The tectum and the aqueduct of Sylvius in hydrocephalus unassociated with myelomeningocele.

The brains of 30 children with hydrocephalus (but not myelomeningocele) were examined. It was found that secondary pressures on the tectum and aqueduct resulting from the hydrocephalus were responsible for further obstruction at this level in 15 of the 30 children and that they contributed to axial distortion in another 11 children. Occlusion of the aqueduct occurred as a result either of these external pressures or of internal gliosis. These events form a self-sustaining cycle which, if broken early, may lead to a more satisfactory control of the hydrocephalus.