Physical Address

304 North Cardinal St.
Dorchester Center, MA 02124

Acquired Toxoplasmosis


KEY FACTS

Terminology

  • Opportunistic infection

    • Caused by parasite Toxoplasma gondii

    • Most common opportunistic CNS infection in AIDS

Imaging

  • CT

    • Ill-defined, hypodense lesions and edema

    • Basal ganglia, thalamus, cerebellum

    • Rim, nodular, target enhancement

  • MR

    • T2 hypointense

    • T1 C+ target sign highly suggestive

  • Thallium-201 SPECT and 18F-FDG PET: Toxoplasmosis lesions are hypometabolic

Top Differential Diagnoses

  • Lymphoma

    • Solitary mass in patient with HIV/AIDS? Lymphoma > toxoplasmosis

    • Lymphoma often restricts on DWI

    • Toxoplasmosis hypometabolic on PET, low relative cerebral blood volume on pMR

  • Other opportunistic infections

    • Cryptococcosis, progressive multifocal leukoencephalopathy (usually does not enhance)

Pathology

  • 20-70% of USA population seropositive for T. gondii

    • Usually reactivation of latent infection

Clinical Issues

  • Fever, malaise, headache

    • Personality change, seizures later

Diagnostic Checklist

  • Multiple target lesions on T1WI C+ that are dark on T2WI

    • Consider toxoplasmosis encephalitis (TE)

  • TE lesions usually resolve in 2-4 weeks

Axial gross pathology specimen sectioned through the ventricles in a patient with HIV/AIDS shows a toxoplasmosis abscess in the right lentiform nucleus
. The lesion is necrotic and poorly demarcated.

(Courtesy R. Hewlett, MD.)

Axial T1WI C+ MR shows several ring-enhancing lesions in the thalami and left occipital lobe
. Note the large lesion showing a classic target appearance
. These lesions were hypointense on T2WI.

Axial FLAIR MR in HIV patient demonstrates a large, hypointense lesion
in the left basal ganglia with extensive surrounding edema
. Another smaller lesion is seen in the left occipital region
. The left basal ganglia lesion showed rim and “target” enhancement on T1WI C+ MR. The most important differential consideration is toxoplasmosis vs. lymphoma.

Axial CBV map from MR perfusion demonstrates low rCBV
, suggesting an infection (toxoplasmosis) rather than lymphoma.

TERMINOLOGY

Abbreviations

  • Toxoplasmosis encephalitis (TE)

Definitions

  • Opportunistic parasitic infection caused by Toxoplasma gondii

    • Most common opportunistic CNS infection in patients with AIDS

You're Reading a Preview

Become a Clinical Tree membership for Full access and enjoy Unlimited articles

Become membership

If you are a member. Log in here

Related Posts