Adenoid hypertrophy (AH) is a prevalent condition among pediatric populations, with prevalence rates estimated to be between 35% and 70% globally (1). It is a significant contributor to upper airway obstruction, leading to chronic nasal congestion, snoring, sleep-disordered breathing, and, in severe cases, cognitive impairment (2–4). Accurate evaluation of nasopharyngeal airway dimensions and adenoid size is critical for differentiating between physiological growth and pathological hypertrophy; however, standardized normative values exhibit considerable variability across different age groups and geographic regions.

In the diagnosis of AH, the adenoid-to-nasopharynx (A/N) ratio is a crucial imaging parameter for evaluating adenoid size and the extent of hypertrophy (5). Although previous studies have affirmed the reliability and clinical applicability of this measurement (6), they exhibit several limitations that warrant further investigation. For instance, the study by Acar et al. established the A/N ratio as a “useful, tolerable, and confident diagnostic method” for pediatric patients (6), but it was limited by a relatively small sample size (n = 46). In contrast, a comprehensive analysis by Guo et al. investigated 1,188 children aged 8 months to 13 years, utilizing machine learning techniques to analyze lateral nasopharyngeal radiographs. Their findings indicated an accuracy comparable to that of radiologist evaluations (5). Nonetheless, this study was restricted to treated cases, potentially introducing selection bias by omitting symptomatic children who did not require intervention. Furthermore, neither this study nor the preceding one provided detailed age-stratified analyses of nasopharyngeal dimensional changes. Additionally, the diagnostic thresholds for the A/N ratio exhibit considerable variability across different studies. Some research designatesan A/N ratio of ≤0.60 as normal, a ratio of 0.61–0.70 as indicative of moderate hypertrophy, and a ratio of ≥0.71 as suggestive of pathologic hypertrophy (7). Conversely, other studies classify a ratio of 0.61–0.70 as indicative of hypertrophy (8). This discrepancy highlights the lack of consensus and emphasizes the necessity for standardized, age-specific diagnostic criteria.

To address the limitations of previous research, our large-scale retrospective study analyzed 2,629 pediatric outpatients who underwent lateral nasopharyngeal radiography, thereby providing significantly enhanced statistical power and clinical generalizability compared to earlier investigations. This extensive dataset facilitates the establishment of precise, age-stratified reference ranges (1–3, 4–6, 7–9, and 10–12 years) for both A/N ratios and nasopharyngeal dimensions within a real-world outpatient population.

This extensive retrospective study provides significant insights into the age-specific development of the adenoids and nasopharynx in children, establishing percentile-based reference ranges for AD, ND, and the A/N ratio across four pediatric age groups (1–12 years). Our findings underscore significant limitations in the current fixed diagnostic criteria for AH, emphasizing the necessity of age-stratified thresholds for accurate clinical assessment.

