Minimal asymmetry of the brain: a normal variant

Normal cerebral asymmetry, well-known to neuroradiologists, is not widely recognized by radiologists in general. In our review of CT brain scans, 31 of 300 patients with a negative neurologic examination and no history of birth injury, head trauma, or seizure had recognizable asymmetry of the frontal horns of the lateral ventricles. The right frontal horn and the right cerebral hemispheres were larger than the left twice as often as left were larger than right. The right frontal lobe was wider than the left in 44% of patients and extended as far anteriorly or more anteriorly than the left in 22% of patients. The right central hemispheric mass tended to be wider than the left, resulting in slight displacement of the pineal gland to the left, in approximately 45% of cases. The posterior end of the left Sylvian fissure projected farther posteriorly in 10% of the patients. Occipital petalia and a more posterior position of the calcified glomus of the choroid plexus of the lateral ventricle were both common on the left side of 56%. Earlier studies of the brain by other methods have also shown asymmetry. An awareness of these anatomic asymmetries in normal individuals should preclude the erroneous diagnosis of an atropic or mass lesion.