Brain abscess: Intracradiac Shunt

Case Report : 55 year old female presented with left sided focal seizures.  On examination, she had mild pyramidal weakness of left upper and lower limbs. Left plantar was extensor. There was cortical sensory loss on left upper and lower limbs. CVS examination  showed loud P2 and Ejection systolic murmur over the pulmonary area.  On MRI there is smooth ring enhancing lesion, which appeared bright on DW-MRI suggesting abscess. CXR and CT chest showed grossly dilated main pulmonary artery as well as branches. Echo showed ostium secundum ASD with  intracardiac shunt and moderately severe pulmonary artery hypertension.  Final diagnosis of brain abscess secondary to intracardiac shunt was made.   Submitted by Dr Rahul Rajeev DM (Neurology) Std, Dr Sumer Sethi, MD Radiology

The most common cyanotic heart diseases associated with brain abscess are tetralogy of Fallot and transposition of great vessels. In patients with cyanotic heart disease with the right to left shunt, venous blood in the heart bypasses the pulmonary circulation, thus preventing the phagocytosis of the infective organisms by the pulmonary macrophages. These patients also have polycythemia that increases blood viscosity. The resultant hypo perfusion of areas in the brain and metabolic acidosis predisposes to seeding of the infective foci into areas of microinfarcts. In a patient with an ASD, a paradoxical embolus can cause a brain abscess, although few such cases are reported in literature.