Several of the neurological disorders associated with AIDS have characteristic radiographic presentations which can be helpful in diagnosis. It is important that the clinician be familiar with these MRI patterns, since MRI scans often are interpreted by a radiologist who may be unfamiliar with HIV infection or who may not be familiar with the patient's history. Summarized below are the radiographic and clinical features of three common neurological disorders: HIV-associated dementia, CMV encephalitis, and progressive multifocal leuko-encephalopathy (PML). The clinical features of these disorders are distinct and are summarized in the table. If these disorders are suspected, contrast cranial MRI imaging should be performed. The following patterns are useful in corroborating the diagnoses.

• HIV-associated dementia: MRI scans generally show both central (ventricular enlargement) and cortical atrophy. Ill-defined patchy areas of increased signal within the deep white matter are seen on T2 weighted images. There will be no contrast enhancement.
  
  
• CMV encephalitis: About 50% of scans will be normal or show only atrophy. Periventricular inflammation with contrast enhancement may be seen in about half of patients.
  
  
• Progressive multifocal leukoen-cephalopathy: There is a very characteristic and almost pathognomonic change. Multifocal areas of demyelination (bright on T2 weighted image, hypodense on T1 weighted images) are seen. As opposed to the changes seen in HIV-associated dementia, those in PML are asymmetrical and generally involve the subcortical white matter. No mass effect or contrast enhancement is seen. Using these guidelines, diagnosis of these common neurologic problems can be made more easily.