Imaging of the aging brain. Part II. Pathologic conditions.

The most common pathologic disorders in the elderly result in dementia, movement disorders, and/or focal neurologic deficit. Neuroimaging, particularly magnetic resonance (MR), provides a unique window into the diagnosis and understanding of such diseases. The most common cause of dementing illness is Alzheimer disease (enlarged cerebrospinal fluid spaces, focal medial temporal lobe abnormal signal intensity, cortical iron). Since the initiation of MR imaging, important questions are being asked about the role of white matter disease (signal hyperintensities) in primary degenerative dementia and the nosology of vascular dementia. Parkinsonian disorders are characterized by generalized brain atrophy and dopaminergic site (e.g., putamen, pars compacta of the substantia nigra) iron or pigmentary accumulation best visualized in disease that responds poorly to dopamine replacement therapy. A key role of imaging in the elderly is the noninvasive exclusion of mass lesion (e.g., hematoma, neoplasm). MR imaging is exquisitely sensitive for the detection of the two common abnormalities that cause focal neurologic deficit in the elderly--infarction and intracerebral hematoma.