Morphometric study of the midsagittal MR imaging plane in cases of hydrocephalus and atrophy and in normal brains

BACKGROUND AND PURPOSE: Midsagittal morphologic changes often aid in the di agnosis of hydrocephalus. Stretching and upward displacement of the corpus callosum, widening of third ventricular recesses, and decreased mammillopon tine distance have been described as indicating the possibility of hydrocep halus. Quantitative studies are scarce. We performed retrospective, quantit ative analysis to verify and quantify changes in midline morphology that mi ght differentiate hydrocephalus and ventriculomegaly due to atrophy. METHODS: Sagittal MR imaging studies of 22 patients with hydrocephalus and 32 patients with atrophy were analyzed, as were 42 studies with normal find ings. The studied parameters included mammillopontine and mammillocommissur al distances, callosal height at two points, and the distances between the lines passing through the chiasm (chiasmal line) and the edge of the callos al splenium. Various angles between the chiasmal line and surrounding struc tures were measured. Similar measurements were done with the line passing t hrough the third ventricular floor segment anterior to the mammillary bodie s (third ventricular line). RESULTS: In hydrocephalus, mammillopontine distance decreased, mammillocomm issural distance increased, the third ventricular floor segment was concave in most cases, and the chiasmal line rotated clockwise. These changes were not seen in atrophy. Callosal height was increased in hydrocephalus signif icantly more than in atrophy. CONCLUSION. Specific changes of the midsagittal plane in hydrocephalus, som e of which have not been described previously, can be observed and quantifi ed, which might aid in differentiating this condition from atrophy.