Aqueduct stenosis. Case review and discussion.

Twenty-seven cases of hydrocephalus associated with aqueduct stenosis are reviewed, and a further nine cases discussed in which hydrocephalus was present and the aqueduct was stenosed but some additional feature was present. This was either a meningocoele or an encephalocoele, or else the aqueduct was not completely obstructed radiologically at the initial examination. The ratio of the peripheral measurement from the inion to the nasion to the distance between the inion and the posterior lip of the foramen magnum is presented for each case with an outline of the ventricles. The cases behave as would be expected if the aqueduct was being blocked by the lateral compression of the mid-brain between the enlarged lateral ventricles. On reviewing these cases and other evidence it is suggested that non-tumourous aqueduct stenosis is more likely to be the result of hydrocephalus than the initial cause. The response to treatment is reviewed and a high relapse rate noted. It is suggested that assessment of the extracerebral pathways may be advisable before undertaking third ventriculostomy or ventriculo-cisternostomy.