1.Patient selection
The two methods are mainly used for local transanal resection of low and high benign rectal tumors. The literature suggests that transanal endoscopic microsurgery (TEM) can be used to remove benign rectal and extrarectal masses such as neuroendocrine tumors, retrorectal cysts, anorectal-vaginal septal masses, and also to repair high rectovaginal fistulas, but there is limited experience with treatment of rare indications.TEM can also be used to treat anastomotic strictures, rectal prolapse, high external dilator fistulas, and pelvic drainage via the rectum.
The current indications for local excision have been expanded to include curative treatment of early-stage rectal cancer or palliative treatment, the latter of which primarily includes patients who refuse radical resection or who are not suitable candidates for surgery for progressive rectal cancer. Endoscopic polypectomy of occasionally detected cancers is an indication for local excision, especially in the case of clot-free polyps or when there is a particular concern about whether the margins are positive.
The use of transanal minimally invasive surgery (TAMIS) goes beyond local excision to include repair of rectourethral fistulas, distal rectal freeing, rectal foreign bodies, and most importantly, transanal TME using TAMIS.
The question remains as to which patients will benefit from TAMIS for early rectal cancer, and endorectal ultrasound (ERUS) and pelvic MRI are required for preoperative staging; ERUS is more sensitive for determining the presence of deep bowel wall invasion, while MRI is superior for evaluating rectal mesenteric lymph nodes and CRM.
Based on the imaging results, the NCCN guidelines clearly recommend that as a treatment option, the tumor should have the following characteristics: (1) movable and non-fixed; (2) less than 3 cm; (3) involving less than 1/3 of the peri-intestinal margin; (4) not exceeding the submucosa (T1), (5) moderately to highly differentiated; and (6) low risk histopathological features. On the other hand local resection should be avoided for lymphovascular invasion, perineural invasion and high-risk tumors with mucinous component.
2. Surgical technique
TEM was first proposed by Dr. Buess in 1980 and is mainly used to resect non-tipped rectal polyps that cannot be resected endoscopically. The authors also invented the surgical proctoscope and tools that facilitated the application of this new rectal surgical technique and ensured precision due to the use of binoculars and 3D for visualization.
The equipment includes a rigid proctoscope that can be fixed to the operating table, carbon dioxide compression, suction, and rectal pressure monitoring devices. The proctoscope has a diameter of 4 cm and is available in adjustable lengths of 12 cm and 20 cm, making it necessary to know the position of the damage in the rectum at the time of application. The removable panel of the proctoscope allows for easy insertion of long instruments, easy aspiration, and with the stereoscope the physician can see damage up to 6 times larger. Recently, some physicians have also preferred to link the device to laparoscopic video.
For anterior compromise, the patient should be in the prone position and for posterior compromise, the patient should be in the lithotomy position. Rectal inflation should be maintained at 10-12 mmHg to ensure that the rectal wall is distended and the tumor is exposed. A monopolar electric knife is used to free the tumor starting 10-15 mm from the tumor margin. For adenomas located in the perineal portion of the rectum, mucosal resection should be performed carefully to avoid entry into the abdominal cavity.
For extraperitoneal adenomas and all invasive carcinomas, the standard treatment should be total resection. Total resection followed by caudal anastomosis should also be performed for perirectal adenomas in the middle and lower rectum. Invasive cancers located in the lateral and posterior walls may be resected with some perirectal fat and 1 or 2 adjacent lymph nodes to check for metastases.
Local resection of low-risk perforations by TEM is possible and requires either a tumor in the posterior quarter of the bowel wall with the perforation 18-20 cm from the tumor or a tumor in the anterior or lateral wall with the perforation 15 cm from the tumor; tumors at the anal verge are not suitable. The resection bed is usually closed with 3-0 polydioxanone sutures and must be closed if it enters the peritoneal cavity, whereas it can be closed without sutures if the resection bed is below the peritoneal retrusion. The surgical specimen should be marked and positioned for pathologic evaluation of the margins.
TEM has not been accepted by all colorectal surgeons, mainly because of the high cost of the device and the steep learning curve. These drawbacks have encouraged surgeons to try other transanal procedures.
TAMIS emerged in 2009 and uses a multi-channel transanal single fixation, combined with common laparoscopic instruments such as laparoscopic cameras and standard laparoscopic carbon dioxide compression, for both intracavitary and extracavitary procedures. A review study showed a total of 8 TAMIS platforms for local resection of rectal tumors. Regardless of the platform, the principles of TAMIS are consistent, with the most obvious advantage being fixability.
3. Early postoperative outcomes
Few deaths have been reported in the literature, with deaths mainly related to tumor metastasis or the use of TEM for palliative treatment of progressive disease. Overall complications fluctuate from 6 to 31%, with a balanced distribution of benign and malignant tumors. Perioperative complications include bleeding and intraperineal perforation, the latter requiring open surgery. Postoperative bleeding ranges from 1-13% and mostly resolves spontaneously or requires blood transfusion. Approximately 5% of patients require reoperative management.
TAMIS is a relatively new technique, with results derived mainly from retrospective studies and case reports. 6 % of patients had positive microscopic margins and a 4 % recurrence rate at 6 and 18 months, as reported by Albert et al. Intraoperative complications were 8%, postoperative comorbidities were 19%, and only 1 patient required reintervention.
