This article includes discussion of intracranial subdural empyema, pachymeningitis interna, purulent pachymeningitis, subdural abscess, parafalcine subdural empyema, and posterior fossa subdural empyema. The foregoing terms may include synonyms, similar disorders, variations in usage, and abbreviations.
Intracranial subdural empyema represents infection arising in the cleavage plane between the cranial dura mater and the arachnoid. Although the condition is traditionally associated with sinusitis or otitis, it may also occur as a complication of other cranial or dental infections, neurosurgical procedures, or cranial trauma. Intracranial subdural empyema represents one of the most dangerous of all intracranial processes because it can spread rapidly to cover an entire cerebral hemisphere or much of the posterior fossa, producing a rapidly expanding, potentially fatal mass lesion. In this article, the author reviews the pathogenesis, clinical features, diagnosis, and treatment of this disorder.
• Intracranial subdural empyema represents loculated infection in the potential space between the outer layer of the meninges, the dura, and the arachnoid. This area encompasses a large intracranial area in which infection can rapidly spread to cover, and compress, an entire hemisphere or much of the posterior fossa.
• The condition is most commonly a complication of sinusitis or otitis, particularly in males in later childhood, adolescence, or early adulthood, but may also occur as a complication of neurosurgical procedures. The condition may be preceded by epidural abscess.
• Subdural empyema should be suspected in any febrile patient with rapidly developing signs indicating involvement of an entire cerebral hemisphere.
Historical note and terminology
The fact that ear infections could progress to delirium and death was known to ancient writers including Hippocrates (Wispelwey et al 1997), but the association of this process with intracranial extension of infection was not understood. Although a case suggestive of subdural empyema was described by Richter in 1773 (Courville 1939), recognition of subdural empyema as a distinct clinical and pathological entity did not occur until the mid-19th century (Courville 1939; Kubik and Adams 1943). Major case series in the past century included those of Kubik and Adams, Courville, and Schiller and colleagues (Courville 1934; Courville 1939; Kubik and Adams 1943; Schiller et al 1948). Early terms for the condition included "pachymeningitis interna" (to distinguish the entity from epidural abscess, termed "pachymeningitis externa") and "purulent pachymeningitis." Association of intracranial subdural empyema with sinus and ear infections came through case series published in the late 19th and early 20th centuries (Courville 1934; Courville 1939; Kubik and Adams 1943).
Subdural empyema was initially purely a clinical diagnosis, and its rapid progression and malignant course were such that Le Beau termed intracranial subdural empyema "the most imperative of all neurosurgical emergencies" (Le Beau et al 1973). Before the advent of MRI, diagnosis of subdural empyema was made by burr holes, angiography, or, beginning in the mid-1970s, by CT. Treatment was invariably surgical, with antibiotics being assigned an adjunctive but not curative role. The introduction of MRI, however, has provided a rapid, noninvasive method for diagnosing and following subdural empyemas too small to require surgery (Weingarten et al 1987; Sze and Zimmerman 1988; Komori et al 1992; Ogilvy et al 1992). With the widespread use of CT and then MRI, mortality from subdural empyema has fallen, and it has become possible (in occasional, carefully selected cases) to treat a subdural empyema with antibiotic therapy alone (Mauser et al 1985; Leys et al 1990; Obana and Rosenblum 1992; French et al 2014).
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