The main structures related to the standard endoscopic endonasal approach have been already described in details in the homonymous section of the pituitary adenomas chapter (see Chap. 1). Although the anatomy of the nasal and paranasal cavities is the same, during surgical treatment of craniopharyngiomas, there are some relevant structures, which it is useful to focus on, especially in case of extended approaches.

First of all, whether a pedicled nasoseptal flap should be used, its anatomy has to be understood. The flap consists of the mucoperiosteum and mucoperichondrium of the nasal septum, and it is pedicled on the posterior septal artery, a branch of the sphenopalatine artery. The posterior septal artery arises from the sphenopalatine artery, branch of the internal maxillary artery, in the pterygopalatine fossa and bifurcates into a superior and inferior branch with the latter being the larger one. The branches of the posterior septal artery then form a dense network along the septum to supply the inferior two thirds of the septum and a large portion of the nasal floor.

As well, the configuration of the sphenoid sinus has to be addressed properly: the sphenoid sinus could present an extreme variability in terms of size and shape and, above all, degree of pneumatization. Accordingly, in the adulthood, the sphenoid sinus could be identified as follows: sellar (≅75 %), presellar (≅24 %), and conchal (≅1 %). The sellar type of sphenoid sinus is the most common; in this case the air cavity extends into the body of sphenoid below the sella and as far posteriorly as the clivus. On the other hand, in the presellar type of sphenoid sinus, the air cavity does not penetrate beyond a vertical plane parallel to the sellar floor, whereas in the conchal type, the area below the sella is a solid block of bone without an air cavity [22].

During the approach, after all the sphenoidal septa have been flattened down, the posterior and lateral walls of the sphenoid sinus are visible. The sellar floor is positioned at the center of the surgical field with the cavernous sinuses laterally to it and the planum sphenoidale above with the bony protuberances of the optic nerves laterally to it and the clival indentation below. The bony prominences of C4 and C5 segments of the internal carotid artery (ICA) [23] can be seen laterally to the sellar floor and, above them, the optic nerves prominences can be observed; between them the optocarotid recesses lie. The ICA prominences are more evident as more the sphenoid sinus is pneumatized; the molding can be different depending on the shape and course of the carotid arteries. It is useful to remind that the bone covering the artery at the level of the sphenoid sinus may be very thin, especially at bony lateral aspects of the tuberculum sellae. The lateral optocarotid recess (LOCR) lies in between the inferior aspect of the optic nerve and the lateral aspect of the carotid artery bone protuberances and corresponds to the optic strut; it varies in depth accordingly to its degree of pneumatization. On the other hand, the medial optocarotid recess (MOCR) can be identified at the medial confluence of the optic and carotid bone protuberances.

Immediately above the sellar floor, the angle formed by the convergence of the sphenoid planum with the sellar floor can be observed; this latter structure, recently named “suprasellar notch” [24], from an endoscopic standpoint resembles a “mirror image” of the tuberculum sellae. It is limited superiorly by a line joining the 2 lateral optocarotid recesses, inferiorly by a line crossing just above the superior margin of the sella, and laterally by the medial aspect of the parasellar tract of the carotid arteries.

Once the bone of the sella and of the planum sphenoidale has been removed, venous sinuses that interconnect the cavernous sinuses appear: the intercavernous connections are named on the basis of their relationship to the pituitary gland; the anterior, or superior, intercavernous sinus passes anterior to the hypophysis, while the posterior, or inferior, intercavernous sinus passes behind the gland. However, these intercavernous connections can run at any site along the anterior, inferior, or posterior surface of the gland, or eventually they may be absent. There is also a large intercavernous venous connection, i.e., the basilar sinus that passes posteriorly to the dorsum sellae and upper clivus and connects the inferior and posterior aspects of both cavernous sinuses.

The dura is opened and it is possible to explore the entire suprasellar region. It should be said that a brief intercarotid distance – measured at the level of the supraclinoid tracts – could narrow the width of the endonasal corridor. Though, when adopting an extended endoscopic endonasal approach, this feature should be carefully evaluated preoperatively.

As well, the anatomical variability of the optic chiasm as related to the anterior skull base and surrounding structures should be highlighted: several anatomical studies showed that about 80 % of the optic chiasms overlie the diaphragm sellae, so defined as normal positioning. The remaining 20 % was equally distributed between the prefixed variant – when sitting above the tuberculum sellae – and the postfixed variant – when lying over to the dorsum sellae.

