Subdural empyema

Subdural empyema (SDE) is uncommon, but nonetheless can account for a significant number of intracranial infections.

Subdural empyemas account for approximately 20-33% of all intracranial infections.

Clinical presentation depends to some degree on the aetiology. When empyemas result from sinusitis or mastoiditis they are often associated with seizures, focal neurological deficits and rapid deterioration in conscious state, progressing from obtundation to coma 1. Empyemas that occur secondary to prior trauma or surgery are usually more indolent clinically.

In the most common scenario patients develop subdural empyemas as a result of frontal sinusitis. There are two putative mechanisms of spread 3:

  1. direct extension
  2. indirect: secondary to thrombophlebitis

Direct spread, resulting from erosion of the posterior wall of the frontal sinus (the corollary of Pott's puffy tumour) is relatively uncommon. Thrombophlebitis of communicating veins is thought to be the most common cause of spread 3.


Complications are relatively common and may be the cause of presentation. They include:

CT is usually the first investigation performed, and often is the only one required as patients usually expediently proceed to theatre for evacuation.


Subdural empyemas typically resemble subdural haematomas in their shape and the relationship to sutures and dural reflections. They are typically crescentic in shape (compared to epidural empyemas which are typically lentiform) although collection pockets may appear bi-convex (see case 1). A surrounding membrane that enhances intensely and uniformly following contrast administration is typically identified.


Appearance on MRI is similar to that on CT although there is a greater ability to detect contrast enhancement. Furthermore, the content of the collection can demonstrate restricted diffusion (see case 1).

MRI is also more sensitive to the complications of subdural empyemas, e.g. cerebritis, cerebral abscess, venous thrombosis.

Mortality associated with subdural empyemas now approaches 10%, compared with approximately 15-40% in the pre-CT era 1.

Successful treatment is predicated on prompt diagnosis, followed by surgical evacuation of the collection and administration of appropriate antibiotics.

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Article information

rID: 13827
Section: Pathology
Synonyms or Alternate Spellings:
  • Sub-dural empyema (SDE)
  • Subdural empyemas

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Cases and figures

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    Case 1: T1 C+
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    Case 1: DWI
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    Case 2: T2
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    Case 2: T1 C+
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    Case 3: with concurrent porecephalic cyst posteriorly
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    Subdural collecti...
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