The nasal cavity and paranasal sinuses form a complex anatomical and functional unit involved in humidification and conditioning of inspired air, mucociliary clearance, resonance of voice, and protection of the craniofacial structures. The paranasal sinuses comprise the paired maxillary, frontal, ethmoid, and sphenoid sinuses, which communicate with the nasal cavity through relatively narrow drainage pathways. Considerable anatomical variation exists within the sinonasal region. Variations involving the nasal septum, middle turbinate, ethmoid air cells, uncinate process, and osteomeatal complex are commonly encountered. Important variants include deviated nasal septum, septal spur, concha bullosa, paradoxical middle turbinate, agger nasi cells, Haller cells, Onodi cells, variations of the uncinate process, and abnormalities of ethmoid and frontal sinus pneumatization. Although many anatomical variants are incidental, some may narrow important drainage pathways and potentially contribute to impaired sinus ventilation and mucociliary clearance. Their recognition becomes particularly important before FESS because the surgeon operates in close proximity to the orbit, skull base, optic nerve, and internal carotid artery. CT is the preferred imaging modality for detailed assessment of sinonasal bony anatomy. Thin-section CT with multiplanar evaluation allows accurate identification of subtle anatomical variants and demonstrates their relationship with adjacent critical structures. Recognition of variants such as Onodi cells is especially important because of their potential relationship to the optic nerve and internal carotid artery. The prevalence of sinonasal anatomical variants differs between populations and studies. Differences may be related to ethnicity, geographic factors, patient selection, CT technique, and definitions used for individual variants. The present study was therefore undertaken to determine the prevalence and distribution of anatomical variations of the nasal cavity and paranasal sinuses in patients undergoing CT PNS and to assess their clinical and surgical relevance.

A hospital-based cross-sectional study was conducted in the Department of Radiodiagnosis, Dr. K. N. Singh Memorial Institute of Medical Sciences, Barabanki, Uttar Pradesh, over a period of 18 months following Institutional Ethics Committee approval. Patients referred for CT PNS were screened for eligibility. Patients aged >18 years, referred for CT PNS, of either sex, and providing informed consent were included. Patients with previous sinonasal surgery, sinonasal malignancy, facial trauma, pregnancy, age below 18 years, or refusal to participate were excluded. The initial sample size was calculated using an estimated prevalence of 62%, 95% confidence level, and 10% allowable precision. The calculated sample size was approximately 91 and was rounded to 100. During the study period, 138 eligible patients were ultimately evaluated and included in the final analysis. Clinical details, demographic characteristics, and presenting complaints were recorded using a structured proforma. Common indications for CT included nasal obstruction, suspected DNS, chronic sinusitis, headache, and facial pain. CT examinations were performed using a 16-slice Siemens SOMATOM Scope scanner. Patients were examined in the supine position, and non-contrast CT was performed with axial acquisition and multiplanar assessment. The nasal cavity, paranasal sinuses, osteomeatal complex, and adjacent osseous structures were evaluated. The anatomical structures assessed included the nasal septum, septal spur, middle and inferior turbinates, concha bullosa, paradoxical middle turbinate, agger nasi cells, Haller cells, Onodi cells, ethmoid bulla, uncinate process, accessory maxillary ostium, and frontal sinus development and pneumatization. Categorical variables were expressed as frequencies and percentages, while continuous variables were summarized using mean and standard deviation. Statistical analysis was performed using IBM SPSS Statistics version 26.0. A p value <0.05 was considered statistically significant

A total of 138 subjects were included. There were 63 males (45.65%) and 75 females (54.34%), giving a male-to-female ratio of 0.84:1. The mean age was 37.6 ± 9.8 years. The 31–40-year age group represented the largest proportion of the study population (47.1%). Nasal obstruction was the most common indication for CT PNS, accounting for 32.60% of examinations. This was followed by suspected DNS (22.46%), chronic sinusitis (21.73%), headache (16.66%), facial pain (5.79%), and post-traumatic evaluation (0.72%). DNS in any form was the most frequent nasal septal abnormality, occurring in approximately 87.7% of subjects. Left-sided deviation was observed in 38.4%, right-sided deviation in 32.6%, and S-shaped deviation in 16.66%. Septal spur was present in 34.78%. Among turbinate-related abnormalities, inferior turbinate hypertrophy was present in 45.65%, concha bullosa in 38.4%, and paradoxical middle turbinate in 21.7%. Agger nasi cells were the most frequent osteomeatal complex-related variant, occurring in 82.6% of subjects. Accessory maxillary ostium was present in 36.95%, enlarged ethmoid bulla in 32.6%, and Haller cells in 31.15%. Onodi cells were identified in 26.8%, while pneumatization of the uncinate process was seen in 10.86%. Variations of the uncinate process included medial deviation in 21.73%, lateral deviation in 7.97%, and pneumatization in 10.86%. Regarding the frontal sinus, hypoplasia was identified in 44.92% of subjects, aplasia in 5.07%, and hyperpneumatization in 3.62%. Major anatomical variations Anatomical variant Prevalence DNS – any form 87.7% Agger nasi cells 82.6% Inferior turbinate hypertrophy 45.65% Concha bullosa 38.4% Accessory maxillary ostium 36.95% Septal spur 34.78% Enlarged ethmoid bulla 32.60% Haller cells 31.15% Onodi cells 26.80% Paradoxical middle turbinate 21.70% Pneumatized uncinate process 10.86%

