Arterial Branching Patterns Supplying the Left Upper Lobe of the Lung and Their Incidence: A Systematic Review

<b>Objective</b>: The arterial anatomy of the left upper lobe exhibits the greatest variability in branching patterns among all pulmonary lobes. This lobe is commonly described as having four segments: the fused apicoposterior segment (S1+2), the anterior segment (S3), and the lingular segments (S4 and S5). Each segment may contain subsegments with distinct vascular supplies. Although several studies have examined patterns and diversity of branching, a comprehensive assessment of the incidence of these variations has not yet been performed. <b>Methods</b>: This systematic review was conducted in accordance with a protocol registered in PROSPERO (CRD42024546839). The search was performed between December 2023 and February 2024. A systematic search of databases was carried out to identify publications describing arterial branching patterns supplying the left upper lobe of the lung in adults. Furthermore, we collected and analyzed data on the relationship between the different origins of the lingular arteries and the corresponding bronchial and venous patterns. The AUQA tool was used to perform bias assessment. Data extraction included study characteristics, participant demographics (listed in AUQA), and anatomical variables based on the Yamashita classification of LUL arterial patterns and the number of branches supplying the left upper lobe. <b>Results</b>: In total, 15 publications were included (3313 cases). Lobar vasculature was firstly categorized more broadly, analyzing the number of branches from the left pulmonary artery, which supplies the left upper lobe, most commonly four branches. Then, analysis based on the Yamashita classification was performed, and Type A (A3, A(1+2) a+b, A(1+2) c) was established as the most common variant. <b>Conclusions</b>: The left upper lobe is most commonly supplied by four different arterial branches, followed by three and five. Differences in arterial branching patterns between Asian and Western populations may represent an important distinguishing factor. According to Yamashita's classification, Type A (A3, A1+2a+b, A1+2c) is the most frequently observed pattern. Further attention should be directed to the relationship between the presence of a common trunk and the origin of the lingular arteries. Detailed knowledge of this anatomy remains fundamental for segmental thoracic surgery.