CT Assessment of the Presence of Septation Between the Frontal Sinus and Supraorbital Ethmoid Cells: A Retrospective Study

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CT Assessment of the Presence of Septation Between the Frontal Sinus and Supraorbital Ethmoid Cells: A Retrospective Study

https://doi.org/10.21203/rs.3.rs-3809282/v1

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Background

Supraorbital ethmoidal cells (SOEC) are air-filled ethmoidal cells found in the orbital plate of the frontal bone. It is located close to the frontal recess and sinus and is usually separated by a thin bony septum from the frontal sinus. Unaddressed SOEC can lead to failed or complicated endoscopic sinus procedures, residual fungal elements, or mucocele. Moreover, improper localization during the procedure may contribute to an increased risk of orbital and skull base injuries.

Objectives

To determine the presence of septation between the frontal and the supraorbital ethmoid cell based on radiological imaging and to study the degree of SOEC pneumatization.

Methods

A retrospective study that included 244 computed tomography images of the paranasal sinuses was conducted from November 2022 to April 2023 at King Abdullah bin Abdulaziz University Hospital (KAAUH).

Results

This study included 244 participants. Most participants (55.7%) were female, with the largest age group falling between 18 and 28 (34.8%). Most cases (60.7%) had bilateral Supra-Orbital Ethmoidal Cells.

The pneumatization of SOEC was classified into three types based on its lateral extension on computed tomography images. Majority of patients were found to have type 1 pneumatization, followed by type 2 then type 3. Most cases showed septation between the frontal and SOEC on both the right (74.1%) and left (59.3%) sides. According to this study, there is no association between many factors such as gender, age, chronic rhinosinusitis, pneumatization of the sinuses, and the occurrence of septation between the frontal and SOEC.

Conclusion

Surgeons should have heightened awareness regarding the complexity of the anatomical variation of the frontal sinus and SOEC. A new classification is proposed regarding the degree of pneumatization of SOEC that has value in understanding the anatomy and planning the surgical approach.

Supraorbital ethmoid cell

frontal sinus

pneumatization

septation

Humans have four pairs of paired sinuses, all of which are lined with pseudostratified columnar epithelium: the frontal sinuses are located above the eyes within the frontal bone, the ethmoid sinuses are formed from several air cells within the ethmoid bone between the nose and eyes, and the sphenoid sinuses are found within the body of the sphenoid bone, where the giant pair is the maxillary sinuses, which are located under the eyes in the maxillary bones (1).

An anterior ethmoid cell between the first and third ethmoturbinals extends to form the frontal sinus, which is underdeveloped at birth. Most of the development occurs between the ages of five and late adolescence (2). Frontal sinus development and enlargement lead to more evolvement and expansion of agger nasi cells of the ethmoidal sinuses, which may extend posteriorly, leading to the narrowing of the frontal recess and contributing to frontal sinusitis (3).

The frontal sinuses develop independently of each other, which contributes to a variable degree of asymmetry in size and shape; regarding the variations, aplasia is a common variant, and the literature reported more bilateral frontal sinuses aplasia than unilateral aplasia, which even showed a higher percentage among females' individuals, related to the degree of pneumatization in addition to other factors affecting the frontal sinuses size including climate and ethnicity (1, 3).

Males tend to have a more prominent frontal sinus than females, accounting for the prominent frontal bossing observed in many (4).

The ethmoid bone comprises a cluster of cells with a complicated structure that drains all the paranasal sinuses. At birth, there are 3 to 4 ethmoid air cells. By adulthood, there are 5 to 15 paired cells. On either side of the septum, they are located midway between the eyes (1).

