Head CT > Degenerative > Alzheimer's Disease > Imaging


Alzheimer's Disease - Imaging

Because of its low sensitivity and specificity for the diagnosis of Alzheimer's disease, imaging is typically not used to rule in Alzheimer's disease but rather to rule out other causes of dementia. Nevertheless, in the right clinical context Alzheimer's disease appears radiographically as diffuse cerebral atrophy with enlarged lateral ventricles and widened sulci on CT. On thin-section (3 mm thick) coronal T1-weighted MR, medial temporal lobe atrophy primarily in the amygdala, hippocampus, and parahippocampal gyrus may be visually evident. Utilizing MR volumetric measurements, the hippocampal formation may be quantitatively determined to show focal atrophy. In addition, the temporal horns, supracellar cisterns, and Sylvian fissures may exhibit focal symmetric or asymmetric enlargement.


MR has been chosen for the above images because of its ability to show greater detail in Alzheimer's disease.
The image on the left is a thin-section coronal T1-weighted MRI of an individual with Alzheimer's.
The arrows indicate focal, assymetric atrophy of the right medial temporal lobe.
Also visible on the left are the dilated lateral and third ventricles most likely due to diffuse atrophy.
The image on the right is an age-matched control for comparison.



FDG PET reveals temporoparietal metabolic deficits in patients with Alzheimer's disease. Although asymmetry is not uncommon, usually certain brain structures show metabolic sparing including the basal ganglia, thalamus, cerebellum, and primary sensorimotor cortex. Finally, on SPECT imaging bilateral temporoparietal hypoperfusion as well as decreased uptake in the medial temporal lobes and cingulated regions may be exhibited.


Both images above are SPECT images using Tc-99 in an individual with severe Alzheimer's disease.
The image on the left is taken as if looking at the patient's left hemisphere, and vice versa for the image on the right.
The arrows indicate bilateral frontal, temporal, and parietal hypoperfusion as seen by areas of hypodensity.
FL = frontal lobe; TL = temporal lobe; PL = parietal lobe



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