Asymmetry of the prefrontal lobe in patients with attention deficit hyperactivity disorder: A three-dimensional volumetric magnetic resonance imaging study

Abstract

Asymmetries have been reported in several regions of the brain of patients with developmental disorders such as autism, developmental language disorder, and attention deficit hyperactivity disorder (ADHD). This study focused on age-related anatomical asymmetries of the prefrontal lobe, which can be manifestations of regional specialization of systems organization where there are functional differences between the left and right hemispheres, in children with ADHD. Subjects were 7 right-handed boys with ADHD aged 6–12 years and 5 age-matched controls. Exclusion criteria were full-scale intelligence quotient less than 80, comorbid learning disorder or developmental delay, evidence of medical or neurological disease on examination or by history, or Tourette's syndrome. No subjects met criteria for conduct disorder or oppositional disorder. Volume of the frontal and prefrontal lobes was determined using a workstation and the prefrontal-to-frontal lobe and left-to-right volume ratios were calculated. Both control and ADHD groups had a larger aggregate volume of left frontal and prefrontal lobes than of right frontal and prefrontal lobes. The leftward bias of the frontal lobe was significantly pronounced in ADHD subjects than in control subjects (P = 0.026). In addition, the leftward bias of the prefrontal lobe was more pronounced in ADHD subjects than in control subjects (P = 0.0041). The left-to-right volume ratio of the prefrontal lobe increased with age in both groups. The left-to-right volume ratio of the frontal lobe was more pronounced in ADHD (r = 0.922, P = 0.0014) than control group (r = 0.521, P = 0.414). In addition, the left-to-right volume ratio of the prefrontal lobe was more pronounced in ADHD (r = 0.903, P = 0.0029) than control group (r = 0.701, P = 0.219). These findings support the argument that right-sided prefrontal structural anomalies may occur disproportionately in ADHD.