The literature is lacking of profound anatomical descriptions of this complex area. It is primordial to obtain this anatomical knowledge in order to achieve efficiency and safety at the endoscopic endonasal approaches of this region. In this study, high-resolution CT was applied to measure the foramen rotundum distances to the contralateral side, midline, vidian canal, optic nerve, rotundum angle, anterior nasal spine, its angle with the floor of the nose, and its positions and types.

The asymmetry found in the distance from FR to the midline axis was compared to some previous studies. Mohebi et al. [9] found to have asymmetrically distances from FR to the midline axis, larger on the left side (19.34 ± 2.17mm) than the right side (19.00 ± 2.07mm) (P value 0.03). Kasmsiri et al. [10] have described the average distance from midline to the left FR as 19.11 mm (SD 2.34 mm) and 17.67 mm to the right FR (SD 1.7) (P value 0.046). Gozde Serindere et al. [2] discovered a significant difference in the distance from midline to the right and left FR. The gender calculated measurements showed an asymmetry between the two sides larger for male compared to female on the right side (P value 0.048). This serves as important information that can be used by the endoscopic skull base surgeon when trying to safely localize the FR during the approaches through the SS.

In bilateral foramen rotundum distance, Mikail et al. [7] study of 320 coronal CT of adult Japanese in 2015 by using the same methodology reported a significant bilateral foramen rotundum distance between the men and women. Less similar study of Kim et al. [11] has reported that the distance between the foramina rotunda was a little greater in the anterior segment in general.

In the present study, the distance between FR and VC (horizontal, vertical, and direct distances) measurements have shown no significant differences. The P values were 0.471, 0.521, and 0.072, respectively. Mohebi et al. [9], have discovered the same results; FR distances to VCs were symmetrical in horizontal, vertical, and direct, and no statistically significant difference (P = 0.764, 0.676, and P = 0.952, respectively). With the study of Kasmsiri [10], the average horizontal, vertical, and distances from FR to VC reported no significant difference between the right and left sides. According to Gozde et al. [2], there is a significant difference in the distance from the horizontal, vertical, and direct distances from the right and left FRs to VCs.

The gender comparison in the present study showed no significant distance in both right and left sides. The P values 0.765, 0.879, 0.621, 0.297, 0.992, and 0.227 are for direct, horizontal, and direct distances, respectively. The same symmetrical distances between genders were measured by Gozde [2] in his study, and the P values 0.202, 0.984, 0.217, 0.934, 0.453, and 0.738 are for right and left direct, horizontal, and vertical distances, respectively. This is important as EETs require a corridor that crosses the maxillary sinus or ablates or displaces the soft tissue contents of the PPF and removes partially the pterygoid process or completely to reach and control the surgical fields. The necessary dimensions of this corridor is often difficult to be estimated during the preoperative planning. In order to anticipate the dimensional needs of the corridor, EETAs can be better conceptualized (and estimated preoperatively) by vertical and horizontal imaginary lines that cross the vidian and rotundum foramina, respectively.

The primary trigeminal neuralgia (TN) can occasionally occur without neurovascular compression. Another mechanism than neurovascular compression may play a role in TN, and investigation of potential mechanism by measuring the sizes of the foramen rotundum on high-resolution computed tomography (CT) image, focusing on the primary TN without vascular compression during surgery, may help to rule out all other mechanisms [12].

In Pengfei et al.’s study [12] in the Chinese population, the diameter appeared narrow, with a mean distance of 2.52 ± 0.43mm on the right side and 2.65 ± 0.45mm on the left side, without a statistical difference between the right and the left side (P value 0.28). A cadaveric dissection study conducted by Kocaogullar et al. [13] reported an average diameter of FR (3.11mm) in cadaver specimens (3.44mm) in skulls without a statistical significance between the right and left in a study of 52 specimens (cadaver and skull). Also, Nadire Unver Dogan [14], in a study conducted in Turkey, had observed no statistical significance (P>0.05) between both sides in the average longitudinal diameters (4.48±1.15 mm in the right, 4.36±0.66 mm in the left) and average transverse diameters but wider in size.

