Olfactory Fossa Evaluation as a Maxillary Sinus Development Using Cone Beam Computed Tomography

Abstract

In our study, we aimed to evaluate the risk of skull base perforation during endoscopic sinus surgery in individuals with hypoplasic maxillary sinuses using Cone Beam Computed Tomography (CBCT). We included 52 patients with bilateral maxillary sinus hypoplasia and 52 patients with normal maxillary sinus in the study. Reviewing paranasal CBCT scans, we noted the olfactory fossa depths and lateral lamella lengths of all the groups and compared between the hypoplasia groups and the control group. Compared the maxillary hypoplasia sinus individuals with the control group, both the olfactory fossa depths and the lateral lamina length were different in the maxillary hypoplasic individuals. In individuals with hypoplasic maxillary sinus, the olfactory fossa depth and the lateral lamina length values are higher, which increases the risk of complications in endoscopic sinus surgery.

Introduction

Endoscopic approach in paranasal sinus surgery is a method frequently preferred by otolaryngologists due to low postoperative morbidity. Major complications should be avoided as these surgeries are generally performed to improve the quality of life of the individual [1–3]. Anatomical variations should always be kept in mind before the procedure, and tomography images of the region should be examined in detail to minimize the complication rate that may occur. Otherwise, complications will be inevitable. The most serious complication encountered in the region is the trauma of the anterior skull base during the procedure and subsequent formation of CSF fistulas. The most common site of this complication is the cribriform plate lateral lamella. Individuals with deeper olfactory fossa (OF) also have longer lateral lamina (LL), which causes iatrogenic skull base injuries [4]. In particular, the region where the anterior ethmoid artery penetrates the skull base is considered to be the area that has the lowest resistance of the entire skull base [5]. In the classification made by Keros in the early 1960s and still in use today, Keros divided the olfactory fossa into three categories according to OF depth [4]. Kainz et al. [6] showed that the risk of injury to the anterior skull base during surgery is increased in Keros type III. Therefore, developmental disorders of the paranasal sinuses are an important factor to be considered in endoscopic sinus surgery. The maxillary sinus is the largest in terms of volume among paranasal sinuses, and the maxillofacial region can be examined in detail in most Cone Beam Computed Tomograph (CBCT) scans. Maxillary sinus hypoplasia (MSH) were reported in 1.73% –10.4% of patients with sinus symptoms [7–11].

CBCT is generally referred to as dentistry in the literature and stands out with its price, ergonomics and lower radiation emission compared to conventional tomography. CBCT’s became important for the Otorhinolaryngology and Plastic Surgery fields as well as they provide information about the head and neck region and their image quality increases day by day[12].

We did not find a study in the literature that measured the OF depth and LL length with CBCT in individuals with MSH. In this retrospective/archival, radio-anatomical study, we aimed to investigate the olfactory fossa depths and lateral lamella lengths of patients with MSH in comparison to the controls with normal maxillary sinuses. This study is significant in that it is based on the purpose of creating a morphological model to prevent injury to the relevant structures during endoscopic sinus surgeries in individuals with MSH.

Materials and Methods

In this retrospective study, we evaluated CBCT images of 104 patients (52 patients with maxillary sinus hypoplasia, 52 patients with normal maxillary sinus) who applied to us for different reasons. The scans of these 104 patients were retrospectively retrieved from the database of the Department of Dentomaxillofacial Radiology, Dentistry Faculty of University. The study protocol was approved by the Clinical Ethics Committee of Inonu University (approval no. 2020/949). CBCT images were acquired with the patients in the standard supine position (scanning time, 14–18 s, exposure time 3.6 s, kVp = 110, mA = 1–20; voxel size 0.2mm3) using the same device (NewTom 5G, QR Verona, Verona, Italy). All images were analyzed with the aid of Quantitative Radiology (QR) NNT version 2.21 imaging software. All CBCT scans were evaluated by the same observer (S.B.D.). The intra class correlation coefficient (ICC) was used to determine intrarater reliability. ICC values were 0.92 for the classifications of the right side and 0.90 for the classifications of the left side. The exclusion criteria for the all group included poor image quality with severe artefacts, a systemic bone disease of the mid-facial region, craniofacial syndrome, a cleft lip or palate, history of sinus surgery, previous orthognathic surgery, and age < 18 years.

