title: MR imaging of hippocampal asymmetry at 3T in a multiethnic, population-based sample: results from the Dallas Heart Study.
abstract: OBJECTIVE
  Asymmetry of the hippocampus is regarded as an important clinical finding, but limited data on hippocampal asymmetry are available for the general population. Here we present hippocampal asymmetry data from the Dallas Heart Study determined by automated methods and its relationship to age, sex, and ethnicity.
  
  
  METHODS
  3D magnetization-prepared rapid acquisition of gradient echo MR imaging was performed in 2082 DHS-2 participants. The MR images were analyzed by using 2 standard automated brain-segmentation programs, FSL-FIRST and FreeSurfer. Individuals with imaging errors, self-reported stroke, or major structural abnormalities were excluded. Statistical analyses were performed to determine the significance of the findings across age, sex, and ethnicity.
  
  
  RESULTS
  At the 90th percentile, FSL-FIRST demonstrated hippocampal asymmetry of 9.8% (95% CI, 9.3%-10.5%). The 90th percentile of hippocampal asymmetry, measured by the difference in right and left hippocampi volume and the larger hippocampus, was 17.9% (95% CI, 17.0%-19.1%). Hippocampal asymmetry increases with age (P=.0216), men have greater asymmetry than women as shown by FSL-FIRST (P=.0036), but ethnicity is not significantly correlated with asymmetry. To confirm these findings, we used FreeSurfer. FreeSurfer showed asymmetry of 4.4% (95% CI, 4.3%-4.7%) normalized to total volume and 8.5% (95% CI, 8.3%-9.0%) normalized by difference/larger hippocampus. FreeSurfer also showed that hippocampal asymmetry increases with age (P=.0024) and that men had greater asymmetry than women (P=.03).
  
  
  CONCLUSIONS
  There is a significant degree of hippocampal asymmetry in the population. The data provided will aid in the research, diagnosis, and treatment of temporal lobe epilepsy and other neurologic disease.
authors.affiliation: Department of Radiology, Donald W. Reynolds Cardiovascular Clinical Research Center, University of Texas Southwestern Medical Center, Dallas, Texas 75390-8896, USA.
authors.forename: R T
authors.initials: RT
authors.lastname: Lucarelli
authors.forename: R M
authors.initials: RM
authors.lastname: Peshock
authors.forename: R
authors.initials: R
authors.lastname: McColl
authors.forename: K
authors.initials: K
authors.lastname: Hulsey
authors.forename: C
authors.initials: C
authors.lastname: Ayers
authors.forename: A R
authors.initials: AR
authors.lastname: Whittemore
authors.forename: K S
authors.initials: KS
authors.lastname: King
mesh_terms: D000328:Adult; D004833:Epilepsy, Temporal Lobe / Q000473:pathology; D005006:Ethnicity; D005260:Female; D007839:Functional Laterality; D006624:Hippocampus / Q000033:anatomy & histology*; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods / Q000592:standards; D008279:Magnetic Resonance Imaging / Q000379:methods* / Q000592:standards*; D008297:Male; D008875:Middle Aged; D009929:Organ Size; D012016:Reference Values; D013781:Texas