In advanced ESS, a clear surgical understanding of the anatomic variations in the sphenoid sinus and its pneumatization is helpful since they may place the patient at an increased risk of intraoperative complications with a mortality incidence of about 1% [14].

The Güldner classification defines four types of SSP.7 In line with other authors [15,16,17,18,19], the sellar type was the predominant pattern (58.7%) in our study, followed by the presellar type (27.2%). In previous literature, the sellar type is reported in very high percentages ranging between 78.5 and 93% [16,17,18,19]. In our study, the conchal type was detected in 8.5% of cases, greater than reported in the literature (1–2%) [17,18,19]. No conchal type was detected by Wang et al. [20], Dal Secchi et al. [15], or Anusha et al. [21]. The conchal non-pneumatized sphenoid was always considered to be a contraindication for a transsphenoidal approach to the sella [22].

Preoperative CT scans can help to identify bone protrusion of the ICA and ONC into the SS and their dehiscence to help avoid possible injuries during surgery [20]. In our study, ICA protrusion into the SS occurred in 26.3% of cases, similar to Dal Secchi et al. (26%) [15] and Sirikci et al. (26.1%) [10]. Dehiscence of the ICA was identified in only 2 cases (0.4%). In the literature, ICA protrusion generally has a wide range, from 5.2 to 67.0% [9, 16], while its dehiscence ranges from 1.5–5% [1, 15, 16], to 1.5–30% [8, 9, 21].

The rate of ONC protrusion was 13%, in accordance with the literature (range 2.3–35.6%) [8, 9, 16, 21], while dehiscence was 1.5%, lower than the literature (range 0.7–30.6%) [1, 8, 9, 16, 21]. ONC injury by protrusion or dehiscence can occur as a major complication when the IS is attached to it and has to be removed. The risk of injury may lead to defects in the visual field, visual acuity or blindness [11]. The ONC is at greater risk of injury when Onodi cells are present [23]. We found that 2% of our patients presented with the ON protruding into Onodi cells.

Dehiscence and/or protrusion of neurovascular structures are closely associated in cases with high SSP. This should prompt the surgeon to endeavor to preserve them from accidental injury since the bony wall over these structures may be very thin. We found frequent ICA and ONC protrusion in the sellar and postsellar types of SP, similar to earlier studies [15, 24].

Variations in the SS include deviations of the IS and the presence of AS. These are often deviated and attached to the bony wall covering the ICA or ONC. During ESS, care must be taken not to fracture these septa as this may have catastrophic consequences such as uncontrollable bleeding, retrobulbar hematoma, proptosis and diplopia [1, 25]. It has been reported that only one in four IS are located in the midline [26]. In our study, IS was deviated in 60.4% of individuals: in 30.1%, it was attached onto the ICA protuberance and in 14.3% into the ONC protrusion. Poirier et al. [27] reported attachment of the IS onto the ICA in 3.4%, Batra et al. [28] in 37.5% and Dziedzic et al. [26] in 49% of cases. In our work, we identified that 30.4% presented AS similar to levels reported by Anusha et al. [16] Jaworek-Troc et al. [29] reported that AS were present in 78.0% of cases, similar to levels reported by Akgül et al. [17]. Aksoy et al. [25] reported that AS originated in the ICA protuberance in 47.7% of cases while they were associated with the ONC protuberance in 17.5%, comparable to our data. This indicates that deviated IS and AS cause an increased risk of ICA and/or ONC injury; therefore, their presence should be considered during ESS.

The present results and comparison with the relevant literature confirm that risky variants are more likely to occur in the presence of well pneumatized SS. For successful ESS, surgeons should have excellent knowledge of the anatomical relationships present in the sphenoid sinus, and detailed examination of the preoperative CT scans is very important to avoid an increased risk of intraoperative complications. For this purpose, we recommend the use of neuronavigation system in case of important and risky anatomical variations (widely enunciated in this work) of sphenoid sinus and not to use drill and surgical chisel to avoid injuries of vital structures, in particular when approaching IS attaching to protruded ICA or ONC.