Brain abscess is a focal bacterial or fungal infection of the brain. Treatment is neurosurgical drainage of pus followed by long-term antibiotic treatment. In spite of successful treatment of the infection, long-term cognitive problems or mental fatigue may ensue. The reason for this dysfunction may be a continuing inflammatory state or damage to brain tissue caused by the abscess. The investigators will evaluate these possibilities with the use of [18F]deoxyglucose-positron emission tomography (FDG-PET) and electroencephalography (EEG) in patients who have been treated for brain abscess and who experience cognitive problems and/or fatigue. FDG-PET may identify both inflammation and altered neuronal activity (the latter indicating damage to brain tissue), and EEG may identify altered neuronal activity, including changes in neuronal network activity.

Brain abscess is a focal bacterial or fungal infection of the brain, which results in a pus-filled cavity within the brain parenchyma. The incidence is approximately 1/100 000 per year, and all age groups are affected. Treatment is neurosurgical drainage of pus followed by long-term antibiotic treatment. Previously, the capsule that surrounds the pus was removed surgically; this is not usually done anymore. In spite of successful treatment of the infection, patients may experience long-lasting cognitive problems or mental fatigue. The reason for this brain dysfunction is not known.

The investigators formulated two hypotheses to explain why some patients experience long-lasting cognitive problems and/or fatigue: 1) The brain abscess caused damage to brain tissue, interrupting neuronal networks underlying cognition or 2) The abscess or the remaining capsule causes a long-lasting inflammatory state of the brain, affecting neurotransmission and cerebral function.

In this prospective study, the investigators evaluate brain abscess patients by cognitive examination by a neuropsychologist at 2 and 12 months after treatment. Participants then undergo [18F]deoxyglucose-positron emission tomography (FDG-PET). An inflammatory state in the abscess area would be identified by the FDG-PET signal. Likewise, a change in neuronal (neocortical) function would be detectable from a change in the FDG-PET signal. Participants also undergo EEG investigation to establish whether fatigue is related to alterations in EEG parameters: alpha, theta, and delta activity.

Importantly, brain damage caused by the abscess may be irreversible and functional improvement of the patient would probably have to rely on compensatory strategies, whereas an inflammatory state could probably be modified by anti-inflammatory treatment.

Further, the prognosis for the patients' cognitive problems and fatigue is probably different if the underlying cause is inflammation rather than tissue damage.

Inclusion criteria:

• Patients who have completed treatment for brain abscess and who agree to participate.

Exclusion criteria:

• Patients who cannot undergo neuropsychological investigation due to unconsciousness
• Patients who cannot undergo neuropsychological investigation, being mentally too ill
• Patients who suffer from dementia
• Patients who cannot undergo FDG-PET due to claustrophobia
• Patients who cannot undergo EEG due to panic attacks
• Age under 16.

Patients older than 16 years, who have completed treatment for brain abscess and who agree to participate.

Patient data will be published on a group basis without identifiable characteristics. Publication will be in an international, peer-reviewed medical journal.