Easy Identification of Optimal Coronal Slice on Brain Magnetic Resonance Imaging to Measure Hippocampal Area in Alzheimer's Disease Patients

Abstract

Introduction: Measurement of an- hippocampal area or volume is useful in clinical practice as a supportive aid for diagnosis of Alzheimer's disease. Since it is time-consuming and not simple, it is not being used very often. We present a simplified protocol for hippocampal atrophy evaluation based on a single optimal slice in Alzheimer's disease.

Methods: We defined a single optimal slice for hippocampal measurement on brain magnetic resonance imaging (MRI) at the plane where the amygdala disappears and only the hippocampus is present. We compared an absolute area and volume of the hippocampus on this optimal slice between 40 patients with Alzheimer disease and 40 age-, education- and gender-mateched elderly controls. Furthermore, we compared these results with those relative to the size of the brain or the skull: the area of the optimal slice normalized to the area of the brain at anterior commissure and the volume of the hippocampus normalized to the total intracranial volume.

Results: Hippocampal areas on the single optimal slice and hippocampal volumes on the left and right in the control group were significantly higher than those in the AD group. Normalized hippocampal areas and volumes on the left and right in the control group were significantly higher compared to the AD group. Absolute hippocampal areas and volumes did not significantly differ from corresponding normalized hippocampal areas as well as normalized hippocampal volumes using comparisons of areas under the receiver operating characteristic curves.

Conclusion: The hippocampal area on the well-defined optimal slice of brain MRI can reliably substitute a complicated measurement of the hippocampal volume. Surprisingly, brain or skull normalization of these variables does not add any incremental differentiation between Alzheimer disease patients and controls or give better results.

Figure 1

Three sections through the hippocampus and amygdala show their different proportions. Slice A through amygdala is the first notice/signal during viewing MRI slices from anterior/front to back. Slice B contains both hippocampal and amygdala areas on the slice, and it is not appropriate yet for evaluation. The optimal slice for hippocampal area measurement is slice C with the hippocampus only, without any part of amygdala. It is the first slice going back where amygdala disappears.

Figure 2

A detailed view of left mediotemporal structures on the optimal slice of brain MRI. Anatomical structures are labeled as follows: 1: hippocampal fimbria; 2: alveus; 3: parahippocampal gyrus; 4: subiculum; 5: hippocampal fissure; 6: uncus of the parahippocampal gyrus.