March 3, 2010

Cerebral Toxoplasmosis

Axial T1W MR image post contrast shows a ring enhancing mass with "target appearance" in the left lentiform nucleus with marked surrounding edema, resulting in midline shift in an AIDS patient.

Facts: Cerebral Toxoplasmosis
  • Infection with parasite Toxoplasma gondii
  • Manifested clinically as acute, symptomatic infection or reactivation of latent infection in immunocompromised hosts. It can be seen as a self-limited infection in immunocompetent hosts, or congenital infection
  • Etiology: ingestion of raw or undercooked meat, food or water containing tissue cysts or oocytes, transplacental, blood transfusion, solid organ transplantation
  • In immunocompromised hosts, 50% presents with CNS disease (encephalitis, meningoencephalitis, seizures, mental status change, etc)
MR Imaging Appearance
  • Ring enhancing lesions with marked surrounding edema
  • Most common location = basal ganglia and gray-white matter junction of cerebral hemisphere
  • Low signal on T1WI, intermediate/low/high signal on T2WI. May be hemorrhagic
Distinguishing Features from Lymphoma
  • Toxoplasmosis and lymphoma are two most common enhancing intracranial masses in AIDS patients
  • Toxoplasmosis tends to be multiple, and lesions are usually smaller than lymphoma
  • On conventional MRI, they may look similar.
  • On DWI/ADC, toxoplasmosis shows less restriction than in lymphoma.
  • On MR spectroscopy, toxoplasmosis shows increased lactic and lipid peak (opposite in lymphoma)
  • Toxoplasmosis is metabolically inactive on FDG-PET
  • After 2-4 weeks of antitoxoplasma treatment, some healing should be seen on imaging of toxoplasmosis
  1. Lin EC, et al. Practical differential diagnosis for CT and MRI, 2008.
  2. Domino FJ. 5-minute Clinical Consult 2007.
  3. Castillo M. Neuroradiology companion: methods, guidelines, and imaging fundamentals, 3rd edition, 2006.
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