CT provides excellent visualization of the complex bony anatomy of the sinonasal region and is particularly valuable for identifying anatomical variations before FESS. The present study demonstrated a high prevalence of a wide range of sinonasal anatomical variants among 138 symptomatic patients. The study showed a slight female predominance, with females accounting for 54.34% and males 45.65%. The mean age was 37.6 ± 9.8 years, and almost half of the participants belonged to the 31–40-year age group. This distribution is consistent with the population commonly referred for investigation of chronic or recurrent sinonasal symptoms. Nasal obstruction was the most common indication for CT, followed by suspected DNS, chronic sinusitis, and headache. This pattern emphasizes the importance of anatomical obstruction in patients presenting with sinonasal complaints. CT is particularly useful because clinical examination may not adequately demonstrate abnormalities involving the deeper osteomeatal complex, ethmoid labyrinth, frontal recess, and sphenoethmoidal region. Deviated nasal septum DNS was the most common major abnormality in the present study, occurring in approximately 87.7% of subjects. Left-sided deviation was slightly more frequent than right-sided deviation. The prevalence was comparable with previously published CT-based studies. Bolger et al. reported DNS in approximately 79%, while Kumar et al. and Pérez-Piñas et al. reported frequencies of 88% and 80%, respectively. The clinical significance of DNS depends primarily on its degree and location. Mild deviations may be asymptomatic, whereas marked deviation may narrow the nasal airway and contribute to obstruction. In selected patients, severe septal deviation may also influence the osteomeatal complex and sinus drainage. However, the high prevalence of DNS in the general symptomatic population emphasizes that its presence alone should not be interpreted as proof of causation for chronic rhinosinusitis. Septal spur Septal spur was identified in 34.78% of subjects. Septal spurs frequently coexist with septal deviation and can produce focal narrowing or mucosal contact points. They are particularly relevant during septoplasty and FESS because they can restrict surgical access and alter the relationship between the nasal septum and adjacent turbinates. Turbinate variations Concha bullosa was present in 38.4% of subjects. This was lower than the 53% reported by Bolger et al. but comparable with several other studies. Concha bullosa represents pneumatization of the middle turbinate. When sufficiently large, it can reduce the width of the middle meatus and potentially compromise osteomeatal complex ventilation. Nevertheless, the mere presence of concha bullosa does not establish a causal relationship with chronic rhinosinusitis; its significance depends on size, location, and associated abnormalities. A paradoxical middle turbinate was observed in 21.7%. This variant is characterized by abnormal curvature of the middle turbinate and may narrow the middle meatus or alter access to the osteomeatal complex. Its identification is therefore important during preoperative assessment. Inferior turbinate hypertrophy occurred in 45.65% of subjects. It may contribute significantly to nasal obstruction and frequently coexists with DNS. Enlargement may result from inflammatory or allergic processes or may represent compensatory hypertrophy on the side opposite a significant septal deviation. Agger nasi cells Agger nasi cells were the most frequent osteomeatal complex-related anatomical variant, occurring in 82.6% of subjects. This was consistent with the high prevalence reported in previous CT studies, although lower than the 98.5% reported by Bolger et al. Agger nasi cells are located anterior to the attachment of the middle turbinate and form an important component of the frontal recess. Their size and configuration may influence frontal sinus drainage. Recognition of these cells is particularly important during frontal sinus surgery because incomplete understanding of the frontal recess anatomy may result in inadequate clearance or injury to adjacent structures. Haller cells Haller cells were identified in 31.15% of subjects. Their prevalence was broadly comparable with previous studies, although lower than the 45% reported by Bolger et al. Haller cells are infraorbital ethmoid cells located along the orbital floor. When large, they may narrow the maxillary infundibulum and influence maxillary sinus drainage. Their close relationship with the orbit makes their identification important during endoscopic surgery. Onodi cells Onodi cells were present in 26.8% of subjects. This was similar to the 29% reported by Kumar et al. and the 24% reported by Pérez-Piñas et al., but higher than the 14% reported by Bolger et al. Onodi cells represent posterior ethmoid cells that extend posteriorly and/or superiorly relative to the sphenoid sinus. Their most important clinical implication is their potential close