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Subdural Hygroma

Summary

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  • Subdural hygroma is a collection of cerebrospinal fluid (CSF) in the subdural space without blood
  • Often occurs following head trauma or neurosurgical procedures
  • Imaging shows a crescent-shaped, extra-axial fluid collection with CSF density on CT and CSF signal characteristics on MRI

Pathophysiology

  • Proposed mechanisms include:
    • Tearing of arachnoid membrane, allowing CSF to enter subdural space
    • Redistribution of CSF due to altered CSF dynamics
    • Expansion of subdural space due to brain atrophy or decreased intracranial pressure
  • May resolve spontaneously or progress to chronic subdural haematoma

Demographics

  • Can occur in all age groups
  • More common in:
    • Elderly patients with brain atrophy
    • Infants with traumatic birth or child abuse
    • Patients following neurosurgical procedures or head trauma

Diagnosis

  • Often asymptomatic and discovered incidentally
  • When symptomatic, may present with:
    • Headache
    • Altered mental status
    • Focal neurological deficits
    • Seizures (rare)
  • Clinical history of recent head trauma or neurosurgical intervention is important

Imaging

  • CT findings:
    • Hypodense, extra-axial, crescent-shaped fluid collection
    • Density similar to CSF (0-20 Hounsfield units)
    • No enhancement with contrast
    • May cause mild mass effect
  • MRI findings:
    • T1: hypointense (isointense to CSF)
    • T2: hyperintense (isointense to CSF)
    • FLAIR: suppressed signal (unlike subdural haematoma)
    • DWI: no restricted diffusion
    • No enhancement on post-contrast images
  • Differentiation from chronic subdural haematoma can be challenging

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  • A 70-year-old patient with gait disturbance and cognitive impairment underwent an intraventricular shunt for normal pressure hydrocephalus (albeit without classical imaging appearances).
  • The patient had a persistent headache post-operatively. On the third post-operative day, an MRI showed bilateral subdural collections containing small regions of susceptibility (due to blood product) that resulted in effacement of the lateral ventricles.

Treatment

  • Asymptomatic cases:
    • Conservative management with close monitoring
    • Serial imaging to assess for resolution or progression
  • Symptomatic cases or significant mass effect:
    • Surgical evacuation (burr hole drainage or craniotomy)
    • Subdural-peritoneal shunt placement in recurrent cases
  • Treat underlying cause (e.g., CSF leak repair)
  • Address predisposing factors (e.g., anticoagulation management)

Differential diagnosis

Differential Diagnosis Differentiating Feature
Chronic Subdural Haematoma Hygroma has lower density on CT; no blood products on MRI
Arachnoid Cyst Hygroma follows CSF signal on all MRI sequences; arachnoid cyst may have different signal
Subdural Empyema Empyema shows rim enhancement on contrast MRI and restricted diffusion; hygroma has no enhancement or DWI restriction
Epidural Haematoma Hygroma is crescent-shaped and crosses sutures; epidural haematoma is typically biconvex and does not cross sutures
Cerebral Atrophy Hygroma more likely to be focal; atrophy shows generalised sulcal widening with vessels in traversing the CSF space