Objective To study the pathological and MR image characteristics of congenital hydrocephalus in Wistar rats. Methods Six Wistar rats with congenital hydrocephalus were found among 9 rats in a litter. The rat heads at age of 7, 14 and 21 days, respectively, were made MR imaging, cut and put into Bouin fixative solution and cut into continuous coronary sections. The viscera organs were also routinely fixed in formalin and prepared for histopathological examination. Results One day old neonates could usually be detected as being hydrocephalic revealing a slightly doming of their heads. Severe hydrocephalus was depicted by MR images. The cerebrospinal fluid was of slightly yellowish color, transparent, with no peculiar smell. No inflammatory cells were found in the cytological smears. The viscera organs did not show obvious abnormalities. The skull was weakly developed with poor ossification. The brain showed a thin cortex, with dilatation of lateral ventricles and partial adhesion, stenosis or obstruction of the cerebral aquaeductus. Some clumps of exfoliated cells were present in the third ventricle. No alterations were observed in the choroid plexuses. Conclusion Our findings in this study indicate that it is a congenital disease. The hydrocephalus is caused by stenosis and obstruction of aquaeductus, showing typical characteristic pathological and MRI alterations. ebrainshowedath ductus.Someclum Conclusion Our