RESUMO
Hydrocephalus refers to distension of the cerebral ventricles, usually as the result of obstruction somewhere along the pathway of the cerebrospinal fluid circulation. Hydrocephalus ex vacuo means ventricular enlargement in the presence of cerebral atrophy or irreversible loss of brain parenchyma. According to morphologic change of ventricular enlargement, the mechanism and results of treatment are quite different. MRI improves diagnostic accuracy in patients with hydrocephalus because of its ability to show small obstructing lesion and anatomical changes. To evaluate differential points, we compared patients with obstructive hydrocephalus and non-obstructive hydrocephalus. T1-weighted sagittal images were retrospectively analyzed in 19 patients with obstructive hydrocephalus, 22 non-obstructive hydrocephalus, and 36 normal subjects. On midsagittal section, we evaluated mamillopontine distance, thickness and shape and position of the corpus callosum, and antero-inferior portion of the 3rd ventricle. The average mamillopontine distance was 11.5mm for normal subjects, 8.2mm for obstructive hydrocephalus group, and 13.6mm for non-obstructive hydrocephalus group(p < 0.01). Dilatation of the anterior inferior portion of the 3rd ventricle was seen only in 11 patients of obstructive hydrocephalus group. Average thickness of the corpus callosum at the level of the foramen of Monro was 7.5mm for normal subjects, 5.1mm for obstructive hydrocephalus group, and 4.4mm for non-obstructive hydrocephalus group(p < 0.01). There was a difference in the shape of corpus callosum between obstructive hydrocephalus and non-obstructive hydrocephalus group. It is concluded that mamillopontine distance, thickness and shape of the corpus callosum, dilatation of the antero-inferior 3rd ventricle could be good differential points between obstructive hydrocephalus and non-obstructive hydrocephalus.