The designation subdural empyema (less accurately termed a subdural abscess) refers to a collection of pus in the potential space between the dura and the arachnoid. It usually results from extension of infection from primary foci in the ears or sinuses. It is an infrequent complication of intracranial surgery, and may rarely represent a metastatic infection from a remote focus
Predisposing, Factors and Pathologic Features.
More than half of the cases of subdural empyema develop in patients with chronic paranasal sinus infection, usually frontal. An acute exacerbation of the sinusitis just prior to the development of the subdural infection is common. Osteomyelitis of the frontal bone and an epidural abscess often accompany subdural empyema. Chronic otitis media and mastoiditis result in subdural empyema less often than formerly. Postoperative infection, penetrating wounds, infection in subdural hematomas, bacteremia, pulmonary infection, and (very rarely) bacterial meningitis are other sources of subdural empyema.
Infection spreads from the sinuses or mastoid by direct erosion of bone and dura or through, infected veins. Thrombosis of cortical veins is observed in 90 per cent of fatal cases. Once pus forms in the subdural space it spreads widely over the convexity of the hemisphere and mesially along the falx. Rarely, the exudate extends beneath the falx to the opposite side. Purulent subarachnoid exudate is usually present immediately subjacent to the subdural exudate.
Streptococci, often non-group A or anaerobic strains, are implicated most commonly, but a wide variety of gram-negative organisms are also found. Postoperative infections are usually due to Staphylococcus aureus.
The symptoms and signs of antecedent sinusitis, otitis, or osteomyelitis often blend into those of subdural empyema. Swelling and erythema of the tissues overlying the primary infection may be prominent, and per :ussion of the underlying bone may evoke considerable pain. In the early stages, pain or headache is mild and is limited to the area over the subdural infection. As the illness progresses, headache becomes generalized and severe; concomitantly high fever, chills, vomiting, and nuchal rigidity develop. Progressive obtundation, culminating in coma within 48 to 72 hours, occurs in untreated cases.
Focal or generalized seizures and hemiparesis are common. Sensory deficits and visual field defects and dysphasia also occur. Although these signs are in part attributable to the compressive effects of a mass lesion, the associated thrombophlebitis of cortical veins and the consequent infarction of cerebral tissue are probably of equal importance. In the late stages, the intracranial pressure is- severely increased, but papilledema is rare except in chronic cases in which the clinical course has been modified by antimicrobial therapy. Without treatment, death usually occurs within a few day- of onset of focal neurologic signs.
The cerebrospinal fluid pressure is elevated, and the fluid characteristically contains a few hundred to a thousand or more neutrophils, a normal amount of sugar, and no organisms. Roentgenograms of the skull may show destructive changes in the frontal or mastoid bones. Carotid angiography and diagnos burr hole examination help to distinguish suL dural empyema from brain abscess.
You Must Follow Subdural Empyema Treatment Guidelines
The patient with a subdural empyema requires prompt and adequate surgical drainage by multiple burr holes or craniotomy Surgical treatment of the accompanying sinusitis- frontal osteomyelitis, or mastoiditis is a secondary consideration and is usually postponed until the acute intracranial infection has subsided.
Vigorous systemic therapy with penicillin (10 million to 20 million units daily) and/or other antimicrobials, depending on the background of the case, is begun before surgery and continued until the infection has been completely controlled. The results of smear and culture of pus obtained at the time of operation may dictate changes in the antimicrobial regimen. Bacitracin or other antimicrobial drugs are commonly instilled into the subdural space at the time of operation and for a variable period thereafter.