Frontoethmoidal cells in the frontal recess are defined as an anatomical variation of the anterior ethmoidal cells that alter the drainage pathway of the frontal sinus and may extend to the frontal sinus and ostium. Bent et al. (5) described four distinct types of frontoethmoidal cells, with type 1 enlisted as the most common variant followed by type 2, type 1 defined as a single cell superior to agger nasi and in the outflow of the frontal sinus, while type 2 is a row of cells superior to agger nasi, and in type 3 the cells would extend cranially into the frontal sinus cavity. The definition of type 4 was modified lately as cells extending into the frontal sinus with a length of more than 50% of the frontal sinus height. This cell's presence contributes to the increasing difficulty of frontal sinus surgery and is associated with the persistence of paranasal sinus disorders regardless of proper management (3, 6).

In 2016, Wormlad et al. (7) introduced the International Frontal Sinus Anatomy Classification (IFAC), published depending on the tri-planar CT scan, classifying the frontal recess cells based on their anatomical origin into three groups. The first group includes the anterior cells, which push the frontal sinus drainage pathway medially, posteriorly, or posteromedially; it includes agger nasi cell (ANC), supra agger cell (SAC), and supra agger frontal cell (SAFC). The second group consists of the posterior cells, which push the frontal sinus drainage pathway anteriorly, including the supra bulla cell (SBC), supra bulla frontal cell (SBFC), and supraorbital ethmoid cell (SOEC). The last group includes the frontal septal cell (FSC) and the medial cells, which push the frontal sinus drainage pathway laterally.

The presence of SOEC is associated with low-lying anterior ethmoidal artery which can lead to failed or complicated endoscopic sinus procedures. (8) Furthermore, it can be mistaken for frontal sinus when it is well pneumatized laterally. If identification failed during functional endoscopic sinus surgery (FESS), residual fungal elements or mucocele would be missed. Moreover, improper localization during the procedure may contribute to an increased risk of orbital and skull base injuries. Therefore, correctly identifying these variants should be emphasized due to their effect on the long-term outcome of sinus surgery (2, 7).

Based on radiological imaging, we aim to determine the presence of septations between the frontal and the supraorbital ethmoid cell.

Data collection and study population

This is a retrospective study that included 244 computed tomography images of the paranasal sinuses and was conducted from November 2022 to April 2023 at King Abdullah bin Abdulaziz University Hospital (KAAUH) in Riyadh. The Left and right sides were considered individually.

All patients included were 18 years of age and above. Patients with a history of nasal and paranasal sinus surgery, Allergic fungal rhinosinusitis, nasal neoplasm, or other factors that distorted the anatomy of the sinuses were excluded.

Online access to medical records for extraction of data. Three trained medical students obtained the patient information, and two otolaryngology physicians and a radiologist reviewed the CT scans.

The study was approved by the ethics review committee at KAAUH; since no information revealed the patient's identity, the study falls under the informed consent waiver criteria.

Radiological measurements

The data were collected from the PACS system at KAAUH. The CT examination was performed with an IQon Spectral CT Philips machine. Technical parameters for the CT scans follow universal CT sinus protocol, as shown in (Table 1). The CT scan image analysis and review were performed by two otolaryngology surgeons and a radiologist.

Table 1

Technical parameters for gathering and analyzing the tomographic images.
Technical settings
kV	mAs	Thickness/slice increment	Window (Width/ Level)
125	80	0.90 mm	2000 HU/200

Analysis of the computed tomography

To measure the degree of pneumatization of the SOEC, the orbital plate of the frontal bone on the coronal cuts was used as a reference for measurement. Two imaginary lines were drawn along the vertical axis; perpendicular to the orbital plate, the first line is along the Lamina papyracea, and the second line is located at the midorbital plane (Table 2), illustrating the SOEC degree of pneumatization (Fig. 1).

Table 2

Classification of the SOEC degree of pneumatization:
Type	description
Type 1	Pneumatization is medial to Lamina papyracea line
Type 2	Pneumatization limited to the midorbital line
Type 3	Pneumatization exceeding the midorbital line

Regarding the assessment of the presence of septation between the frontal sinus and SOEC, axial CT images was studied with the parameters. Two otolaryngology surgeons reviewed different axial cuts to look for the presence of bony septum. Some patients have more than one bony septum, as demonstrated in (Fig. 2).

