Evaluation of olfactory fossa depth using computed tomography in South Indian population: A retrospective study

Divya Teja Patil; L Yashas Ullas; A Chaithanya; S Dhanvarsha; Aluru Venkata Sai Nikhilendra Reddy; Harshadeepa Srinivasa

doi:10.4103/jomr.jomr_20_21

ORIGINAL ARTICLE

Year : 2021 | Volume : 9 | Issue : 2 | Page : 40-44

Evaluation of olfactory fossa depth using computed tomography in South Indian population: A retrospective study

Divya Teja Patil¹, L Yashas Ullas¹, A Chaithanya¹, S Dhanvarsha², Aluru Venkata Sai Nikhilendra Reddy³, Harshadeepa Srinivasa⁴
¹ Department of Radiodiagnosis, Sri Devaraj Urs Academy of Higher Education and Research Centre, Kolar, Karnataka, India
² Department of Medicine, Chinmaya Mission Hospital, Bengaluru, Karnataka, India
³ Department of Radio-Diagnosis, Sri Devaraj Urs Academy of Higher Education and Research Centre, Kolar, Karnataka, India
⁴ Department of Medicine, Sapthagiri Institute of Medical Sciences, Bengaluru, Karnataka, India

Date of Submission	05-Jun-2021
Date of Decision	11-Jul-2021
Date of Acceptance	12-Jul-2021
Date of Web Publication	30-Aug-2021

Correspondence Address:
L Yashas Ullas
No. 59/2 Kannur Village and Post Hennur Baglur Main Road, Bengaluru - 562 149, Karnataka
India

Source of Support: None, Conflict of Interest: None

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DOI: 10.4103/jomr.jomr_20_21

Abstract

Context: Anatomical variations are very important in planning a paranasal sinus (PNS) surgery. Currently, there are limited data on olfactory depth in the South Indian subpopulation. Aim: The aim of this study was to determine the olfactory fossa (OF) depth using Computed Tomography (CT) in the South Indian population. Settings and Design: This retrospective study was conducted in radiology, Sri Devaraj URS Medical College, Tamaka, Kolar. Materials and Methods: A single radiologist analyzed computed tomography (CT) and medical records of 287 patients from October 2020 to March 2021. OF depth (Keros classification) was considered the primary outcome variable. Statistical Analysis Used: Descriptive analysis was carried out by mean and standard deviation for quantitative variables, frequency, and proportion for categorical variables. P < 0.05 was considered statistically significant. Data were analyzed using coGuide_V.1.0. Results: The mean age was 44.2 years in the study population. Among the study population, 183 (63.76%) were male, and the remaining 104 (36.24%) were female. In people with Keros classification right side, 62 (21.60%) falls under Type I, 209 (72.82%) were Type II, and 16 (5.57%) were Type III. In people with Keros classification left side, 33 (11.50%) were Type I, 240 (83.62%) were Type II, and 14 (4.88%) were Type III. Conclusion: Keros Type II OF was more common in the study population, and the least common was Type III. The knowledge of OF depth may help the radiologists analyze this region's scans and minimize complications associated with surgeries in this delicate area.

Keywords: Anterior cranial fossa, computed tomography, keros classification, olfactory fossa, paranasal sinus

How to cite this article:
Patil DT, Ullas L Y, Chaithanya A, Dhanvarsha S, Sai Nikhilendra Reddy AV, Srinivasa H. Evaluation of olfactory fossa depth using computed tomography in South Indian population: A retrospective study. J Oral Maxillofac Radiol 2021;9:40-4

How to cite this URL:
Patil DT, Ullas L Y, Chaithanya A, Dhanvarsha S, Sai Nikhilendra Reddy AV, Srinivasa H. Evaluation of olfactory fossa depth using computed tomography in South Indian population: A retrospective study. J Oral Maxillofac Radiol [serial online] 2021 [cited 2023 Mar 29];9:40-4. Available from: https://www.joomr.org/text.asp?2021/9/2/40/325043

Introduction

The olfactory fossa (OF) is seen in the anterior cranial fossa as depression and a cribriform plate of ethmoid forms its floor. This bony plate is delicate and separates the nasal cavity from the anterior cranial fossa. OF is bounded medially by crista galli and laterally by the lateral lamella of the cribriform plate of the ethmoid.^[1] The olfactory bulbs and tracts are present in OF. The thinnest and extremely variable part of the anterior skull base is the OF, which is dehiscent in about 14% of patients.^[2] Three main forms of OF were noted by Keros after analyzing 450 cadaveric skulls. The classification was based on the level of the ethmoid roof. The depth of the OF in Keros Type I is 1–3 mm; in Type II, 4–7 mm; and Type III, 8–16 mm. Due to the high incidence of complications during surgeries in Keros Type III OF is called “dangerous ethmoid”.^[3],[4],[5]

