The procedure is typically performed using a rigid 0° endoscope , 18 cm in length, and 4 mm in diameter (Karl Storz Endoscopy, Tuttlingen, Germany), as the sole visualizing tool. The 30–45° angled endoscopes are usually employed to explore the cystic cavity after its emptying. The nasal and sphenoidal steps of the procedure are performed following the same principles of the standard pituitary approach for pituitary adenomas [14–17]. A binostril 3–4 hand technique is usually adopted; as for standard pituitary surgery, the middle turbinate is not routinely removed but, rather, simply lateralized with an elevator and is repositioned back at the end of the procedure. After a wide sphenoidotomy and sellar bone opening, a relatively small dural opening is performed that is large enough to work through and pass a 4-mm rigid endoscope but is not so large to not extend to the inferior sellar pole or the lateral sellar edges so that a dural margin will remain circumferentially to help hold the possible reconstruction materials in position. Care should also be taken to selectively open the dura only, while not penetrating the pituitary gland; should the gland be pushed anteriorly, a vertical gland incision may be needed to enter the cyst [1]. The cyst membrane is then punctured with a spinal needle or opened sharply with microscissors or with a microblade, causing the clear CSF immediately pouring forth (Figs. 15.1 and 15.2). A small fragment may be taken from the anterior cystic membrane, if any is recognizable, and the specimen is sent to pathology for the histopathological diagnosis. An inspection of the cystic cavity is performed using the 0° endoscope and subsequently with the angled scopes (30° and 45°) to visualize the lateral, posterior, and superior cyst walls, making sure the lesion is not a cystic tumor and looking for potential communication of the cyst with the subarachnoid space (Fig. 15.3). Anyway, most of the time, soon after the cyst drainage, the superior and lateral portions of the cyst collapse, making the intracystic exploration more difficult. In such cases, it can be effectively employed the so-called diving technique, popularized by Locatelli et al. [18]. Such maneuver is a similar technique used by laparoscopic surgeons in creating the pneumoperitoneum: the endoscope is inserted inside the residual cavity, and the continuous irrigation through the irrigation sheath permits the temporary reflating of the cyst cavity, allowing a more complete inspection from its inside. During such maneuvers, enlarging the possible communication into the subarachnoid space should be avoided, which may cause the transformation of a possible low-flow CSF leak into a high-flow CSF outflow, which is far more difficult to treat. Nevertheless, the insertion of the infundibulum into the diaphragma should be carefully inspected, as defects may be present in this location, and although small, they may be a site for postoperative CSF leak [1, 4]. Furthermore, any attempt to dissect the cyst wall off of the pituitary gland should be avoided, given the risk of worsening pituitary dysfunction [1, 14].

A key step of the endoscopic endonasal transsphenoidal treatment of sellar or sellar/suprasellar arachnoid cysts is the avoidance of their recurrence and, in case of communicating cysts, the prevention of the postoperative CSF leak. Thus, the dead space left by the emptying of the cyst, even though it may be partially reduced by the collapse of the cyst walls, needs to be completely filled, since “Natura abhorret a vacuo” (“Nature abhors a vacuum”) [19, 20]. Several different materials have been proposed as “filler” of the sellar dead space, either autologous, heterologous, or synthetic [19–25]. If a definitive diaphragmatic defect is visualized, the tissue graft filling should, whether possible, partially obliterate this defect. Indeed, the filling should be sized enough to not overpack the sella, thus causing excessive optic apparatus compression. It is believed that the filling of the cyst cavity prevents the sella from refilling with CSF in the short period, while it likely induces scar formation to the diaphragma and parasellar arachnoid, recreating the natural partition between the sella and subarachnoid space in the longer period [1]. Subsequently, the dura should be reconstructed, and one of the reliable methods for the reconstruction is the extradural closure of the defect eventually supported by a pedicled nasoseptal flap [19, 20, 23, 26]. A Valsalva maneuver is performed to ascertain effectiveness of the reconstruction, and tissue glue is applied over the reconstruction with the double function of sealing the reconstruction and holding the materials in place [20]. The use of the lumbar drain is debated, and it may be reserved to those cases where an intraoperative CSF leak of high grade (Grade 3) is evident [20].