Brain Edema 

Definition

Brain edema = abnormal accumulation of water within brain parenchyma leading to increased brain volume, raised intracranial pressure (ICP), and impaired cerebral perfusion.

Why Brain Edema is Dangerous?

🔴 Monroe–Kellie Doctrine

The cranial vault contains:

• Brain tissue → ~80%
• Blood → ~10%
• CSF → ~10%

Total volume remains constant.
Increase in one component must be compensated by reduction in another.

When compensation fails → ICP rises → cerebral perfusion pressure falls → ischemia → herniation → death

Cerebral Perfusion Pressure Relationship

CPP = MAP – ICP

• Normal ICP: 5–15 mmHg
• ICP > 20–22 mmHg → pathological
• CPP < 60 mmHg → ischemic risk

Classification of Brain Edema

Brain edema is broadly divided into:

1. Vasogenic edema
2. Cytotoxic edema
3. Interstitial (hydrocephalic) edema
4. Osmotic edema
5. Hydrostatic edema (rare, controversial)

1. Vasogenic Edema

 Definition

Edema caused by blood–brain barrier (BBB) disruption leading to extracellular fluid accumulation.

 Pathophysiology

• Tight junction breakdown between endothelial cells
• Plasma proteins leak into extracellular space
• Osmotic gradient pulls water into interstitium
• Mainly affects white matter

 Causes

• Brain tumors
• Abscess
• Trauma
• Hemorrhage
• Inflammation
• Post-radiation injury

 Imaging Appearance

Clinical Clues

• Gradual onset
• Often reversible
• Responds well to corticosteroids

2. Cytotoxic Edema

Intracellular swelling due to failure of cellular ionic pumps, mainly Na⁺/K⁺ ATPase.

 Pathophysiology

• Energy failure → ATP depletion
• Na⁺ accumulates intracellularly
• Water follows sodium → cellular swelling

Affects:

• Neurons
• Astrocytes
• Endothelial cells

👉 Primarily affects grey matter

 Causes

• Ischemic stroke
• Hypoxic brain injury
• Severe hypoglycemia
• Toxins
• Early traumatic brain injury

Imaging Characteristics

 Key Clinical Insight

👉 Cytotoxic edema is irreversible early marker of infarction
👉 Does NOT respond to steroids

3. Interstitial Edema (Hydrocephalic Edema)

Fluid accumulation due to CSF transudation across ventricular lining.

 Pathophysiology

• Increased intraventricular pressure
• CSF migrates into periventricular white matter

 Causes

• Obstructive hydrocephalus
• Aqueductal stenosis
• Tumor blocking CSF pathways

Imaging Clues

• Periventricular lucency
• Ventricular dilation
• Seen best on FLAIR MRI

Treatment Principle

👉 CSF diversion (EVD, VP shunt)

4. Osmotic Brain Edema

Occurs when plasma osmolality decreases relative to brain osmolality, causing water entry into brain tissue.

Pathophysiology

Brain adapts slowly to osmotic changes. Rapid serum osmolar reduction causes:

• Cellular swelling
• Diffuse cerebral edema

🧾 Causes

• Rapid correction of hypernatremia
• Hyponatremia
• Dialysis disequilibrium syndrome
• SIADH
• Excess hypotonic fluids

Clinical Clue

👉 Diffuse global cerebral edema
👉 No focal lesion

5. Hydrostatic Edema

Occurs due to increased capillary hydrostatic pressure.

Rarely discussed but seen in:

• Severe hypertension
• Posterior reversible encephalopathy syndrome (PRES)

Clinical Manifestations

Early Signs

• Headache
• Nausea
• Vomiting
• Altered mentation

Late Signs

• Papilledema
• Cranial nerve palsies
• Cushing reflex
• Hypertension
• Bradycardia
• Irregular respiration

Terminal

• Herniation
• Brainstem failure

Radiological Diagnosis

CT Brain

Fast and first-line in emergency.

Findings:

• Hypodensity
• Sulcal effacement
• Ventricular compression
• Midline shift

MRI Brain

Gold standard for early edema detection.

Sequences:

• DWI → cytotoxic edema
• FLAIR → vasogenic / interstitial
• ADC → infarct confirmation

Management of Brain Edema 

Stepwise Management

1. General Neuroprotective Measures

Head Position

• Elevate head 30°
• Maintain neutral neck alignment

Oxygenation

• Maintain SpO₂ > 94%
• Avoid hypoxia

Hemodynamics

• Maintain adequate CPP
• Avoid hypotension

2. Osmotherapy

Mannitol

Dose:

• 0.25–1 g/kg IV bolus

Mechanism:

• Plasma osmolarity increase
• Draws water from brain

Monitoring:

• Serum osmolarity (<320 mOsm/kg)
• Renal function

Osmotic Brain Edema — CONTRAINDICATED / MAY WORSEN

Mechanism

Occurs due to:

• Hyponatremia
• Rapid fall in plasma osmolality
• Dialysis disequilibrium

Why Mannitol Is Dangerous

• May further worsen osmotic imbalance
• Can cause rebound cerebral edema

👉 Treatment = Correct underlying osmolar disorder

Diffuse BBB Breakdown / Late Injury — RISK OF REBOUND EDEMA

In severe BBB disruption:

• Mannitol may enter brain tissue
• Water follows → worsens edema

Hypertonic Saline

Common regimens:

• 3% saline bolus
• 23.4% saline in refractory ICP

Advantages:

• Maintains intravascular volume
• Less diuresis than mannitol

3. Ventilation Strategy

Hyperventilation

• Temporary rescue therapy
• Target PaCO₂: 30–35 mmHg

Mechanism:

• Cerebral vasoconstriction
• Reduced cerebral blood volume

4. Corticosteroids

Indications

✔ Tumor edema
✔ Abscess edema

Contraindicated

❌ Traumatic brain injury
❌ Ischemic stroke

Drug:

• Dexamethasone preferred

5. CSF Drainage

• External ventricular drain
• Useful in hydrocephalus

6. Sedation and Metabolic Suppression

• Propofol
• Barbiturate coma in refractory ICP

7. Temperature Control

• Prevent hyperthermia
• Therapeutic hypothermia (select cases)

8. Surgical Decompression

Indications

• Malignant cerebral edema
• Refractory ICP

Procedures:

• Decompressive craniectomy
• Tumor resection
• Hematoma evacuation