Functional endoscopic sinus surgery (ESS) is a minimally invasive technique used to treat sinusitis. This causes a significant reduction in the symptoms, the disease process, and reduces the rate of postsurgery complications compared to other techniques. It is paramount for the surgeon to be aware of variations in the OF and ethmoidal roof region to prevent complications such as cerebrospinal fluid leakage and anterior ethmoidal artery injury due to iatrogenic trauma to the skull base, especially the lateral lamella of the cribriform plate.^[6],[7],[8]

Preoperative imaging needs to be carried out to identify various anatomical variants of the OF, the marginal thickness of the cribriform plate, and the variable width of the cribriform plate in the anterior and posterior third. Imaging modalities such as computerized tomographic (CT) scans and digital volume tomography helps in the evaluation of the OF bony configuration. Computed tomography (CT) is used to detect the type and extent of anatomical perturbations in the nose and paranasal sinus region.^[4] Although radiological studies have been done in the past on the occurrence of the different types of variants of OF, studies in the Indian population are limited.^{[9],[10],[11],[12]}

Currently, there are limited data on OF depth in the South Indian subpopulation. Thus, the present study aims to evaluate the depth of the OF using CT in the South Indian population.

Objective

To classify the OF depth according to Keros classification.

To determine the association between gender with Keros classification of OF depth.

Materials and Methods

Study population and study site

The study population was all the patients who attended the department of radiology of Sri Devaraj Urs Medical College, Tamaka, Kolar.

Inclusion criteria

All patients who underwent contrast-enhanced/noncontrast CT brain and PNS.

Exclusion criteria

Patients aged <18 years and above 90 years
Patients with neoplastic lesions of the PNS
Patients with fractures/trauma to the PNS.

Study design

The study was a retrospective record-based study.

Sample size and sampling method

All the 287 patient records, which fulfill the inclusion and exclusion criteria, attended the department from October 2020 to March 2021 were included in the study.

Ethical considerations

The study was approved by the institutional review board and the ethics committee of the hospital.

Data collection tools and clinical examination

Demographic data were retrieved from the records, and a single radiologist measured the OF depth from the CT images according to the protocol used by Shama and Montaser.^[8] The OF depth was calculated from the coronal sections at the section of maximum depth by drawing three lines.

Line A: Horizontal line connecting the bony boundaries of orbital foramina (inferior).

Line B: Vertical line joining the junction of the lateral lamella and fovea ethmoidalis with line A.

Line C: Vertical line joining lateral bony boundary of the cribriform plate to that of line A.

Computed tomography used was Siemens SOMATOM (16 slice configuration) with the patient in the supine position.

Statistical method

OF depth (Keros classification) was considered the primary outcome variable. Gender was considered an explanatory variable. Descriptive analysis was carried out by mean and standard deviation for quantitative variables, frequency, and proportion for categorical variables. All quantitative variables were checked for the normal distribution within each category of an explanatory variable using visual inspection of histograms and normality Q-Q plots. Shapiro–Wilk test was also conducted to assess normal distribution. Shapiro–Wilk test P > 0.05 was considered a normal distribution. The association between categorical explanatory variables and the quantitative outcome was assessed by comparing the mean values. The mean differences along with their 95% confidence interval was presented. Paired t-test was used to assess statistical significance. The categorical outcomes were compared using Chi-square test. P < 0.05 was considered statistically significant. Data were analyzed using coGuide software. V.1.0.^[13]

Results

A total of 287 participants were included in the final analysis.

The mean age was 44.2 years in the study population. Among the study population, 183 (63.76%) were male, and the remaining 104 (36.24%) were female. The mean OF depth right side was 5.3 mm in the study population. In people with Keros classification right side, 62 (21.60%) had Type I, 209 (72.82%) had Type II, and 16 (5.57%) had Type III. The mean OF depth left side was 5.42 mm in the study population. In people with Keros classification left side, 33 (11.50%) had Type I, 240 (83.62%) had Type II, and 14 (4.88%) had Type III [Table 1].

Table 1: Summary of baseline parameter (n=287)

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The mean OF depth on the right side was 5.3 ± 1.25 mm and on the left side was 5.42 ± 1.21 mm. The difference between right and left was statistically significant (P value 0.006) [Table 2].

Table 2: Comparison of mean olfactory fossa depth at right and left positions (n=287)

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Among the male participants, 40 (21.86%) had Type I Keros classification right side, 135 (73.77%) had in Type II, and 8 (4.37%) had in Type III. Among the female participants, 22 (21.15%) were in Type I Keros classification right side, 74 (71.15%) in Type II, and 8 (7.69%) in Type III. Among the male participants, 24 (13.11%) were in Type I Keros classification left side, 149 (81.42%) in Type II, and 10 (5.46%) in Type III. Among the female participants, 9 (8.65%) in Type I Keros classification right side, 91 (87.50%) in Type II, and 4 (3.85%) in Type III. There was no significant difference among males and females in Keros classification on both right and left sides [Table 3].

