Patients and study design
After the study was approved by the Institutional Review Boards of Peking University First Hospital and Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College (2020149), patients with ultralow rectal cancer were prospectively recruited from December 2020 to January 2022. The inclusion criteria included the following: (1) male patients who were diagnosed with primary rectal cancer; (2) Rectal cancer with a distance of the tumor from the anal verge (AV) of 3–5 cm; (3) Body mass index (BMI) ≥28 kg/m2; (4) laparoscopic Distal Rectal Transection via transanterior obturator nerve gateway (TANG); (5) The preoperative anal function was evaluated normal. The exclusion criteria as following: (1) transection of the rectum via the conventional approach or transanal approach; (2) hand-sewn anastomosis; (3) palliative resection or confirmed distant metastasis; (4) Hartmann’s procedure or abdominoperineal resection; (5) combined resection due to adjacent organs invaded. Before the procedure, all patients signed an informed consent. The study was registered in ClinicalTrials.gov (number NCT05067413).
Surgical procedure
All surgical procedures were performed by two surgeons (X.W. and J.T.) with extensive experience. After general anesthesia induction, the patient was placed in the modified Lloyd-Davies position. A trans-umbilical incision was made, and a 10-mm camera port was placed. The pneumoperitoneum at insufflation pressures of 12 to 15 mmHg was used. The port position was similar to that used in nonobese patients. When splenic flexure mobilization was required, and additional 5-mm port may be inserted in the right upper quadrant when splenic flexure mobilization was required. Another 5-mm trocar (trocar F) was placed between the umbilicus and the symphysis pubis, which was used to retract the rectum cephalad when TANG approach was taken (Fig.1). The procedure was carried out as a conventional LaTME, including dissecting the inferior mesenteric artery (IMA) and vein, mobilizing the upper rectum and the sigmoid colon, and taking down the splenic flexure when necessary. Then, the dissection of the pelvic rectum was started.
Anterior peritoneal reflection (APR) dissection at the highest line
The upper rectum was pulled cephalad, revealing a “n”-shaped membrane bridge between the rectum and the bladder. An anterior incision line was made along the "n"-shaped membrane bridge rather than the anterior peritoneal reflection (APR) or 1~2 cm above the APR, with seminal vesicle glands visible on the caudal side of the incision line (Fig2, Fig3a).
Suspending the APR to enlarge the operating space of the anterior rectal wall
After incising the highest line of the APR, the peritoneal tissue was suspended ventrally to the anterior abdominal wall with a transabdominal suture to maximize the free space of the anterior rectal wall, which facilitates the exposure of the Denonvilliers’ fascia and the protection of the neurovascular bundle (NVB). The anterior operation space of the pelvis inlet before incision (Fig.3b), after suspension (Fig.3c) and after incision and suspension (Fig.3d) were measured and recorded.
Traction and counter-traction applied with a cotton tape
To provide better exposure, a cotton tape was tied around the rectum to facilitate the upward retraction. Adequate continuous traction and counter-traction enable the identification of the correct dissection plane. When dissecting the left lateral rectal ligament (LRL), the assistant's left-hand clamp grasped the cotton tape to pull the sigmoid colon toward the right upper abdomen, and the right-hand forceps should lift the seminal vesicles and prostate to provide countertraction (Fig.4a,4a’). Likewise, when the right LRL was dissected, the cotton tape was used to push the bowel toward the left upper abdomen (Fig.4b,4b’).
Resection of the pelvic rectum on tripartition
The pelvic rectum dissection can be divided into three parts: seminal vesicle zone, prostate zone and intersphincteric zone. In each zone, we recommend performing the dissection firstly in the posterior, then in the anterior, and finally in the lateral of the rectum (Fig.5a). In the seminal vesicle zone, dissection starts from the posterior aspect of the rectum and proceeds along the retrorectal space. At the S3 to S4 level, the pre-hypogastric nerve fascia fuses with the rectal visceral fascia to form the rectosacral fascia (RSF). The two layers of fascia were also gradually fused in the lateral direction with space narrowing. Once the anterior mobilization was completed, the triangular structure of LRL can be easily identified (Fig.5b). When taking the posterior-to-lateral-to-anterior sequence, there might a higher probability to lead to the wrong plane and NVB injury (Fig.5b, designated by blue dotted arrow). In the prostate zone, the Waldeyer’s fascia was firstly incised to enter the supralevator space, and then dissected along the posterior space of Denonvillier’s fascia. The middle rectal arteries arising from the internal iliac artery may be identified in this zone, which were complicated with NVB and prone to bleeding (Fig.5c). The intersphincteric plane between the puborectalis and the internal sphincter was cautiously dissected when coloanal anastomosis or intersphincteric resection was necessary.
Trans-anterior Obturator nerve gateway to transect the distal rectum
Intracorporeal transection can be rather difficult in obese male patients due to narrow pelvic width and limited stapler articulation. The TANG approach has proven to be an alternative approach to transect the rectum more distally, more vertically with the less stapler cartridges for ultralow rectal cancers. For obese male patients, the gateway was constructed as follow: the right lateral pelvic peritoneum was incised to expose the Retzius space and vesicohypogastric fascia. After the obturator vessels and nerve were identified, the gateway was subsequently opened through the total mesorectal excision (TME) compartment and the lateral compartment. The flexible linear stapler was placed via TANG approach to transect the distal rectum vertically.[7]The pelvic inlet of TME compartment, Outlet of TME compartment, length between inlet and outlet and inlet of TANG compartment were measured during the operation (Fig.6a). The dominant angle refers to the theoretical rotation angle difference of linear stapler, which is calculated according to the trapezoid size and geometric model (Fig.6b).
Data collection and follow-up
The clinicopathological data, including age, BMI, ASA, Neoadjuvant therapy, Pathologic stage, tumor size, histopathological data and hemoglobin (Hb), albumin (Alb) and carcinoembryonic antigen (CEA) levels, were collected. The operation-related characteristics were recorded, included: 1) operation time, intraoperative blood loss, preservation of LCA, preventive ileostomy, anastomotic height from AV, distal resection margin; 2) pelvic width and calculated dominant angel: suspended inlet, highest incision inlet, length of increased inlet, intraoperative measurement of pelvic width, time of TANG building, dominant angle; 3) short-term outcomes: postoperative complications, obturator nerve injury, re-operation, mortality rate, postoperative hospital stay and genitourinary dysfunction. The patients were advised to undergo examinations every three months for the first year and then every six months in the following year.