**3. Abdomino-perineal resection (miles' operation): surgical procedure**

Abdomino-perineal resection was developed by Sir William Miles to reduce the burden of local recurrence in rectal cancer surgery. For decades, Miles' operation was considered the standard of care for all rectal cancer, being the only therapeutic option for these patients. However, the development of perioperative local and systemic therapies, a better understanding of the pathologic tumor dissemination mechanisms [27], and thanks to the development of less mutilating techniques, such as sphincter preservation, TME and LAR, the indication for abdomino-perineal resection have consistently decreased in the decades [28]. First indication of Miles' procedure is ultra-low rectal tumors in which a negative distal margin cannot be obtained. The concept of negative resection margin in rectal surgery has been widely debated among the surgical community. The milestone concept of the "5-cm margin" was challenged by the development of neoadjuvant therapy and the development of TME. To date, a distal resection margin of 1 cm is considered acceptable in case of

ultra-low rectal cancer, in the context of a multimodal treatment plan [29]. Moreover, Miles' procedure is indicated in case of involvement of external sphincter or levator ani complex. The abdomino-perineal resection is also the treatment of choice for anal squamous cell carcinoma, when chemoradiation therapy fails [30].

### **3.1 Surgical steps of miles' operation**

The intraperitoneal steps of the abdomino-perineal resection are equivalent to the steps of LAR; hence, you can refer to the appropriate section for it.

Once the dissection reaches the extraperitoneal rectum, TME is performed circumferentially, until the levator ani fascia is reached. It can be recognized because the mesorectum with adipose yellow tissue ends and the white appearance of the levator ani fascia becomes visible. The left colic vein is identified at its confluence in the IMV, and it is sectioned. From this point, the sigmoid mesocolon is sectioned. Now, the proximal section of the colon can be performed with the laparoscopic or robotic mechanical stapler, and the perineal phase can start. The surgeon and the assistant move to the perineal area, which is exposed by lifting patients' legs upward.

A retractor system is positioned, commonly the Lone Star (Lone Star Medical Products Inc., Houston, TX, USA) is used. The perianal region is sectioned circumferentially, 1 cm from the external sphincter margin. It is paramount for the oncological outcome of this procedure to remove the sphincter complex en bloc. The dissection is performed along the pelvic floor and the levator ani fascia. Posteriorly, the surgeon can start form the perineal raphe, from the coccyx along the margin of the sacrum, reaching the plane that was previously dissected in the intra-abdominal phase of the intervention. The dissection proceeds laterally by sectioning the levator ani muscles, and anteriorly, where the vagina or the prostate and urethra are found, in female and male, respectively. At this point, the circumferential perineal dissection is complete, and the surgical specimen can be extracted through the perineum. After accurate washing of the perineal area, the perineum is closed by layers. This is a crucial step, because abdomino-perineal resection often results in perineal wound defects. In addition to risk factors related to wound healing defects, such as smoking, advanced oncologic status and alcohol consumption, the introduction of neoadjuvant radiotherapy significantly increased the rate of wound defects [31] and neoadjuvant chemoradiation and wound complications are predictors of long-term perineal pain [32]. Wound dehiscence in Miles' procedure is the topic of numerous studies, searching for a valid standard closure method of the perineum. However, no ideal solution currently exists, and different approaches have been attempted with more or less success. Primary closure, with levator ani muscles reapproximated with multiple absorbable stitches, remains the most frequent technique. When this closure cannot be obtained, the use of biological or synthetic mesh can be considered [33]. Biological mesh appears to be a valid option, especially in terms of hernia prevention. Its role in preventing wound infections and dehiscence is less clear. Moreover, reconstruction with myocutaneous flap can be considered in selected cases [34]. Regardless the different options, abdominoperineal resection results often in wound defects that deeply affect patient's quality of life and morbidity, as well as hospitalization and healthcare-associated costs. When the wound fails to heal, a conventional negative pressure wound therapy (NPWT) device can be considered. In a recent systematic review, the use of NPWT represents an encouraging tool in reducing surgical site infection and wound dehiscence in these patients [35].

Once the perineum is sutured, pneumoperitoneum is reinduced. After accurate hemostasis, a surgical drain is placed in the pelvic cavity, the colic stump is brought to the abdominal wall – in the area identified and marked before surgery – and the colonostomy is created.
