During the period between April 2013 and July 2019, a non-randomized controlled study was performed at two tertiary centers; Oncology Centre of Mansoura University and Policlinico Umberto Primo surgery department of SAPIENZA university of Rome after referral from the clinical oncology and nuclear medicine department. After diagnosis of ultralow rectal cancer, a written informed consent was obtained from patients after full explanation of the procedure, the likely outcome and the potential complications that may occur. Digital rectal examination was conducted to assess the distance of lower tumor margin from the anal verge and the anal tone. Anesthetic fitness and tumour markers (CEA) were assessed. Pelvis MRI and/or endorectal ultrasound (EUS), abdomen and chest CT scan and colonoscopy with biopsy were done for all cases. Re-evaluation after neoadjuvant chemo-radiotherapy by MRI and EUS. Inclusion criteria included a very low rectal cancer below 5 cm from the anal verge with normally continent and tumor-free external anal sphincter. Neoadjuvant treatment was given to all patients with T3 or node positive tumors. Exclusion criteria were T4, metastatic tumors and fecal incontinence. Fifty patients were excluded from the study (Fig.1). One hundred and ten patients with ultralow rectal adenocarcinoma, with matched age and sex (table 1), were non-randomly classified into two equal groups: the control group included 55 patents that underwent sphincter sparing by open ISR with TME (O-ISR Group) and the 2nd group included 55 patents that underwent Transanal minimally invasive ISR with TME (TAMIS Group).

Surgical technique:

In open ISR, the inferior mesenteric vessels were highly ligated. After full mobilization of the left colon and splenic flexure was done, the plane for TME was followed down in the pelvis superficial to the hypogastric fascia as low as possible to enter into the posterior intersphincteric plane. A non-endoscopic perineal phase was then initiated using an anal lone-star retractor to expose the anal canal. Both the mucosa and the muscular layer were incised 1cm below the tumor margin to transect the internal anal sphincter (IAS) and then closed by purse string sutures. The dissection continued between IAS and the external anal sphincter (EAS) starting posteriorly then laterally, where EAS is easier to identify, then anteriorly where the plane presented more adhesions with the urethra in male or vagina in female till reaching the abdominal dissection. Proximal division of the specimen started just below the site of inferior mesenteric vessels ligation and continued till division of the marginal artery at the site of the required anastomosis. The Specimen extraction and division was done extra-anal. A defunctioning ileostomy was done in all cases.

In TAMIS-TME, using a lone star retractor, the 1st step was to divide and close the anal canal by purse-string suturing to enter the intersphincteric plane. Using TEo platform (Karl Storz, Tuttilingen, Germany) (fig. 2) with a 4 cm size operating proctoscope diameter, Transanal endoscopic dissection was initiated and continued in the intersphincteric plane starting posteriorly then laterally. Partial or high ISR started at the dentate line to remove the upper half of IAS for ultralow tumors at 3 to 4.5 from anal verge. Total or low ISR started 1 cm below the dentate line, removing the whole of IAS for tumours below 3 cm from the anal verge. The endoscopic dissection continued in the same sequence as the control group along the levator ani. Then continue posteriorly till reaching as much as possible, then dissection continued laterally and anteriorly to reach the peritoneal reflection. Then, the laparoscopic phase was initiated to ligate the inferior mesenteric vessels and mobilize the splenic flexure and left colon. The peritoneal reflections were then divided to connect to the transanal part. The specimen was then extracted transanally and the Colo-anal anastomosis was done in two layers. A defunctioning ileostomy was done in all cases.