For pulmonary nodule diagnosed as GGO on imaging, wedge resection and anatomic segmentectomy are both options if adequate margins can be obtained during surgery, and they can also provide patients with good prognosis and respiratory function status [3,4,5]. Occasionally, lung lesion may appear at the intersegmental boundary between two segments. In this case, resection of either segment is not sufficient to provide a negative resection margin. In our patient, for example, the lesion was a subcentimeter pure GGO next to the subsegmental border between S9 and S10b. Based on imaging features, early-stage lung adenocarcinoma is highly suspected, and after comprehensive evaluation, it is recommended that the patient needs surgery. After careful analysis of HRCT, we found that combined subsegmentectomy of S9 and S10b could provide safe margins and help to preserve subsegments of S10a and S10c. Finally, our surgical protocol was a combined subsegmentectomy for this patient.

In minimally invasive surgery, basal segmental resection of the lung is particularly challenging because lung structures are located deep within the lung parenchyma, anatomical variations may exist in different patients, and delineation of the intersegmental plane is difficult [6, 7]. As in our case, S9 and S10b are sub-segments inside the right basal segment. In previous studies, we have described in detail the technical procedure for single direction thoracoscopic basal segmentectomies using the transinferior ligament approach and the stem-branch method in detail [8]. However, in our case, the surgical procedure was much more complicated because two segments and sub-segments needed to be treated simultaneously and the target structure was located much deeper in right lower lobe. The intersegmental border between S7 and S10 was cut open along the intersegmental septa. Only after that we can approach the deep segmental and subsegmental hili of S9 and S10b. This was called the open-door process. We dissected along the stems of the basal bronchi and vasculature, tracking their branches and identifying them using a stem-branch approach based on their positional relationships obtained in preoperative planning. Finally, we successfully performed this complex combined basal subsegmentectomy. The advantage of the open-door method is that in the face of the intricate surgical field, it can be exposed to the operator as much as possible, so that the targeted lung segment resection can be completed more accurately and other lung segments that should be preserved can be avoided by mistake. The limitation of this technique is that it requires surgeons to be very familiar with the anatomical structure of the lungs, which can be challenging for beginners.

In conclusion, thoracoscopic combined basal subsegmentectomy of RS9 + 10b can be performed through the inferior pulmonary ligament approach by using the method of stem-branch in a single-direction manner.