Bacterial brain abscess formation in post-irradiated patients: What is the possible pathogenesis?

• We analyse the role of radiotherapy in pathogenesis of bacterial brain abscess.
• Either tumour erosion or osteonecrosis are common in post-irradiated patients.
• Radiation-related temporal lobe necrosis was also a predisposing factor.
• Both radiation effects and tumour effects are the possible pathogenesis.

BackgroundUntil recently, post-radiotherapy brain abscess was considered rare, but it has become an increasingly important aetiology. Discussions of the relationship between bacterial brain abscess and radiotherapy (RT) are rare in the literature. Our clinical study was conducted to analyse the role of RT in the pathogenesis of bacterial brain abscess.MethodsFor our retrospective study, 146 patients with bacterial brain abscess were recruited. Ten patients with a history of RT before brain abscess formation were reviewed.ResultsEight of these patients underwent RT treatment for nasopharyngeal carcinoma, one for olfactory neuroblastoma, and another for nasal plasmacytoma. Three showed presence of temporal lobe radiation necrosis neighbouring abscess. Eight patients were shown to have the evidence of tumour invasion. Seven had evidence of nasal infection or otitis media. Statistically significant differences between the RT and non-RT patients were observed for radionecrosis, bone defects between the middle fossa/sphenoid sinus, and the presence of nasal infection/otitis media. The mortality rate was 30%.ConclusionThis study shows possible pathogenesis of bacterial brain abscess formation in post-irradiated patients, which is complicated by both radiation effects and tumour effects. Skull base deficits (either from tumour erosion or osteonecrosis) and nasal/ear infection were significantly different in patients who received radiation vs. those who did not. Radiation-related temporal lobe necrosis was also a predisposing factor. Further study based on a proper patient cohort is warranted.