Specific Imaging Findings

The most common finding in HIV encephalopathy is diffuse brain atrophy, which is progressive and more prominent in the patients with dementia. White matter lesions which are better seen on MRI are the second most common finding. They are characteristically diffuse; however, patchy, focal or punctate lesions may also be seen. They are of low attenuation on CT and T2 hyperintense, while isointense to minimally hypointense and therefore inconspicuous on T1-weighted images. The abnormalities show increased diffusion and typically spare the subcortical U-fibers. Contrast enhancement and mass effect are absent and the overlying gray matter may appear atrophic. Typically, it has a “cloud-like” appearance which may involve both hemispheres and cross the corpus callosum. These abnormalities may improve with treatment. At the start of the disease, MRS shows low NAA and high choline and myo-inositol. In the chronic stages all metabolites are low. Perfusion studies show low relative cerebral blood flow. DTI shows low fractional anisotropy throughout the brain including the normal-appearing white matter.

Pertinent Clinical Information

HIV-related encephalopathy is the most common cause of dementia in younger individuals (20–45 years of age). Its incidence is declining possibly due to the widespread use of highly active anti-retroviral therapy (HAART) given to nearly all infected patients. The most prominent symptoms include cognitive impairment and motor dysfunction. Attention, speed of information processing, and learning efficiency are primarily impaired. Brain involvement is present in over 90% of HIV infected patients.