|Ahead of print publication
Computed tomographic study on the prevalence of the Onodi cell
Beryl S Ominde1, Joyce Ikubor2, Patrick S Igbigbi1
1 Department of Human Anatomy and Cell Biology, Delta State University, Abraka, Nigeria
2 Department of Radiology, Delta State University Teaching Hospital, Oghara, Nigeria
|Date of Submission||23-Mar-2022|
|Date of Decision||01-Feb-2023|
|Date of Acceptance||02-Feb-2023|
|Date of Web Publication||10-Apr-2023|
Beryl S Ominde,
Department of Human Anatomy, Delta State University, P.M.B. 1, Abraka
Source of Support: None, Conflict of Interest: None
Context: The prevalence of the Onodi cell varies in different populations. Its involvement in sinus pathology is characterized by varied clinical symptoms due to its proximity to the internal carotid artery and optic nerve. Endoscopic surgical management of sinus pathologies poses a great risk of injury to these neurovascular structures. Aim: This study elucidates the prevalence of the Onodi cell in a Nigerian Teaching Hospital. Setting and Design: This was a retrospective cross-sectional study conducted in the Radiology unit of a Teaching Hospital in Nigeria. Materials and Methods: Brain computed tomography (CT) images of 336 patients aged ≥20 years were evaluated for the presence of the Onodi cell. The study was approved by the institution before accessing the digital images. The age and gender of patients and the presence and location of the Onodi cell were recorded. Statistical Analysis Used: Data were entered in Statistical Package for Social Sciences version 23 for analysis of prevalence and subsequent comparisons using the Chi-square test. The significance level was considered at P < 0.05. Results: The prevalence of Onodi cell was 16.4% and was only observed unilaterally with a slightly lower frequency on the right (27, 8.0%) than the left (28, 8.3%). The prevalence did not show any significant side or gender differences (P > 0.05). Conclusion: The Onodi cell was present in the studied population, thus highlighting the need for their preoperative recognition on CT to abate iatrogenic complications during endoscopic surgeries.
Keywords: Onodi, pneumatization, sinus, spheno-ethmoidal, sphenoid
| Introduction|| |
The Onodi cell is the most posteriorly located ethmoidal air cell whose pneumatization advances posteriorly and supero-laterally towards the anterior region of the sphenoid sinus. It is also referred to as the spheno-ethmoidal cell and drains into the nasal cavity through the superior meatus., This cell was first described by Adolf Onodi in 1903. It is manifested by a transverse septum that divides the sphenoid sinus into two floors. The cell is completely delineated from other posterior ethmoidal cells by a bony septum. The occurrence of this cell varies in different populations with a prevalence ranging from 3% to 37.2%.,,,,
Individuals with the Onodi cell are usually asymptomatic; hence, the cell is usually an incidental radiologic finding. However, it may extend laterally to lie contiguous to the internal carotid artery (ICA) and optic nerve hence, increasing the risk of their involvement in sinus pathologies such as infection, mucocele, sinusitis, fungal balls, and papillomas with a subsequent predisposition to neurovascular complications during Functional Endoscopic Sinus Surgery (FESS).,,, The pathologies may recur due to poor drainage and ventilation of the cell leading to stasis of the secretions which predisposes to infection. Onodi cell pathologies present with more optic than nasal symptoms due to compression and inflammation of the optic nerve leading to retro-bulbar optic neuropathy, optic neuritis, orbital apex syndromes, and consequent visual loss.,, During endoscopic transsphenoidal resection of tumors in the sellar and parasella regions, the Onodi cell interferes with the exposure of the sella floor and this may limit the complete excision of the tumors. Therefore, radiological identification of the Onodi cell and its relationship with these structures prior to FESS and skull base surgery is paramount. Computed tomography (CT) offers a high resolution that accurately depicts the complex anatomy of the paranasal sinuses.,, This study was intended to evaluate the computed tomographic brain images of adult Nigerians for the presence of Onodi cells. The study also sought to investigate whether the Onodi cell showed any association with gender or predilection to either side.
| Materials and Methods|| |
This descriptive cross-sectional retrospective study utilized brain CT images purposively sampled from the Picture Archiving Communications Systems (PACS) database at the Radiology department of a Tertiary Hospital in Nigeria. These images were acquired using a 64-slice CT scanner (Toshiba Aquilon, Japan, 2009) at 120kV and 300 mA tube potential. We sought ethical authorization from the Hospital's Research Committee (Reference number; EREC/PAN/2020/030/0371) before the commencement of this study. The study utilized CT images of patients who were referred to the Radiology Department over a span of 5 years between June 1, 2015 and June 30, 2020 with chronic headaches and suspected intracranial tumors or bleeds and intracerebral or pulmonary embolism. Images of both male and female patients aged 20 years and above were used. This lower age limit was used since the paranasal sinuses attain their definitive adult size at the age of 20. Our exclusion criteria entailed; images with paranasal sinus pathologies such as cysts, infection, and polyps, images with skull base tumors, sella and parasella pathologies, craniofacial trauma, and evidence of previous sinonasal or skull base surgery. Furthermore, we excluded CT images with artifacts, asymmetry due to inappropriate patient positioning, images lacking the patient's demographic data, and images of patients less than 20 years of age.
