Morphological analysis of progressive hydrocephalus and shunt-dependent arrested hydrocephalus. An experimental study

This experimental study was performed to determine if surgically treated feline hydrocephalus could produce any morphological and physiological changes in the periventricular tissue. The result was analyzed with clinical outcome, comparing two differently prepared models in which the biomechanical characteristics of the container property of the brain were altered. Craniectomies were performed in adult mongrel cats and the dura mater was left untouched in group A, while the dura was incised in crucial fashion in group B. Thirty-four animals underwent ventriculopleural shunt surgery 6-8 weeks after kaolin induction into the cisterna magna. In 19 animals, no shunt was implanted; they served as sham controls. These and 10 normal animals were subjected to transmission electron microscopic study or measurement of white matter water content. The regions studied were divided into three sections according to their depth from the ventricular surface (W1, W2 and W3). Considering the efficacy of shunting, the increased water content observed in preshunt animals decreased and was almost identical to normal controls after effective diversion surgery. On the other hand, the animals with ineffective shunt failed to normalize the water content and the figures were similar to the time-matched sham animals. These trends were preserved in groups A and B, but water content was much higher in group B. On histological observation, the chronological profile of subependymal extracellular space (W1, W2) in chronic condition did not correspond to the chronological changes in water content, while both changes observed after successful shunt were apparently linked. Subependymal glial proliferation was increased in volume as a function of time in all animals observed, but this was much more marked in group A than group B. Furthermore, gliosis was more evident in shunted animals than in the other group and was more prominent in cats with effective shunts than in those with ineffective shunts. These histological changes and clinical outcome were not closely related in this study. These results indicated that: (1) The shunting procedure itself could promote subependymal gliosis and this progresses unexpectedly even if CSF pressure is low enough after effective shunting. (2) This histological change is not necessarily a sufficient explanation for clinical improvement after successful shunting. (3) A biomechanical characteristic of the differently treated container property of the brain exerts an influence on the histological change and change in CSF dynamics in periependymal tissue mostly at an early stage of hydrocephalus rather than at a later stage. Therefore early treatment should be considered while avoiding an overindication for shunting.