Progression of Experimental Infantile Hydrocephalus and Effects of Ventriculoperitoneal Shunts: An Analysis Correlating Magnetic Resonance Imaging with Gross Morphology

Abstract

Although previous ultrasonographic studies did monitor ventricular enlargement successfully in experimentally-induced models of feline hydrocephalus, the resolution of neuroanatomic detail was relatively poor after placement of a ventriculoperitoneal (VP) shunt because the skull had ossified over the coronal sutures. Therefore, the present study employed magnetic resonance imaging to follow the progression of ventriculomegaly more accurately, as well as to evaluate the compensatory effects of VP shunting. Hydrocephalus was induced in kittens between 7 and 10 days old by injection of kaolin into the cisterna magna. Age-matched controls received similar injections of saline. At 9 to 14 days after the kaolin injection, the hydrocephalic animals received VP shunts. Anesthetized kittens were scanned at various intervals before and after shunt placement and were killed for morphological correlation. The features observed on the magnetic resonance imaging scans were consistent with the gross morphological changes that accompanied ventricular enlargement. The lateral ventricle began to enlarge as early as 1 day after the kaolin injection, and within 3 days, both the occipital and temporal horns, along with the 4th ventricle, showed signs of moderate dilatation. By 5 days, a bilateral communication had been established through the septum pellucidum. Continued expansion of the ventricular system occurred from 6 to 20 days after injection, to the point where the cerebral cortex was reduced to less than 25% of its original thickness. The internal capsule was stretched and edematous, the caudate nucleus was compressed ventrolaterally, and the cerebellar hemispheres were eroded and/or compressed. Animals in which shunts were successfully placed demonstrated a dramatic improvement in behavior, and a reduction of about 50% in the size of the lateral ventricles within 2 days. In some cases, the lateral ventricles became slit-like within 1 week. When they were killed, about half of the animals that received shunts exhibited mild to moderate ventriculomegaly. These results indicate that magnetic resonance imaging is an excellent method for visualizing the morphological changes associated with this animal model, that these alterations occur soon after the onset of hydrocephalus, and that VP shunting can successfully reduce ventriculomegaly.