[The MR findings on the corpus callosum of normal young volunteers].

The size and shape of the corpus callosum of twenty-seven normal young volunteers (age 18-31 years, 17 men and 10 women) were investigated using a superconducting high field (1.5 T) MRI unit. The length of the corpus callosum was 71.1 +/- 5.1 mm (mean +/- S.D.) and the height was 24.9 +/- 2.1 mm. The length ratio of the corpus callosum to the brain was 43.9 +/- 2.3% with the ratio of the height 25.0 +/- 2.3%. The callosal index (height/length) was 35.4 +/- 2.9%. The area of the corpus callosum in the midsagittal plane was 681.4 +/- 93.6 mm2 (min. 563 mm2 to max. 902 mm2). We divided the corpus callosum into three segments: rostrum and genu; anterior and posterior trunks; splenium. Each part accounts for one third of the total area of the corpus callosum. The genu and splenium were generally equal in thickness. The minimal thickness of the trunk was 3 mm with the maximal one 9 mm. The posterior trunk was never thicker than the anterior one. The posterior part of the posterior trunk showed thinning and concavity in almost all cases. So-called impressio corporis callosi was observed in 12 cases (44.4%). Thirteen cases (48.1%) showed a shallow concave configuration at the anterior dorsal surface of the corpus callosum. Six cases of these were thought to be due to compression by the pericallosal artery. This finding was not detected in the posterior portion of the corpus callosum. This concavity was also seen in infants. The thinning of the posterior part of the posterior trunk was seen after the development of the splenium, but the concave configuration at the anterior dorsal surface of the corpus callosum may be encountered before the full development of the genu and splenium.