Transnasal transsphenoidal surgery has developed significantly over recent decades. The cooperative work between neurosurgeons and ear, neck and throat surgeons has been essential for this development. The introduction of the endoscope was another landmark. Compared with the microscope, the endoscope enabled additional expansion of this surgical technique, thereby increasing the possibility of resecting lesions not otherwise eligible for transnasal transsphenoidal surgery.1 With the emergence of the endoscopic expanded endonasal approach, areas such as the clivus, the petrous bone, the middle cranial fossa and the infratemporal fossa became accessible.2 An extensive sphenoidotomy with septation resection is necessary to create an adequate surgical corridor.3

Intrasphenoid septations are bony structures found in the sphenoid sinus with several anatomical conformations. Because they are located in the sinus walls, they are often adjacent to surrounding structures, especially the internal carotid artery (ICA), which can increase the risk of expanded transsphenoidal surgeries during septation resection (Fig. 1).

Figure 1.

(a) CT scan axial view of an intersphenoid septation in the left internal carotid artery protuberance (ICAp) and (b) intraoperative view (0° endoscope) showing the same septation in the left ICAp.

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ICA injury is one of the most dramatic intraoperative complications. This injury can lead to a challenging surgical scenario featuring rapid blood loss that can result in patient exsanguination.4 An appropriate pre-operative radiologic evaluation of the sphenoid sinus and its septations is necessary to prevent this complication.

Previous articles have described the frequency of intrasphenoid septations in the ICA protuberance (ICAp).1–5 The majority of these articles have found fewer intrasphenoid septations than our surgical and pre-operative findings. The current article describes the frequency of intrasphenoid septations in the ICAp among a sample of 421 patients analysed using computed tomography (CT) scans and compares these findings with those of previous studies.

We identified 189 male and 232 female patients (mean age: 39±21.4 years). The most frequent type of sinus was type 4 (61% of cases) (Table 1).

A total of 359 patients (85.3%) had intersphenoid septations. Out of these septations, 135 (37.6%) were found in the ICAp. Totals of 44.7% and 43.5% of patients with type 4 and 5 sinuses had intersphenoid septations in the ICAp, respectively; only 14.1% of patients with type 3 sinuses had these septations in the ICAp. Patients with types 1 or 2 sinuses did not have ICAp-adjacent septations.

Accessory septations were found in 255 patients (60.6%). These septations were present in only one-quarter of patients with type 2 sinuses, whereas most of those with types 3, 4 or 5 sinuses had septations. Septations were located in the ICAp of 140 patients (54.9% of those with accessory septations; 25.4%, 42.8% and 52.2% for types 3, 4 and 5, respectively). The maximum numbers found were 2, 3, 5, and 4 for types 2, 3, 4, and 5, respectively, whereas the maximum numbers found in the ICAp were 2, 3, and 3 for types 3, 4, and 5, respectively.

The number of patients with septation in the ICAp, regardless of type, was 219 (52%). Those patients were older than those without septations (43±18 vs. 34±23; p<0.0001); no significant difference was observed with regard to sex (females comprised 55% of all cases in both groups, p=0.963). Patients with types 4 and 5 sphenoid sinuses were more common than those with type 3 (Table 2).

Of the 351 patients with type 3, 4 or 5 sphenoid sinuses, 219 (62.4%) had septations in the ICAp. A total of 322 patients (91.7%) had intersphenoid septations; of these patients, 135 (41.9%) had septations in the ICAp. Of the 244 patients with at least one accessory septation, 140 (57.4%) had a septation in the ICAp.

The expanded endonasal transsphenoidal approach marked a breakthrough in skull base surgery. With its development, lesions previously inaccessible using the conventional endonasal route (e.g., those in the cavernous sinus, the planum sphenoidale, the middle cranial fossa, Meckel's cave, the suprasellar region and the clivus) could be accessed.2 To obtain appropriate exposure and accommodate the surgical endoscopic instruments, a wide sphenoid sinus opening is required with intrasphenoid septation resection.3

Intrasphenoid septations are naturally occurring bony structures inside the sphenoid sinus that divide it into compartments. They are divided into intersphenoid and accessory septations. The association with fusion lines between ossification centres (synchondrosis) and the septation positions might explain their origin.6,7 In general, one or more intersphenoid septations are present. They show great variability; therefore, they typically create two asymmetric compartments: right and left. Accessory septations occur in different positions and are also common. Both can be found in structures adjacent to the sphenoid sinus increasing the risk of neurovascular damage during surgery, especially when they are located in the ICAp. Cope previously described this complication in 1917.6

In our study, CT scans revealed that 219 patients (52%) had septations in the ICAp. Among patients with type 3, 4, or 5 sinuses (i.e., well-pneumatised sphenoid sinuses), this prevalence was even higher (62.4%).

Our data contrast with those of previous papers showing a smaller prevalence.5,8–12 However, Fernandez-Miranda et al. showed radiologic prevalence of 85% among patients with at least one septation in the ICAp.3

Renn and Rhoton found intersphenoid septations next to the ICA channel in 32% of cadavers.5 Sethi described intersphenoid septations in the ICAp in 40% of 30 cadavers in an endoscopic study in 1995.8 Unal et al. and Abdullah et al. reported 30% and 31% of septations of the sphenoid sinus attached to the wall of the ICA, respectively, using CT scans.10,12

Elwany et al. found that 12.9% of patients had septations in the bone surrounding the ICAp in an endoscopic study with 93 cadavers.9 Hamid et al. showed frequencies of 4.7% and 6.75% for intersphenoid and accessory septations in the ICAp, respectively.11 Both of these studies represent the lowest frequencies in the literature.

The current findings support the need for a pre-operative radiologic study on intrasphenoid septations. Appropriate knowledge concerning their position and their relationship to surrounding structures might significantly decrease the risk of surgery catastrophes due to vascular injuries.

Pre-operative CT scans are the radiological evaluation of choice because they adequately visualise bone structures. The analysis of the axial, coronal, and sagittal planes as well as their 3 dimensional reconstruction ability allow radiologists to accurately determine whether a septation is close to the structures surrounding the sphenoid sinus (e.g., the ICA).3,13–16

With regard to sinus classification, patients with type 4 or 5 sinuses were more likely to have septations in the ICAp than patients with type 3 sinuses. The aeration process that the sphenoid body undergoes explains this result. When the ICA is pronounced, it can substantially bulge into the pneumatised sinus, thereby increasing the area that is susceptible to a septation attachment.13

The fact that sinuses are more pneumatised in older people might explain the higher mean age of the patients who showed a relationship between septations and the ICAp.17

The present study describes the anatomical findings of a large, multiracial population. To our knowledge, it is the largest series regarding this issue.

The high frequency of intrasphenoid septations in the ICAp requires an appropriate pre-operative radiologic study. Furthermore, careful attention should be paid during transsphenoidal surgery to reduce potentially serious vascular injuries.

The authors declare no conflicts of interest.