Abstract
The frontal sinus is undoubtedly a great challenge; not only because of the anatomical variations of the frontal sinus ostium (FSO), but also because of the proximity of vital structures that can complicate dissection at this level. Consistent and easily identifiable landmarks and measurements could assist safe entry into the FSO. In this study, we identify standard distances from the choana to the posterior border of the FSO in males and females using high-resolution computed tomography (HRCT) scans. A total of 118 (left sides) sinus computed tomography scans were retrospectively selected and studied (unilateral analyses). The vertical and horizontal distances between posterior border of the FSO and nasal choana were measured using sagittal HRCT. The mean vertical distance from the posterior border of FSO to the choana was 31.18 ± 5.62 mm and the mean horizontal distance from the posterior border of FSO to the choana was 40.87 ± 6.02 mm. The measurements obtained in this study add anatomic knowledge that can serve as a better intraoperative localization of the FSO.
Keywords: Frontal sinus ostium, Nasal choana, Computed tomography, Endoscopic sinus surgery
Introduction
Endoscopic sinus surgery (ESS) is one of the most otorhinolaryngologically performed surgeries [1, 2]. Nowadays ESS has been applied beyond the nasal cavity and the paranasal sinuses extended to the orbit and skull base [3–4].
Despite the advancement of the endoscopic technologies, instrumentation, and the proper imaging modality, endoscopic management of frontal sinus disease remains a difficult task [5–6]. The identification and exposure of the frontal sinus ostium during ESS are challenging due to the variable anatomy that hide its location, the narrow opening of the frontal sinus ostium (FSO), and the vital anatomic structures surrounding the outflow pathway such as the cribriform plate, orbit and anterior ethmoid artery [7]. Lynn-Macrae et al. reported in their study major and catastrophic injuries caused by sinus surgery, including CSF leak (24%), diplopia (17%), brain damage (15%), and death (5%) [8]. Therefore, frontal sinus surgery, the most challenging paranasal sinus surgery, requires meticulous preoperative planning to prevent any complications [9]. In order to minimize the risk of complications, consistent and easily identifiable landmarks and measurements could potentially expedite a safe exposure of the frontal sinus.
In this study, we identify standard vertical and horizontal distances from the nasal choana to the posterior borders of the FSO in males and females using high-resolution computed tomography (HRCT) scans. These measurements should provide objective data to more efficiently access the frontal sinuses.
Materials and Methods
Case Data
We retrospectively evaluated data from 118 patients (118 scans) who underwent sinus CT between September 1, 2023 and December 30, 2023. Patients were chosen randomly. Patients with fibro-osseous lesions or congenital skull base anomalies, skull base malignancies or other causes of skull base bony erosion (e.g., mucoceles), choanal erosion and significant motion artifacts that impaired the visualization of the frontal sinuses were excluded from the study. Demographic data were collected on all patients, including age at the time of CT, sex, as well as patients’ diagnoses. According to diagnosis we assigned the patient to 9 groups.
Equipment and Scanning Protocol
CT examinations were performed by 16 slice multidetector row, CT scanner (Aquilion 16 system, Toshiba Medical Systems Corporation, Tokyo, Japan) (kVp = 120, mAs = 100, FOV = 240 mm, slice thickness = 1 mm) and saved as digital imaging and communications in medicine (DICOM) files. The DICOM images were viewed and analyzed using medDream software, the standard software used by this medical institution. Bone-view images were used for making the measurements. On multiplanar reconstruction, axial, coronal, and sagittal were seen simultaneously and allowed for measurements in the actual scale.
Imaging Analysis
All the scans were reviewed by a single observer who is an otorhinolaryngologist. Measurements were performed for left frontal sinuses. As a first step, the relevant parasagittal planes were identified for analysis. Considering that we want to find the frontal sinus ostium attached to the orbital wall, we chose the parasagittal cut medial to the nasolacrimal duct. Next, a vertical line was drawn through the posterior edge of frontal sinus ostium at the point of upturn of the skull base. A second horizontal line was drawn from the choana orthogonal to the vertical line. Then, the horizontal and vertical distance between the choana and posterior edge of frontal sinus ostium was measured (Fig. 1).
Fig. 1.
Sagittal CT image of the paranasal sinuses detailing the vertical and horizontal distances from the posterior border of frontal sinus ostium (FSO) to Choana
Statistical Analysis
Statistical analysis was conducted using the SPSS statistical software (version 27). A descriptive analysis of the data was performed. Univariate Analysis of Variance was performed between the studied groups. The relationships between measurable variables were tested by correlation analysis and linear regression analysis. p-Value of < 0.05 was considered statistically.
