Abstract
Purpose
Identification and exposure of the frontal sinus recess (FSR) during endoscopic sinus surgery (ESS) are challenging due to the variable anatomy, the narrow opening of the frontal sinus ostium (FSO), and the proximity of vital anatomic structures. Hence, a strong understanding of frontal sinus anatomy is required to prevent intracranial entry. Consistent and easily identifiable landmarks and measurements could assist safe entry into the FSO. In this study, we determine 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.
Methods
A radiographic analysis was performed at a tertiary care medical center. Measurements from the ANS to the NFB and ASB, and from the columella to the NFB and ASB were made using sagittal HRCT. Thirty-two HRCT scans were analyzed by three observers, and the mean distances and standard deviations were calculated.
Results
The mean distance from the ANS to the NFB was 52.3 ± 3.4 mm in men and 47.7 ± 3.5 mm in women (p < 0.0001). Mean distance from the ANS to the ASB was 61.8 ± 4.1 mm in men and 56.5 ± 4.1 mm in women (p < 0.0001). Mean distance from the columella to the NFB was 58.9 ± 2.3 mm in men and 53.0 ± 3.3 mm in women (p < 0.0001), and from the columella to the ASB was 67.9 ± 3.7 mm in men and 61.3 ± 4.1 mm in women (p < 0.0001).
Conclusion
While performing FSR exposure in ESS, it is recommended to stay a distance of less than 66.9 mm in men and 60.6 mm in women from the columella to minimize intracranial complications.
1
Introduction
Endoscopic sinus surgery (ESS) was first introduced in Europe during the 1970s and was brought to the US in the 1980s . Since then, ESS has undergone many advances aimed at improving visualization of important structures in order to limit complications and achieve more complete surgeries. Despite these advancements, endoscopic management of frontal sinus disease remains a difficult task and requires a strong understanding of frontal sinus anatomy . Although numerous minimally invasive techniques have been introduced to address frontal sinus disease , intracranial entry is not uncommon in cases of advanced pathologies such as allergic fungal sinusitis, inverted papillomas, osteomas, or frontal sinus encephaloceles. Despite all the developments in ESS, over the past 30 years, major orbital and intracranial complications are estimated to occur in 0.05% to 2% and 0.32% to 0.9% of cases respectively . In order to minimize the risk of complications, a solid understanding of paranasal sinus anatomy is essential. Additionally, anatomic reference points that are consistent and easily recognized provide landmarks to safely localize and expose all paranasal sinuses .
The identification and exposure of the frontal sinus recess (FSR) during ESS are challenging due to the variable anatomy, the narrow opening of the frontal sinus ostium (FSO), and the vital anatomic structures surrounding the outflow pathway. The frontal sinus connection to the nasal cavity is quite variable. Cadaveric studies have shown the most common origin of the frontal sinus is a pit (furrow) originating within the FSR. Usually, there are a maximum of four pits present, each of which has the potential to develop into the frontal sinus. Across the population, there is significant variability in the number of furrows present and which furrows develop into a sinus . It is this variation that makes FSR surgery challenging.
The outflow tract of the frontal sinus is bounded by the agger nasi cell anteriorly and the ethmoid bulla posteriorly. Removing the posterior wall of the agger nasi or the anterior wall of the ethmoid bulla should presumably open the FSR. Unfortunately, the anatomy is not quite simple, and historic data by Lothrop showed only a 47% direct communication between the frontal sinus and the ethmoid infundibulum . Instead, there are frequently frontal cells which lie superior to the agger nasi and depending on their location and pneumatization can obstruct the outflow pathway of the frontal sinus .
Given this complicated and variable connection of the frontal infundibulum to the nasal cavity, consistent and easily identifiable landmarks and measurements could potentially expedite a safe exposure of the frontal sinus. Previous anatomic studies have determined important estimates of the distances from the anterior nasal spine (ANS) to the sphenoid sinus, optic nerves, ethmoid arteries, and carotid arteries. In this study, we identify standard distances from the ANS and columella to the anterior and posterior borders of the FSO in males and females using high-resolution computed tomography (HRCT) scans. These measurements should provide additional objective data to more efficiently access the frontal sinuses.
2
Materials and methods
Twenty-seven female patients and thirteen male patients undergoing subsequent HRCT scans of the paranasal sinuses were randomly selected. Individuals with a history of previous frontal sinus surgery, trauma, or neoplasm were excluded from the study given our interest in bony anatomy and landmarks. A total of 32 patients (23 females and 9 males) were included in this analysis. The average age of the included patients was 54 years, (range 22 to 73). Sequential 0.75 mm axial cuts were obtained using a General Electric HRCT scanner. Multiplanar reconstructions in the bone format were constructed in the sagittal and coronal planes. With these reconstructions measurements were made using the IDX Imagecast CT imaging software (IDX Systems Corporation).
Measurements for each patient were made from the ANS and columella (both left and right) to the nasofrontal beak (NFB) and anterior skull base (ASB) border of the FSR ( Fig. 1 ) using the sagittal reconstruction images. Additionally the nasofrontal angle (NFA) was calculated as the junction of a vector along the nasal floor (NF) and a vector from the columella to the NFB ( Fig. 1 ). For each patient, measurements were obtained by three independent observers, and the resulting values were averaged and standard deviations and confidence intervals calculated. Statistical comparison between males and females was performed using Student’s t -test for continuous variables. All tests were two-tailed and significance level was set at p < 0.05. The above analyses were performed using Microsoft Office Excel 2007 (Microsoft Corporation, Redmond, WA). We also calculated the intraclass correlation using PASW Statistics 18 (SPSS Inc., Chicago, IL).
The protocol for this study was reviewed and approved by the Institutional Review Board of the University of Miami, Miami, Florida.
2
Materials and methods
Twenty-seven female patients and thirteen male patients undergoing subsequent HRCT scans of the paranasal sinuses were randomly selected. Individuals with a history of previous frontal sinus surgery, trauma, or neoplasm were excluded from the study given our interest in bony anatomy and landmarks. A total of 32 patients (23 females and 9 males) were included in this analysis. The average age of the included patients was 54 years, (range 22 to 73). Sequential 0.75 mm axial cuts were obtained using a General Electric HRCT scanner. Multiplanar reconstructions in the bone format were constructed in the sagittal and coronal planes. With these reconstructions measurements were made using the IDX Imagecast CT imaging software (IDX Systems Corporation).
Measurements for each patient were made from the ANS and columella (both left and right) to the nasofrontal beak (NFB) and anterior skull base (ASB) border of the FSR ( Fig. 1 ) using the sagittal reconstruction images. Additionally the nasofrontal angle (NFA) was calculated as the junction of a vector along the nasal floor (NF) and a vector from the columella to the NFB ( Fig. 1 ). For each patient, measurements were obtained by three independent observers, and the resulting values were averaged and standard deviations and confidence intervals calculated. Statistical comparison between males and females was performed using Student’s t -test for continuous variables. All tests were two-tailed and significance level was set at p < 0.05. The above analyses were performed using Microsoft Office Excel 2007 (Microsoft Corporation, Redmond, WA). We also calculated the intraclass correlation using PASW Statistics 18 (SPSS Inc., Chicago, IL).
