The hippocampus: detailed assessment of normative two-dimensional measurements, signal intensity, and subfield conspicuity on routine 3T T2-weighted sequences

Purpose: The hippocampus has a critical role in many common disease processes. Currently, routine 3 Tesla structural MRI is a mainstay of clinical diagnosis. The goal of our study is to evaluate the normal variability in size and/or conspicuity of the hippocampal subcomponents in routine clinical 3 Tesla high-resolution T2-weighted images to provide a basis for better defining pathological derangements. Additionally, we utilize diffusion data acquired from a 17.6 Tesla MRI of the hippocampus as a benchmark to better illustrate these subcomponents. Methods: The hippocampus was retrospectively assessed on 104 clinically normal patients undergoing coronal T2-weighted imaging. The conspicuity of the majority of hippocampal subcomponents was assessed in each portion of the hippocampus. Additionally, easily applicable cross-sectional measurements and signal intensities were obtained to evaluate the range of normal, as well as inter- and intra-subject variability. Results: The normal range of cross-sectional measurements of the hippocampal subcomponents was calculated. There was minimal side-to-side variability in cross-sectional measurements of hippocampal subcomponents (< 5%) with the exception of the subiculum (R>L by 8.3%) and the CA4/DG (R>L by 5.8%). The internal architecture showed high variability in visibility of subcomponents between different segments of the hippocampus. Conclusions: Confident clinical assessment of the hippocampus requires a thorough knowledge of hippocampal size and signal, but also the internal architecture expected to be seen. The data provided in this study will provide the reader with vital information necessary for distinguishing a normal from abnormal exam.