MR imaging brings clarity to one source of dementia

Vascular disease in the brain may dictate the onset of dementia in the elderly, according to a study published in the September issue of Radiology.

Debate on the association between dementia and cerebrovascular disease is as old as imaging itself. But even though the causes of dementia are multiple-and many remain unknown-some imagers point at cerebrovascular disease as one of the most relevant.

Radiologist Dr. Aart Spilt and colleagues at the University Medical Center of Leiden in the Netherlands explored the connection between structural brain damage and total cerebral blood flow. They prospectively enrolled 17 elderly patients with late-onset dementia, 16 subjects of the same age with normal cognitive function, and 15 young healthy controls.

Using MRI, they found that demented elderly individuals showed significantly more structural brain damage and lower cerebral blood flow than normal subjects, even among the elderly.

"Clinicians should be aware that hypotension-as well as hypertension-needs to be prevented to diminish the periods with low cerebral blood flow," Spilt said.

Elderly patients with dementia showed significantly higher scores for number and extent of white matter areas with signal hyperintensity and lower magnetization ratios than healthy subjects of similar age. Patients with dementia also showed a cerebral blood flow that was 108 mL/min lower than normal elderly subjects. The difference was also statistically significant.

The imaging protocol included:

-1.5T scanning;

-dual turbo spin-echo sequence;

-a gradient-echo phase-contrast technique with velocity encoding of 100 cm/sec for blood flow measurement;

-a 3D gradient-echo pulse sequence for magnetization transfer imaging; and

-total brain blood flow analysis with an independent workstation.

Although uncooperative patients posed a challenge, MRI allowed researchers to monitor both structural and functional changes in these patients. Blood flow and structural brain damage were easily seen on T2-weighted MR images, Spilt said.

Researchers know that patients presenting with Alzheimer's and other forms of dementia accumulate amyloid plaque in the brains. But the type of gene mutation causing it affects less than 5% of these patients.

Many elderly patients who are dementia-free, on the other hand, also present with amyloid plaque deposits in their brains. Researchers need to further investigate the relationship between dementia and cerebrovascular disease as a separate cause.