The sphenoid and ethmoid sinuses were evaluated on the 3–5-mm-thick axial slices along with sagittal and coronal reformatted images using bone window. The most posteriorly located ethmoidal air cell with posterior and lateral extension was recognized as an Onodi cell. The occurrence of this cell was evidenced by a transversely oriented bony septum that divides the sphenoid sinus into two floors. The data obtained from the images including age, gender, presence or absence of Onodi cell, and location/side of this cell were subjected to statistical analysis using Statistical Package for Social Sciences (SPSS) version 23 (IBM® Armonk, New York), summarized in percentages and presented in tables. We used the Chi-square test to ascertain the association of the Onodi cell with regard to side and gender. This was considered significant at P < 0.05.
| Results|| |
We analyzed CT images of 336 adult patients with more males (199,59.2%) than females (137,40.8%). The mean age of the patients was 53.29 ± 18.18 years and the age range was 20–99 years. The Onodi cell was seen in 55 patients (16.4%) and occurred only unilaterally. We did not observe the bilateral existence of this cell. The occurrence on the right (27, 8.0%) was slightly lower than on the left (28, 8.3%); hence, no significant side differences were observed in both males and females (P > 0.05). The prevalence on the right was higher in males (18, 9.0%), while females had a higher frequency of the Onodi cell on the left (14,10.2%). However, the gender differences were not statistically significant (P > 0.05) [Table 1], [Figure 1]a and [Figure 1]b.
|Figure 1: (a) Coronal reformatted image showing right Onodi cell. (b)Sagittal image depicting the Onodi cell. (Original)|
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| Discussion|| |
We report the occurrence of the Onodi cell with a prevalence of 16.4%. This was higher than 5.3% and 7.27% documented in previous Nigerian studies by Oghenero et al. and Onwuchekwa and Alazhigha in Osun and Rivers state, respectively. These differences can be ascribed to differences in genetics, geographical factors, study design, and sample sizes. Similarly, variation in the prevalence of the Onodi cell in the Indian population was demonstrated by Thimmaiah and Anupama, Singh et al., Tiwari and Kardam, and Shrestha et al. who documented frequencies of 24.07%, 17.9%, 3.9%, and 3% respectively. The prevalence in Saudi Arabia ranged between 11.4% and 31.4%., Our prevalence was higher than the reports from Mexico (7.3%) and lower than the documented reports from Turkey (25.3%), Iran (37.2%), and Portugal (29.5%).,,, Therefore, the prevalence herein was within the range documented in the literature. The discrepancies in the prevalence may perhaps be attributed to differences in genetics, environmental and geographical factors, and the variant patterns of ethmoidal sinus pneumatization. The dissimilarities in the sample size in addition to the slice thickness of CT images used may also contribute to the population variances.
In comparison with the findings of an Indian study, the unilateral occurrence of Onodi cells in the current study was lower on the right and higher on the left side. Consistent with our findings, Oghenero et al. did not observe the bilateral existence of this cell. On the contrary, Ravindra and Devika observed bilateral spheno-ethmoidal cells in 8.1% of their patients. We report no statistically significant association between this cell and side or gender, hence implying its possible fortuitous occurrence.
The awareness of the presence of Onodi cells is important because it may pneumatize further and extend towards the neighboring optic nerve along with the internal carotid artery. Furthermore, this cell may likewise be involved in disease conditions such as mucoceles which may subsequently cause rhinogenic optic neuritis or other forms of optic neuropathy., Therefore, preoperative radiological evaluation is imperative before FESS and neurosurgical procedures to avoid injury to the adjacent vital anatomical structures., Moreover, in cases of a pneumatized anterior clinoid process, the optic nerve may be engulfed within the spheno-ethmoidal cell., Intraoperatively, the Onodi cell may be presumed as the sphenoid sinus leading to incomplete surgical clearance., In the presence of an Onodi cell, it is recommended that surgical clearance should be done in an infero-medial direction to avoid inadvertent injury to the optic nerve. The Onodi cell can cause accidental penetration into the middle cranial fossa during FESS. Additionally, its coexistence with a pneumatized crista galli can cause iatrogenic penetration into the anterior cranial fossa.
| Conclusion|| |
The prevalence of the Onodi cell in our study varied from previous literature reports. Their preoperative recognition on CT is therefore important in abating iatrogenic complications during endoscopic surgeries in our population.
Strength of the study
Computed tomography is the best imaging modality for evaluating the variant pneumatization patterns of the paranasal sinuses. Hence, the use of CT in this study was appropriate in the evaluation of the Onodi cell.
Limitations of the study
The study excluded images with sinus pathology hence, the prevalence of Onodi cell lesions such as sinusitis, mucoceles, and papillomas and the involvement of the neighboring anatomical structures were not evaluated. Furthermore, the images used in this study were obtained from one hospital.
Future research directions
A multicentered study with a larger sample size could be done to assess the prevalence of the Onodi cell in Nigeria. We also recommend further studies to evaluate the pathologies of the Onodi cell, and the associated challenges and complications of endoscopic surgical management of these pathologies in Nigeria.
We would like to acknowledge Priscilla Ejiroghene and Emmanuel Akpoyibo who assisted with data collection and analysis.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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