[Anatomical classification of and laparoscopic surgery for left-sided colorectal cancer with persistent descending mesocolon].

Objective: To investigate anatomical morphology and classification of persistent descending mesocolon (PDM) in patients with left-sided colorectal cancer, as well as the safety of laparoscopic radical surgery for these patients. Methods: This is a descriptive study of case series. Relevant clinical data of 995 patients with left colon and rectal cancer who had undergone radical surgery in Fujian Medical University Union Hospital from July 2021 to September 2022 were extracted from the colorectal surgery database of our institution and retrospectively analyzed. Twenty-four (2.4%) were identified as PDM and their imaging data and intra-operative videos were reviewed. We determined the distribution and morphology of the descending colon and mesocolon, and evaluated the feasibility and complications of laparoscopic surgery. We classified PDM according to its anatomical characteristics as follows: Type 0: PDM combined with malrotation of the midgut or persistent ascending mesocolon; Type 1: unfixed mesocolon at the junction between transverse and descending colon; Type 2: PDM with descending colon shifted medially (Type 2A) or to the right side (Type 2B) of the abdominal aorta at the level of the origin of the inferior mesentery artery (IMA); and Type 3: the mesocolon of the descending-sigmoid junction unfixed and the descending colon shifted medially and caudally to the origin of IMA. Results: The diagnosis of PDM was determined based on preoperative imaging findings in 9 of the 24 patients (37.5%) with left-sided colorectal cancer, while the remaining diagnoses were made during intraoperative assessment. Among 24 patients, 22 were male and 2 were female. The mean age was (63±9) years. We classified PDM as follows: Type 0 accounted for 4.2% (1/24); Type 1 for 8.3% (2/24); Types 2A and 2B for 37.5% (9/24) and 25.0% (6/24), respectively; and Type 3 accounted for 25.0% (6/24). All patients with PDM had adhesions of the mesocolon that required adhesiolysis. Additionally, 20 (83.3%) of them had adhesions between the mesentery of the ileum and colon. Twelve patients (50.0%) required mobilization of the splenic flexure. The inferior mesenteric artery branches had a common trunk in 14 patients (58.3%). Twenty-four patients underwent D3 surgery without conversion to laparotomy; the origin of the IMA being preserved in 22 (91.7%) of them. Proximal colon ischemia occurred intraoperatively in two patients (8.3%) who had undergone high ligation at the origin of the IMA. One of these patients had a juxta-anal low rectal cancer and underwent intersphincteric abdominoperineal resection because of poor preoperative anal function. Laparoscopic subtotal colectomy was considered necessary for the other patient. The duration of surgery was (260±100) minutes and the median estimated blood loss was 50 (20-200) mL. The median number of No. 253 lymph nodes harvested was 3 (0-20), and one patient (4.2%) had No.253 nodal metastases. The median postoperative hospital stay was 8 (4-23) days, and the incidence of complications 16.7% (4/24). There were no instances of postoperative colon ischemia or necrosis observed. One patient (4.2%) with stage IIA rectal cancer developed Grade B (Clavien-Dindo III) anastomotic leak and underwent elective ileostomy. The other complications were Grade I-II. Conclusions: PDM is frequently associated with mesenteric adhesions. Our proposed classification can assist surgeons in identifying the descending colon and mesocolon during adhesion lysis in laparoscopic surgery. It is crucial to protect the colorectal blood supply at the resection margin to minimize the need for unplanned extended colectomy, the Hartmann procedure, or permanent stomas.