AH is a prevalent condition affecting approximately 35%–70% of pediatric populations worldwide, positioning it among the most common otolaryngological disorders in children (1). A study conducted in Istanbul, Turkey, which employed portable telescope examination, revealed age-specific prevalence rates of AH: 27% in children aged 5–7 years, decreasing to 19.5% in the 8–10 year age group, and 19.9% among those aged 11–14 years (11). Utilizing an A/N ratio greater than 0.62 as the diagnostic criterion, the prevalence of AH in 12-year-old children was found to be 17.6% (12). Nasal endoscopy is considered the gold standard for diagnosing AH, as it allows for direct visualization of adenoid size and morphology within the nasopharynx (13, 14). However, due to the challenges associated with obtaining cooperation from pediatric patients and the potential discomfort associated with the procedure, lateral nasopharyngeal radiography serves as an excellent non-invasive alternative (5, 15). Research has established a significant correlation between the A/N ratio and endoscopic findings in the diagnosis of AH (16). In our study, the prevalence rates of AH (both moderate and pathological) diagnosed via the A/N ratio demonstrated a clear age-dependent trend: 79.4% in the 1–3 years age group, 74.5% in the 4–6 years group, 54.3% in the 7–9 years group, and 39.8% in the 10–12 years group (Table 1). This observation suggests a gradual decline correlated with advancing age. Nonetheless, the notably high prevalence rates (79.4% in the 1–3 years age group and 74.5% in the 4–6 years age group) raise concerns about the potential overestimation of AH when employing the A/N ratio criteria, particularly among preschool-aged children. The growth and development of adenoids in children represent a multifaceted process that typically commences shortly after birth, characterized by a period of rapid expansion during early childhood. Peak adenoid development is generally observed between the ages of 3 and 7 years (17). During this developmental phase, adenoids attain their maximum size and functional capacity, which is intricately associated with the maturation of the child's immune system (18). Our findings from lateral nasopharyngeal radiography indicate that peak adenoid development occurs between the ages of 4 and 6 years, followed by a modest increase from ages 7–12 years (Table 1). Correlation analysis further revealed a weak positive association between age and adenoid size (Figure 1A). Notably, in contrast to the relatively gradual growth rate of adenoids, the nasopharyngeal cavity expands at a more accelerated rate with advancing age (Table 1). Additional correlation analysis demonstrated that the positive association between age and ND is stronger than that between age and AD (Figure 1B). Previous research has documented a progressive increase in ND from ages 4–5 to 14–15 years (19). It is noteworthy that the nasopharyngeal free airway space in children aged 10–11 years does not diminish, despite an increase in adenoid thickness. This phenomenon can be attributed to the downward displacement of the hard palate, which results in an enlargement of the free airway space as a result of growth (19). This observation may elucidate the inverse relationship between age and the A/N ratio identified in our study (Figure 1C). Within our study cohort, the median A/N ratio exhibited a distinct age-dependent decline: 0.68 (range 0.11–0.95) for children aged 1–3 years, 0.67 (0.17–0.94) for those aged 4–6 years, 0.61 (0.16–0.93) for ages 7–9 years, and 0.56 (0.26–0.88) for ages 10–12 years. The differences among these age groups were statistically significant (Table 1), reinforcing the observation that the prevalence of AH decreases with age, in accordance with prior research (11). Additionally, our findings revealed no significant sex-based differences in these developmental changes, which is consistent with previous studies (11). In addition to physiological growth patterns, extrinsic factors such as obesity may significantly influence nasopharyngeal dimensions. Arens et al. demonstrated that obesity contributes to upper airway obstruction through mechanisms such as pharyngeal fat deposition and mechanical compression, with 45% of obese children with obstructive sleep apnea syndrome (OSAS) exhibiting adenotonsillar hypertrophy. Notably, residual obstruction persists in half of these children following adenotonsillectomy, indicating that obesity-related structural changes (e.g., fat infiltration in lateral pharyngeal walls) may independently affect nasopharyngeal development (20). Furthermore, Daar et al. reported that obese children exhibit significantly higher rates of AH (34% compared to 6% in non-obese controls) and tonsillar hypertrophy (16% compared to 4%) (21). In addition to obesity, allergic conditions also play a critical role in modulating nasopharyngeal dimensions. Specifically, allergic rhinitis has been shown to significantly increase the risk of adenotonsillar hypertrophy (odds ratio = 2.95) through Th2-mediated inflammatory pathways (22). This causal relationship is further substantiated by a recent Mendelian randomization study, which indicates that genetic predisposition to allergic diseases—particularly allergic rhinitis (odds ratio [OR] = 1.14) and allergic asthma (OR = 1.12)—significantly increases the risk of chronic adenotonsillar disease, while no reverse association has been identified (23). Although our study provides normative data for the general pediatric population, these comorbid conditions may necessitate careful consideration in the clinical interpretation of radiographic measurements. Future research should focus on elucidating the specific impacts of these factors on adenoid and nasopharyngeal development to enhance the refinement of diagnostic criteria.