Results
Our study comprised of 118 patients: 56 (47.5%) females and 62 (52.5%) males. The patients’ ages ranged between 16 and 80 years, averaging at 42.42 years and with a standard deviation of 14.20 year.
The mean vertical distance from the posterior border of frontal sinus ostium to the choana was 31.18 ± 5.62 mm. The mean horizontal distance from the posterior border of frontal sinus ostium to the choana was 40.87 ± 6.02 mm.
Gender comparisons revealed no significant differences in terms of vertical and horizontal distance from the posterior border of frontal sinus ostium to the choana. The comparison of parameters according to the genders is shown in Tables 1 and 2.
Table 1.
Descriptive analysis
| Patients | N (%) | Vertical distance, Mean ± SD (mm) | Horizontal distance, Mean ± SD (mm) |
|---|---|---|---|
| Total | 118 | 31.18 ± 5.62 | 40.87 ± 6.02 |
| Sex: | |||
| Male | 62 (52.5%) | 32.39 ± 5.51 | 41.03 ± 7.18 |
| Female | 56 (47.5%) | 29.84 ± 5.49 | 40.69 ± 4.44 |
| Diagnosis: | |||
| CRSwNPa | 62 (52.5%) | 32.04 ± 5.8 | 41.69 ± 5.10 |
| AFRSb | 8 (6.8%) | 32.35 ± 3.36 | 38.10 ± 2.42 |
| Phc of sinonasal tumor surgery | 5 (4.2%) | 32.32 ± 6.63 | 42.94 ± 5.47 |
| Phc of mucormycosis | 4 (3.4%) | 32.25 ± 5.75 | 41.02 ± 5.06 |
| Csf leak repair | 7 (5.9%) | 28.60 ± 2.42 | 42.25 ± 3.49 |
| Pituitary adenoma | 4 (3.4%) | 24.02 ± 3.36 | 39.82 ± 0.69 |
| Face trauma | 4 (3.4%) | 32.56 ± 4.82 | 36.67 ± 5.83 |
| Eye trauma | 3 (2.5%) | 31.33 ± 11.37 | 39.46 ± 8.00 |
| Patients not presenting sinus complaints | 21 (17.8%) | 29.67 ± 4.96 | 39.71 ± 9.64 |
a Chronic rhinosinusitis with nasal polyposis; b Allergic fungal rhinosinusitis; c Past history
Table 2.
Univariate analysis of variance
| Dependent variable | Source | Type III Sum of Squares | df | Mean Square | F | Sig. |
|---|---|---|---|---|---|---|
| Vertical distance | Sex | 85.421 | 1 | 85.421 | 2.874 | 0.093 |
| Diagnosis | 276.149 | 8 | 34.519 | 1.161 | 0.330 | |
| Sex * diagnosis | 204.463 | 7 | 29.209 | 0.983 | 0.448 | |
| Horizontal distance | Sex | 1.117 | 1 | 1.117 | 0.030 | 0.863 |
| Diagnosis | 167.533 | 8 | 20.942 | 0.559 | 0.809 | |
| Sex * diagnosis | 202.192 | 7 | 28.885 | 0.771 | 0.613 |
There were no significant differences between different diagnoses and different sinus involvement in terms of Vertical and horizontal distance from the posterior border of frontal sinus ostium to the choana. The study parameters according to the different diagnoses are presented in Tables 1 and 2.
There was no significant correlation between study parameters and age. As Table 3 shows, there was a significant negative correlation between vertical and horizontal distance from the posterior border of frontal sinus ostium to the choana (p = 0.035). Linear regression analysis identified a weak negative association between vertical and horizontal distances (Adjusted R2 = 0.030, p = 0.035) (Table 4).
Table 3.
The findings of pearson correlation analysis between the vertical and horizontal distances from the FSO to Choana and age
| N = 118 | Vertical distance | Horizontal distance | Age | |
|---|---|---|---|---|
| Vertical distance | Pearson correlation | 1 | -0.195* | 0.054 |
| Sig. (2-tailed) | 0.035 | 0.562 | ||
| Horizontal distance | Pearson correlation | -0.195* | 1 | -0.088 |
| Sig. (2-tailed) | 0.035 | 0.342 | ||
* Correlation is significant at the 0.05 level (2 tailed)
Table 4.
