Brain Abscess Revealing an Undiagnosed Atrioventricular Septal Defect With a Common Atrium in a Young Adult.

Brain abscess is an uncommon but life-threatening intracranial infection that most often arises from contiguous spread but may also occur through hematogenous dissemination in patients with congenital heart disease. This is usually associated with defects that permit right-to-left shunting of septic emboli. Its occurrence in association with atrioventricular septal defect (AVSD) is rarely reported, particularly as the initial presentation in adulthood. We report an 18-year-old male who presented with a generalized tonic-clonic seizure preceded by a 4-day history of frontal headache. Examination revealed digital clubbing, conjunctival plethora, and a pansystolic murmur. Neuroimaging demonstrated a right frontal lobe abscess. Cardiac evaluation identified atrial flutter and a previously undiagnosed AVSD with a large atrial component resulting in a common atrium and a ventricular component with predominantly left-to-right shunting, without echocardiographic evidence of pulmonary hypertension. The patient recovered fully with complete radiological resolution after surgical drainage of the abscess, and remained clinically stable at 6-month follow-up. In patients with AVSD and a common atrium, the absence of atrial septation due to the large atrial component permits mixing of systemic and pulmonary venous blood that may result in chronic hypoxemia. This intracardiac communication may also allow septic material to bypass pulmonary clearance. Brain abscess may therefore represent the initial manifestation of AVSD with a common atrium, highlighting the importance of careful cardiovascular examination and timely echocardiographic evaluation in patients presenting with a brain abscess of unclear origin.