The underlying arachnoid and subarachnoid spaces are usually unaffected, but a large subdural empyema may produce a mass effect.

Further, a thrombophlebitis may develop in the bridging veins that cross the subdural space, resulting in venous occlusion and infarction of the brain.

With treatment, including surgical drainage, resolution of the empyema occurs from the dural side, and, if it is complete, a thickened dura may be the only residual finding.

In addition, most patients are febrile, with headache and neck stiffness, and, if untreated, may develop focal neurologic signs, lethargy, and coma.

The CSF profile is similar to that seen in brain abscesses, because both are parameningeal infectious processes.