Hydrocephalus and CSF Diversion

Hydrocephalus is an abnormal accumulation of cerebrospinal fluid within the ventricular system, arising from an imbalance between its production, circulation, and absorption. Cerebrospinal fluid diversion, by shunting or endoscopic techniques, is the principal surgical response, and its close coupling with intracranial infection is the reason this topic sits within the neuroinfection and inflammatory group.

Definition

Hydrocephalus is an abnormal accumulation of cerebrospinal fluid in the cerebral ventricles due to disturbed cerebrospinal fluid circulation or absorption; cerebrospinal fluid diversion is the redirection of cerebrospinal fluid, by an implanted shunt or by creating an alternative pathway endoscopically, to relieve it.

Scope

This entry describes hydrocephalus as a disturbance of cerebrospinal fluid dynamics and the concept of cerebrospinal fluid diversion that addresses it, with emphasis on how infection both causes hydrocephalus and complicates the devices used to treat it. It is a reference overview of mechanisms and relationships, not a description of operative or device-management protocols.

Core questions

• How does an imbalance between cerebrospinal fluid production, circulation, and absorption produce hydrocephalus?
• What distinguishes obstructive from communicating patterns of hydrocephalus?
• How does cerebrospinal fluid diversion, by shunt or endoscopic third ventriculostomy, relieve hydrocephalus?
• Why does infection both cause hydrocephalus and complicate the devices that treat it?

Key concepts

• Cerebrospinal fluid production, circulation, and absorption
• Obstructive versus communicating hydrocephalus
• Cerebrospinal fluid shunt (e.g. ventriculoperitoneal)
• Endoscopic third ventriculostomy as an alternative diversion
• Post-infective hydrocephalus
• Shunt and device-associated infection

Mechanisms

Cerebrospinal fluid is produced, circulates through the ventricular system and subarachnoid space, and is absorbed; hydrocephalus results when this balance is disturbed, either by obstruction of flow within or at the outlets of the ventricles (obstructive pattern) or by impaired absorption with patent pathways (communicating pattern). Cerebrospinal fluid diversion relieves the accumulation either by an implanted shunt that drains cerebrospinal fluid to another body cavity or by an endoscopic third ventriculostomy that creates an internal bypass. The relationship with infection runs in both directions: meningitis and ventriculitis can scar the cerebrospinal fluid pathways and cause post-infective hydrocephalus, while implanted shunts and external drains are themselves portals for healthcare-associated infection.

Clinical relevance

Hydrocephalus and cerebrospinal fluid diversion are placed alongside the neuroinfections because the two are tightly linked: central-nervous-system infection is an important cause of hydrocephalus, and the devices used to divert cerebrospinal fluid are a leading source of healthcare-associated ventriculitis and meningitis. Understanding these relationships supports critical appraisal of the relevant evidence and guidelines. This entry describes mechanisms and is not a basis for individual diagnostic or treatment decisions.

Epidemiology

Hydrocephalus occurs across the lifespan, from congenital and infant forms to normal-pressure hydrocephalus in older adults, and a substantial share of cases worldwide is attributable to infection. Cerebrospinal fluid shunts and external ventricular drains, while effective, carry a recognised risk of device-associated infection, which links hydrocephalus management to healthcare-associated central-nervous-system infection.

Seminal works

• stone-2014
• jeppsson-2013
• tunkel-2017

Frequently asked questions

Why is hydrocephalus grouped with neuroinfections in this taxonomy?

Because infection and hydrocephalus are tightly linked: meningitis and ventriculitis can scar cerebrospinal fluid pathways and cause hydrocephalus, while the shunts and drains used to divert cerebrospinal fluid are a leading source of healthcare-associated central-nervous-system infection.

What is the difference between obstructive and communicating hydrocephalus?

Obstructive hydrocephalus results from a blockage to cerebrospinal fluid flow within or at the outlets of the ventricular system, whereas communicating hydrocephalus arises when the pathways remain open but cerebrospinal fluid absorption is impaired.