Summary

We describe a case of cerebral abscess in a 53-year-old lady with a background of congenital heart defect. She has an atrial septal defect with atrial septal aneurysm, which remained undiagnosed until this clinical presentation. She presented with a short history of right-sided hemiplaegia and neuroimaging revealed a heterogeneous lesion in the left frontoparietal region. Neuronavigation-guided left frontoparietal craniotomy was performed to debulk the lesion and preoperatively frank pus was drained, which grew Streptococcus constellatus. She was successfully treated with antibiotics for 6 weeks and her clinical condition improved. We believe that the patients’ previous dental extraction has possibly resulted in a paradoxical embolism through the atrial septal defect bypassing the pulmonary circulation. The MRI scan picture was misleading, as it was initially thought to be a high-grade brain tumour.