MORPHOLOGY OF ACALLOSAL BRAINS AS ASSESSED BY MRI IN 6 PATIENTS LEADING A NORMAL DAILY-LIFE

The pattern of anatomical features of the brain revealed by magnetic r esonance imaging (MRI) is described in six patients incidentally ident ified as having acallosal brains. The complex of morphological feature s associated with complete agenesis of the corpus callosum included la teral displacement of slit-like anterior hems of the lateral ventricle s (bullhorn-like shape), dilatation of the posterior hems of the later al ventricles, absence of the septum pellucidum, lateral displacement of the cingulate gyri, complete separation of fornices and the presenc e of the anterior commissure and longitudinal callosal bundles (Probst 's bundles). No compensatory enlargement of the anterior commissure wa s seen in the patients. The planimetrically measured cross-sectional a reas of the anterior commissures were between 2.0 and 4.2 mm(2) (mean 3.1) (in ten normal subjects they were 4.5, SD 0.4; range 3.8-5.2 mm(2 )) and were reduced in four and normal in two patients. Inconstant mor phological features were an absence of the posterior commissure and a radial pattern of the sulci and gyri on the medial aspect of the hemis pheres. Conventional clinical testing revealed no abnormalities except a slight impairment of walking heel-to-toe in two patients. None of t he patients had subjective restrictions of activities of daily life, w hich shows the efficacy of unknown compensatory processes.