Abstract
In recent years several reports have noted that aqueduct stenosis may result from compression to the midbrain caused by enlarged lateral ventricles. The purpose of this report is to discuss the possibility of this “secondary” aqueduct stenosis.
Ninety patients with infantile hydrocephalus aged one week to four years were studied and classified radiologically into three groups: (A) 17 cases of hydrocephalus with aqueduct stenosis; (B) 25 cases of communicating hydrocephalus; and (C) 48 cases of hydrocephalus with Arnold-Chiari malformation.
In group (A) all of the patients were examined by ventriculography using water-soluble contrast media such as Conray, Dimer-X or metrizamide. Based on the ventriculographic appearance, the forms of the aqueduct stenosis were divided into two types; one showed uniformly narrowed lumen of the aqueduct and the other funnel-shaped stenosis of the aqueduct. Pneumoencephalography or metrizamide CT-cisternography was performed in eight cases of this group and they demonstrated apparent opacification of the ambient cistern except for one case. From these observations, it was concluded that the aqueduct stenosis could not be regarded from the morphological point of view as the product of compression to the midbrain. The fact that the ambient cistern was clearly visualized by radiological studies and considered to be patent may be an objection to the possibility of “secondary” aqueduct stenosis because the ambient cistern should be obstructed if the aqueduct is occluded by lateral compression of enlarged lateral ventricles.
In group(B) ventriculography or pneumoencephalography revealed that the lumen of the aqueduct was unusually large in many of the patients and the width of the aqueduct was closely related with the degree of the hydrocephalus. Therefore, the aqueduct was not considered to be gradually narrowed in the course of progressive hydrocephalus.
In group (C) the aqueduct in ventriculography showed a characteristic figure that was supposed to be pathognomonic of the Arnold-Chiari malformation. The aqueduct was rather distended in its caudal end in the lateral view of the ventriculogram but the lumen of the aqueduct was extremely narrowed in the AP view. CT-cisternography was performed in six cases of this group and gave clear opacification of the ambient cistern. The specific appearance of the aqueduct and patency of the ambient cistern in this group may indicate that the aqueduct stenosis seen in the Arnold-Chiari malformation is one of the developmental anomalies of this malformation, not the product of hydrocephalic forces.