Study Design

We accepted MSH as maxillary sinus with half or less of the maximum horizontal or vertical linear dimension of the orbit on the same side as described by Sirikçi et al. [10]. Only bilateral MSH patients were examined. We investigated the coronal CBCT scans in which the crista galli, perpendicular plate and OF were clear to measure OF depth and LL length. As described by Keros [4] OF was measured and classified according to the position of the cribriform plate concerned to the ethmoid roof (Fig. 1). The measurements were classified into types I, II, and III for both sides. Types variants are accepted as follows;

Fig. 1.

Showing olfactory fossa depth according to keros classification a Keros I b Keros II c Keros III

Type I-OF depth lower than 3.0 mm.

Type II-OF depth between 4.0 and 7.0 mm.

Type III-OF depth higher than 7.0 mm.

We also measured LL length which from horizontal cribriform plate and fovea ethmoidalis between the cribriform plate as the lateral boundary (Fig. 2).

Fig. 2.

Showing lateral lamina length measurements

Results

In the study, 50% of the cases are control and 50% are experimental group. The groups do not differ according to gender (p = 0.382). While 65.4% of the cases are women, 34.6% are men. (Table 1).

Table 1.

Frequency distributions

	Normal (n = 26)	Hypoplasic Maxillary Sinus (n = 26)	Total (n = 52)	p
Female	15 (57.7)**	19 (73.1)	34 (65.4)	0.382
Male	11 (42.3)	7 (26.9)	18 (34.6)

^*Chi-square test **Frequency (Percentage)

Mean age value does not differ according to the groups (p = 0.694). While the mean age value of the control group was 34.4, it was 35.9 in the experimental group. (Table 2).

Table 2.

Comparison of ages by groups

	Mean	Standard deviation	Minimum	Maximum	p*
Normal	34.4	14.7	19.0	65.0	0.694
Hypoplasic Maxillary Sinus	35.9	12.5	20.0	60.0
Total	35.1	13.6	19.0	65.0

^* Independent samples t test

The mean value of the OF depth varies according to the groups (p < 0.001). While the mean value of OF depth in the control group was 3.54, it was obtained as 5.53 in the experimental group.

The mean value of LL length differs according to the groups (p < 0.001). While the mean LL length value was 4.57 in the control group, it was 5.61 in the experimental group. In the control group, mean value of OF depth does not differ according to gender (p = 0.243). While the average value of OF in women was 3.38, it was obtained as 3.76 in men. The mean LL length value does not differ according to gender (p = 0.503). While the mean length value of LL was 4.46 in women, it was 4.71 in men. In the experimental group, the mean value of OF depth does not differ according to gender (p = 0.527). While the mean value of OF in women was 5.65, it was obtained as 5.21 in men. The mean LL length value does not differ according to gender (p = 0.412). While the mean LL length value was 5.77 in women, it was obtained as 5.19 in men (Table 3).

Table 3.

Comparisons by groups

		n	Normal (n = 52)		Hypoplasic Maxillary Sinus (n = 52)		p*
			Mean ± ss	Mean (min–max)	Mean ± ss	Mean (min–max)
Olfactor Fossa Depth	Female	68	3.38 ± 0.89	3.48 (1.8–4.96)	5.65 ± 1.57	5.5 (2.2–9.4)
	Male	36	3.76 ± 1.43	3.66 (1.7–47.04)	5.21 ± 2.39	4.85 (1.5–9.4)
	Total	104	3.54 ± 1.15	3.51 (1.74–7.04)	5.53 ± 1.81	5.5 (1.5–9.4)	< 0.001
	p		0.243		0.527
Lamina Height	Female	68	4.46 ± 0.91	4.36 (2.3–6.06)	5.77 ± 1.14	5.61 (3.3–9.08)
	Male	36	4.71 ± 1.57	4.97 (1.89–7.71)	5.19 ± 2.46	5.4 (1–9.4)
	Total	104	4.57 ± 1.23	4.6 (1.89–7.71)	5.61 ± 1.6	5.55 (1–9.4)	< 0.001
	p*		0.503		0.412

Bold values indicate significant difference at p < 0.05

*Independent samples t test

Statistical Method

The data were analyzed with IBM SPSS V23. The compliance with normal distribution was examined with Kolmogorov Smirnov and Shapiro Wilk. Independent samples t test was used to compare normally distributed data. The data conforming to normal distribution were presented as mean ± standard deviation. The -square test was used to compare categorical data. Categorical data were presented as frequency (percentage). The level of significance was taken as p < 0.050.

