降结肠系膜旋转不良（PDM）是指妊娠第五个月末降结肠系膜未能与后方及侧方的壁腹膜融合，导致降结肠内移或右移，降结肠系膜腹侧粘连和缩窄，肠系膜下动脉（IMA）右移、其分支多支共干比例高、肠系膜下静脉紧邻边缘血管弓等解剖学特征。结直肠癌合并PDM可能导致腹腔镜手术难度增大、结肠缺血和术后吻合口漏风险增加。本文就PDM的胚胎学成因、解剖学特征、诊断及分型、PDM合并结直肠癌的腹腔镜手术策略，结合笔者实践展开探讨。掌握PDM的结肠走行变异、粘连特点和血管分支模式，提高术前诊断率，做好术前规划，术中应注意保护拟切端肠管血运。在腹腔镜结直肠癌手术时，右半结肠癌应注意分离回结肠系膜与左半结肠之间的粘连，左半结直肠癌合并PDM行D3手术时，采取保留IMA根部的第253组淋巴结清扫，可能有助于减少肠缺血的风险。

Persistent descending mesocolon(PDM) refers to the failure of the descending mesocolon to fuse with the lateral or posterior abdominal wall peritoneum by the end of the fifth month of pregnancy. This condition is characterized by the descending colon moving towards the midline or to the right, adhesions and shortening of the descending mesocolon, rightward displacement of the inferior mesenteric artery (IMA) with a higher incidence of multiple branches sharing a common trunk, and the inferior mesenteric vein lying closely adjacent to the marginal vessels, among other anatomical features. PDM may increase the difficulty of laparoscopic colorectal cancer surgery and the risk of colonic ischemia and postoperative anastomotic leakage. Here we discuss the embryological etiology, anatomical characteristics, diagnosis and classification, and strategies for laparoscopic colorectal cancer surgery in the presence of PDM, based on the author's practical experience. Understanding the variations in the course of the intestinal tract, adhesion characteristics, and vascular branching patterns of PDM can improve preoperative diagnostic rates, facilitate preoperative planning, and ensure the protection of blood supply to the intended resection margins during surgery. During laparoscopic colorectal cancer surgery, attention should be paid to adhesiolysis between the descending mesocolon and the ileocecum in right-sided colon cancer cases. In left-sided rectal cancer cases with concomitant PDM undergoing D3 surgery, preserving the origin of the inferior mesenteric artery and dissecting the No. 253 lymph nodes may reduce the risk of colonic ischemia.