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 diagnosis of hydrocephalus. Stretching and upward displacement of the corpus callosum, widening of third ventricular recesses, and decreased mammillopontine distance have been described as indicating the possibility of hydrocephalus. Quantitative studies are scarce. We performed retrospective, quantitative analysis to verify and quantify changes in midline morphology that might 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 findings. The studied parameters included mammillopontine and mammillocommissural distances, callosal height at two points, and the distances between the lines passing through the chiasm (chiasmal line) and the edge of the callosal splenium. Various angles between the chiasmal line and surrounding structures were measured. Similar measurements were done with the line passing through the third ventricular floor segment anterior to the mammillary bodies (third ventricular line). RESULTS In hydrocephalus, mammillopontine distance decreased, mammillocommissural 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 significantly more than in atrophy. CONCLUSION Specific changes of the midsagittal plane in hydrocephalus, some of which have not been described previously, can be observed and quantified, which might aid in differentiating this condition from atrophy.