FRCA Notes

Hydrocephalus

This topic isn't actually mentioned in the curriculum, rather just its sequelae of raised ICP and the need for shunt insertion.

Nevertheless, it appeared as a CRQ in 2022 (90% pass rate), with the examiners labelling it a 'straightforward question'.

Resources

  • Hydrocephalus is a congenital or acquired condition in which there is an excessive accumulation of CSF within the head
  • Incidence:
    • Congenital paediatric hydrocephalus: 0.5 in 1,000 live births
    • Adult normal pressure hydrocephalus: 5 in 100,000
  • Can be classified as communicating or non-communicating, as well as congenital or acquired
Communicating Non-communicating
Congenital Achondroplasia
Craniofacial syndromes		 Sylvian aqueduct stenosis
Chiari malformation
Vein of Galen aneurysm
Dandy-Walker syndrome
Acquired SAH or IVH
Choroid plexus papilloma
Post-infectious		 Tumours
Cerebellar haemorrhage
Post-inflammatory adhesions

Communicating hydrocephalus

  • Free flow and transmission of CSF pressure waves from the ventricles into the basal cisterns and spinal CSF channels
  • Typically there is impaired CSF reabsorption into the dural venous sinuses
    • E.g. from blockage of the arachnoid granulations by RBC breakdown products following haemorrhage
  • Uncommonly there is over-production of CSF e.g. choroid plexus papilloma
  • There is increased intraventricular pressure, causing cerebral distension and compression
  • Can often safely drain CSF by lumbar route

Non-communicating hydrocephalus

  • A.k.a. obstructive hydrocephalus, due to blockage of CSF flow at any point within the ventricular system
  • One of the more common causes is stenosis of the aqueduct of Sylvius, which can be internal, congenital or by external compression e.g. pineal tumour
  • There is often acutely, significantly raised ICP
  • Unlikely to be able to be safely drained via the lumbar route and needs direct drainage e.g. external ventricular drain

Normal pressure hydrocephalus

  • A variant of communicating hydrocephalus characterised by a chronic (over years) development of:
    • Progressive gait impairment
    • Cognitive decline
    • Urinary incontinence
  • The baseline ICP is often normal and there aren't features of raised ICP

Other types

  • External hydrocephalus - accumulation of CSF in the basal cisterns
  • Ex-vacuo hydrocephalus - secondary enlargement of the ventricles due to atrophy of the brain tissue

  • Features depend partially on pathology, site of CSF flow obstruction and rapidity of onset

  • Headache; worse in the morning and on raising ICP e.g. lying flat, leaning forward, sneezing/coughing/straining
  • Vomiting, typically without nausea
  • Diplopia (CN VI palsy)
  • Reduced upwards gaze (Parinaud's syndrome)
  • Seizures
  • Impaired conscious level

  • Chronic hydrocephalus leads to altered gait, cognitive decline, urinary incontinence, headaches and enlarged ventricles

  • Standard neuroimaging, although may be difficult to interpret

  • CSF dynamics e.g. intrathecal/intraventricular saline infusion test
    • Measure CSF outflow resistance and therefore patient's CSF absorptive capacity
    • Can be used to assess shunt function
    • Units of measurement are the Rout (mmHg/min)

  • May not need intervention in the asymptomatic patient with chronically enlarged ventricles under normal pressure
  • Drug treatment for symptomatic hydrocephalus is often ineffective

External ventricular drains

  • Ventricular drains are typically inserted for:
    • Acute onset hydrocephalus e.g. following SAH or tumours
    • Facilitating removal of infected apparatus in shunt-dependent patient
    • Administration of intraventricular drugs
  • Inserted into the frontal horn of a lateral ventricle
  • Zeroed to the foramen of Munro (∽external auditory meatus)

  • Lumbar drains are another option, inserted for:
    • Intracranial procedures to facilitate surgical exposure
    • Spinal cord protection during AAA surgery
    • Decompression of post-operative sub-galeal scalp collections

    Complications of EVD
    Haemorrhage
    Displacement of the catheter
    Seizures
    Infection (5 - 20%)

Shunt

  • Diversion of CSF from right lateral ventricle (or sometimes left lateral ventricle, or lumbar spine)
    • Temporary → external receptacle
    • Permanent → shunt into peritoneal cavity, pleural cavity or right atrium
  • Shunts are typically antibiotic- or silver-coated to reduce infection risk
  • See: anaesthesia for shunt insertion

Endoscopic third ventriculostomy

  • For non-communicating hydrocephalus
  • Bypasses obstructions to CSF flow at the level of the aqueduct of Sylvius
  • Benefits from avoiding complications of shunts, and obviates shunt dependency

Subsection

  • Normal ICP is lower in neonates and infants; 0 - 6mmHg
  • Children with congenital hydrocephalus are more likely to have:
    • Multisystem disorders, including cardiac defects or major spinal defects
    • Comorbidities such as cerebral palsy or epilepsy
  • Children often present for repeated or revision surgeries

Paediatric-specific symptoms

  • Irritability
  • Drowsiness
  • Bulging fontanelles
  • Increased head circumference (infants)
  • Propensity to apnoeic episodes (neonates)