What is a subdural hygroma?

Subdural Hygroma: Definition and Clinical Significance

A subdural hygroma is a collection of cerebrospinal fluid (CSF) in the subdural space, typically occurring through tears in the arachnoid membrane that allow CSF to leak into the subdural compartment. 1, 2

Pathophysiology and Etiology

• Subdural hygromas form when CSF leaks through arachnoid tears into the subdural space, creating a fluid collection with low oncotic pressure compared to venous blood 3, 2
• Common causes include:
  • Traumatic brain injury (most common cause) 4
  • Spontaneous intracranial hypotension (SIH) due to spinal CSF leaks 1, 5
  • Post-meningitis complication 6
  • Non-traumatic causes (less common) 3

Clinical Presentation

• Many subdural hygromas are asymptomatic and discovered incidentally 2
• When symptomatic, presentations may include:
  • Headache, particularly orthostatic (positional) headache in cases associated with SIH 5, 1
  • Neurological deficits if significant mass effect develops 4
  • Symptoms of underlying condition (e.g., postural headache in SIH) 5

Diagnosis

• MRI of the brain with contrast is the preferred imaging modality for suspected subdural hygroma 1
• CT scan shows hypodense subdural collection without enhancement or neomembrane, with minimum 3mm distance between skull and brain 4
• When SIH is suspected, imaging of the entire spine is recommended to identify potential CSF leak sites 5, 1
• Diagnostic criteria include:
  • CSF-like fluid density/intensity on imaging
  • Absence of blood products or membrane formation
  • Location in subdural space 4

Classification

Based on pathophysiology, traumatic subdural hygromas can be classified into three groups 4:

• Group Ia: Simple hygroma without ventricle dilation or mass effect
• Group Ib: Associated with ventricular dilation (external hydrocephalus form)
• Group II: With significant mass effect requiring intervention

Treatment Approach

• Treatment should be guided by the patient's symptoms, underlying cause, and presence of mass effect, with small or asymptomatic hygromas managed conservatively while treating any underlying CSF leak, and symptomatic hygromas with significant mass effect requiring surgical drainage. 1

For Asymptomatic or Minimally Symptomatic Hygromas:

• Conservative management with observation and serial imaging 1, 2
• Most resolve spontaneously as the brain re-expands 2

For Hygromas Associated with SIH:

• Treat the underlying CSF leak as the primary management strategy 1
• Epidural blood patch (EBP) is the first-line treatment 1
• Maintain bed rest in supine position as much as possible 1
• For persistent leaks requiring surgical intervention, repair of the dural defect may be necessary 5, 1

For Symptomatic Hygromas with Mass Effect:

• Surgical drainage via burr hole is indicated 1, 4
• In spinal subdural hygromas, lumbar puncture may be effective in achieving resolution 7

Complications and Monitoring

• Potential complications to monitor for:
  • Transformation into chronic subdural hematoma 2
  • Cerebral venous thrombosis, particularly in cases associated with SIH 1, 5
  • Superficial siderosis in cases of persistent CSF leaks 1
  • Neurological deterioration due to mass effect 4

Post-Treatment Management

• For patients treated with EBP for SIH-related hygromas:
  • Maintain supine position with head elevated as comfortable 1
  • Lie flat as much as possible for 1-3 days after procedure 1
  • Minimize bending, straining, stretching for 4-6 weeks 1
  • Follow-up imaging to assess resolution 1

Prognosis

• Most subdural hygromas resolve spontaneously without specific treatment 2
• Outcome is typically related to the primary condition (e.g., head injury) rather than the hygroma itself 2
• A small percentage may progress to chronic subdural hematomas if predisposing conditions persist 2