301 Intraventricular Haemorrhage on the Left Side of the Brain Induces Left-Handedness

Abstract

Background: Prematurely born children are more often left-handed than their term born peers. It is unknown if this excess left-handedness, a marker for the extent of cerebral lateralisation, is caused by cerebral lesions.Methods: In a cohort of 221 preterm born infants (gestational age <= 32 weeks and/or birth weight <= 1500 grams), brains were serially examined in the neonatal period using cranial ultrasound (US) to detect intraventricular haemorrhage (IVH), periventricular leukomalacia (PVL) and other abnormalities. At age 7 to 10 years, magnetic resonance imaging (MRI) was done, and hand preference and current IQ were measured. MRI and US were classified as normal, mildly abnormal, or severely abnormal, blinded to handedness data.Results: Children with severely abnormal US (IVH grade III/IV, cystic PVL grade II/III, thalamic lesion, focal infarction or haemorrhage at the level of the convexity) had an increased chance to become left-handed: odds ratio (OR) severely abnormal US versus normal US 4.1, 95% CI 1.6 to 10.0, p=0.003. This was confirmed by MRI scans at school age: OR severely abnormal MRI versus normal MRI 4.0, 95% CI 1.5 to 10.7, p=0.005. Findings were attributable to IVH. Left-sided IVH showed a higher chance for left-handedness (OR left-sided IVH versus no IVH 4.4, 95% CI 1.7 to 11.3, p=0.002), whereas right-sided IVH did not. Neonates with left-sided mild IVH (grade I and II) still showed an increased chance for left-handedness: OR mild left-sided IVH versus no IVH 4.0, 95% CI 1.5 to 10.9, p=0.007. PVL was not related to left-handedness.Conclusion: Our findings strongly indicate that even a small intraventricular haemorrhage affecting the left side of the brain induces left-handedness. This is likely related to the role of the subependymal germinal matrix in the developing brain.