changes that alter the excitability of neurons.

Neurotransmitter imbalances such as an acetylcholine excess or γ-aminobutyric acid (GABA, an inhibitory neurotransmitter) deficiency have been proposed as causes.

Causes of Epilepsy #2

Certain epilepsy syndromes have been linked to specific genetic mutations causing ion channel defects.

Types of Seizures #1

Partial Seizures

Simple partial seizures

Complex partial seizures

Partial seizures evolving to secondarily generalized seizures

Unclassified Seizures

Inadequate or incomplete data

Types of Seizures #2

Generalized Seizures

Absence seizures

Atonic seizures

Myoclonic seizures

Tonic seizures

Tonic–clonic seizures

Status Epilepticus

Continual seizures

Do not stop spontaneously

Many types

If untreated or not stopped can lead to death due to respiratory failure

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