Usefulness of MRI measures of entorhinal cortex versus hippocampus in AD

Objective: MRI-based measurements of hippocampal atrophy are a sensitive in dicator of the early pathologic degeneration of the medial temporal lobe in AD. However, AD pathology appears first in the transentorhinal/ entorhinal cortex, not the hippocampus. The authors tested the hypothesis that MRI-ba sed measurements of the entorhinal cortex are more sensitive than measureme nts of hippocampal volume in discriminating among three clinical groups; co ntrols, patients with a mild cognitive impairment (MCI), and patients with mild probable AD. Methods: The authors studied 30 controls, 30 patients wit h MCI, and 30 patients with AD who were matched among clinical groups on ag e, gender, and education. All underwent a standardized MRI protocol from wh ich the authors made measurements of hippocampal volume, entorhinal cortex volume, and the cumulative length of the medial border of the entorhinal co rtex. Results: Pairwise intergroup differences (p < 0.01) were found for al l MRI measurements with the exception of the cumulative length of the entor hinal cortex, which did not differentiate controls from MCI patients. Where as the hippocampal and entorhinal cortex volume measurements provided sligh tly better intergroup discrimination than the entorhinal distance measureme nt, overall differences in discriminating ability among the three MRI measu rements were minor. Conclusions: Despite the theoretical rationale for the superiority of entorhinal measurements in early AD, the authors found MRI m easurements of the hippocampus and entorhinal cortex were approximately equ ivalent at intergroup discrimination. Measurements of the hippocampus may b e preferable because MRI depiction of the boundaries of the entorhinal cort ex can be obscured by anatomic ambiguity, image artifact, or both.