The findings of linear regression analysis regarding the effects of horizontal distance from the FSO to the Choana on vertical distance from the FSO to the Choana
| β | Std. Error | Sig. | AR2 | |
|---|---|---|---|---|
| Constant | 3.518 | < 0.001 | ||
| Horizontal distance | -0.195 | 0.085 | 0.035 | 0.030 |
Dependent variable: vertical distance
Discussion
Endoscopic frontal sinus surgery still proposes technical challenges to surgeons, owing to the considerable anatomic variation of the frontal sinus drainage pathway, as well as its proximity to 2 vulnerable areas, the lamina papyracea and the Anterior skull base [10–11]. These challenges create the potential for surgical failure, including incomplete surgery, which can lead to recurrent or persistent frontal sinus disease, postoperative stenosis, or iatrogenic complication with major negative sequelae including severe epistaxis, retroorbital hematoma, blindness, cerebrospinal fluid leak, and/or intracranial bleeding [12–13].
Given the boundaries of dissection in frontal sinus surgery (the Anterior skull base and medial orbital walls), we believe that measurements to the FSO boundaries from known anatomical landmarks can assist surgeons during surgery in this region and provide a rapid means of confirming one’s surgical position. In addition, evaluation of frontal recess cells and FSO is the most difficult in patients affected by chronic rhinosinusitis with advanced sinus disease, due to a large number of possible anatomical changes caused by the chronic inflammatory disease. In principle, knowledge of reproducible anatomical landmarks becomes paramount in difficult cases with significant anatomic distortion and severe disease [14].
The nasofrontal beak, anterior aspect of the middle turbinate and aggernasi cell are reliable landmarks to identify the anterior border of frontal sinus ostium [15]. However, these landmarks have a large degree of variation. The following makes these landmarks inconsistent: variable sized frontal beak, different types of air cells around frontal recess area, and variant incidences of ANC [16].
On the other hand, finding the posterior border of frontal sinus ostium is more difficult and important than the anterior border of frontal sinus ostium for several reasons: (1) during frontal recess surgeries, the AEA marks the posterior border of the ostium. In general, it is found one cell behind the frontal ostium along the skull base [17]. Accurate localization of the AEA is highly crucial during frontal sinus surgery because its deep situation, complicated relations with vital structures such as (lamina papyracea, Skull base and olfactory fossa) and extensive variations make it a high-risk territory for surgeons [18]. (2) posterior border of frontal sinus was placed at the point of upturn of the skull base. There is inherent variability of anterior skull base anatomy, therefore, there is a high risk of skull base injury and Csf leak [19]. In addition, the surgeon must find the ostium among the complex and highly variable anatomy of the ethmoid sinus. Hence, we measure the vertical and horizontal distance from the nasal choana to the posterior border of FSO, using high-resolution computed tomography (HRCT) scans, because the nasal choana is a fixed landmark and vertical and horizontal distant is not affected by highly variable anatomy of the ethmoid sinus. Furthermore, endoscopic measurement of vertical and horizontal distance from the posterior border of FSO to the nasal choana is possible and practical.
To the best our knowledge, no previous studies have estimated these distances. Previously, Eloy et al. has measured the distances from the columella and anterior nasal spine (ANS) to the nasofrontal beak (NFB) and anterior skull base (ASB) using high-resolution computed tomography (HRCT) scans. They have recommended to stay a distance less than 66.9 mm in men and 60.6 mm in women from the columella to minimize the risk of inadvertent intracranial complications [7].
In our study, the mean vertical distance between the nasal choana and frontal sinus ostium in sagittal cuts was 31.18 ± 5.62 mm with a range of 17.8 to 44.4 mm while the mean horizontal distance between the nasal choana and frontal sinus ostium in sagittal cuts was 40.87 ± 6.02 mm with a range of 4 to 52 mm.
It is worth noting that, the vertical and horizontal distances between the nasal choana and FSO displayed no statistically significant differences according to sex. Most importantly, our study revealed no significant effect of the different diagnosis and different sinus involvement on vertical and horizontal distance. Since the vertical and horizontal distances between FSO and the nasal choana were not affected by age, sex and different sinus involvement, they can be used to identify the FSO.
This study is limited by the use of HRCT measurements to determine these anatomic distances. As a result, the accuracy of these measurements may be influenced by software and human errors. In order to apply these measurements intraoperatively, a cadaveric study may be necessary.
Conclusion
The current work updates the knowledge about the position of FSO from a CT perspective to improve surgeons’ awareness of FSO location in the endoscopic field in the way for optimum and safe surgery.
Funding
None.
Declarations
Human/Animal Rights Retrospective Study
This study involves data analysis.
Informed Consent
Retrospective study.
Conflict of Interest
The authors declare no conflicts of interest.
Footnotes
Publisher’s Note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
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