A retrospective study on variations of uncinate process of ethmoid bone using cone-beam computed tomography

Abstract

Background: 

Uncinate process (UP) is a key landmark in the lateral wall of the nose which plays a vital role in the ventilation of paranasal sinuses and is also the first structure to be resected during functional endoscopic sinus surgery (FESS). The variations in this structure can lead to intraoperative and postsurgical complications during the FESS procedure.

Aim: 

The aim of this study was to evaluate the variations of UP of ethmoid bone using cone-beam computed tomography (CBCT).

Materials and Methods: 

Retrospective data of 100 cone-beam computed radiographic CBCT images of paranasal sinuses were evaluated using CS 3D version 3.10.12 software for variations in the superior attachment of UP (SAUP) using Landsberg and Friedman and the presence of pneumatization of UP. Out of 100 CBCT images, 56 were of males and 44 were of females.

Statistical Analysis Used: 

Chi-square test was used for statistical analysis.

Results: 

In our study, a total of 200 sides in 100 CBCT images were studied and Type I SAUP (51%) was observed as the most common type, followed by Type II (17%), Type IV (11.5%), Type III (10%), Type V (6.5%), and Type VI (4%) is the least common type observed. No statistically significant difference was observed among gender regarding SAUP. Pneumatization of UP was seen in 7% of cases, out of which 4% were in males and 3% were in females.

Conclusion: 

Preoperative analysis of UP variations using CBCT can reduce intraoperative and postoperative complications during FESS with less radiation exposure.

INTRODUCTION

The uncinate process (UP) is a hook-like extension in the wall of the lateral nasal cavity which extends from the ethmoid process of inferior turbinate to the frontal recess superiorly.[¹] It is a slender, sickle-shaped bony leaflet with an almost sagittally orientated curvature running parallel to the anterior surface of the ethmoid bulla and one of the important structures in the osteomeatal complex (OMC), which is a common pathway of drainage for anterior ethmoid, maxillary, and frontal sinuses.[²]

UP directs the contaminated inspired air away from the sinuses and the more sterile expired air into the sinuses thus playing a key role in the ventilation of the middle meatus and the sinuses. Therefore, any anatomical variations in this structure can increase the risk of sinus mucosal disease.[³] Apart from this, UP is also a key anatomical structure taken into consideration during functional endoscopic sinus surgery (FESS).[⁴]

FESS is a minimally invasive surgical procedure done for those patients with persistent and recurrent sinusitis even after nonsurgical treatments, to relieve sinus blockages and improve breathing.[⁵] During this procedure, the uncinate must be resected first to gain access to the ethmoid infundibulum and maxillary sinus ostium.[⁴]

The superior attachment of UP (SAUP) is highly variable. Preoperatory analysis of these variations is important for the surgeon to perform a safe uncinectomy as aggressive uncinectomy performed by pulling the UP out in patients with a SAUP in the cranial base, is a risk factor in developing a cerebrospinal fluid leak. This SAUP also determines the frontal sinus drainage pathway, which is associated with frontal rhinosinusitis. Finally, incomplete uncinectomy has been linked to a higher risk of surgical failure.[⁶]

The commonly used method for evaluating the paranasal sinuses is a computed tomography (CT) scan, and the coronal section is the preferred imaging plane for the evaluation of SAUP. However, even using CT, examination of anatomical variations of UP is still difficult and is associated with higher radiation exposure.

After the first introduction of the cone-beam CT (CBCT) system for dentomaxillofacial imaging in 2001, studies have concentrated on the viability of CBCT in a number of applications, including the diagnosis of disorders with the nose and paranasal sinuses. It provides a high-contrast resolution when compared to multidetector CT scanners (MDCTs). Flat panel CBCT scanners typically have less metal artifact effect along with less radiation exposure than MDCT.[⁷] Literature search could not identify any studies of UP using CBCT.

Taking into consideration, the importance of UP and the advantages of CBCT than MDCT, the current study was planned to review the anatomical variations of UP using CBCT.

MATERIALS AND METHODS

This retrospective study was conducted in the Department of Oral Medicine and Radiology using 100 paranasal sinuses CBCT scans.

Inclusion and exclusion criteria

CBCT images of patients showing paranasal sinuses within the age range of 20–65 years with adequate image quality were included in this study.

The scans with pan facial trauma, sinonasal surgeries, sinonasal tumors, and artifacts in the area of interest were excluded from the study.

Study design

All the images were viewed using CS 3D version 3.10.12 software. The necessary adjustments with regard to contrast and density were done to improve the visibility of the UP. Coronal section is used to see the variations in superior attachment and pneumatization of UP.

The SAUP is classified into six types based on the classification given by Landsberg and Friedman.[⁸] Pneumatization of the UP was also noted down.

Statistical analysis

Obtained data regarding the gender, type of SAUP, and the presence of pneumatization of UP were documented on a Microsoft Excel spreadsheet, and statistical analysis was carried out using Statistical Package for the Social Sciences (SPSS) (SPSS: An IBM Company) version 20 IBM, Armonk, New York, United States of America. Chi-square test is used for comparisons among males and females. If P < 0.05, the difference was considered statistically significant and P ≥ 0.05 was considered statistically nonsignificant.

RESULTS

A total of 100 CBCT scans (200 sides) are evaluated. Distribution of study population according to gender is shown in Table 1.

Table 1: Distribution of study population according to gender

Type of superior attachment of uncinate process

In this study, the prevalence of different types of SAUP observed is Type I in 102 sides out of 200 sides (51%), Type II in 34 sides (17%), Type III in 20 sides (10%), Type IV in 23 sides (11.5%), Type V in 13 sides (6.5%), and Type VI in 8 sides (4%) [Graph 1 and Figure 1].

