Endoscopic procedures through the foramen interventriculare of Monro under stereotactical conditions.

The foramen interventriculare of Monro is an anatomical narrowness for the endoscopic access to the third ventricle. The effective mechanical angle to pass the foramen interventriculare from a frontal bore hole depends on the diameter in the plane of entrance, the depth of the foramen, and the diameter of the endoscope. Under the pathological conditions of a hydrocephalus internus the foramen interventriculare is enlarged. By means of stereotactical guidance, it is possible to reach the third ventricle accurately without damaging anatomical structures around the foramen interventriculare. The endoscopic technique under stereotactical guidance using a rigid endoscope is sufficient and safe to perform ventriculostomies in cases of hydrocephalus occlusus. Best clinical results were obtained in patients with benign aqueduct stenosis or with a tumor in this region compressing the aqueduct. In all patients no further shunt operation was necessary. The path through the foramen interventriculare should be considered also for biopsies in the third ventricle. Calculation of the foramen interventriculare trajectory prevents perforation of the roof of the third ventricle containing the main deep veins. Lesions in the foramen interventriculare like colloid cysts can also be approached very accurately by means of stereotactical calculation. However the endoscopic technique with the at present obtainable instruments does not allow removal of the whole lesion. Even so a free passage to the third ventricle can be achieved by reducing the size of the cyst by means of coagulation and sucking off the colloid material.