From the Guidelines
Toxoplasmosis typically presents on brain MRI as multiple ring-enhancing lesions, particularly in the basal ganglia and corticomedullary junction, as noted in the guidelines by the Infectious Diseases Society of America 1.
Key Features of Toxoplasmosis on Brain MRI
- Multiple ring-enhancing lesions
- Predilection for the basal ganglia and corticomedullary junction
- Target appearance with an eccentric nodule (the "eccentric target sign")
- Frequently surrounded by vasogenic edema
- In immunocompromised patients, especially those with AIDS, lesions tend to be multiple and bilateral
- In immunocompetent individuals, solitary lesions are more common
Diagnostic Considerations
- T2-weighted images usually show hyperintense lesions with surrounding edema
- On T1-weighted images post-contrast, the characteristic ring enhancement becomes evident
- Diffusion-weighted imaging may show restricted diffusion in the abscess cavity
- Clinical correlation with serology and response to anti-toxoplasma therapy is crucial for definitive diagnosis
- Brain biopsy may be necessary in cases where diagnosis remains uncertain, as suggested by guidelines for treating opportunistic infections among HIV-exposed and infected children 1.
Treatment and Management
- Anti-toxoplasma therapy, typically sulfadiazine plus pyrimethamine with leucovorin, is the standard treatment
- Clinical response to treatment can help confirm the diagnosis
- In cases of uncertainty, further diagnostic tests such as F-fluoro-2-deoxyglucose-positive emission tomography may be helpful in distinguishing Toxoplasma abscesses from primary CNS lymphoma, although its accuracy is not high and availability may be limited 1.
From the Research
Toxoplasmosis Presentation in Brain MRI
- Toxoplasmosis can present with single or multiple nodular or ring-enhancing lesions with surrounding edema on MRI scans 2.
- Atypical radiological features have been reported, including solitary thalamic localization of brain toxoplasmosis mimicking brain tumors 2.
- Hemorrhagic lesions are frequently found on cranial MRI scans in cerebral toxoplasmosis, particularly in AIDS patients 3.
- The commonest MRI findings reported in toxoplasmosis are ring-enhancing hypodense lesions in basal ganglia or cortical gray matter 3.
- Diagnosis can be obtained by finding organisms in the cerebrospinal fluid or in stereotactic biopsy samples of the brain lesion 2.
Treatment and Diagnosis
- The choice of drugs for treating cerebral toxoplasmosis is limited, with pyrimethamine and sulfonamide being the most commonly used combination 4.
- Clindamycin is an alternative choice, and spiramycin has poor central nervous system penetration but is useful for treatment of toxoplasmosis during pregnancy 4.
- Treatment may be started empirically in any patient with HIV infection and multiple brain lesions, with repeated neuroimaging needed to assess efficacy of treatment 4.
- Tissue diagnosis should be established in patients who do not respond to treatment, who have solitary lesions, or in patients without AIDS 4.
Clinical Findings
- Cerebral toxoplasmosis is a relatively rare disorder that usually affects immunocompromised patients, particularly those with HIV/AIDS 2.
- If untreated, cerebral toxoplasmosis is uniformly fatal, making prompt diagnosis and treatment essential 2.
- Clinical manifestations of infection in immunocompromised patients include the development of encephalitis, with approximately 30% of patients with AIDS who are latently infected eventually developing toxoplasmic encephalitis 5.