Statistical analysis

The results are shown in tables and graphs, including the sociodemographic factors, frequency, and percentage of patients with CRS and other co-morbidities. Fisher’s Exact test is applied to identify the statistically significant association between different variables. Data is analyzed using descriptive and inferential statistics to determine the association between different CRS parameters with Septation and Degree of Pneumatization. If p < 0.05, there is a statistically significant association between the tested variables. The SPSS Software (by IBM) version 27.0.1 analyzes this complex data.

Descriptive Statistics of Patients

According to (Table 3), this study included 244 participants. The majority of participants (55.7%) were female, while (44.3%) were male. Participants ranged in age from 18 to 83 years, with the largest age group falling between 18 and 28 (34.8%), followed by 29 to 39 (32.0%). Less of the following age groups were represented: (20.5%) were between the ages of 40 and 50, (9.0%) were between the ages of 51 and 60, (1.6%) were between the ages of 62 and 72, and (2.0%) were between the ages of 73 and 83. In terms of supraorbital ethmoidal cells. Figure 3 demonstrates that the majority of cases (60.7%) had bilateral cells. Whereas (17.6%) had unilateral SOEC, (11.9%) on the left, and (5.7%) on the right on the other hand (21.7%) participants had absent SOEC.

Table 3

*Sociodemographic and other clinical parameters of patients (n = 244)*
		Frequency	Percent
Gender	Male	108	44.3
	Female	136	55.7
	Total	244	100.0
Age	18–28 Years	85	34.8
	29–39 Years	78	32.0
	40–50 Years	50	20.5
	51–61 Years	22	9.0
	62–72 Years	4	1.6
	73–83 Years	5	2.0
	Total	244	100.0
Supra Orbital Ethmoidal Cells	Not Present	53	21.7
	Present on Right	14	5.7
	Present on Left	29	11.9
	Bilateral	148	60.7
	Total	244	100.0
Degree of Pneumatization on Right Side	Type 1	103	63.6
	Type 2	38	23.5
	Type 3	21	13.0
	Total	162	100.0
Degree of Pneumatization on Left Side	Type 1	112	63.3
	Type 2	31	17.5
	Type 3	34	19.2
	Total	177	100.0
Septation between Frontal Sinus and Ethmoidal Sinus on Rt Side	Not Present	42	25.9
	Present	120	74.1
	Total	162	100.0
Septation between Frontal Sinus and Ethmoidal Sinus on left Side	Not Present	72	40.7
	Present	105	59.3
	Total	177	100.0

In terms of the degree of pneumatization, (63.6%) and (63.3%) of cases, respectively, had type 1 pneumatization on both the right and left sides. Whereas (23.5%) and (17.5%) of cases, respectively, had type 2 pneumatization on both the right and left sides. (13.0%) and (19.2%) of cases, respectively, had type 3 pneumatization on the right and left sides (Fig. 4).

Most cases showed septation between the frontal and SOEC on both the right (74.1%) and left (59.3%) sides, whereas the remainder had no septation (Fig. 5).

Association between overall Septation between Frontal and Ethmoidal Sinuses with CRS, its Types, and Degree of Pneumatization

(Table 4) shows the results of this study regarding the relation between the presence of septation between the frontal sinus and SOEC and several factors related to gender, age, chronic rhinosinusitis, and pneumatization of the sinuses. According to the results, as shown in Table 4, there is no association between gender or age and the presence of septation. The results further demonstrate that the presence of septation between the frontal sinus and SOEC wasn’t significantly associated with chronic rhinosinusitis (p = 0.200). Moreover, no statistically significant association between septation and either chronic rhinosinusitis with or without polyposis was observed when the data were independently analyzed for the participants (p = 0.505 and p = 0.651, respectively). In addition, it was found that the presence of septation wasn’t significantly associated with the degree of pneumatization on the right side (p > 0.05), with a larger percentage (62.7%) of the participants having type 1 pneumatization out of the total number of participants with septation. The degree of pneumatization of the left side, likewise, wasn’t significantly associated with the presence of septation (p = 0.610).

