Rounding of the hippocampus in Alzheimer's disease: a study by routine coronal magnetic resonance imaging.

Purpose: On routine coronal images, we have recognized atrophied hippocampi that appear round in patients with Alzheimer's disease (AD). The purpose of this study was to evaluate rounding of the hippocampus in patients with AD and to elucidate whether this change is a useful radiological marker of atrophy of the hippocampus.

Materials And Methods: We enrolled 14 patients with moderate AD (Mini-Mental State Examination score 16.2 +/- 3.3) and 15 patients without dementia or neurological deficits as the control group. For measurement of the hippocampus, we used T2-weighted coronal images parallel to the floor of the fourth ventricle. Two observers measured the dimensions of the long and short axes of the hippocampal body of 28 hippocampi from 14 patients with AD and 30 hippocampi from 15 controls. As a marker of rounding of the hippocampal body, we calculated the ratio of the short axis length to the long axis length (the rounding ratio) of the hippocampus.

Results: We observed apparent atrophy of the long axis of the hippocampus in patients with AD. An unpaired t-test indicated significant differences in the long axis length and the rounding ratio between the control and AD groups (P < 0.01) in the measurements of both observers. However, there was no significant difference in the short axis length. With a threshold of 0.7 in the rounding ratio, the sensitivity was 85.7% and the specificity was 66.7%.

Conclusion: The hippocampus appears round on coronal images in the presence of moderate AD. The rounding ratio of the hippocampus is a useful and facile indicator of hippocampal atrophy.