relationship with the optic nerve and, in some cases, the internal carotid artery. Failure to identify this anatomy before posterior ethmoid or sphenoid surgery may increase the risk of optic nerve or vascular injury. Therefore, careful evaluation of the posterior ethmoid and sphenoid region on axial and coronal CT images is essential. Uncinate process Pneumatization of the uncinate process occurred in 10.86%, while medial and lateral deviations were observed in 21.73% and 7.97%, respectively. The uncinate process is an important component of the osteomeatal complex and its configuration influences the drainage pathways of the maxillary and anterior ethmoid sinuses. Knowledge of uncinate anatomy is particularly important during uncinectomy because its relationship with the orbit, lacrimal apparatus, and maxillary infundibulum varies considerably between individuals. Frontal sinus variations Hypoplastic frontal sinus was observed in 44.92%, while complete aplasia was present in 5.07%. Hyperpneumatization occurred in 3.62%. Frontal sinus development is highly variable, and asymmetry, hypoplasia, and aplasia may represent normal anatomical variants. Correct recognition is therefore important before frontal sinus surgery to prevent misinterpretation of developmental anatomy as pathological abnormality. Comparison With Previous Studies The prevalence of the major anatomical variations in the present study was broadly comparable with previously published CT studies. Anatomical variant Present study Bolger et al. Kumar et al. Pérez-Piñas et al. DNS 87.7% 79% 88% 80% Septal spur 34.8% 30% 32% 28% Concha bullosa 38.4% 53% 36% 41% Paradoxical middle turbinate 21.7% 27% 20% 18% Agger nasi cells 82.6% 98.5% 78% 88% Haller cells 31.1% 45% 28% 26% Onodi cells 26.8% 14% 29% 24% Pneumatized uncinate process 10.9% 9% 12% 8% Minor differences between studies may be explained by differences in sample characteristics, geographic and ethnic factors, CT technique, diagnostic definitions, and whether symptomatic or asymptomatic populations were studied. Clinical Implications The findings have important implications for radiological reporting and surgical planning. DNS and septal spurs may contribute to nasal obstruction and restrict endoscopic access. Concha bullosa and paradoxical middle turbinate may narrow the middle meatus. Agger nasi cells are important landmarks in the frontal recess, while Haller cells may narrow the maxillary infundibulum and have a close relationship with the orbit. Onodi cells deserve particular attention because of their potential relationship with the optic nerve and internal carotid artery. Variations in the uncinate process may alter maxillary sinus drainage and complicate uncinectomy. Consequently, CT PNS should not be limited to assessment of mucosal thickening or sinus opacification. A systematic assessment of the nasal septum, turbinates, osteomeatal complex, ethmoid labyrinth, frontal recess, sphenoethmoidal region, and critical adjacent structures is essential, particularly in patients undergoing FESS. Limitations This study has several limitations. First, it was a single-center, hospital-based cross-sectional study, limiting generalizability to the broader population. Second, all participants were symptomatic patients referred for CT PNS, introducing potential selection bias. Third, an asymptomatic control group was not included. Furthermore, the relationship between individual anatomical variants and symptom severity was not assessed using standardized symptom scores or multivariable statistical analysis. Endoscopic correlation and postoperative surgical outcomes were also not evaluated. Future multicentric studies with larger samples, standardized clinical scoring systems, endoscopic correlation, and postoperative follow-up would provide stronger evidence regarding the clinical significance of individual anatomical variants.

Sinonasal anatomical variations are extremely common among patients undergoing CT PNS. In the present study, DNS and agger nasi cells were the most frequently encountered abnormalities, followed by inferior turbinate hypertrophy, concha bullosa, accessory maxillary ostium, enlarged ethmoid bulla, Haller cells, and Onodi cells. The prevalence of most major variants was broadly comparable with previously published Indian and international CT studies. Although many anatomical variations are incidental, some may contribute to nasal obstruction or impaired sinonasal drainage, while others have major implications for surgical safety. CT PNS provides an essential anatomical roadmap for the sinonasal region and should therefore be systematically evaluated for variations involving the nasal septum, turbinates, osteomeatal complex, frontal recess, ethmoid labyrinth, and sphenoethmoidal region. Particular attention should be given to Haller and Onodi cells and their relationship to the orbit, optic nerve, and internal carotid artery before endoscopic intervention.

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