Although lobotomy is still recommended as a standard surgical procedure for lung cancer, segmentectomy that reveal farthest excision of pulmonary tumor and farthest preservation of normal lung tissues, has extended its surgical indications to some early stage lung cancer. Multi-center retrospective study found that the curative effect of segmentectomy for stage Ia lung cancer is similar to lobotomy, with no difference in recurrence rate and 5-year survival rate.7-9 it also be associated with fewer postoperative complications and better lung function.10,11 Cerebral embolism is a serious complication in the early postoperative period, occurring in 0.2–1.2% of surgical lung cancer cases.12 In this case, we present an rare case of cerebral embolism after segmentectomy. There was only one risk factor for cerebrovascular disease (long-term smoking history) before surgery, and relevant preoperative examination did not indicate the risk of cerebral embolism ( AF and Hypercoagulability). Electrocardiograph monitoring was also used all through the the first postoperative day, later a Holter electrocardiography was performed. We found no AF in the postoperative period. So we highly suspicious cerebral embolism was caused by a thrombus in the PVS because there were no other suspected sources.
Pulmonary vein directly connects to the left cardiac system. Because of this anatomical feature，thrombus in the PVS may leads to a cerebral thrombosis. Left upper lobectomy more likely to results in a longer pulmonary vein stump, which provides an explanation for the higher incidence of cerebral embolism after left upper lobectomy than after other types of lobectomy.3,13,14 Those researches indicated that the length of the PVS is an important factor affecting thrombus formation. In 2015, The pulmonary vein branching pattern of right upper lung was classified into four types by three-dimensional CT angiography.15 In this case, besides V2a and V2b, we did not find the independent draining veins of posterior segment (S2). Thus we suppose that it belongs to ‘‘anterior with central vein type, Iab type’’, which V1a and V1b drained into V. ant, V2a and V2b drained into V. cent. This variation is the most common pattern of right upper lung and present in 54 %-83.2 % of patients.15,16 To furthest preserve venous drainage of the residual segment, we didn't ligate the V2a and V2b. However the draining veins of posterior segment (S2) must have been divided at the time of dividing the parenchyma. A diagram of the venous anatomy is made according to the CT scan and intraoperative findings (Figure 1C). The PVS was thick enough for chunky thrombosis. However, because no lung enhanced CT scan was performed before and after surgery, how veins were divided is not exactly clear. So we consider this blind procedure might leave a long and irregular PVS. Furthermore, the intersegmental veins in separating intersegmental plane might also be injured by stapler.
Previous researches indicated that endothelial injury and immune cells plays an important role in thrombogenesis in the PVS.4,12 In our case, after dividing the draining veins with stapler, interlocking nails stabed into the endothelium and leaved behind in the tissue of PVS. Endothelial injury consequently activated the extrinsic pathway of the coagulation cascade and resulted in thrombus formation in the PVS. The pathological examination of the removed thrombus is composed of fibrin along with abundant neutrophils and erythrocytes, which also suggesting a inflammatory response caused by tissue injury (Figure 3).
According to our case, the surgical procedure seems to be an important factor for cerebral embolism after segmentectomy. We suggested that before divide the veins of posterior segment, the branches of the central vein should be cautiously isolated, with the subsegmental veins kept intact. In addition, we recommend using silk thread or hemolok instead of using surgical stapling device to divide the veins. Furthermore several researches have demonstrated that preoperative computed tomography 3-dimensional (3D) reconstruction helps in asserting the number, size, and direction of vessels.17-19 Checking the preoperative 3D model before operation may help the surgeon to perform a more accurately and safer dissection of the branches of the pulmonary vessels.
In conclusion, this is the first case of a cerebral embolism presumably caused by a thrombus in the PVS after segmentectomy for lung cancer. The thrombus might have been formed in the PVS due to the long and irregular PVS and tissue injury caused by surgical stapling device in the early postoperative period.