What is the role of imaging studies in the workup of CNS toxoplasmosis in HIV infection?

Updated: Jul 11, 2017
  • Author: Gulshan Uppal, MD; Chief Editor: Niranjan N Singh, MBBS, MD, DM, FAHS, FAANEM  more...
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Answer

A brain CT scan or MRI with and without contrast is indicated for all patients presenting with altered mental status, headaches, seizures, or focal neurologic signs. MRI clearly is the superior technique but is not available universally.

Single or multiple hypodense or hypointense lesions in white matter and basal ganglia with mass effects may be observed on CT or MRI scans. Lesions may enhance in a homogeneous or ring pattern with contrast (see the images below). Imaging studies may be normal in diffuse toxoplasmosis.

T1-weighted MRI after gadolinium contrast shows a T1-weighted MRI after gadolinium contrast shows a hyperintense lesion in the left cerebellar hemisphere.
T2-weighted MRI demonstrates intense edema surroun T2-weighted MRI demonstrates intense edema surrounding the lesion.

Single lesions favor the diagnosis of lymphoma over that of toxoplasmosis. However, while multiple lesions are more common than single lesions in toxoplasmosis, in one study 27% of patients had a single lesion on CT scan. In the same study, 14% had a single lesion on MRI. MRI is more sensitive than CT scan in detecting multiple lesions.

Several MRI patterns have been described in cerebral toxoplasmosis. A concentric target sign is a recently described MRI sign on T2-weighted imaging of cerebral toxoplasmosis; it has concentric alternating zones of hypointensity and hyperintensity. [7]

If the initial imaging study is normal or shows atrophy or focal signal abnormalities (but no mass lesion), diagnostic consideration should be given to meningitides, AIDS dementia complex, or progressive multifocal leukoencephalopathy.

If imaging shows one or more focal mass lesions with impending herniation, an open biopsy with decompression is indicated. Treatment for lymphoma, toxoplasmosis, or other opportunistic infections and neoplasms is initiated, depending on biopsy results.

If imaging shows one or more focal mass lesions without impending herniation, additional studies are warranted.


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