This is a 74-year-old male who had undergone surgery for a left frontal parasagittal transitional meningioma (WHO grade I). One month after this surgery, he consulted for infection of the surgical wound, which had a central dehiscent area from which purulent material was coming out. The patient had had no fever, his general condition was good and he had a normal neurological examination. A magnetic resonance imaging (MRI) performed at that time showed, adjacent to the craniectomy site, a hypodense subdural collection, with bubbles inside, which was peripherally enhanced after gadolinium administration. The craniotomy was reopened and a purulent epidural collection emerged, which was evacuated and sent for microbiological study. Empirical antibiotic therapy was started with intravenous ceftazidime and vancomycin. Bacterial cultures were negative. The patient was discharged with oral treatment with ciprofloxacin and cotrimoxazole for two weeks.

One and a half months after discharge, the patient was brought to the emergency department for a generalised tonic-clonic seizure. He had been febrile for the previous days with no other clinical data of interest. On physical examination he was in good general condition, afebrile, had a Glasgow Glasgow of 15/15, showed no neurological focality and the surgical wound showed no evidence of infection. Anticonvulsant treatment was started and a CT scan was performed, which revealed a predominantly hypodense subdural collection, with peripheral enhancement after contrast administration and a convex internal margin towards the brain parenchyma. Air persisted within the collection.
Empirical antibiotic treatment was started with ceftazidime and vancomycin. With the diagnostic suspicion of recurrence of subdural empyema, a third craniectomy was performed which revealed a subdural collection with a purulent appearance that was evacuated. Samples were sent for microbiology from the drained material and from a craniectomy specimen adjacent to the collection which was removed for therapeutic purposes due to possible infection and embedded in thioglycollate broth for processing.

After 5 days of incubation, growth of Proprionibacterium acnes (P. acnes) was observed after subculture in solid medium and in anaerobic atmosphere of the enrichment broth. An antibiogram by E-test was performed, showing resistance to metronidazole and sensitivity to penicillin, amoxicillin-clavulanate, ceftazidime, clindamycin and vancomycin. Treatment with vancomycin and ceftazidime was discontinued and amoxicillin-clavulanic acid was started. The patient's evolution was good and he was discharged with oral amoxicillin for one month and a diagnosis of "recurrence of post-surgical subdural empyema due to Propionibacterium acnes".