Diseases in the sinonasal region are quite common in the population. Since the sinuses drain into the osteomeatal complex region, inflammation or anatomical variations in that area can cause obstructions, negatively affecting the drainage and ventilation of the sinuses and creating a predisposition for paranasal sinus diseases [1]. There are also studies that find it still controversial whether variations in the sinonasal region cause sinusitis [8, 9]. Aşantoğrul et al. [10] stated that anatomical variations can disrupt nasal airflow, affecting sinus development and volume. A study by Mendiratta et al. [11] reported that variations play a role in the etiology of chronic recurrent rhinosinusitis. There are differences in the osteomeatal complex between individuals, as well as between the right and left sides of the same individual. Additionally, there are differences among ethnic groups [12].
CT is of great importance in the evaluation and diagnosis of the region. CT is the gold standard that provides detailed information about the anatomy of the osteomeatal complex, serves as a roadmap in surgical operations and offers a good research opportunity for all sinus diseases [5, 13]. Coronal CT, in particular, is more useful [9, 11].
Although functional endoscopic sinus surgery (FESS) is a reliable technique applied in the sinonasal region, orbital-ocular and intracerebral complications can occur due to important anatomical neighbors and frequently encountered anatomical variations in the area [14].
Expansion of the bulla ethmoidalis, concha bullosa, paradoxical middle nasal concha and septal deviation are anatomical variations that narrow the middle nasal meatus. Haller cells and lateral deviation of the uncinate process narrow the infundibulum, while pneumatization of the nasal septum (especially the posterior part) narrows the sphenoidal recess. This creates a suitable environment for sphenoid sinus diseases. Agger nasi cells are formations that narrow the frontal sinus drainage channel [15].
Septal deviation is known as the deviation of the nasal septum from the median plane. Elahi et al. [16] measured the angle between the midline formed by the crista galli and the anterior nasal spine in the coronal plane and the most deviated point of the septum, categorizing it into three groups according to the degree: mild (< 9 degrees), moderate (9–15 degrees) and severe (> 15 degrees). If the septal deviation is excessive and accompanied by a septal spur, the middle meatus and infundibulum narrow, making surgical intervention difficult [17]. While Aşantoğrol et al. [10] reported septal deviation as the most common variation with a frequency of 66.7% and Agrawal et al. [5] reported septal deviation with a frequency of 83%, septal deviation was the second most common variation in our study (67.5%).
Septal spur occurs mostly on the side of the deviation and septal spur was observed in 40% (54 people) of the people with septal deviation in our study. The number of people in whom septal spur was observed without septal deviation was only 5. Turna et al. [18] reported the prevalence of septal spur as 19.9% in their study including 1160 individuals, while Aşantoğrul et al. [10] reported it as 29.1%. In our study, this rate was 29.5%.
Concha bullosa is frequently seen in the middle concha and narrowing of the middle meatus and sinus drainage pathways, impaired ventilation and distortion of the uncinate process may occur after hypertrophy of the middle concha [19].
SNC pneumatisation is generally rarely investigated in the literature. SNC are the least reached and most neglected turbinates during FESC [20]. When pneumatisation is excessive, symptoms such as headache may be observed even in the absence of sinonasal inflammation [21].
Karamatzanis et al. [22] found that the most common cause of nasal obstruction was septum deviation and the second most common cause was nasal concha hypertrophy. INC hypertrophy is usually bilateral, and in this case, surgical treatment is considered appropriate. Bilateral INC hypertrophy is generally associated with allergic and non-allergic rhinitis, while unilateral INC hypertrophy develops secondarily to compensate for septal deviation. Vasomotor rhinitis and chronic hypertrophic rhinitis can also cause INC hypertrophy [22, 23].
The paradoxical MNC, which is defined as a medial inclination of the MNC, is another variation that causes nasal obstruction and ventilation problems [11]. Most studies have not associated paradoxical MNC with sinusitis [24, 25]. Some studies have indicated that it could cause mucosal inflammation [26].
Agger nasi cells are close to the lacrimal sac and this proximity is important in dacryocystorhinostomy (DCR). Additionally, they are adjacent to the frontal recess and uncinate process and these structures are landmarks for proper access to the nasolacrimal drainage system [27].
Haller cells are anterior ethmoid air cells that expand towards the orbit. They are located close to the maxillary sinus ostium, making them a potential cause of maxillary sinusitis and a complicating factor in maxillary sinus surgery. Nasal and paranasal sinus pathologies can also cause nasolacrimal duct obstruction [28].
Onodi cells, also known as sphenoethmoidal air cells are the posterior-most ethmoidal air cells. They pneumatize lateral, superior or superolateral to the sphenoid sinus [29]. Thimmaiah and Anupama [30] classified pneumatization superiorly as type I, superolaterally as type II, and laterally as type III. Due to the close proximity of onodi cells to the optic nerve and internal carotid artery, it is important to identify them before sinus surgeries to prevent injuries. MDCT is highly preferred for their detection [30].
Previous studies indicated that the pneumatization of the crista galli originated from the ethmoid labyrinth, whereas new studies indicate that the pneumatization of the crista galli originates from the frontal sinuses [31]. Pneumatization of the crista galli is a low-incidence variation in the literature and may communicate with the frontonasal duct, leading to sinusitis or mucocele formation [32].
Septa are significant variations that can be observed in the maxillary, frontal, and sphenoid sinuses. These septa can lead to iatrogenic injuries such as sinus membrane perforation [33]. In the mentioned sinuses, unilateral and bilateral septa can be found, as well as two and three septa in a single sinus. In a study by Gülbeş et al. [34], they defined 10 groups according to the number of septa (no septa on both side, 1 septa on one side, 2 septa on one side, 1 septa on both sides, 2 septa on both sides, 2 septa on one side and 1 septa on the other side, 3 septa on one side, 3 septa on one side and 1 septa on the other side, 3 septa on one side and 2 septa on the other side, 3 septa on both sides ) and the most common group was the group with a single septa on one side (28.3% maxillary sinus septa, 28% frontal sinus septa, 25.3% sphenoid sinus septa). The incidence of variations detected in some studies are given in the Table 3.
Table 3
Comparison of the incidence of variations identified in some studies
| | SD (%) | ANC (%) | OC (%) | HC (%) | SNCP (%) | MNCP (%) | PMNC (%) | CGP (%) |
| Bolger et al [35] | - | 98.5 | - | 45.1 | - | 53 | 26.1 | 83.7 |
| Maru and Gupta [36] | 55.9 | 88.5 | 9.8 | 36.1 | - | 42.6 | 11.5 | 1.6 |
| Qudah [37] | 18 | 63 | - | 20 | 17 | 51 | 28 | 8 |
| Kaygusuz et al [38] | 72.7 | 61.6 | 8.0 | 16.1 | - | 45.4 | 13.1 | 22.2 |
| Kumar et al [12] | 62 | 56 | 14.5 | 20.7 | - | - | - | - |
| Gouripur et al [9] | 70 | 98 | 6 | 14 | - | 12 | 16 | - |
| Agrawal et al [5] | 83 | - | - | 13 | - | 58 | 4 | - |
| This study | 67.5 | 73.5 | 36.5 | 29.5 | 22 | 47.5 | 19 | 4 |
| SD, septal deviation; ANC, agger nasi cell; OC, onodi cell; HC, haller cell; SNCP, superior nasal concha pneumatization; MNCP, middle nasal concha pneumatization; PMNC, paradoxical middle nasal concha; CGP, crista galli pneumatization. |