What is subdural empyema?

Subdural empyema is defined as the accumulation of pus between the dura mater and the arachnoid membrane, which are layers surrounding the brain and spinal cord. This condition typically arises from an infection, often stemming from adjacent structures such as the sinuses or after a cranial injury. The presence of pus indicates that there is an ongoing inflammatory response, often due to bacteria, leading to the collection of infected fluid in the subdural space. This condition can result in increased intracranial pressure and neurological deficits if not treated promptly.

In the context of the other options, while fluid accumulation in the lungs refers to pulmonary complications, blood in the cerebrospinal fluid pertains to conditions like subarachnoid hemorrhages, and infection in the spinal cord usually indicates conditions like myelitis. None of these options accurately describe the specific nature of subdural empyema, which is strictly characterized by the presence of pus.