Entry into the Cyst of the Septum Pellucidum

At this time we enter into the cyst of the septum pellucidum. We can recognize it nicely if we have been careful in keeping the midline. We can recognize the right and the left walls of the cyst the septum pellucidum. Here, we are gently opening the upper part of the cavum septum pallucidum, and keeping our surgical field clean from blood, we can slowly recognize the two leaves of the cyst of the septum pellucidum. The dissection must be very gentle.

As you can see, we progress millimeter by millimeter, and recognition of the lowest part of the corpus callosum is very important here. We have reached the lowest part of the corpus callosum, we are entering into the cyst of the septum pellucidum. We enlarge our callosotomy up and down, we recognize the two walls of the cyst of the septum pellucidum, there is no choroid plexus, of course, this is the anatomical landmark that is mandatory. There are no veins into the cyst of the septum pellucidum, so we recognize the cyst from the lateral ventricle very nicely. No veins and no choroid plexus.

We are sure of our anatomical landmarks, we are sure of the midline, and we can modify the position of our self-retaining retractor, gently deepening our self-retaining retractor into the callosotomy in order to enlarge a little bit the vision, and visualize nicely the cavity of the cyst of the septum pellucidum. In the depth of the cavum septum pellucidum, we have to recognize the two bundles of the fornix that are anatomically physiologically separated by the presence of the cyst of the septum pellucidum. Under the floor of this cyst, we can recognize the tumor by transparency through the last layer of ependyma of the cavum septum pellucidum.

With the navigation, we are sure of the presence of our instrumentation at the level of the upper pole of the tumor. At the very end of the cyst of the septum pellucidum, we can enlarge the very last millimeters of our callosotomy in order to expose completely the anterior pole of the tumor and the posterior pole of the tumor. We recognize very nicely the presence of right and left white bundles of the fornix that must be respected very gently, the right bundle of the fornix, the left bundle of the fornix, the tumor is indicated by narrow navigation probed at this time.

We can open the very thin layer that covers the upper pole of the tumor. We recognize very nicely the typical aspect of pilocytic astrocytoma of the optic pathways into the third ventricle. We continue our opening of the last layer in the floor of the cavum septum pellucidum, and we expose nicely the upper pole of the tumor. Tumor is easy to recognize because of its color, its structure and of its bleeding pattern typical of pilocytic astrocytoma.