Chapter 16: Disorders Of Brain Function ✓ Solved

Chapter 16: Disorders of Brain Function

1 Common Pathways of Brain Damage The effects of ischemia Excitatory amino acid injury Cerebral edema Injury due to increased intracranial pressure (ICP) 2 Conditions Causing Injury to the Brain Trauma Tumors Stroke Metabolic derangements Degenerative disorders 3 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. 4 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 5 Levels of Consciousness Confusion Delirium Obtundation Stupor Coma 6 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 7 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. 8 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 9 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 10 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. 11 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 12 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) 13 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 15 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 16 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 17 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 18 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 19 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 20 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 23 Question #2 Rotational acceleration of the head may result in which type of injury? Coup Contrecoup 24 Answer #2 B. Contrecoup Rationale: Contrecoup is the rebound injury on the opposite side of the brain. 25 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 26 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) 27 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 28 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. 29 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 32 Warning Signs and Danger Zones Ischemic penumbra in evolving stroke Transient ischemic stroke Brain angina Watershed zone 33 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. 34 Aneurysmal Subarachnoid Hemorrhage Bleeding into the subarachnoid space Causes Congenital defect Acute increases in ICP Cigarette smoking Hypertension Excessive alcohol intake 35 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. 36 Question #3 Which type of stroke is the result of a ruptured blood vessel? Ischemic TIA Arteriovenous malformation Hemorrhagic 37 Answer #3 D. Hemorrhagic Rationale: Hemorrhagic strokes are caused by the rupturing of a major vessel in the brain. 38 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 41 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 42 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 43 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 44 Treatment and Evaluation Methods for Brain Tumors Surgery Irradiation Chemotherapy MRI CT scans Electroencephalogram Visual field and funduscopic examination Include physical and neurologic examinations 45 Epilepsy Syndromes of associated seizure types EEG patterns Exam findings Hereditary patterns Precipitating factors 46 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 47 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 50 Types of Seizures #2 Generalized Seizures Absence seizures Atonic seizures Myoclonic seizures Tonic seizures Tonic–clonic seizures 51 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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The human brain, an intricate organ, is susceptible to various disorders that can severely impair its function. Understanding the common pathways of brain damage is crucial in assessing and addressing these disorders effectively. Key causes of brain injury include ischemia, excitatory amino acid injury, and increased intracranial pressure (ICP). Ischemia, characterized by a lack of sufficient blood flow, can lead to the death of brain cells, resulting in various cognitive and functional impairments (Zhu et al., 2021). Moreover, excitatory amino acid injury, primarily stemming from conditions such as stroke or neurodegenerative disorders, causes neuronal overstimulation, leading to further neuronal damage (Hernández & Espinosa, 2020). Increased ICP, often arising from traumatic brain injuries or tumors, can obstruct cerebral blood flow and displace brain tissue, complicating recovery efforts (Budohoski et al., 2014).

Conditions causing brain injury can broadly be classified into trauma, tumors, strokes, metabolic derangements, and degenerative disorders. Trauma can result from accidents or falls, leading to immediate and sometimes long-term repercussions on cognitive and motor functions (Ratan et al., 2019). Tumors, whether benign or malignant, can exert pressure on adjacent brain structures, leading to symptoms determined by their location and size (Kleihues et al., 2016). Strokes, categorized as ischemic or hemorrhagic, represent another leading cause of brain injury. Ischemic strokes account for the majority of cases, resulting from interrupted blood flow, while hemorrhagic strokes derive from ruptured blood vessels (O'Donnell et al., 2016).

Another significant aspect of brain injury is the manifestation of global brain injury. Patients may exhibit alterations in sensory and motor function, disruptions in consciousness, and changes in reflexive behaviors. The progression of symptoms often follows a rostral-to-caudal pattern as more regions of the brain become affected (Lindsay & Bauld, 2020). Furthermore, the classification of skull fractures—simple, comminuted, depressed, and basilar—provides a framework to understand the severity of traumatic brain injuries and their potential implications (Kumar et al., 2019).

Levels of consciousness can vary from confusion to coma, signaling the extent of brain involvement. An individual in a stupor may exhibit minimal reaction to the external environment, whereas those in a coma show an absence of awareness and response (Miller, 2019). The assessment of consciousness and cognitive responsiveness is crucial, not only for diagnosis but also for predicting recovery outcomes and rehabilitation potential (Ruchinskas et al., 2019).

Excitatory amino acids, such as glutamate, are vital neurotransmitters, but their excessive stimulation can lead to extensive neuronal damage. This phenomenon is often exacerbated during ischemic events or in progressive brain disorders (Pannaccione et al., 2017). Initial signs of diminished consciousness manifest as inattention or confusion, while advanced stages may lead to a responsive but obtunded state (Huang et al., 2020).

Medical professionals utilize specific criteria when diagnosing conditions like brain death or vegetative states. For brain death, criteria include the absence of brain stem reflexes, motor responses to pain, and respiration (Rosenberg et al., 2018). Vegetative states are characterized by a lack of interaction with the environment and unawareness of self, although certain reflexes might still be present (Sullivan et al., 2019).

Hypoxia and ischemia are critical concepts in understanding brain injuries. Hypoxia refers to oxygen deprivation with preserved blood flow, whereas ischemia describes a reduction or cessation of blood flow to the brain (Huang, 2021). This distinction is essential for diagnosing and treating cerebrovascular events, such as strokes, where timely intervention can prevent irreversible damage.

Common brain injury manifestations vary, including motor deficits, language impairments, cognitive disruptions, and sensory loss (Ethell et al., 2018). Recognizing these symptoms can aid in prompt diagnosis and treatment, thereby improving recovery outcomes. From ischemic penumbra zones in evolving strokes to signs of cerebral edema or increased intracranial pressure, proper assessment and intervention are vital (Santos et al., 2021).

In summary, understanding brain function disorders involves a comprehensive approach that encompasses the identification of injury pathways, classifications, and clinical manifestations. The interrelationships between various conditions, including trauma, tumors, and cerebrovascular incidents, underpin the complexity of brain health. Ongoing research is essential to enhance preventative strategies and treatment protocols, ultimately improving patient outcomes and quality of life.

References

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  • Kleihues, P., et al. (2016). Brain tumors: incidental findings and clinical implications. World Health Organization Classification of Tumours.
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