What organism is responsible for ring-enhancing brain lesions in AIDS patients?

Toxoplasma gondii is the organism most commonly associated with ring-enhancing brain lesions in AIDS patients. This protozoan parasite is particularly opportunistic in individuals with advanced immunosuppression, such as those living with HIV/AIDS.

As the immune system weakens due to the progression of HIV infection, Toxoplasma can reactivate from a latent state, leading to the development of cerebral toxoplasmosis. The lesions typically appear as ring-enhancing lesions on brain imaging, often localized in the basal ganglia or corticomedullary junction. These lesions result from the formation of abscesses in brain tissue, where the organism invades and multiplies, accompanied by an inflammatory response that creates the characteristic ring enhancement seen on CT or MRI scans.

While other organisms can affect the central nervous system in AIDS patients, such as Cryptococcus neoformans, cytomegalovirus, or Mycobacterium avium complex, they usually present with different imaging findings or pathologies. For example, cryptococcal infections may lead to meningoencephalitis rather than focal lesions, cytomegalovirus commonly causes a more diffuse pattern of involvement that does not typically exhibit ring enhancements, and Mycobacterium avium complex primarily causes dissemin