Prevalence and anatomical characteristics of medial-basal segment in right lung

OBJECTIVES The anatomic features and surgical techniques focusing on the right medial-basal segment (RS7) are few reported. This study aimed to accurately define the new nomenclature and classifications of B7 anatomy, elucidate its prevalence and anatomical characteristics and summarize the surgical outcomes.METHODS Between August 2019 and February 2022, 5023 patients were admitted for pulmonary nodules. Their chest computed tomography images were obtained. All of the images were reconstructed in 3 dimensions. The RS7 were screened according to their new definition and statistically analysed for their anatomical characteristics.RESULTS The bronchovascular anatomy of S7 can be newly classified into 6 types: B7a type, B7p type, B7o type, B7t type, BX7a type and BX7t type. The B7 anterior to the inferior pulmonary vein (IPV) was B7a (a, anterior) (3617/5023, 72%). The B7 posterior to IPV was B7p (p, posterior) (306/5023, 6.1%). The B7 over IPV was B7o (o, over) (904/5023, 18%). The B7 through IPV was B7t (t, through) (7/5023, 0.14%). An abnormal origin of B7 was named the BX7 type. The BX7 anterior to IPV sharing a common trunk with B8 was named BX7a (a, anterior) (176/5023, 3.5%). The BX7 through IPV originated from B10 and was named BX7t (t, through) (13/5023, 0.26%). 0.2% (12/5023) of patients had the nodules in RS7 and underwent RS7 surgery.CONCLUSIONS The variation pattern of B7 is far more complex than expected. The results of this study can help surgeons better understand S7 and perform segmentectomies more accurately. The right medial-basal segment (RS7) is the smallest volume of all lung segments.