Validation of hippocampal volumes measured with one manual and two automated methods using FreeSurfer and IBASPM in chronic major depressive disorder

Abstract

Dear Editor, We really thank the authors for having interest in our paper [1] and also for the valuable comments. Making a golden standard protocol for volumetric study has been thought to be difficult to realize and a ground gold standard for in vivo hippocampal volumetric study is still uncertain. But, as far as we know, Dr. CR Jack performed very precisely validated protocol for hippocampus volumetry with phantom [2] and we adopted a protocol very similar with Jack’s method for the validation of two automated hippocampal volumetry [1]. Although Jack et al. reported rightward hippocampal asymmetry in their previous paper, using the posterior commissure as the posterior boundary of hippocampus did not cover the whole hippocampus. Because the MRI slice thickness of 4 mm was relatively thick compared to recent MRI acquisition methods, just one slice’s tilting could make the large asymmetry of hippocampal volume [3]. This posterior boundary criterion was not used in a more recent study of Jack et al. [4]. We cannot agree with the opinion that there has been consensus on the rightward asymmetry of hippocampal volume. Even though the authors referenced some papers showing the asymmetry of hippocampal volume [3, 5–7], there also have been many papers reporting the symmetric hippocampal volume [8–11]. Moreover, a meta-analysis study [5], which the authors referenced reported the rightward asymmetric range of −1.16∼4.74 (mean 0.74, asymmetry = [right − left]/(right + left)/2×100%). Only four studies showed larger right hippocampal volumes over 100 mL compared to left hippocampal volumes. The rest of the eight papers showed very symmetric hippocampal volumes (mean right– left differences=6.69 mL; range, −53.0∼55.5 mL), and the conclusion of the rightward hippocampal asymmetry of normal subjects could not be found in the paper. Another review paper on the normal values of hippocampal volume introduced three papers on rightward hippocampal asymmetry, two papers on leftward hippocampal asymmetry and one paper on symmetric hippocampal volume [4]. So, the significant rightward asymmetry of hippocampal volume could still not be concluded, but we could partially agree with the possibility of rightward asymmetry of hippocampal volume, because there have been a bit more papers reporting rightward asymmetry of hippocampal volume than papers reporting leftward asymmetry, and our data showed rightward asymmetry, although it was statistically not significant (P= 0.109). If more subjects were included, there was the possibility of change of significance level. The lack of rightward frontal brain asymmetry and leftward occipital asymmetries in normal women’s brain was reported [12, 13]. Because the subjects enrolled in our study were all women, the effect of sexual dimorphism could be considered as a variable for the hippocampal asymmetry. We have aimed for enough sample sizes distributed throughout the age spans used in a previous paper (20∼26 years old, 17 cases; 27∼33 years old, 17 cases; 34∼40 years old, 18 cases) [3], as the authors suggested; but, in our study [1], the sample sizes of normal women were Neuroradiology (2009) 51:203–204 DOI 10.1007/s00234-008-0490-7