Laphatrada YurasakpongKaissar YammineTaweetham LimpanuparbSirorat JantaArada ChaiyamoonNutmethee KruepungaKrai MeemonAthikhun SuwannakhanLebanese American University Medical Center-Rizk HospitalLebanese American UniversityFaculty of Medicine, Khon Kaen UniversityMahidol University2022-08-042022-08-042021-09-01Clinical Anatomy. Vol.34, No.6 (2021), 872-88310982353089738062-s2.0-85105180230https://repository.li.mahidol.ac.th/handle/123456789/77929The azygos lobe (AL) is an accessory lobe of the right lung with prevalence between 0.4 and 1.2%. The aim of the present review is to provide a better estimate of the frequency of the AL and to examine its relationships with other variables such as population, diagnostic methods, and co-occurring illnesses. Studies published between 1899 and October 2020 were searched through three electronic databases; Google Scholar, PubMed, and JSTOR. Titles, abstracts, and full texts of the retrieved entries were screened to determine their appropriateness for inclusion. A total of 88 studies relating to 1,033,083 subjects met the inclusion criteria. A random-effects meta-analysis yielded an overall prevalence of 0.30% (95% CI: 0.0024–0.0035, I2 = 97.9%). Linear regression and subgroup analysis revealed a negative correlation (ρ = −0.540, p <0.001) between AL prevalence and sample size; studies with smaller sample sizes had higher prevalences. The AL prevalence in individuals with congenital pulmonary defects, 5.2% (95% CI: 0.0018–0.0086, I2 = 0%), was 17 times higher than the overall prevalence (z = 6.65, p <0.001), suggesting associations with other abnormalities and possibly a genetic predisposition. In addition to an evidence-based synthesis of AL prevalence, this study demonstrates publication bias and small-study effects in the anatomy literature. Awareness of the AL is crucial for radiologists when they interpret unusual radiological findings and for surgeons when they operate in the region.Mahidol UniversityMedicineArticleSCOPUS10.1002/ca.23737