A 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, with a number of antecedent causes. including 3:
- frontal sinusitis : vast majority
- mastoiditis / otitis media
- surgical intervention
- seeding of existing subdural haematoma
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.
Complications are relatively common and may be the cause of presentation. They include:
In the most common scenario patients develop subdural empyemas as a result of frontal sinusitis. There are two putative mechanisms of spread 3:
- direct extension
- 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.
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 on 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).
Treatment and prognosis
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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- 1. Sadhu VK, Handel SF, Pinto RS et-al. Neuroradiologic diagnosis of subdural empyema and CT limitations. AJNR Am J Neuroradiol. 1 (1): 39-44. AJNR Am J Neuroradiol (abstract) - Pubmed citation
- 2. Miller ES, Dias PS, Uttley D. Management of subdural empyema: a series of 24 cases. J. Neurol. Neurosurg. Psychiatr. 1987;50 (11): 1415-8. doi:10.1136/jnnp.50.11.1415 - Free text at pubmed - Pubmed citation
- 3. Scheld WM, Whitley RJ, Marra CM. Infections of the central nervous system. Lippincott Williams & Wilkins. (2004) ISBN:0781743273. Read it at Google Books - Find it at Amazon
Synonyms & Alternative Spellings
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