Figure 1: Types of SAUP observed: (a) Type 1: Insertion into the LP. (b) Type 2: Insertion into the posterior wall of agger nasi cell. (c) Type 3: Insertion into the LP and junction of the middle turbinate with the cribriform plate. (d) Type 4: Insertion into junction of middle turbinate with the cribriform plate. (e) Type 5: Insertion into the ethmoid skull base. (f) Type 6: Insertion into the middle turbinate. UP: Uncinate process, SAUP: Superior attachment of UP, LP: Lamina papyracea

In both males and females, Type I SAUP was observed as most common type among both right and left sides [Graphs 2 and 3]. Bilaterally, a similar type of attachment is seen in 92% of cases (n = 92) and different types are observed in 8% of cases (n = 8).

No statistically significant difference was observed among males and females [Tables 2 and 3].

Table 2: Association between gender and superior attachment of uncinate process type on right side (Chi-square tested)

Table 3: Association between gender and superior attachment of uncinate process type on left side (Chi-square tested)

Pneumatization

Pneumatization of UP [Figure 2] is seen in 7% of cases (n = 7) out of which 4 are in males and 3 are in females [Graph 4]. Unilateral pneumatization is seen in 3 cases and bilateral pneumatization is seen in 4 cases [Graph 5].

Figure 2: Pneumatization of UP. (a) Unilateral pneumatization of UP on right side. (b) Bilateral pneumatization of UP. UP: Uncinate process

DISCUSSION

The OMC in the middle meatus of the nasal cavity is the common pathway of drainage for maxillary, frontal, and anterior ethmoidal sinuses. Any anatomical variations in this complex can lead to chronic sinusitis.

Recently, FESS has replaced the use of the transmaxillary operation, which removes the entire damaged mucous membrane while the FESS procedure attempts to retain the mucosa. UP in OMC is considered the consistent landmark for FESS and the first structure to be removed. The most common variation seen in UP is the variability in its superior attachment and less common is pneumatization of UP or uncinate bulla. Pneumatization of UP can cause obstruction of the OMC by narrowing the middle meatus and the infundibulum thus leading to sinusitis and resection of this pneumatized UP will relieve this obstruction.[⁹]

There are many classifications in the literature given for SAUP. Among them, the recent one is given by Landsberg and Friedman.[⁸] They classified SAUP into six types as follows:

1. Type 1: Insertion into the lamina papyracea
2. Type 2: Insertion into the posterior wall of agger nasi cell
3. Type 3: Insertion into the lamina papyracea and junction of the middle turbinate with the cribriform plate
4. Type 4: Insertion into the junction of the middle turbinate with the cribriform plate
5. Type 5: Insertion into the ethmoid skull base
6. Type 6: Insertion into the middle turbinate.

The inferior portion of the UP is well visible and can be easily recognized by surgeons even with 0° endoscope but the superior segment of the UP is no longer visible behind the anterior insertion of the middle turbinate. The most commonly used imaging technique is CT. However, it is associated with high radiation exposure and low contrast. CBCT, which is a recent advancement in oral and maxillofacial imaging, will overcome this disadvantage of CT and is also cost-effective when compared to MDCT.

CBCT is most commonly used for dental diagnosis. Hence, based on the advantages of CBCT over CT and the importance of UP, this study was planned to elaborate on the uses of CBCT.

In our study, the most common type of SAUP observed is Type I (51%), followed by Type II (17%), Type IV (11.5%), Type III (10%), Type V (6.5%), and Type VI (4%) is the least common type observed. This variation in SAUP was previously documented in other studies using CT [Table 4].

Table 4: Comparision with percentages obtained in previous studies

According to the abovementioned table, the studies were done by Calvo-Henriquez et al.,[¹⁰] Landsberg and Friedman,[⁸] and Turgut et al.[¹¹] also concluded Type 1 SAUP as the most common type, which is in accordance with the present study. The studies were done by Patla et al.,[¹²] Kansu,[¹³] and Kumar et al.[¹⁴] has shown the most prevalent type as VI, II, and II, respectively, which is not in accordance with the present study.

In the present study, similar type of attachment bilaterally was noticed in 92% of cases which is similar to the study done by Landsberg and Friedman[⁸] where they observed similar attachments in 93% of cases and lower than the 96% observed by Arun et al.[¹] and higher than 65%, 66.67% observed by Turgut et al.,[¹¹] Calvo-Henriquez et al.,[¹⁰] respectively.

In the present study, pneumatization of UP is seen in 7% of cases out of which 4% are in males and 3% are in females. In males out of 4, 1 is present in right, 1 in the left, and 2 are seen bilaterally. The lower prevalence of pneumatization of UP than the present study was noticed in the studies done by Shalini and Gopal (4%),[¹⁵] Srivastava and Tyagi (1.6%),[²] Tuli et al. (4%),[¹⁶] and Calvo-Henriquez et al. (3.41%).[¹⁰] The higher prevalence than the present study is noticed by Kumar et al. (13%)[¹⁴] and Ahmmed (14.65%).[¹⁷]

CONCLUSION

Preoperative evaluation of SAUP and pneumatization can decrease the intraoperative and postoperative complications during the FESS procedure thus protecting vital structures such as the cranial base and middle meatus. This can also decrease the chances of recurring rhinosinusitis. Using CBCT, these variations of UP can be evaluated with less radiation exposure and low cost when compared to MDCT.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.