- Toxoplasma gondii – intracellular protozoan. Infects humans via cat feces, ingestion of raw or undercooked meat, shellfish, unwashed fruits and vegetables
- Healthy patients – asymptomatic, becomes latent in neuroparenchyma
- Latent infection reactivated when immunocompromised, like HIV when CD4 count drops bellow 100 cells per cu.mm.
- Pyrimethamine-sulfadiazine and folic acid reduces size of lesions within a fortnight
- Ring-enhancing abscesses centered in basal ganglia, thalamus, along corticomedullary junction
- Varying degrees of perilesional edema and mass effect
- Nodular enhancement is seen, but sometimes absent in the immunocompromised
- MRI: hypo on T1, hyper on T2/FLAIR. Target sign on T2 due to central hyper intensity (fluid), peripheral hypo (mural blood) and outer ring of bright perilesional edema
- Primary CNS lymphoma in immunocompromised: lymphomas show more diffusion restriction, much higher Thallium 201 SPECT and Fluorine 18 FDG uptake
Camacho, Daniel LA, J. Keith Smith, and Mauricio Castillo. “Differentiation of toxoplasmosis and lymphoma in AIDS patients by using apparent diffusion coefficients.” American journal of neuroradiology 24.4 (2003): 633-637.