HIV encephalopathy is seen in 10-30 % of HIV patients. The pathology is subacute encephalitis  with multinucleated giant cells and microglial nodules which is followed by demyelination and cerebral atrophy. Myelin loss, gliosis, macrophage infiltration, vacuolation and necrosis are seen. The clinical syndrome, AIDS Dementia complex is characterised by cognitive impairment, memory loss, personality changes, headaches, seizures, gait disturbances, tremors  and motor symptoms. The most common radiological abnormality is atrophy. It is distributed symmetrically in the periventricular white matter and centrum semiovale with relative sparing of the subcortical fibers and posterior fossa. There is slow, progressive spread to involve the entire white matter. The lesions are isointense in T1 and hyperintense in T2. There is no mass effect or enhancement. CT scan is hypodense. There is a good correlation between the progress of lesions in MRi and clinical changes.

Bilateral periventricular hyperintensities due to demyelinating encephalitis in HIV.

HIV encephalopathy- Bilateral , symmetrical white matter hyperintensities in the periventricular and callosal regions. 

Atrophic changes can be seen without white matter changes. Occasionally , the white matter changes can be subtle and can be confused with the normal peritrigonal pallor, differentiated only by progression of radiological and clinical changes. Spectroscopy shows decreased N Acetyl Aspartate and increased choline peaks and changes in the glutamate and glutamine levels.  PET shows changes in subcortical grey matter before they are detected in MRI.