How does a subdural empyema differ from a brain abscess?

A subdural empyema is a collection of pus outside the brain, in the subdural space between the dura and arachnoid, whereas a brain abscess is an encapsulated collection of pus within the brain parenchyma itself.

Why is the anatomy of the subdural space relevant to subdural empyema?

The subdural space is a continuous plane over the surface of the brain, so once pus enters it can spread relatively freely over the convexity and along the falx, which is why the infection can progress rapidly.

Subdural Empyema

Subdural empyema is a collection of pus in the space between the dura mater and the arachnoid membrane. Because this space offers little resistance to the spread of infection over the surface of the brain, subdural empyema is regarded as one of the most time-critical of the focal intracranial suppurative infections.

Definition

Subdural empyema is a suppurative infection forming a collection of pus in the subdural space, between the dura mater and the arachnoid, most often as a complication of sinus or middle-ear infection, meningitis, or cranial surgery and trauma.

Scope

This entry describes subdural empyema as an anatomically defined intracranial collection: the compartment it occupies, the sources from which it arises, how it spreads over the cerebral convexity, and how it relates to the other focal and diffuse central-nervous-system infections. It is a reference description and does not provide surgical or antimicrobial protocols.

Core questions

What anatomical compartment defines a subdural empyema and how does this differ from epidural and parenchymal collections?
From what sources does pus reach the subdural space?
Why does the anatomy of the subdural space allow infection to spread rapidly over the brain surface?
How does subdural empyema relate to meningitis and to brain abscess?

Key concepts

Subdural space (between dura and arachnoid)
Suppurative collection over the cerebral convexity or along the falx
Contiguous spread from paranasal sinus or middle-ear infection
Association with meningitis and venous complications
Distinction from epidural abscess and brain abscess
Post-traumatic and post-surgical subdural infection

Mechanisms

Most subdural empyemas arise by contiguous spread from infection of the paranasal sinuses or middle ear, with organisms reaching the subdural space directly or through the emissary veins; others follow meningitis, cranial trauma, or surgery, including infection of a pre-existing subdural collection. Because the subdural space is a continuous plane interrupted only by the dural folds, pus can spread relatively unimpeded over the cerebral convexity and along the falx, and the associated inflammation can provoke cortical venous and sinus thrombosis. The result is a combination of an expanding extra-axial collection and inflammation of the underlying brain.

Clinical relevance

Subdural empyema is important in neurosurgical infection practice as a focal, rapidly progressive suppurative collection that frequently arises from sinus or ear infection and that may coexist with meningitis. Understanding the compartment it occupies and how it spreads supports critical reading of the relevant evidence. This entry describes the entity and is not a basis for individual diagnostic or treatment decisions.

Epidemiology

Subdural empyema is uncommon among intracranial infections, but it is clinically important because of its tendency to progress rapidly. It is reported most often as a complication of paranasal sinus or middle-ear infection, and it may follow meningitis, trauma, or surgery; reported cases and series describe its association with these antecedent infections.

Seminal works

tunkel-2017
brouwer-2014

Frequently asked questions

How does a subdural empyema differ from a brain abscess?: A subdural empyema is a collection of pus outside the brain, in the subdural space between the dura and arachnoid, whereas a brain abscess is an encapsulated collection of pus within the brain parenchyma itself.
Why is the anatomy of the subdural space relevant to subdural empyema?: The subdural space is a continuous plane over the surface of the brain, so once pus enters it can spread relatively freely over the convexity and along the falx, which is why the infection can progress rapidly.