Skull base pathologies encompassing the suprasellar lateral area, including the lateral aspect of the planum sphenoidale and a tight junction region of the OC, the ACP, and the ICA and its dural rings, still pose a unique surgical challenge for neurosurgeons in terms of subsequent morbidity and achievement of gross total resection.[1, 12, 18, 20, 26] These pathologies typically involve intra- and extracranially, tend to displace the ON from above and/or below, erode osseous and dural structures, and even involve the ICA bifurcation. Hence, TCAs for complete resection of these lesions have a high potential morbidity, even for skilled and experienced neurosurgeons. Today, endoscopy, which offers a wider, close-up view of the surgical field, is used broadly in skull base surgery. Although it has the disadvantage of increasing the rate of CSF leakage, potential advantages of EEA compared to conventional TCAs include avoiding brain retraction, improved visualization, better protection of surrounding neurovascular structures, and shorter hospital stay.[5, 7, 8, 14–16] These advantages are similar when comparing the EEA and different TCAs for lesions involving the lateral area of the suprasellar region. The EEA not only provides the most straightforward surgical route parallel to the growth axis of the tumor but also, most importantly, allows for better control of the paraclinoidal ICA, which constitutes a lateral barrier to directly approaching these regions through the sphenoid sinus. However, the intricate anatomical complexity and lack of anatomical detail suitable for surgical exploration make these regions among the most challenging areas to approach.
In this paper, we describe the surgical anatomy of the lateral area of the suprasellar region from the endoscopic perspective, termed the “parasuprasellar” area. Moreover, we introduce EESO and EEIO approaches to access this complex area. The same techniques were applied in 12 consecutive patients harboring tumors and aneurysms involving the parasuprasellar area. To the best of our knowledge, this is the first report on the EESO and EEIO approaches
Approach Selection and Technical Considerations
Our results validate that the EESO and EEIO approaches can effectively manage lesions involving the parasuprasellar area, as well demonstrated in our illustrations (Figs. 5–11). In our experience, when tumors simultaneously invade the intrasellar, suprasellar and lateral to the parasuprasellar area, such as pituitary adenomas or craniopharyngiomas, the EEIO approach should be considered first. If the tumor is not safely exposed or still has an invisible portion, even after pulling it downward, the EESO approach should be selected to allow for additional exposure of the lateral tumor. When the lesion originates in the parasuprasellar area, such as ACP meningiomas or paraclinoid aneurysms, the EEIO approach can also be considered first to remove the lesion on the medial or lateral side of the paraclinoidal ICA. Similarly, if the lesion cannot be completely removed through the corridor below the ON, a combined EESO approach can be applied in most cases. It must be emphasized, however, that not all lesions involving this area are indications for EESO and EEIO approaches. Indeed, a primary TCA or staged operation may be indicated when the lesion involves the intracranial to the parasuprasellar area and is mainly located subdurally.
Of note, the use of the EESO or EEIO approach alone is rather rare and most often requires a combination of the endoscopic endonasal midline approach and/or transcavernous approach. We can choose from different combinations according to the size and location of the lesion(s). For example, the transtuberculum/transplanum approach can be conveniently combined with the single EESO approach to provide better access to anterior cranial fossa meningiomas with lateral extension (case 1). Similarly, the combination of the transcavernous approach and EEIO approach has the potential for achieving complete resection of ACP meningiomas or pituitary adenomas involving the CS (cases 4, 6, 7 and 8). The EESO and EEIO approaches can be used as a complement to the midline approach and transcavernous approach and are extremely useful to access extensive pathologies for more complete resection while limiting morbidity.
Graduated Stepwise EEIO Approach
In our practice, the EEIO is a graduated, stepwise approach based largely on the lesion location, size and extent. Our anatomy and clinical cases demonstrate how to assemble multiple surgical corridors to provide personalized access to complex parasuprasellar lesions. In Case 10, in which the left paraclinoid aneurysm was located just below the ON, successful clipping of the aneurysm was achieved using a pure EEIO approach (Fig. 6).