Table 4

*Association between overall Septation between Frontal sinus and Supra-Orbital Ethmoidal Cells (SOEC) with CRS and Pneumatization and other parameters*
		Septation Between Frontal and SOEC		Sig. Value
		No	Yes	Sig. Value
Gender	Male	17	71	0.857
	Male	44.7%	47.0%
	Female	21	80
	Female	55.3%	53.0%
	Total	38	151
	Total	100.0%	100.0%
Age	18–28 Years	13	59	0.784
	18–28 Years	34.2%	39.1%
	29–39 Years	13	49
	29–39 Years	34.2%	32.5%
	40–50 Years	8	26
	40–50 Years	21.1%	17.2%
	51–61 Years	3	13
	51–61 Years	7.9%	8.6%
	62–72 Years	1	1
	62–72 Years	2.6%	0.7%
	73–83 Years	0	3
	73–83 Years	0.0%	2.0%
	Total	38	151
	Total	100.0%	100.0%
Chronic Rhino sinusitis	No	26	85	0.200
	No	68.4%	56.3%
	Yes	12	66
	Yes	31.6%	43.7%
	Total	38	151
	Total	100.0%	100.0%
Chronic Rhino sinusitis with Polyposis	No	32	117	0.505
	No	84.2%	77.5%
	Yes	6	34
	Yes	15.8%	22.5%
	Total	38	151
	Total	100.0%	100.0%
Chronic Rhino sinusitis without Polyposis	No	32	119	0.651
	No	84.2%	78.8%
	Yes	6	32
	Yes	15.8%	21.2%
	Total	38	151
	Total	100.0%	100.0%
Degree of Pneumatization of Right Side	Type 1	13	89	0.096
	Type 1	72.2%	62.7%
	Type 2	1	36
	Type 2	5.6%	25.4%
	Type 3	4	17
	Type 3	22.2%	12.0%
	Total	18	142
	Total	100.0%	100.0%
Degree of Pneumatization of Left Side	Type 1	25	87	0.610
	Type 1	71.4%	61.3%
	Type 2	5	26
	Type 2	14.3%	18.3%
	Type 3	5	29
	Type 3	14.3%	20.4%
	Total	35	142
	Total	100.0%	100.0%

Figure 6 demonstrates the relation of septation on the right and left sides in relation to CRSwNP and CRSsNP.

Where (26.7%) of left-sided septations were found in patients with CRSwNP in comparison to (21%) in patients with CNSsNP, whereas right-sided septations were found similar in percentages (22.5%) and (20.8%) in patients with CRSwNP and CNSsNP respectively.

Supraorbital ethmoidal cells (SOEC) are air-filled cells found in the orbital plate of the frontal bone, which were found to be in 78.3% out of 244 cases enrolled in this study, in comparison to 69.11% out of 123 cases among Filipinos (9). 2.6% out of 144 among Koreans, 64.6% out of 82 among Caucasians (10), 5.4% out of 202 Chinese subjects (11), and 6% among 150 Japanese cases (12). SOEC was found to be bilateral in around 60 percent of the participants in this study.

More than half of the patients had a deviated nasal septum as a primary diagnosis, followed by chronic rhinosinusitis with nasal polyps.

In this study, we didn’t find a significant association between SOEC with gender, age, or certain diseases; throughout the literature, we didn’t find any similar study comparable to our study results.

In terms of the degree of pneumatization on the right side, the results show a significant association between type 1 pneumatized sinuses and right sided septation. Out of 244 participants in the current study, 151 had septation between the frontal sinus and SOEC, with nearly equal gender distribution. They were primarily young and middle-aged adults, ranging in age from 18 to 39. The presence of septation didn’t significantly correlate with either gender or age. Almost half of the participants had septation between the frontal sinus and SOEC had chronic rhinosinusitis.