Table 3: Summary of Kero'S classification with gender (n=287)

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The overall mean OF depth, right side, was 3.79 mm in Type I, it was 5.59 mm in Type II, and it was 7.33 mm in Type III. The overall mean OF depth, left side, was 3.11 mm in Type I, it was 5.64 mm in Type II, and it was 7.17 mm in Type III. Among the male participants, the mean OF depth, right side, was 3.79 mm in Type I, it was 5.65 mm in Type II, and it was 7.33 mm in Type III, and the mean OF depth left side was 3.12 mm in Type I, it was 5.5.69 mm in Type II, and it was 7.27 mm in Type III. Among the female participants, the mean OF depth right side was 3.79 mm in Type I, it was 5.49 mm in Type II, and it was 7.33 mm in Type III, and the mean OF depth left side was 3.10 mm in Type I, it was 5.55 mm in Type II, and it was 6.93 mm in Type III in the study population [Table 4].

Table 4: Summary of Keros classification and olfactory fossa depth with gender-wise distribution (n=287)

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Discussion

In the present study, the mean age of the participants was 44.2 ± 18.6 years, and the majority of them were males (63.76%). Most of the participants had Keros Type II OF (72.82% right side and 83.62% left side), followed by Keros Type I OF. There was no statistically significant gender-wise difference observed in the distribution of Keros classification in this study.

The mean OF depth was 5.3 ± 1.25 mm on the right side and 5.42 ± 1.2 mm on the left side in the present study. Similarly, Babu et al. have reported that the mean depth of OF on the right side is 5.27 ± 1.72 mm and 5.25 ± 1.65 mm on the left side in their study.^[14] The mean depth in the studies by Jacob and Kaul and Salroo et al. was 5.08 and 4.9 mm, respectively.^[1],[15]

In the present study, the majority of the participants had Type II OF on both sides (72.82% right side and 83.62% left side) followed by Type I OF on both sides (21.60% right side and 11.50% left side). Similarly, many authors have reported Keros Type II as the predominant type OF. In the original study by Keros, Type II was the most common Type OF, followed by Type I, which was conducted in Germany.^[3] Studies by Elwany et al. and Güldner et al. reported 64%, 56.8% of the cases as Keros Type II, followed by 13%, 42.5% of the cases as Keros Type I, respectively.^[7],[16] Many Indian studies also reported Keros Type II as the common OF type. Studies by Babu et al. and Salroo et al. reported Keros II in 61%, 74.6% Keros I in 29%, and 17.5% in Kashmir and Kerala.^[14],[15] This suggests that there is a risk of inadvertent intracranial entry through the lateral lamella if they undergo ESS in these populations. Gauba et al. noted that Keros classification helps provide an objective assessment of the anatomy of the anterior skull base and thereby guide the surgeon during surgical procedures in this region and may help to improve the safety profile of the procedure.^[17]

The mean age of the participants was 44.2 ± 18.6 years, and the majority of the participants were males (63.76%), in this study. No statistically significant difference was observed in the distribution of Keros classification between males and females. A similar pattern was observed in Babu et al. and Salroo et al. with a mean age of 44.5 years and 36.76 (±13.82) years, the majority were male participants, and no statistically significant gender-wise difference in the distribution of Keros classification was observed.^[14],[15] In contrast, in a study by Basti et al. in South Karnataka, Type 1 Keros was more common in the male population and Type II in females,^[18] whereas Elwany et al. reported that Keros Type II was found more frequently in men and Keros Type I in women.^[7] This significant difference in the result between the current study and other studies may be attributed to the difference in the population of different ethnicity and races.

Although the occurrence of Keros Type III is low in the present study, it was slightly more among males and on the left side. Due to its long length of the lateral lamella, the Keros Type III is considered to be more susceptible to iatrogenic lesions during frontoethmoidal surgery.^[19],[20]

Computed tomography has contributed greatly in the medical field to diagnose, to evaluate different sinonasal diseases, and to understand important anatomical landmarks. Several studies have documented this fact highlighting the importance and precision of radiographic evaluation of the ethmoid roof and its validity in providing safe surgical procedures.^[19],[21] Thus, it is mandatory for successful ESS to do an optimal preoperative evaluation, including CT scan, and surgeons should have a thorough knowledge of paranasal anatomy. These asymmetries in the anatomy of OF need to be kept in mind to prevent complications.^[22]

Conclusion

The majority of the participants were under of Keros Type II, followed by Type I and Type III. Adequate data on the variability of the anatomy of the olfactory area are very helpful in the preoperative workup of patients with diseases of the nose and paranasal sinuses. Inadequate attention to the anatomy of this area can lead to damage of the cribriform plate and structures of the olfactory analyzer with corresponding consequences such as rhinoliquorrhoea, meningitis, loss of the sense of smell, and brain abscesses.

Acknowledgments

We acknowledge the technical support in data entry, analysis, and manuscript editing by “Evidencian Research Associates.”

Financial support and sponsorship

The project was self-funded. No external agency had funded the project.

Conflicts of interest

There are no conflicts of interest.

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