Regarding Case 2, we found during the operation that a recurrent ACP meningioma was severely adhered to the ON and ICA and extended into the right OC. Thus, anterior clinoidectomy was applied, and the tumor tightly attached to the ACP and the ICA bifurcation was completely removed (Fig. 7). It should be noted, however, that complete anterior clinoidectomy is not mandatory and that the extent of bony removal should be tailored to each case based on intraoperative need. If only the lateral region of the paraclinoidal ICA needs to be exposed or to obtain distal vascular control, partial anterior clinoidectomy should be considered; however, complete anterior clinoidectomy should be performed if the tumor involves the ACP and causes evident hyperplasia or the lesion has extended the ICA bifurcation or even more. Such resection can reduce the risk of tumor recurrence. Most importantly, a corridor accessing the lateral region of the supraclinoidal ICA is established while removing the involved ACP and the dura that envelops it. Nonetheless, this technique can only be implemented by experienced surgeons due to the complicated procedures and potential risks.
In Case 9, a lateral projecting paraclinoid aneurysm was encountered. In view of its position and orientation, we first performed anterior clinoidectomy to expose the lateral region of the paraclinoidal ICA. Then, the OA was dissociated and temporarily clipped, but the VEP was changed, which indicates that severing of the OA would lead to serious visual impairment (Fig. 8E and H). Finally, we attempted to expose the aneurysm neck between the OA and ON and successfully clipped the aneurysm through the ACP triangle (created by anterior clinoidectomy) (Fig. 8F and G).
In Case 4, the tumor involved the intrasellar, suprasellar, CS, and encased ICA and its bifurcation. The optic strut was drilled first, and the OA completely wrapped by the tumor was selectively dissected to further remove the hyperplastic ACP (Fig. 9F-H). Thus, the tumor on the medial and lateral region of the supraclinoidal ICA can be completely removed via an enlarged EEIO corridor (Fig. 9I and J). In our case series, only this case in which the OA was sacrificed occurred when preoperative DSA showed that the OA was not visible and the patient’s intraoperative VEP stabilized. As expected, the patient's vision remained stable after surgery.
The special location of such lesions is often responsible for vision loss related to intracranial and/or intracanalicular ON involvement. Ten patients in our series presented with varying degrees of vision loss; thus, improvement and preservation of visual function is a priority for this surgery. Remarkably, in our series, visual improvement occurred in 7 patients but was unchanged in 4, and only 1 patient with recurrent ACP meningioma developed visual deterioration. This demonstrates that gentle pulling of the ON during resection will hardly affect visual function under VEP monitoring. Postoperative visual deterioration has been mainly related to injury of the subchiasmatic perforators, providing the main blood supply to the optic chiasma. Accordingly, the potential risk of injuring visual acuity may not be increased by extra manipulation in the supraoptic region. Furthermore, while applying the EEIO approach, endoscopy provides early and direct visualization of the subchiasmatic perforators, allowing for adequate dissection and protection. Last but most importantly, this approach allows for direct 270° decompression of the intracanalicular ON and prompt removal of the involved dura and hyperostotic bone. Nevertheless, as mentioned above, these procedures must be carried out in an extremely delicate and careful manner. When removing bone, the eggshelling technique with continuous irrigation of saline must be followed to prevent thermal injury to the ON. We believe that if sufficient decompression is performed without the risk of further injury, vision problems may be reversed.
Limitations of the Study
The current study has several limitations that need to be considered. First, although no ICA or ON injury occurred in our series, they are still our primary concern when managing parasuprasellar lesions. Second, cadaveric specimens are useful models to investigate surgical approaches, but they do not fully capture the clinical environment. Indeed, these corridors are relatively narrow in individuals who do not harbor such lesions. Finally, the learning curve is extremely steep and requires a high level of expertise in comprehensive skull base surgery, including both microsurgical cerebrovascular and endoscopic skills. Consequently, practice in the cadaver laboratory is mandatory to develop familiarity with these precise and meticulous operations before they are applied clinically.