Our study significantly contributes to the field by establishing the first comprehensive percentile-based reference ranges (P5–P95) for AD, ND, and A/N ratio in outpatient children aged 1–12 years, thereby addressing a critical gap in age-stratified diagnostic standards (Table 3) (1, 13). The observed reference ranges indicate dynamic developmental patterns: while AD remains relatively stable (median 14–15 mm across age groups), ND shows a progressive increase (21–27 mm), which correlates with a decline in the A/N ratio from 0.68 to 0.56. This finding is consistent with a Brazilian study involving 320 participants aged 4–16 years (all nasal breathers without prior adenoidectomy), which reported A/N ratios of 0.67 ± 0.04 at ages 4–5 years, decreasing to 0.52 ± 0.05 at ages 14–15 years (19). This physiological trajectory highlights the limitations of fixed diagnostic thresholds, which tend to disproportionately classify younger children as pathological (e.g., 42% of 1–3-year-olds vs. 13.7% of 10–12-year-olds met the A/N ≥ 0.71 criteria) (Table 1). Previous studies have indicated that nasopharyngeal airway restriction is most prevalent during the preschool and early school years, as AD often expands more rapidly than the physiological growth of ND (18). Moreover, the variability in adenoid and nasopharyngeal growth patterns among individuals complicates the establishment of a standardized diagnostic threshold (17). Some children may exhibit accelerated growth of the nasopharyngeal space, resulting in a more significant reduction in the A/N ratio, while others may demonstrate slower growth rates. This individual variability highlights the necessity for age-specific or growth-adjusted diagnostic criteria that more accurately reflect the dynamic changes occurring in the nasopharyngeal region throughout childhood development (5).

The discordance between age-specific percentiles and fixed diagnostic criteria (Figure 4) highlights significant risks of systematic misclassification. For instance, according to the current thresholds (≥0.61), 79.6% of children aged 1–3 years would be classified as having moderate-to-severe hypertrophy. However, our data indicate that these values fall within the range of normal developmental variation (P25–P75: 0.62–0.75). These findings advocate for the adoption of age-stratified diagnostic criteria, potentially utilizing percentile thresholds (e.g., P95) of the A/N ratio for the diagnosis of AH. A systematic review by Major et al. identified significant limitations in current diagnostic modalities for AH, noting that no single optimal screening tool is available due to inherent trade-offs between accuracy, accessibility, and safety. Notably, lateral radiography—the most commonly employed method in clinical practice—exhibited inconsistent performance, with sensitivity ranging from 61% to 75% and specificity from 41% to 55% for adenoid size assessment (13). This further corroborates our findings concerning the substantial misclassification risks associated with the application of fixed A/N ratio thresholds across different age groups. Although Caylakli et al. (16) proposed a significant correlation between the A/N ratio and endoscopic findings in the diagnosis of AH; however, their study was constrained by a relatively small sample size (n = 85) and a broad age range (2–12 years). These methodological limitations highlight the imperative for the establishment of age-stratified diagnostic criteria for A/N ratios, as advocated in our current research. Additionally, we align with the perspective of Major et al. (13) that a multifaceted diagnostic approach—combining radiographic indices with a thorough clinical history—can effectively mitigate the shortcomings of individual diagnostic methods and enhance overall accuracy in both the identification and exclusion of AH.

The inter-rater reliability analysis demonstrated substantial agreement (Kappa = 0.76; 95% CI: 0.73–0.78) between radiologists in classifying AH severity using A/N ratios, with a simple agreement rate of 84.2%. This level of agreement aligns with findings from Kolo et al. (24), who reported Kappa values of 0.67–0.82 for subjective assessments of nasopharyngeal radiographs among otolaryngologists and radiologists, further supporting the reproducibility of radiographic evaluations in clinical practice.

This study has several limitations. The single-center retrospective design may introduce selection bias, limiting the generalizability of findings to the broader pediatric population. The absence of nasoendoscopic evaluation prevents direct validation of radiographic measurements, and the lack of a systematic clinical symptom assessment restricts correlation with functional outcomes. Future prospective multicenter studies should incorporate endoscopic evaluation and comprehensive clinical assessments to validate age-specific A/N ratio thresholds and improve diagnostic accuracy for adenoid hypertrophy across different age groups.

This study provides evidence-based tools for age-specific adenoid reference ranges, highlighting deficiencies in the existing fixed A/N ratio thresholds that may lead to misdiagnosis in pediatric populations. The newly established percentile-based ranges (P5-P95) for AD, ND, and A/N ratio across four age groups (1–3, 4–6, 7–9, and 10–12 years) offer a more accurate diagnostic reference. The findings support the use of these age-specific criteria to enhance AH diagnosis and reduce misclassification risks. Future research should validate these thresholds through multicenter studies and integrate them with comprehensive clinical assessments.