What is the management approach for an adult patient with sunken flap syndrome post-craniotomy?

Management of Sunken Flap Syndrome Post-Craniotomy

Early cranioplasty is the definitive treatment for sunken flap syndrome and should be performed urgently when neurological deterioration occurs, with temporizing measures (Trendelenburg positioning, intravenous hydration, and elevation of VP shunt valve pressure if present) used only as a bridge to surgery. 1, 2, 3

Immediate Recognition and Diagnosis

Sunken flap syndrome occurs when the scalp sinks below the level of the skull defect edges, creating a pressure gradient where atmospheric pressure exceeds intracranial pressure, leading to neurological deterioration. 4, 5

Key diagnostic features to identify:

• Depression of the scalp below the plane of the skull defect 6, 4
• Postural (orthostatic) headaches that worsen when upright—present in 83% of symptomatic cases 1, 4
• Progressive neurological deficits that localize to the craniectomy site (hemiparesis, altered mentation, aphasia) 2, 5
• Symptoms that improve when lying flat (Trendelenburg position) 1, 3

Obtain emergent non-contrast head CT immediately to assess for:

• Paradoxical herniation (brain shifting toward the craniectomy defect) 4
• Subdural fluid collections (present in 11% of cases) 1
• Decreased size of surgical cavity or ventricular compression 6
• Midline shift toward the craniectomy side 4

Risk Factors and Timeline

The syndrome typically develops 3 to 5 months post-craniectomy, affecting approximately 11-25% of patients after decompressive craniectomy. 4

High-risk features include:

• Smaller craniectomy surface area (<80 cm²) 4
• Presence of VP shunt causing excessive CSF drainage 3
• Larger infarct volumes 4
• Delayed cranioplasty (>3 months) 4
• Older age 4

Temporizing Management (Bridge to Surgery Only)

These measures provide only temporary improvement and should never delay definitive cranioplasty: 1, 2, 3

1. Trendelenburg positioning (head declined 15-30° relative to feet) to increase cerebral blood flow and reduce atmospheric pressure gradient 1

2. Aggressive intravenous hydration to increase intracranial pressure and counteract the pressure differential 1

3. If VP shunt is present: Immediately elevate valve pressure or temporarily clamp the shunt to reduce CSF drainage 3

4. Avoid upright positioning until cranioplasty is performed 2, 4

Critical pitfall: Do not mistake temporary improvement with temporizing measures as resolution of the syndrome—these patients still require urgent cranioplasty. 2, 3

Definitive Treatment: Cranioplasty

Cranioplasty should be performed urgently (within days to weeks, not months) once sunken flap syndrome is diagnosed. 6, 2, 5

• Early cranioplasty (within 10 weeks of craniectomy) successfully reverses neurological deficits, though complication rates may be slightly higher than delayed cranioplasty 7, 6
• Patients demonstrate substantial improvements in functional, cognitive, and physical outcomes after cranioplasty 2
• The benefit of reversing neurological deterioration outweighs the marginally increased surgical risk of early cranioplasty 6, 2

Ensure adequate bone flap size (at least 12 cm diameter) during cranioplasty to prevent recurrence 7

Life-Threatening Complications to Monitor

Paradoxical herniation is the most severe complication, occurring when the pressure gradient causes brain tissue to herniate toward (not away from) the skull defect. 1, 4

Warning signs requiring immediate intervention:

• Acute deterioration in consciousness (Glasgow Coma Scale decline) 8, 5
• New pupillary abnormalities or anisocoria 8
• Seizures (occur in 22% of severe cases) 1
• Intraparenchymal hemorrhage (22% of severe cases) 1
• Cerebral venous thrombosis (3% mortality rate) 1

If paradoxical herniation develops before cranioplasty can be performed:

• Immediate Trendelenburg positioning 1
• Bolus intravenous fluids 1
• Emergency cranioplasty within hours, not days 4, 5

Special Considerations

Do not confuse sunken flap syndrome with other post-craniotomy complications:

• Recurrent stroke or hemorrhage presents acutely (within hours), not months later 9
• Infection presents with fever, wound erythema, and elevated inflammatory markers 5
• Hydrocephalus causes global neurological decline without postural component 3

Posterior reversible encephalopathy syndrome (PRES) may coexist with sunken flap syndrome and should be considered if seizures or visual disturbances are prominent. 6