The degree of pneumatization of the frontal sinus was described using Guerram’s study, which utilized the midorbital and the supraorbital lines on the axial and coronal plates of the CT scan, Dividing the degree of pneumatization into three types, including aplastic, medium-sized, and hyperplastic. (13)

Throughout the literature, there was no defined method used to describe the degree of SOEC pneumatization, so this study proposes a new classification to describe the degree of SOEC pneumatization inspired by Guerram’s study, utilizing the Lamina papyracea and the orbital plate as landmarks, by drawing two imaginary lines: the first line medial to lamina papyracea and the second line crossing the midorbit. Describing the degree of pneumatization of the SOEC and classifying it into three types, as follows: type one, which is limited to the Lamina papyracea line; type two pneumatization is limited to the midorbital line and finally, type three, where the pneumatization exceeds the midorbital line.

In general, most of our participants were classified as type one degree of pneumatization, which was true also for females; on the other hand, most participants with type three were males.

Knowing the presence of septation between the frontal sinus and SOEC and the degree of pneumatization can help surgeons plan and execute functional endoscopic sinus surgery more effectively. Unaddressed or unopened SOEC can be seen in 11.9% of revision endoscopic sinus surgeries; therefore, it is important to be cautious with preoperative imaging studies. (14) The presence of septation per se can increase the risk of incomplete removal of diseased tissue. Additionally, mucoceles originating from SOEC can be difficult to treat due to their lateral location. (15) Different endoscopic approaches were described in the literature to access far lateral disease involving the SOEC, including endoscopic Draf III and modified hemi-Lothrop procedure. (16) We believe that most of the orbital complications arising from sinonasal diseases, such as mucocele of extensive Allergic Fungal RhinoSinusitis (AFRS), arise from SOEC. Therefore, this grading system for the degree of pneumatization can help in the preoperative planning of the surgical approach for SOEC disease.

Surgeons should have heightened awareness regarding the complexity of the anatomical variation of the frontal sinus, including the septation between the frontal sinus and SOEC on sinus CT scans. A new classification is proposed regarding the degree of pneumatization of SOEC that has value in understanding the anatomy and planning the surgical approach, as the presence of the SOEC is associated with failed or complicated endoscopic sinus procedures due to the complexity of the anatomy. Therefore, correctly identifying these variants should be emphasized due to their effect on the long and short-term outcome of sinus surgery.

This study is inherently limited by the fact that it is retrospective in nature and the relatively small number of participants as it was a single-center study.

The author recommends further studies to be conducted in this area for the result to be generalized to the population, to have more understanding of the anatomical variation and the complexity of that to achieve a precise and uncomplicated surgical approach.

SOEC: supraorbital ethmoid cell

CRS: chronic rhino sinusitis

CRSwNP: chronic rhino sinusitis with nasal polyp

CRSsNP: chronic rhino sinusitis without nasal polyp

authors consent to publish: All authors have been consented to purplish this article for BMC Surgery.

Availability of data and materials: Data from this study is available for sharing at the request of any of the authors.

Ethics approval and consent to participate: The study was approved by the ethics review committee at KAAUH; number (HAP-01-R059), since no information revealed the patient's identity, the study falls under the informed consent waiver criteria.

patient consent to publish: Not Applicable

Competing interests: The authors declare that they have no competing interests.

Funding: None declared.

Acknowledgments

The authors would like to express their deep gratitude to all who participated in this research.

Authors contribution

Conceptualization, A.A and A.M.A; methodology, A.A and A.M.A; data curation, A.M.A, L.A, R.A and H.A.; writing—original draft preparation, L.A, R.A and H.A; writing—review and editing, A.A, A.M.A, L.A, R.A and H.A; supervision, A.A, A.M.A

All authors have reviewed the final manuscript and agreed to the published version of the manuscript.

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No competing interests reported.

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CT Assessment of the Presence of Septation Between the Frontal Sinus and Supraorbital Ethmoid Cells: A Retrospective Study

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