From the endoscopic endonasal perspective, the suprasellar area can be divided into four areas by two ideal planes, one passing through the inferior surface of the chiasm and the mammillary bodies and another passing through the posterior margin of chiasm and the dorsum sellae; these two lines define four regions, i.e., the suprachiasmatic, the subchiasmatic, the retrosellar, and the ventricular (Fig. 6.4) [3].

The retrosellar area can be explored passing with the endoscope between the pituitary stalk and the internal carotid artery, sliding above the dorsum sellae; it encloses the upper third of the basilar artery, the pons, the superior cerebellar arteries, the oculomotor nerves, the posterior cerebral arteries, and lastly the mammillary bodies and the floor of the third ventricle at the level of the tuber cinereum (Fig. 6.5).

Concerning the third ventricle area, it has to be highlighted that, as seen from the endonasal perspective, this cavity can be divided into four areas by means of two ideal planes, one passing through the optic chiasm and the interthalamic commissure and one passing through the posterior edge of the foramen of Monro and the interthalamic commissure. Accordingly, two anterior (infundibular and foraminal) and two posterior (mesencephalic and tectal) areas can be defined (Fig. 6.6). Furthermore, two separate endoscopic endonasal corridors can be identified, namely, the suprachiasmatic and the subchiasmatic [25].

On the other hand, the subchiasmatic route allows the entry into the third ventricle cavity through its floor. In this case the third ventricle is accessed through the tuber cinereum, which is located on the floor of the third ventricle between the pituitary stalk and the mammillary bodies. It has to be stressed that, entering the third ventricle through the tuber cinereum, the extradural removal of the dorsum sellae and eventually of the posterior clinoids along with the anterior transposition of the pituitary gland are useful.

As the endoscope is advanced in an inferior-superior trajectory through the tuber cinereum inside the ventricular cavity, a wide panoramic view is obtained (not only its infundibular area): the thalami and the interthalamic commissure and the foramen of Monro are visualized anteriorly, while the bulging of mammillary bodies can be seen posteriorly.

Finally, passing under the interthalamic commissure, the posterior portion of the third ventricle, i.e., the mesencephalic area, can be reached up to the pineal and suprapineal recesses, the posterior commissure, the habenular commissure, the habenular trigone, the stria medullaris, the tela choroidea, and the beginning of the cerebral aqueduct. The pineal gland and the internal cerebral veins lateral to the pineal gland can be seen as well (Fig. 6.7). The tectal area is generally not accessible through an endoscopic endonasal approach, neither via a suprachiasmatic or a subchiasmatic route.

As a general rule, it should be said that as position and orientation of the microscope could turn around the patient’s head, the same concept should be adopted during the endoscopic endonasal procedure. The position of the endoscope and instruments inside the nasal cavities should be variable and versatile, according to the target surgical area. Whether the surgeon is right-handed or left-handed, the endoscope is inserted, respectively, into the right or left nostril, at the high or low portion of the nasal cavity, with the aim of reaching the area of the surgical field that must be displayed. The first surgeon uses the nostril not occupied by the scope for his first instrument and the other for a second tool, while the second surgeon holds the scope in one nostril and another instrument in the contralateral nostril. This strategy attains to the strictly proper neurosurgical part of the operation, let’s say from the sphenoid sinus on, where a microsurgical attitude with using an instrument for each surgeon’s hand is mandatory. The same principle has to be applied to the surgical instruments; as a matter of fact, their position inside the nasal cavities should allow the most comfortable trajectory in order to reach each visible area of the surgical field, avoiding any conflict with the endoscope.

In case of infradiaphragmatic craniopharyngiomas, the surgical procedure is the same as described for pituitary adenomas (see Chap. 1). The endoscopic endonasal approach begins in the same way; in case of a craniopharyngioma, after the dura is opened, any cystic component of the lesion is aspirated, while the solid component has to be sharply dissected from the sellar walls and/or from the suprasellar cistern trying to not damage this structure to avoid intraoperative CSF leak (Figs. 6.8, 6.9, and 6.10). It has to be stressed that infradiaphragmatic craniopharyngiomas may be purely intrasellar or, more frequently, present a considerable suprasellar extension, pushing upward the diaphragma sellae. Those tumors can be approached via a standard endoscopic endonasal pathway as well. During the removal of infradiaphragmatic craniopharyngiomas, it is often possible to preserve the integrity of the suprasellar cistern: thus far, the sellar floor can remain open allowing the drainage of any eventual fluid part of the lesion inside the sphenoid sinus. The introduction of an X-shaped silastic catheter inside the sella grants the communication of the sella with the sphenoid sinus and/or the nasal cavities also after tissue healing (see Fig. 6.21) [26].