Discussion

In endoscopic sinus surgeries, the importance of OF anatomy, which includes the ethmoidal roof and cribriform plate, is increasing day by day because of the skull base injuries that may occur due to its highly fragile structure [13–15]. There are studies in the literature showing that the probability of iatrogenic injury increases as the OF depth increases [16, 17] Considering the studies examining the relationship between anatomical variations and OF depth, it was shown that there is an increase in OF depth in individuals with excessive vertical facial growth [18]. However, Bayrak et al. [19] explained that Nasal Septum Deviation has no effect on OF depth. When we examined the relationship between maxillary sinus development and OF depth, we observed an increase in OF depth in MSH individuals.

The LL of cribriform plate is the thinnest (0.05 mm) region of the skull base, which makes the LL length important in terms of the formation of iatrogenic CSF fistulas during the endoscopic surgeries of the region [20, 21]. According to Solares et al. [22], as LL height increases, the probability of its penetration into the skull base increases. In a study examining the relationship between LL length and Keros, a correlation was found between them [23].

Although computed tomography is stated as the gold standard in the evaluation of paranasal sinuses [24], CBCT, which was started to be used in the 1990s, has advantages such as excellent and detailed resolution, low radiation and low cost [25, 26]. CBCT was found useful for evaluating the OF and anterior skull base prior to nasal and paranasal sinus surgeries [13, 25]. In this study, OF depth and LL length were evaluated in MSH individuals using CBCT images. Keros classification [4] was used to evaluate the OF depth. In the classification created by Keros according to his research on 450 skulls, type I has a depth of 1–3 mm and is seen at 12%, type II has a depth of 4–7 mm and is seen in 70%, type III has a depth of 7 mm and more and is seen at 18%. Type III is the most risky group and is called “dangerous ethmoid”[6, 27]. The distribution of the study population according to Keros classification is shown in Table 4.

Table 4.

Keros classification of individuals in our study

	Keros 1 n (%)	Keros 2 n (%)	Keros 3 n (%)
Hypoplasic maxilla	14 (13.4)	74 (71.1)	16 (15.3)
Normal	78 (75)	24 (23)	2 (2)

According to the results of our study, both OF depth and LL length values are higher in patients with MSH compared to individuals with normal maxillary sinuses. Kayabasi et al. [14] measured the mean OF depth 5.7 mm in MSH individuals and 4.5 mm in individuals with normal maxillary sinus (P < 0.001). In the same study, they measured LL length values and found them higher in individuals with maxillary sinus hypopalsia (P < 0.001). These results are consistent with the results of our study. Another study measuring LL length found it 3.6 ± 0.8 mm [22].

Angle formed by the lateral lamella of the cribriform plate (LLCP) and the horizontal plane passing through the cribriform plate may play an important role in assessing the risks of endoscopic sinus surgery [21]. The fact that the relevant angle was not measured in this study can be considered as a limitation of our study. Moreover, 2-dimensional evaluation of whether the maxillary sinus, which is a 3-dimensional structure, is hypoplasic or not can be considered as another limitation.

Conclusion

Considering the advantages before endoscopic sinus surgery, CBCT devices can be used instead of CT devices. In individuals with MSH, OF is deeper and LL is longer, and the surgeon should consider that the risk of skull base injury may increase in individuals with hypoplasic maxillary sinuses.

Funding

This study was not funded by any organization.

Declarations

Conflict of interest

Authors declare that he has no conflict of interest.

Ethical Approval

This research was approved by Inonu University Scientific Research and publication ethics committee numbered 2020/949.

Informed Consent

For this type of study, formal consent is not required.