Prevalence and anatomical characteristics of the left medial basal pulmonary segment: a retrospective cohort study using three-dimensional computed tomography reconstruction.

Objectives: The left medial basal pulmonary segment (S7) has been largely overlooked in surgical literature due to the common belief that it is typically absent. This study aimed to determine the prevalence of left S7, identify its anatomical characteristics and evaluate outcomes in patients undergoing S7 segmentectomy.

Methods: We retrospectively analysed 1440 patients who underwent thoracoscopic segmentectomy for ground-glass opacity in the left lower lobe between January 2019 and February 2022 at our hospital. Three-dimensional computed tomography bronchography and angiography (3D-CTBA) images were reconstructed for all patients. The principal outcome was the prevalence and anatomical variation of S7. Secondary outcomes included surgical feasibility and short-term outcomes of S7 segmentectomy.

Results: Six types of left medial basal bronchus (B7) were identified. Type 1: B7 arose from B8 (61.4%); type 2: B7 arose higher than B8-B10 (6.3%); type 3: B7 arose from B9 (5.5%); type 4: B7 arose from both B8 and B9 (1.6%); type 5: B7 arose from both B8 and B10 (0.8%); type 6: B7 was absent (24.4%). Nine (0.6%) patients with nodules in S7 underwent successful thoracoscopic segmentectomy, with no major complications or conversions to lobectomy.

Conclusions: Left S7 is present in approximately 75% of patients. The complex branching patterns of B7 identified highlight the importance of preoperative 3D-CTBA for accurate surgical planning. Our findings suggest that left S7 segmentectomy is feasible and safe when performed with precise anatomical understanding, expanding surgical options for patients with early-stage lung cancer in this segment.