Unilateral Lung Agenesis: A Systematic Review of Prevalence, Anatomical Variants, and Clinical Implications

Background: Unilateral lung agenesis (ULA) is a rare congenital anomaly characterized by the complete absence of one lung, often accompanied by cardiovascular, skeletal, or gastrointestinal malformations. Despite its clinical significance, evidence of prevalence, anatomical variants, and outcomes remain fragmented. This systematic review aimed to synthesize existing data on ULA's prevalence, anatomical classifications, diagnostic approaches, and clinical implications. Methods: Following PRISMA 2020 guidelines, five databases (MEDLINE, Web of Science, CINAHL, Scopus, and EMBASE) were searched from inception to January 2024. Inclusion criteria encompassed case reports, case series, and observational studies on ULA in humans. Risk of bias was assessed using the Joanna Briggs Institute (JBI) checklist. Narrative synthesis was performed due to methodological heterogeneity. Results: Thirty-two studies (137 participants) were included. Right-sided ULA predominated (58%), with poorer prognoses due to mediastinal distortion. Cardiovascular anomalies (40%) were the most common comorbidity. Diagnostic modalities included chest radiography (85%), CT (70%), and bronchoscopy (25%). Schneider-Boyden scale was used to classify the included studies. Risk of bias assessment revealed 65% of studies as low risk, 28% as moderate, and 7% as high risk. Conclusions: ULA necessitates multidisciplinary management, particularly in cases with associated anomalies. Left-sided ULA correlates with better outcomes, emphasizing the role of early imaging. Limitations include reliance on case reports and inconsistent reporting of anatomical variants. Future research should adopt standardized classifications and longitudinal designs to improve evidence quality. Open science framework (OSF): 10.17605/OSF.IO/XVQSP.