Transanal endoscopic microsurgery (TEM) can be used as a curative operation for rectal polyps that are not amenable to colonoscopic resection.  In addition, it may be used in selected patients with rectal cancer. [2, 3] The following indications have been recommended by various surgical societies, including the American Society of Colon and Rectal Surgeons (ASCRS):
Lesions smaller than 3 cm; however, a study by Khoury et al reported the use of TEM to treat benign rectal lesions in the range of 5-8 cm 
Anatomically accessible lesions localized to the bowel wall (T1N0)
Lesions confined to the extraperitoneal region of the rectum
Lesions occupying less than 40% of the circumference of the bowel lumen; however, the use of TEM for giant circumferential rectal adenomas has been reported 
Well-differentiated or moderately differentiated lesions 
Lesions not associated with lymphovascular invasion
Management of rectovaginal ﬁstulas and anastomotic dehiscence management by means of TEM has also been reported. 
Definitive treatment of T2 or T3 rectal lesions with TEM is not recommended.
The use of TEM as palliative surgery for advanced rectal lesions is also acceptable for patients with comorbid conditions and disseminated disease who are otherwise unfit for more radical surgery. [19, 20]
Contraindications for TEM include the following:
Positive lymph nodes
Poorly differentiated tumor
Patient selection is the key consideration, and strict criteria are defined for appropriate candidates. Clinical evaluation and histological grades on preoperative rectal lesions often prove inaccurate in assessing the accurate staging and local spread.  The use of preoperative endoluminal ultrasonography,  pelvic magnetic resonance imaging (MRI), [24, 25] or both is imperative to ensure the most accurate assessment of tumor depth and nodal status. Despite these advancements in clinical staging, as many as 15% of tumors are staged inaccurately.
Standard preoperative preparation is required to prevent complications. Optimizing medical status for anesthesia, when indicated, is important. In addition, prophylaxis for deep vein thrombosis (DVT), a bowel preparation or preoperative rectal irrigation, and preoperative antibiotic prophylaxis are given. A Foley catheter is placed after induction of anesthesia.
Preoperative nutritional status may be the most significant predictor of outcomes. Every effort should be given to assess the patient's nutritional status and to improve it if needed.
TEM offers several advantages over conventional transanal excision. It provides better exposure, visualization, and access to reach lesions higher in the rectum than standard transanal excision. It is associated with less morbidity and quicker recovery time than a radical transabdominal approach.
Winde et al  conducted a prospective study and found that the operating time, blood loss, length of hospital stay, and analgesic requirement associated with TEM were significantly less than those associated with abdominal resection. The recurrence rates of tumors following TEM have been reported to range from 2.4% to 16%, [9, 11, 12, 13, 21, 27, 28] whereas the recurrences rates associated with conventional anal excision range from 4% to 36%. [29, 30, 31]
The major limitations of this procedure are that it requires expensive, highly specialized equipment and has a steep learning curve.  Thus, TEM should be performed by only skilled and experienced surgeons.
No randomized studies have yet compared TEM with traditional local excision and radical resection, owing to limited access to the specialized equipment. To deal with these issues, transanal minimally invasive surgery (TAMIS) was developed.
TAMIS offers several benefits over TEM. It requires minimal setup time, and the use of existing laparoscopic cameras and instruments offers a lower-cost alternative to TEM. Nonetheless, the learning curve is similar. In the hands of experienced laparoscopic surgeons, this technique also provides magnified visualization of tumors by the rectosigmoid junction.  Thus, it is a cost-effective,  innovative, safe, and feasible approach in highly selected patients. 
Although TAMIS is a promising approach, more comparative studies and randomized trials are required to establish the efficacy of the procedure in terms of cancer recurrence rates and overall survival.
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