Disorders of Brain Function.

I. Manifestations of Brain Injury

A. Levels of Consciousness (LOC)

  • Physiology: Requires functioning of both cerebral hemispheres and the Reticular Activating System (RAS) in the brain stem.

  • Progression of Deterioration:

    • Confusion: Disoriented to time, place, or person; memory difficulty.

    • Delirium: Inattentive, lethargic, or agitated.

    • Obtundation: Responds verbally with a word; arousable with stimulation.

    • Stupor: Unresponsive except to vigorous/repeated stimuli.

    • Coma: Does not respond appropriately; sleeplike state.

  • Assessment: Glasgow Coma Scale (GCS) measures Eye Opening, Motor Response, and Verbal Response. Score range: 3 (worst) to 15 (best).

B. Posturing & Reflexes (Rostral-to-Caudal Deterioration)

  1. Decorticate (Flexion): Arms flexed/adducted, legs extended. Lesion in Cerebral Hemisphere or Internal Capsule.

  2. Decerebrate (Extension): Arms extended/rigid, palms turned away. Lesion in Midbrain/Upper Brain Stem. (More severe).

  3. Pupils:

    • Bilaterally small: Diencephalic injury.

    • Fixed and Dilated: Midbrain injury or uncal herniation (CN III compression).

  4. Respiratory:

    • Cheyne-Stokes: Diencephalic injury.

    • Neurogenic Hyperventilation: Midbrain injury (rate >40/min).

    • Ataxic/Apneic: Medullary injury.

C. Brain Death

  • Definition: Irreversible loss of function of the brain, including the brain stem.

  • Criteria: Absence of reflexes, absence of respiration (PCO2 rises to ≥60 mm Hg during apnea test), and identified irreversible cause.

II. Mechanisms of Injury

A. Hypoxia vs. Ischemia

  • Hypoxia: Low oxygen with maintained blood flow (e.g., CO poisoning). Causes euphoria/drowsiness.

  • Ischemia: Reduced blood flow. Interferes with oxygen and glucose delivery + waste removal. More damaging.

  • Global Ischemia:

    • Blood flow inadequate to entire brain (e.g., cardiac arrest).

    • Watershed Infarcts: Occur in border zones between arterial territories.

    • Laminar Necrosis: Short segments of necrosis in cortical layers.

  • Excitotoxicity (The Calcium Cascade):

    • Excess Glutamate opens NMDA receptors.

    • Calcium rushes into the cell, triggering enzymes that destroy DNA and cell membranes.

B. Intracranial Pressure (ICP)

  • Monro-Kellie Hypothesis: Cranial volume = Blood (10%) + Brain (80%) + CSF (10%). If one increases, another must decrease to maintain pressure.

  • Cushing Reflex (Late Sign): Hypertension (wide pulse pressure) + Bradycardia.

  • Herniation Patterns:

    • Cingulate: Displaced under falx cerebri. Signs: Leg weakness.

    • Central Transtentorial: Downward displacement. Signs: Small pupils, Cheyne-Stokes.

    • Uncal: Lateral mass pushes temporal lobe. Signs: Ipsilateral pupil dilation (CN III entrapment).

C. Cerebral Edema

  • Vasogenic: Fluid escapes into extracellular space due to Blood-Brain Barrier disruption (tumors, hemorrhage).

  • Cytotoxic: Intracellular fluid accumulation due to pump failure (hypo-osmotic states, ischemia).

III. Cerebrovascular Disease (Stroke)

A. Ischemic Stroke (87% of cases)

  • Thrombotic: Atherosclerotic plaque, often at bifurcations. Older adults.

  • Embolic: Moving clot (often from Atrial Fibrillation or Left Heart). Sudden onset.

  • Lacunar: Small infarcts in deep penetrating arteries (basal ganglia/brain stem). "Pure motor" or "pure sensory" deficits.

  • Penumbra: The "border zone" of dying cells around a core infarct. Can be saved if flow is restored.

  • Treatment: tPA (tissue plasminogen activator) within 3 to 4.5 hours of onset. CT must rule out hemorrhage first.

B. Hemorrhagic Stroke (Higher Mortality)

  • Intracerebral Hemorrhage: Spontaneous rupture (HTN, age).

  • Aneurysmal Subarachnoid Hemorrhage (SAH):

    • Berry Aneurysms: Found in Circle of Willis.

    • Symptoms: "Worst headache of life," nuchal rigidity, photophobia.

    • Complications: Rebleeding and Vasospasm (focal narrowing 3–10 days post-bleed).

IV. Traumatic Brain Injury (TBI)

A. Types of Hematomas

  • Epidural: Arterial bleed (Middle Meningeal Artery). Between skull and dura. Pattern: Unconscious $\rightarrow$ Lucid Interval $\rightarrow$ Rapid deterioration.

  • Subdural: Venous bleed (Bridging Veins). Between dura and arachnoid. Slower onset. Common in elderly/alcoholics due to brain atrophy.

  • Intracerebral: Bleeding within brain tissue (frontal/temporal lobes).

B. Injuries

  • Coup: Injury at impact site. Contrecoup: Rebound injury on opposite side.

  • Concussion: Transient dysfunction. Possible retrograde/anterograde amnesia.

V. Infections & Neoplasms

  • Meningitis: Inflammation of pia mater/arachnoid.

    • Bacterial: Purulent CSF, high neutrophils, low sugar. Signs: Nuchal rigidity, Kernig sign (resistance to leg extension), Brudzinski sign (neck flexion causes hip flexion).

    • Viral: Lymphocytes in CSF, normal sugar. Less severe.

  • Brain Tumors:

    • Glial: Astrocytomas (most common adult primary), Glioblastoma Multiforme (aggressive).

    • Meningiomas: Benign, slow-growing, outside the brain.

VI. Seizure Disorders

A. Classification

  • Focal: Begins in one hemisphere.

    • Without Impairment: Aware of event.

    • With Impairment: Psychomotor symptoms, automatisms (lip smacking), confusion.

  • Generalized: Both hemispheres involved. Unconsciousness.

    • Tonic-Clonic: Extension (tonic) followed by rhythmic jerking (clonic).

    • Absence: Nonconvulsive, blank stare. Common in children.

    • Atonic: "Drop attacks" (loss of tone).

B. Status Epilepticus

  • Definition: Seizures that do not stop spontaneously or occur without recovery. Medical emergency (respiratory failure risk).

  • Treatment: IV Diazepam or Lorazepam first-line.