Which brain structure changes on CT scans characteristic of Alzheimer disease?

Updated: Apr 12, 2018
  • Author: Tarakad S Ramachandran, MBBS, MBA, MPH, FAAN, FACP, FAHA, FRCP, FRCPC, FRS, LRCP, MRCP, MRCS; Chief Editor: L Gill Naul, MD  more...
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Answer

Answer

Diffuse cerebral atrophy with widened sulci and dilatation of the lateral ventricles can be observed. Disproportionate atrophy of the medial temporal lobe, particularly of the volume of the hippocampal formations (<50%), can be seen.

The hippocampus is one of the earliest affected brain regions in Alzheimer disease, and its dysfunction is believed to underlie the core feature of the disease-memory impairment. Changes in hippocampal volume, shape, symmetry, and activation are reflected by cognitive impairment. [29]

Dilatation of the perihippocampal fissure is a useful radiologic marker for the initial diagnosis of Alzheimer disease, with a predictive accuracy of 91%. [30] The hippocampal fissure is surrounded laterally by the hippocampus, superiorly by the dentate gyrus, and inferiorly by the subiculum. These structures are all involved in the early development of Alzheimer disease and explain the enlargement in the early stages. At the medial aspect, the fissure communicates with the ambient cistern, and its enlargement on CT scans is often seen as hippocampal lucency or hypoattenuation in the temporal area medial to the temporal horn.

The temporal horns of the lateral ventricles may be enlarged. Prominence of the choroid and hippocampal fissures and enlargement of the sylvian fissure may be noted. White matter attenuation is not a feature of Alzheimer disease.


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