Aetiology

Communicating hydrocephalus most commonly results from deficient reabsorption of CSF absorption due to thickening of the leptomeninges - pia-mater and arachnoid - and / or damage to the arachnoid granulations. Causes include:

• post-meningitis:
  • bacterial - pneumococcus more than meningococcus
  • tuberculosis
  • fungal
• subarachnoid haemorrhage - 80% of cases develop some degree of hydrocephalus
• trauma
• neoplastic infiltration in the subarachnoid space
• dural sinus thrombosis - not generally considered as a major cause of hydrocephalus

Less common mechanisms include:

• increased CSF viscosity - high protein content
• excess CSF production - choroid plexus papilloma