Radiologists use software that provides fully automated segmentation of brain images along with a standard, high-resolution 3D T1-weighted imaging machine to compare a patient’s scans with a normative database adjusted for age, sex, and total intracranial volume. Measurements of the hippocampus, which consistently shrinks with neurodegenerative disorders such as Alzheimer’s disease, and its associated temporal horn of the lateral ventricle, which enlarges to fill the space left when the hippocampus shrinks, are compared to the normative database to identify whether the patient’s medial temporal lobe volumes are within the expected range.
Objective Evidence
“This does not replace bedside testing and the physician’s judgment, but our referring physicians have found it extremely helpful in assessing whether the patient has objective evidence of neurodegenerative illness,” Dr. Brewer added. “We have also found that the ‘worried well’ can find a great deal of reassurance in the suggestion that their brain looks a lot like healthy people of their same age. While we would never use the scans to promise the patient they won’t get Alzheimer’s disease, the absence of atrophy, along with relatively normal performance on neuropsychological testing, is pretty reassuring.”
In patients with a clear memory deficit whose scans show evidence of hippocampal atrophy and temporal horn enlargement, more aggressive pursuit of disease-modifying treatment should be considered, Dr. Brewer noted. These drugs are currently only available in clinical trials but are expected to be on the market relatively soon.
“However,” he cautioned, “these medications are likely to have more serious side effects than cholinesterase inhibitors or memantine, so objective evidence of neurodegenerative disease, such as that provided with volumetric imaging, could be quite important in assessing the risk/benefit ratio.”
—Rebecca K. Abma
Suggested Reading
Brewer JB. Fully-automated volumetric MRI with normative ranges: translation to clinical practice. Behav Neurol. 2009;21(1):21-28.