Reverse watershed method applied to thoracoscopic S9 segmentectomy: a retrospective study

For early-stage non-small-cell lung cancer (NSCLC), particularly tumors less than 2 cm in diameter, sublobar resection-including wedge resection and segmentectomy-is often the preferred surgical approach. The difficulty of pulmonary segmentectomy lies in identifying the intersegmental planes. Among all segmental resections, S9 resection is considered one of the most challenging due to the cone-like structure of the S9 segment and its deeply hidden segmental portal. To address this, we designed a modified technique that identifies the S9 segmental plane by temporarily and sequentially occluding A9 + 10 and V10 intraoperatively, thereby avoiding dissection of the S9 segmental hilum. This method, which differs from traditional intersegmental plane identification based on occluding individual segmental arteries or veins, is termed the reverse watershed method. We compared it with the modified inflation-collapse method to explore its advantages and disadvantages in S9 resection.

We retrospectively collected 87 cases of thoracoscopic S9 resection. Patients were categorized into two groups based on the method used for intersegmental plane identification: the modified inflation-collapse method group and the reverse watershed method group. Various preoperative, intraoperative, and postoperative indicators were compared between the two groups.

Eighty-seven patients with surgical data were included: 49 operated using the modified inflation-collapse technique and 34 using the reverse watershed method. Preoperative baseline characteristics showed no significant intergroup differences. Intraoperatively, the reverse watershed method group exhibited a reduced mean operative duration (p < 0.01) and diminished intraoperative blood loss (p < 0.01). Postoperatively, this group showed a lower incidence of air leaks, decreased chest tube drainage volume, and reduced pain severity compared to the modified inflation-collapse group. No significant differences were observed in the duration of chest tube retention, length of postoperative hospitalization, or loss of lung function at the 3-month postoperative review.

Compared to the modified inflation-collapse technique, the reverse watershed method reduces operative time and intraoperative bleeding in S9 resection, decreases the incidence of postoperative air leaks, and results in comparable preservation of lung function.