Hippocampal sulcus width and cavities: comparison between patients with Alzheimer disease and nondemented elderly subjects.

BACKGROUND AND PURPOSE The hippocampal fissure is a fetal sulcus that, except for its most medial part (the superficial hippocampal sulcus), is normally obliterated. Hippocampal cavities are residual cysts attributable to lack of hippocampal fissure obliteration. We hypothesized that either hippocampal sulcus enlargement or an increase in number or size of hippocampal cavities could be associated with medial temporal lobe atrophy (MTA) occurring in Alzheimer disease. METHODS Two observers assessed the maximal hippocampal sulcus width by means of the fimbriosubicular distance at the anterior part of the hippocampal body; as well as the occurrence, number, and size of hippocampal cavities; and the visual rating score of MTA on magnified coronal high-resolution T1-weighted MR images of 21 patients with Alzheimer disease and 15 nondemented elderly controls. RESULTS Both observers found the maximal hippocampal sulcus width significantly larger in patients with Alzheimer disease than in controls (P < .0001). The interobserver averaged fimbriosubicular distance in patients with Alzheimer disease was 2.84 mm (SD = 0.94), approximately twice that of the corresponding distance in nondemented subjects (1.41 mm; SD, 0.58). Both observers found a significant correlation between the fimbriosubicular distance and MTA score (observer 1, r(s) = 0.71; observer 2, r(s) = 0.74; P < .0001). None of the observers found significant differences between patients with Alzheimer disease and nondemented subjects with respect to occurrence, number, or size of hippocampal cavities, nor did they find a significant correlation between the number or size of hippocampal cavities and MTA. Interobserver agreement ranged from moderate to very good. CONCLUSION Enlargement of the hippocampal sulcus, assessed by the fimbriosubicular distance, is associated with MTA in Alzheimer disease, but enlargement of the hippocampal cavities is not.