Neurology and Hypoxia Quiz

Pathology of the Central Nervous System

• The average brain weight is ~1400 gm in men and ~1250 gm in women.
• The brain is covered by three layers of membranes called meninges: dura mater (tough, fibrous outer layer), arachnoid mater (thin, intermediate layer), and pia mater (delicate, inner layer with blood vessels).
• The brain surface has folds called gyri and grooves called sulci.

Outline

• Introduction/Relevant Anatomy
• Developmental Anomalies
• Cerebral Edema, Hydrocephalus, Raised ICP & Herniation
• Infections
• Cerebrovascular Diseases
• Traumatic Brain Injury
• Degenerating Diseases
• Spongiform Encephalopathy
• CNS Tumor

Cerebral Edema

• Excess fluid within the brain parenchyma.
• May be localized or generalized.
• Vasogenic edema: Due to increased vascular permeability or disruption of the blood-brain barrier.
• Cytotoxic edema: Due to perturbation of normal plasma membrane permeability.
• Generalized edema often combines elements of both vasogenic and cytotoxic edema.
• Morphology: Flattened gyri and narrow sulci, compressed ventricles.
• Causes: CNS infections, chronic lung diseases, metabolic disorders.

Complications of Cerebral Edema

• Raised intracranial pressure
• Herniation
• Ischemic injury

Herniation

• Displacement of brain tissue past rigid dural folds or through skull openings due to increased intracranial pressure.
• Types:
  • Subfalcine (cingulate) herniation: Cingulate gyrus of one hemisphere herniates under the falx cerebri, potentially compressing the anterior cerebral artery and causing secondary infarcts.
  • Transtentorial (uncal, mesial temporal) herniation: Medial aspect of temporal lobe herniates through free margin of tentorium, potentially compressing the third cranial nerve (leading to pupillary dilation and impaired ocular movements).
  • Tonsillar herniation: Displacement of cerebellar tonsils through foramen magnum, life-threatening due to brainstem compression and compromising medulla vital centers.

Hydrocephalus

• Accumulation of excessive cerebrospinal fluid (CSF) within the ventricular system.
• Caused by disturbance in formation, flow, or absorption of CSF.
• Results in raised intracranial pressure (ICP) and ventricular dilation.
• Common in children, but can occur in adults.
• Causes (children): Arnold-Chiari malformations, stenosis of the aqueduct of Sylvius, Dandy-Walker syndrome.
• Causes (adults): Tumors (e.g., choroid plexus papilloma), inflammation (meningitis).

Traumatic Brain Injury

• Important cause of death and permanent disability in modern society.
• Types of injury:
  • Skull fractures: May indicate the nature of the fall. Basal fractures are commonly associated with CSF leakage from nose/ears and cranial nerve injury.
  • Parenchymal injury (concussion, contusion, laceration): Transient altered consciousness due to head trauma, resulting in complete neurologic recovery. Contusions typically accompany subarachnoid hemorrhage.
  • Vascular injury: Disruption of vessel walls causing hemorrhage—types include epidural hematoma (arterial blood, rapid expansion), subdural hematoma (venous blood, gradual expansion), intraparenchymal hematoma (within brain tissue), and subarachnoid hemorrhage (arterial bleed).

Cerebrovascular Diseases (CVD)

• Brain injury caused by altered blood flow (ischemia/hypoxia or hemorrhage).
• Stroke: Neurological signs/symptoms of vascular origin with acute onset lasting >24 hours.
• Etiopathogenesis:
  • Ischemia/Hypoxia: Thrombosis, embolism, hypoxia (low oxygen tension, decreased oxygen-carrying capacity, toxic substances)
  • Hemorrhage: Hypertension, aneurysm, developmental malformations.
• Morphology of Ischemia/Hypoxia
  • Focal ischemia: Reduction/cessation of blood flow causing localized area of necrosis (cerebral infarction) and neuronal death (apoptosis/necrosis).
  • Global hypoxic-ischemic encephalopathy: Generalized reduction of cerebral perfusion from cardiac arrest, diminished oxygen capacity, or shock/hypotension. Results in watershed/border-zone infarcts and lamina necrosis.
  • Lacunar infarcts: Small cavitary infarcts/necrotic spaces resulting from thrombosis of deep penetrating arteries, commonly involving the putamen, globus pallidus, thalamus, internal capsule, caudate nuclei, and pons.

Neurodegenerative Disorders

• Progressive loss of specific neuron groups.
• Accumulation of resistant protein aggregates (tangles, plaques, Lewy bodies).

Prion Diseases (Spongiform Encephalopathy)

• Rapidly progressive neurodegenerative disorders caused by aggregation & intercellular spread of misfolded proteins (prions).
• Prion diseases exhibit spongiform changes and rapidly progressive dementia.
• May be sporadic, familial, or transmitted.

Alzheimer Disease (AD)

• Most common cause of dementia in older adults.
• Insidious onset of cognitive impairment.
• Pathologic hallmarks: Amyloid plaques (Aβ peptides) and neurofibrillary tangles (aggregated tau protein).
• Causes neural dysfunction.

Parkinson Disease (PD)

• Hypokinetic movement disorder caused by loss of dopaminergic neurons in the substantia nigra.
• Protein aggregation (Lewy bodies).
• Second most common neurodegenerative disorder affecting individuals ≥65 years.
• Etiology includes mutations in genes encoding a-synuclein, DJ-1, PINK1, and parkin.

CNS Infections

• Infectious agents damage the nervous system by direct injury, initiating an inflammatory response, or immune mechanisms.
• Entry routes: hematogenous, direct implantation, local extension, and along nerves.
• Types of CNS Infections: Meningitis, encephalitis, brain abscess.

Meningitis

• Inflammation of the leptomeninges and CSF within the subarachnoid space.
• Types include:
  • Acute pyogenic (bacterial): Purulent exudate, dense neutrophil infiltration, dilated blood vessels, and edema.
  • Viral (aseptic): Mild lymphocytic infiltrate in leptomeninges.
  • Chronic (tuberculous, treponemal): Granulomatous inflammation, well circumscribed parenchymal masses (tuberculomas).
• Clinical correlates include meningeal irritation (neck stiffness, headache), raised ICP, systemic inflammatory response (fever), and neurologic impairment (photophobia, clouding of consciousness).
• Potential complications like Waterhouse-Frederichsen syndrome (adrenal hemorrhage).
• Diagnostics including CSF analysis (cloudy/purulent, raised WBCs, protein, decreased glucose) and microbiological examination.

Acute Focal Suppurative Infections (Brain Abscess)

• Localized liquefactive necrosis of brain tissue with accompanying inflammation, often caused by bacterial infection.