Deep calcarine sulcus and prominent calcar avis.

MR imaging examinations of the brain 100 consecutive patients, ages ranging from 1 year to 66 years, were evaluated in order to investigate the frequency of a deep calcarine sulcus and prominent calcar avis. Twenty-four cases (24%) were found with a deep calcarine sulcus and prominent calcar avis. These were bilateral in four patients, and unilateral in twenty. Fifteen of the unilateral cases demonstrated a right-sided involvement, and remaining five were left-sided. A deep calcarine sulcus and prominent calcar avis should be distinguished from disorders of neuronal migration and organization such as schizencephaly and heterotopia. Also, based on our findings in this study, we speculate that it is the deep calcarine sulcus and prominent calcar avis which creates the appearance of the so-called accessory occipital ventricle.