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Pathogenesis of aqueductal occlusion in congenital murine hydrocephalus.

In a study of congenital hydrocephalus in the murine mutant (hy-3/hy-3), the authors found that aqueductal stenosis develops during the progression of hydrocephalus. In Stage 1 hydrocephalus (ventricular dilation and open aqueduct), a block in the subarachnoid space over the cerebral convexities causes the lateral and third ventricles to enlarge. The ependyma becomes stretched and a collection of edematous fluid forms in the subependymal layer. In Stage 2 hydrocephalus (edema in white matter around lateral ventricles and compression of quadrigeminal plate), edema develops peripheral to ependyma in the aqueduct and compresses the lateral surfaces of the aqueductal wall to obstruct the lumen. While periaqueductal edema is spreading, the forces of the expanding midline structures and the cystic occiital horns alter the relationship of brain structures. There is no proliferation of glia, but, rather, a "simple stenosis" which results from a combination of ventricular dilation, cerebral edema, brain shift, brain-stem compression, and brain-stem edema. In this study, normal ependymal specializations were observed that indicate a more active functional role for aqueductal ependyma than previously recognized.