Scanning electron microscopy of the ventricular system in normal and hydrocephalic rabbits

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Abstract
The author used the scanning electron microscope to study the ependyma in six control rabbits and six rabbits made hydrocephalic by infusion of silicone oil into the cisterna magna. The ependymal lining of the third ventricle, head of the caudate nucleus, superior angle of the caudate, and atrium of the lateral ventricle was examined. In the hydrocephalic animals, clusters of cilia emanating from the ependyma over periventricular white matter become separated; the author believes this is secondary to ingrowth of new ependymal cell processes covered with microvilli. The addition of these cells to the ependymal surface permits ventricular dilatation without ependymal disruption and provides more surface containing microvilli, presumably capable of increased transventricular fluid transfer. No such changes occur over gray matter masses since their surfaces are not deformed by moderate ventricular dilatation. The morphological alterations in the ependyma that occur in moderate hydrocephalus do not appear to be simply manifestations of ependymal destruction but rather suggest a modification in its function from that of a surface capable of propelling cerebrospinal fluid to one capable of increased transfer of transventricular fluid. As hydrocephalus progresses, compensation may fail because of the relative decrease in microvilli so that the cell surface provides a less efficient mechanism for absorption.