As regards the distribution according to the position of FR regarding the base of lateral pterygoid plate as observed in the table, the FR was online placed in 24.5% of the patients, medially placed in 71.5% of the patients, and in 4% of the total foramens were placed laterally. It is shown from the study that online and medial types are the most common types that is in direct agreement with Mohebbi A. who reported 48%, 50%, and 2%, respectively. Ramanna et al. [15] have presented 50%, 57%, and 3%, online, medially, and laterally placed, respectively. Gozde Serindere observed in his study the same symmetrical results that FR is located 0.570, 0.150, and 0.758 online, medial, and lateral, respectively, located according to gender. This observation may help the better localization of FR in relation to VC and the pterygoid process, in order to facilitate its safe identification and help the surgeon avoid an inadvertent injury to their anatomical integrity.

In the FR position within the sphenoid bone, the present study revealed that the FR was either placed completely within the sinus cavity (type I), 3.5%; a part of FR is in the sinus cavity or partially protruding into the SS (type IIa), 15.5%; FR is tangent to the sinus wall (type IIb), 39.5%; FR is placed completely within the sphenoid bone (type III), 41.5%. Ramanna et al. [15] reported 6%, 32%, 44%, and 18%, respectively. Gozde et al. [2] reported that four patients (4%) had type I FR; 28% and 44% had type IIa and IIb, respectively; and 24% had type III FR. The relations of the SS with surrounding structures are close when the sinus is well pneumatized. The surrounding vessels and nerves are well seen in the sinus cavity as irregularities or ridges. The pneumatization of the sphenoid to the pterygoid processes is an extension of the sinus between the maxillary nerve and the nerve of the pterygoid canal (vidian nerve) [9].

As regards the rotundum angle, comparing the right to the left FR side among the total population, this showed 47.51±10.65o on the left side and 47.57± 9.51o on the right side. The P value was 0.952. Similar with the results with Mohebi et al., 46.76 ± 12.32o is on the right side and 46.40 ± 10.67o on the left side. The P value is 0.647. Gozde et al. reported the right rotundum angle P value of 0.021 and the left rotundum angle P value of 0.275.

The mean distance from the anterior nasal spine to the foramen rotundum was significantly longer in males of 6.36 ± 0.48cm on the right side and 6.47 ± 0.56cm on the left side compared with females (6.10 ± 0.40cm and 6.15 ± 0.40 cm on the right and left sides, respectively). The gender difference was confirmed by P values of 0.004 and 0.002, but the difference between right and left was not significant. On coronal CT angiographies of 34 Egyptians, Ahmed et al. [16] found a gender average of 6.98±0.88cm on right side and 6.93±0.887 on left side compared to 6.58±0.488cm on the right side and 6.62±0.436 cm on the left side. The apparently high numbers can be explained by the columella used as landmark instead of anterior nasal spine used in our study.

The foramen rotundum is related intimately to the lateral wall of the sphenoid sinus. The significance of variations is not fully understood, and the maxillary nerve may be more vulnerable to pathological conditions involving the sphenoid sinus [11].

There have been previous descriptions contained within the literature to evaluate the foramen rotundum localization and its relationship to the surrounding endonasal and skull base landmarks, but to our knowledge, the measurements conducted in this study (size of the angle between the floor of the nasal floor and the foramen rotundum) have not been recorded before, and they will provide surgeons with an additional and reliable description to use during operation.

This study has been carried on 100 adult patients (47 males and 43 females) who undergo paranasal sinus (PNS) computed tomography scan (0.6-mm slices thickness) for any reason, in the Otorhinolaryngology Department of Alexandria Main University Hospital. All individuals younger than 18 years of age, or with known skull base pathology and marked facial deformity, were not included.

There were no significant differences between measurements on the right and left sides regarding the mean distance of the horizontal distance between the foramen rotundum and vidian canal on each side, the vertical distance between the foramen rotundum and vidian canal on each side, the direct mean distance between the foramen rotundum and vidian canal on each side, the mean diameter of foramen rotundum on each side, the mean angle of foramen rotundum on each side, the mean angle between nasal floor and the foramen rotundum on each side, and the mean distance between the foramen rotundum and optic nerve on each side; The P values were 0.471, 0.521, 0.072, 0.283, 0.952, and 0.661, respectively. On the other hand, the distance from the foramen rotundum to the midline was significantly longer on the left side compared to the right side where the distance from the anterior nasal spine to the foramen rotundum was significantly larger on the left side compared to the right side. The P values were <0.001 and 0.048, respectively.

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