Biportal neuroendoscopic microsurgical approaches to the subarachnoid cisterns. A cadaver study

A preclinical cadaver study was performed to develop the technique of biportal neuroendoscopic dissection in the subarachnoid space of the basal cisterns and to test the feasibility, utility, and safety of this new technique. In 23 fresh post-mortem adult human cadavers and 2 formalin-fixed adult human head specimen a total of 33 biportal endomicrosurgical dissections into and within the basal cisterns were carried out. Following suction of cerebrospinal fluid from the subarachnoid space 0 degree-, 30 degrees-, and 70 degrees-lens-scopes (Aesculap AG, Tuttlingen, Germany) with outer diameters of 4.2 mm and trochars with outer diameters of 5 to 6.5 mm were introduced into the surgical field. 6 different endoscopic routes to the basal cisterns and a total of 10 different combinations of these approaches for biportal endoneurosurgery could be described, but it was found that not all of them were useful and safe. The transventricular approach to the prepontine cisterns through the foramen of Monro and the floor of the third ventricle, biportally combined with a subfrontal or a subtemporal approach, turned out to be not safe enough as it was accompanied by traumatization of the fornix at the interventricular foramen and of the hypothalamus at the level of the tuber cinereum due to relaxation and caudal shift of the brain following suction of cerebrospinal fluid to clear the basal cisterns for the subfrontal or subtemporal approaches. Useful and safe endomicrosurgical approaches to the basal cisterns were: 1st subfrontal, either epidural or intradural, 2nd subtemporal, either anterior or posterior, and 3rd frontal interhemispheric. Various biportal combinations of these approaches are estimated to be feasible, useful, and safe enough to be performed during microsurgical procedures in the operating room. The biportal endomicrosurgical strategy allows for effective and safe dissections within the subarachnoid spaces of the basal cisterns. The tip of the microinstruments as well as the neighboring anatomical structures can be nicely controlled at angles of about 60 degrees to 180 degrees depending on the viewing angles of the scopes used and depending on the individual shape of the head. A variety of microsurgical instruments has been tested. A number of these will have to be redesigned for this new technique. Regions suitable for biportal neuroendoscopic subarachnoid preparations are the olfactory groove, the prechiasmatic cistern, the region of the optic chiasm, the entire suprasellar area, parts of the parasellar area, the pre- and perimesencephalic cisterns, and the prepontine cistern.