A review study of TAMIS resection showed an average damage size of 3 cm, an average distance from the anal verge of 7.6 cm, an overall margin positivity rate of 4.36%, a tumor incompleteness rate of 4.1%, and an overall complication rate of 7.4%.
4. Oncological findings
The goal of T1N0M0 rectal cancer treatment is to maximize oncologic outcomes and minimize the long-term impact on QoL. Long-term oncologic outcomes of conventional transanal local excision of T1 tumors show local recurrence rates higher than 29%. The oncologic outcomes of TEM remain controversial, with some studies showing local recurrence rates of less than 10%, while some studies confirming that local recurrence rates with TEM are lower but not significantly different from those with transanal local excision, and studies suggesting that local recurrence rates with TEM for T1 rectal cancer can be as high as 20.5%.
Tytherleigh and Bach showed that the depth of submucosal invasion was the main factor for recurrence, with sm1 recurrence rates being low and sm2-3 recurrence rates similar to those of T2. Local excision of pT1sm1, without lymphovascular invasion, and with a tumor diameter of less than 3 cm had a recurrence rate of less than 5%, while local excision of pT1sm2-3 had a recurrence rate of up to 20%, similar to that of T2. In addition to sm depth of invasion, tumor differentiation, vascular/perineural invasion, positive margins, lymphocytic infiltration, lymph node metastasis, and tumor outgrowth are all poor factors for local recurrence.
According to NCCN guidelines, the standard of care for T2N0M0 rectal adenocarcinoma is TME without adjuvant therapy, as the incidence of lymph node invasion in these tumors is 12-29%. For T2 tumors, simple local excision, local excision followed by postoperative CRT, and preoperative CRT followed by local excision are all being tried. TEM alone is not suitable for T2 or more deeply invasive rectal cancers; CRT after local excision has been disappointing, with a 45% local recurrence rate; neoadjuvant CRT followed by TEM after downstaging has proven to be more promising.
In Lezoche’s prospective study, 70 patients with T2N0 rectal cancer underwent TEM or CRT followed by laparoscopic radical resection; the length of stay, blood loss, and duration of surgery were better in the TEM group than in the radical resection group, and there was no significant difference in the incidence of comorbidities between the two groups. oncologic outcomes such as local recurrence, distant recurrence, overall recurrence, and likelihood of disease-free survival did not differ between TEM and radical resection. These results suggest that TEM is acceptable for patients with elective T2 and no lymph node invasion or distant metastases.
A review by Borschitz showed that local resection of T2-3 rectal tumors after neoadjuvant CRT resulted in complete pathologic remission ypT0 with 0% local recurrence and 4% systemic recurrence; ypT1 with 2% local recurrence and 7% systemic recurrence; ypT2 with 7% local or systemic recurrence; and in the absence of pathologic response, i.e., ypT3, with 21% local recurrence and 12% systemic recurrence.
A prospective study included 27 patients with lower rectal cancer treated with TEM after neoadjuvant CRT, ypT0-2, with a median follow-up of 15 months and a local recurrence rate of 15%. Lymphovascular invasion was an independent adverse factor for local recurrence, while tumor size, ypT status, T-decrease stage, lateral/radiographic margins, and degree of tumor regression were not significantly affected.
A review study comparing TEM with radical surgery for T1-2 rectal tumors concluded that TEM had a higher rate of local recurrence, but there were no statistically significant differences in overall mortality, overall survival, or risk of distant metastasis. There was bias in this study, such as no difference in recruitment of low-risk T1, high-risk T1, and T2 tumors.
5. Functional outcomes
As prolonged proctoscopy and surgery can distend the anal canal and damage the anal dilation muscles, leading to postoperative fecal incontinence. It has been shown that the reduction in anorectal pressure in patients treated with TEM is directly related to the duration of the operation, but does not change control scores or other anorectal parameters.
In the prospective Cataldo study, which included 41 patients, there was no increase in bowel control after TEM, and no significant differences were found in mean preoperative and postoperative incontinence severity scores, FIQL scores, number of bowel movements per day, or ability to delay bowel movements.
A recent study found significant improvements in FISI and FIQL scores after TEM. Patients themselves reported improved QoL after surgery, and this improvement may be attributed to rectal damage and excessive mucus production leading to fecal incontinence, which disappeared after removal of the damage. Furthermore, larger rectal tumors consistently induce an internal anal dilator reflex, reducing anorectal function.
In a 5-year study of functional outcomes and QoL parameters by Allaix et al, as in previous studies, pressure parameters such as anal resting pressure, rectal sensitivity, maximum tolerated volume, and fecal incontinence limits decreased at 3 months postoperatively and returned to preoperative levels at 12 months postoperatively. Anal squeeze pressure did not change significantly compared to preoperative levels, and Wexner incontinence scores and QoL scores increased in the early postoperative period and returned to preoperative levels at 5 years.
Only one study involving functional outcomes after TAMIS removal of rectal polyps showed good short-term outcomes, with no significant change in functional outcomes compared with facility-assisted TEM surgery.
6. Summary
Both TEM and TAMIS are safe, TEM should be used for T1, pathologically well characterized rectal cancer, neoadjuvant CRT before TEM remains controversial, anal function improves after TEM, and for TAMIS there are not yet adequate oncologic and functional outcomes.