1. Patient selection
Transanal total mesorectal excision (TaTME) is primarily used to overcome the technical challenges encountered in laparoscopic TME. Most physicians believe that patients with pelvic stenosis, visceral hypertrophy, or large tumors are suitable for this technique. taTME is suitable for mid to lower rectal cancer. A review study concluded that the indication for TaTME is rectal adenocarcinoma, and contraindications include T4 tumor invasion of the vagina or prostate, no objective response to preoperative CRT of the tumor, tumor invasion of the EAS or levator muscle, BMI greater than 35, recurrent patients, and those who cannot tolerate pneumoperitoneum.
2.Surgical technique
TaTME is a new technique that allows transanal free rectum from distal to proximal. Technical proponents believe that TaTME facilitates radical resection in a narrow or fixed pelvic cavity and guarantees a negative distal margin. Multiport laparoscopy, small-bore laparoscopy, or single-port laparoscopy can assist TaTME. some authors believe that the abdominal portion should be performed first, followed by the transanal portion, while others prefer to perform both simultaneously. Different types of platforms and even robotic TaTME have been reported.
The standard technique consists of two parts: abdominal surgery and transanal surgery. Most abdominal procedures use high ligation of the submesenteric vessels and freeing of the left colon and splenic flexure. The stool is drained through an ileal collaterals stoma, unless a permanent stoma is required.
In transanal surgery, the rectum is explored after placement of a self-fixing puller, and if the tumor is 3 cm above the anal verge, an interanal spreaders are excised after electrocautery incision via the dentate line. After complete resection of the entire rectal wall, the rectum is closed with purse-string sutures and the anterior segment of the anal canal is incised transanally for 4-4.5 cm for transanal platform placement, and CO2 is pressurized to 10-12 mmHg, which is also appropriate for the rest of the resection.
The anterior sacral plane is entered, the rectal mesentery is freed, and resection is performed cephalad along the avascular anterior sacral plane, consistent with the principles of TME. The resection continues medially, laterally, and anteriorly, freeing the perirectal margin, at which point rectal retraction should be avoided so that lateral resection does not become difficult. The sigmoid colon is freed after seeing the peritoneal reflex, and the two groups collaborate to complete the operation. The device and the specimen are removed via the anus, and the sigmoid colon should be resected close to the vascular root, and mesenteric and marginal artery dissection is completed simultaneously with the specimen dissection, and the proximal sigmoid colon and distal anorectal cuff anastomosis are performed.
For low to medium rectal tumors, after posing and self-fixing retraction, the platform is entered transanally and fixed in the anal canal, and the rectal mucosa is ruffled and sutured to keep it away from damage. The whole rectal wall was transected endoscopically, and the distal rectal mucosa was again sutured with pack sutures. The rectal mesentery was freed as above. The specimen was removed transanally, the colon was resected, and the rectal anastomosis was performed using an EEA 33 mm circular anastomosis.
3. Early postoperative results
No deaths were reported in the only review, and complications were 22.7%, mainly infectious complications such as pelvic abscesses and anastomotic fistulas. Another study showed postoperative complications of 26% and anastomotic leak of 5.3%.
4. Oncologic outcomes
The oncologic results of TaTME were obtained from non-randomized retrospective studies. the overall quality of TME was satisfactory. One study showed 10/136 positive CRMs, and most studies reported ≥ 12 lymph nodes acquired. A recent study showed 47 complete resections of the rectal mesentery, 9 near complete resections, 12 median lymph nodes, median radiographic and distal margins of 8 and 10 mm, respectively, 5.3% CRM involvement, 53 R0 resections, and a median overall survival of 96.4% at a median follow-up of 29 months.
Another review has shown the reproducibility of TaTME surgery, with positive CRM marginal results lower than APR and equal to LAR, comparable to rectal mesenteric resection and lymph node dissection. Although more studies are needed to confirm these results, results are now available showing a significantly higher rate of intact rectal mesenteric resection with TaTME than with laparoscopic TME.
5. Functional outcomes
Only one study reported a functional study, with 52/56 patients requiring a colostomy after ileostomy closure, 3 with severe fecal incontinence, and the remaining 49 without a stoma, with a median Wexner score of 4, 14 with a score of more than 7, and 13 reporting difficulty with fecal truncation and emptying.
6. Summary
While TaTME is safe and feasible, the expert consensus is that when TaTME is used for curative purposes, a standard board-approved protocol needs to be available and a colorectal surgeon experienced in minimally invasive or transanal endoscopic procedures is required to perform TaTME. More studies are needed to evaluate oncologic and functional outcomes.
ISR for rectal tumors in T1-3, within 30-35 mm of the anal verge, with or without IAS invasion, is technically feasible, has an acceptable complication rate, and has similar oncologic outcomes to LAP and APR, with acceptable QoL, whereas APR is more commonly used for locally progressive tumors.
APPEAR is a promising technique with the advantage of not damaging the dilation muscle, but it has significant complications as fewer studies have addressed it, and long-term oncologic and functional outcomes are unknown.
TEM and TAMIS are a treatment option for T1 rectal tumors, and according to the NCCN guidelines tumors need to meet a number of criteria. If the pathology report shows submucosal invasion as sm2-3, patients should be told that locally resected pT1sm2-3 tumors with a 20% local recurrence rate should be treated as T2 tumors.
The recommended treatment for T2 rectal tumors is TME without adjuvant therapy. Although still controversial, preoperative CRT followed by TEM/TAMIS appears to be a promising approach for the treatment of T1sm2-3 or T2 tumors.
TaTMEs need to be performed only when a standard protocol approved by the committee is available and by a colorectal surgeon experienced in minimally invasive or transanal endoscopic procedures.
In addition to selecting the correct procedure based on the patient’s tumor characteristics, care should be taken to screen patients who do not require surgery. The “watchful waiting” approach proposed by Habr-Gama et al. is suitable for patients who have achieved complete clinical remission after neoadjuvant CRT, and this approach has achieved 5-year overall survival, and 92% of raw disease-free survival.