Correlation between hippocampal volumes and medial temporal lobe atrophy in patients with Alzheimer's disease

Abstract

Introduction: Hippocampus undergoes atrophy in patients with Alzheimer's disease (AD). Calculation of hippocampal volumes can be done by a variety of methods using T1-weighted images of magnetic resonance imaging (MRI) of the brain. Medial temporal lobes atrophy (MTL) can be rated visually using T1-weighted MRI brain images. The present study was done to see if any correlation existed between hippocampal volumes and visual rating scores of the MTL using Scheltens Visual Rating Method.

Materials and methods: We screened 84 subjects presented to the Department of Neurology of a Tertiary Care Hospital and enrolled forty subjects meeting the National Institute of Neurological and Communicative Disorders and Stroke, AD related Disease Association criteria. Selected patients underwent MRI brain and T1-weighted images in a plane perpendicular to long axis of hippocampus were obtained. Hippocampal volumes were calculated manually using a standard protocol. The calculated hippocampal volumes were correlated with Scheltens Visual Rating Method for Rating MTL. A total of 32 cognitively normal age-matched subjects were selected to see the same correlation in the healthy subjects as well. Sensitivity and specificity of both methods was calculated and compared.

Results: There was an insignificant correlation between the hippocampal volumes and MTL rating scores in cognitively normal elderly (n = 32; Pearson Correlation coefficient = 0.16, P > 0.05). In the AD Group, there was a moderately strong correlation between measured hippocampal volumes and MTL Rating (Pearson's correlation coefficient = -0.54; P < 0.05. There was a moderately strong correlation between hippocampal volume and Mini-Mental Status Examination in the AD group. Manual delineation was superior compared to the visual method (P < 0.05).

Conclusions: Good correlation was present between manual hippocampal volume measurements and MTL scores. Sensitivity and specificity of manual measurement of hippocampus was higher compared to visual rating scores for MTL in patients with AD.

Keywords: Alzheimer's disease; correlation; hippocampus; medial temporal lobe atrophy rating.

Figure 1

Medial temporal lobe atrophy of a 70-year-old male showing T1-weighted images with diffuse cortical, atrophy particularly marked over the medial temporal and perisylvian areas. Red arrow indicates the atrophy of medial temporal areas, e.g., hippocampal, entorhinal, and parahippocampal areas

Figure 2

Hippocampus of a 78-year-old women with early Alzheimer's disease showing bilateral volume loss compared to the cognitively normal healthy elderly (Mean hippocampal volume = 2.77 ± 0.6 on the right and 2.73 ± 0.5 cm³)

Figure 3

Representative three-dimensional outlines of hippocampal areas done on magnetic resonance imaging brain of the subjects and patients from the current study (Pseudoimages generated by ImageJ, National Institute of Health, USA, downloaded free by http://www.imagej.nih.gov/ij. (a-c) have been drawn to show comparison of normal hippocampus (a) in healthy individuals with those with Alzheimer's disease (b). (c) Represents the manually drawn outlines of right medial temporal lobe for comparison

Figure 4

Q-Q plot of hippocampal volumes of patients with Alzheimer's disease to check normalcy of data (x variable). The data are normally distributed. Centering of the data around the mid-line indicates that the data are normally distributed

Figure 5

Correlation between manually measured hippocampal volume and medial temporal lobe atrophy rating obtained by Scheltens Visual Rating Method for medial temporal lobe. Pearson's correlation coefficient (r) was −0.54. The coefficient value was in minus indicating, when one MTL (x) was low, the other value-hippocampal volume (y) also was lower. This indicates a good deal of agreement between two methods