Upon entry into the lateral ventricle the first goal is to identify the Foramen of Monro. This is done by following large veins or the choroid plexus to the Foramen.
Next the third ventricle is entered by passing through the Foramen. First seen are the Mamillary Bodies and the dark crotch or “V” that lies between them. The Infundibular Recess is then identified to establish the midline. In this example an old third ventriculostomy can be seen covered by arachnoidal scar.
The ostomy is then performed. I prefer to use a Bugbee wire as a blunt probe. In that way I have cautery available to thin the floor if needed. I do not use it to “cut” the floor with cautery however as I feel this risks injury to the underlying Circle of Willis and Basilar artery.
I like to enlarge the ostomy with a 2 French Fogarty Balloon Catheter. I inflate it several times as it straddles the ostomy and then inflate it just below the floor. I then gently and slowly pull the inflated balloon back into the ventricle to enlarge the ostomy.
As a final step I inspect the cisternal space below the opening to insure that there is no curtain of arachnoid blocking the ostomy. To further enlarge the opening I move the scope back and forth as it straddles the opening.