Edema Types and Mechanisms

Edema

• Extracellular Edema:
  • Vasogenic: Disruption of the blood-brain barrier (BBB), increasing permeability of blood vessels, common in white matter.
  • Interstitial: Transependymal flow of cerebrospinal fluid (CSF) causing hydrocephalus and fluid accumulation in the ventricles.
• Intracellular Edema:
  • Cytotoxic: Increased intracellular fluid secondary to cell injury, increasing osmotic pressure.
    • Vasogenic brain edema: Extracellular edema due to increased permeability of brain capillaries (BBB breakdown), mainly in white matter.
    • Cytotoxic (cellular) brain edema: Intracellular edema due to osmotic imbalance between the cell and the extracellular fluid, mainly in gray matter.
    • Interstitial (hydrocephalic) brain edema: Extracellular edema in periventricular white matter due to transependymal flow of CSF in hydrocephalus.

Principal Types of Brain Edema

• Cytotoxic edema → Infarction, trauma
• Vasogenic edema → Brain tumor
• Interstitial edema → Hydrocephalus
• Osmotic edema → Hemodialysis

Etiology of Brain Edema

• Space occupying lesions
• Malignancies/tumors
• Hydrocephaly
• Post-traumatic (cytotoxic edema)
• Metabolic disorders (hyperglycemia - common in uncontrolled diabetes)

Herniation

• Anatomic Factors: Rigidness of cranial vault and dural reflections (dural sinuses and dural folds).
• Types:
  • Subfalcine herniation
  • Transtentorial herniation
  • Tonsillar herniation
• Subfalcine: Herniation of Cingulate gyrus under the Falx cerebri. Anterior gyrus regulates motivation, attention, and behavior; posterior gyrus regulates learning and memory.
• Subdural hematoma: Decrease the occupying mass (drain the blood) or secondary to a tumor (resect or not; depending on type)

Transtentorial Herniation

• Compression: Temporal lobe is compressed against the free margin tentorium cerebri, affecting the 3rd cranial nerve.
• Symptoms: Pupil dilation, impaired ocular movement (ipsilateral); compression of the posterior cerebral artery resulting in ischemic injury to the visual cortex.
• Finding: Homonymous hemianopsia with macular sparing.
• Down and Out: Unopposed superior oblique and lateral rectus muscles lead to down and out gaze with mydriasis. Patient loses accommodation resulting in blurry vision.
• Contralateral: Compression in posterior cerebral artery leads to contralateral homonymous hemianopsia with macular sparing

Tonsillar Herniation

• Compression: Displacement of cerebellar tonsils through the foramen magnum resulting in the compression of the brain stem.

Diagnostic Tests for Hydrocephalus

• CT Scan
• MRI
• Surgical drainage
• Diuretics (Mannitol (1.25g/kg IV over 30-60 minutes, may repeat q 6 to 8hrs)

Hydrocephalus

• Increased production or accumulation of cerebrospinal fluid (CSF).
• Communicating: Obstruction mainly produces CSF and accumulation inside.
• Non-communicating: Obstruction in the passage of CSF within the ventricular system.

Cerebrovascular Disorders

• Generalized reduction in blood flow leading to hypoxic ischemic injury in watershed areas (dual supply from two arteries).

  • Watershed zones: Regions of brain receiving dual blood supply branches of two major arteries.
  • Major arteries: MCA, PCA, ACA

Vascular Disorders

• Infarction (80%): Local vascular occlusion (may result in hemorrhages within the parenchyma or subarachnoid space). More common in males, during or after age 70.
• Predisposing factors:
  • Arterial hypertension (HTN)
  • Diabetes Mellitus (DM)
  • Atherosclerosis
  • Smoking

Stroke and Transient Ischemic Attack (TIA)

• Ischemic (80%) most common cause, characterized by a blood clot stopping blood flow to a brain area.

• Hemorrhagic (20%) characterized by weakened or diseased blood vessels rupturing, causing blood leakage into brain tissue.

• Stroke Symptoms: lasting less than 1hr termed TIA.

• TIA Recurrence: 35%.

• Risk Factors: Age, family history, alcohol use, male sex, hypertension, cigarette smoking, hypercholesterolemia, diabetes, use of certain drugs (cocaine, amphetamines)

Intracranial Hemorrhage (ICH)

• Complications:

  • Sleep disorders
  • Confusion
  • Depression
  • Incontinence (urinary/fecal)
  • Pneumonia
  • Swallowing dysfunction, leading to dehydration/malnutrition
  • Immobility (thromboembolic disease, pressure ulcers, contractures)
  • Impaired ADLs, higher brain functions, memory, and verbal communication.

• Evaluation and Diagnosis: Stroke suspected with sudden neurologic deficits, severe headache, unexplained coma, or sudden impairment of consciousness, require immediate neuroimaging to differentiate hemorrhagic from ischemic stroke and detect signs of increased intracranial pressure.

Treatment for Stroke

• Stabilization: Comatose/non-responsive patients (GCS ≤ 8) require airway support.
• Increased intracranial pressure (ICP): Monitor and measure; reduce cerebral edema.
• Supportive care: Correct coexisting abnormalities (fever, hypoxia, dehydration, hypoglycemia, hypertension)
• Pharmacological: Thrombolytic agents (eg, streptokinase), anticoagulants (e.g., aspirin, Plavix), antihypertensives.

Hemorrhages

• Parenchymal (non-traumatic): Common in 50-60-year-olds. Hypertension is a major cause (>/=50%).
• Causes: congenital disorders, trauma,

Aneurysms

• Saccular/dilations: Congenital defect in the media of arteries at points of bifurcation, affecting vessels composing the Circle of Willis (80%).
• Common location: Bifurcation of internal carotid artery branches (ACA).
• More common in women before age 50.
• Critical size for intervention: 4-6mm.
• Treatment: Surgical clipping within 6 minutes of aneurysm detected to prevent irreversible brain damage.

Arteriovenous Malformation (AVM)

• Congenital vascular abnormalities in the brain (cerebral hemispheres, middle cerebral artery).

Trauma (Epidural/Subdural Hematoma)

• 70% of head trauma survivors are permanently disabled.

• Epidural: Rupture of meningeal artery.
• Subdural: Disruption of bridging veins.

Traumatic Parenchymal Injuries

• Concussion: Transient loss of consciousness with paralysis/seizures, followed by complete recovery.
• Contusion: Hemorrhage of superficial brain parenchyma at the impact site.
• Coup: Changes immediately under the impact site.
• Countercoup: Changes at the opposite, distant impact point.

Test your knowledge on the various types of edema affecting the brain, including extracellular and intracellular forms. This quiz covers vasogenic, cytotoxic, and interstitial edema, along with their underlying mechanisms and effects on the brain's physiology.