Introduction
Surgery for low rectal cancer is technically challenging. Traditionally, low rectal cancers were treated with either transanal excision, at the risk of compromising oncologic outcomes, or abdominoperineal resection (APR), which led to a significant impact on a patient’s functional status and quality of life. Several developments have increasingly allowed surgeons to treat low rectal cancers using sphincter-sparing, minimally invasive approaches while at the same time improving long-term oncologic outcomes. First, the introduction of total mesorectal excision (TME) by Dr. Heald in 1979 revolutionized rectal cancer operative technique, resulting in significant decreases in local recurrence. Next, the increased use of neoadjuvant chemoradiation led to downstaging of many primary tumors, further decreases in local recurrence, and an increased rate of sphincter preservation. Advances in minimally invasive surgical techniques have decreased the overall morbidity and mortality of rectal cancer surgery with equivalent oncologic outcomes. , Finally, the advent of transanal endoscopic microsurgery (TEM) provided a platform for transanal surgery and served as the basis for the development of transanal minimally invasive surgery (TAMIS).
Despite improvements in the management of rectal cancer, challenges still exist in treating very low and early-stage rectal cancers. The rapid development of a new generation of more advanced robotic platforms, capable of both improved abdominal and transanal access, combined with the natural adoption of robotics into traditional transanal surgery platforms, has provided new opportunities for minimally invasive approaches to these difficult tumors.
New developments in transanal excision of low rectal cancers
Indications for transanal excision
Due to an aging population, improvements in colorectal cancer screening, and advances in surgical technique, the use of local excision as the primary treatment for rectal neoplasia continues to increase. Local excision is indicated for nearly all benign endoscopically unresectable lesions of the rectum that are accessible by a transanal route. Additionally, current American Society of Colon and Rectal Surgeons (ASCRS) and National Comprehensive Cancer Network (NCCN) guidelines endorse full-thickness local excision as an acceptable, curative-intent treatment option in select patients with cT1N0 rectal cancers and favorable histologic features. , Contraindications to local excision and indications to consider TME after local excision include tumor invasion into the lower third of the submucosa (SM3) or >cT1 on preoperative imaging, cN+ tumors, tumor size greater than 3 cm, lymphovascular invasion, positive margins, or poorly differentiated tumors. , Furthermore, the ASCRS guidelines also include tumor budding and perineural invasion as histology features that should typically prompt a discussion of TME if initially locally excised. From a technical perspective, lesions should be anywhere from 2 to 15 cm from the anal verge and no more than 30% to 50% of the circumference of the lumen to be considered for local excision.
In accordance with multiple studies including the ACSOGZ6041 trial, both NCCN and ASCRS discuss local excision of cT2N0 rectal cancers in patients who have undergone neoadjuvant chemoradiation as an alternative to TME. , , , However, neither society routinely recommends this approach until more data is available regarding long-term outcomes. , Adding a further layer of complexity to the discussion of local excision of rectal cancers is the increasing role of total neoadjuvant therapy (TNT) and organ preservation in locally advanced tumors. It remains to be seen what the ultimate role of local excision will be as both primary treatment of more advanced lesions or as salvage therapy after an initial complete clinical response.
The evolution of transanal surgical platforms in low rectal cancer—from TEM to r-taTME
The development of TEM in the 1980s greatly improved transanal access for the resection of rectal neoplasms, and quickly demonstrated superior outcomes compared to traditional transanal excision with reduced tumor fragmentation, less margin positivity, and decreased local recurrence. , Subsequently, TAMIS, developed in 2009, in conjunction with the first flexible transanal platform, GelPOINT Path (Applied Medical, Rancho Santa Margarita, CA), further expanded accessibility to advanced, transanal surgery. Rapid adoption of TAMIS occurred globally, most notably because standard widely accessible laparoscopic instrumentation familiar to most surgeons are utilized, and the significant capital investment and expertise required for TEM are avoided. Moreover, TAMIS has been shown to produce equivalent surgical outcomes as TEM with significantly shorter setup and operative times.
TAMIS has been demonstrated to have a short learning curve of 10 cases. However, early adopters yearned for improved ergonomics, avoidance of instrument collisions, and improvements in the platform’s ability to perform fine dissection and endoluminal suturing needed to perform more complex operations, such as repair of rectourethral fistula. Combining the improvements in transanal access with the rapid dissemination of robotic colorectal surgery provided an organic pathway to further innovation.
TAMIS was further refined when in 2010 the first robotic transanal surgery was completed in a cadaver by Atallah et al. The first robotic TAMIS (rTAMIS) was completed for rectal cancer in 2012 by Atallah et al. on a uT1uN0 lesion. Several further studies have demonstrated the feasibility and effectiveness of this platform with equivalent outcomes to conventional TAMIS. However, more widespread adoption was limited due to the technical challenges of the da Vinci Si, including difficult docking. A more recent uptake of rTAMIS has occurred with the dissemination of the much more maneuverable da Vinci Xi robotic platform.
Patient selection for rTAMIS is similar to that of traditional TEMS and TAMIS. All patients undergoing TAMIS for malignant indications should undergo a comprehensive staging evaluation including colonoscopy to rule out synchronous lesions, CT chest, abdomen, and pelvis (C/A/P) to evaluate for metastatic disease, pelvic MRI to determine and confirm the presence of cT1 disease, and tumor marker testing. Rigid proctoscopy and physical exam should be performed to confirm the location of the lesion as this is essential for operative positioning. Even in patients undergoing TAMIS for suspected benign indications, strong consideration should be given to performing preoperative pelvic MRI in all cases to confirm the absence of invasive disease and occult nodal metastasis. MRI after local excision obscures the ability to accurately assess initial depth of invasion and nodal status, and may result in overtreatment of early-stage rectal cancers due to the inability to differentiate reactive lymph nodes from those with nodal metastasis.
In the operating room, the patient’s positioning is determined based on several factors. These include the location of the lesion, access to the airway, assistant access, and the ergonomics of the robotic system. The patient should be positioned such that the lesion is dependent to facilitate the easiest dissection. The procedure has been successfully performed in prone jack-knife, lithotomy, and lateral decubitus positions. , Once the patient is sedated and properly positioned, a digital rectal exam should be performed to ensure that the lesion is proximal enough that the transanal access port can be placed without covering the lesion, usually 2 cm or more above the dentate line. Lesions lower than this may be amenable to transanal excision with the initial distal dissection started transanally and carried proximally until the transanal access port can be placed.
For transanal robotic access, a flexible transanal platform must be used, most commonly the GelPOINT Path. Up to five instruments can be placed and a greater separation of the instruments, allowing the surgeon to work with uncrossed instruments which prevents arm clashing. The fulcrum (black line) of the robotic trocars should be placed at the level of the anal sphincters to minimize trauma due to stretch from the working arms. ,
rTAMIS is a new technique and currently there is not a significant body of literature regarding its use. A recent study by Lee et al. demonstrates no difference in the rate of R0 resection or 30-day complications between robotic and laparoscopic TAMIS. Their study does show a higher direct cost for those undergoing rTAMIS vs. TAMIS. At this time there are no studies evaluating the long-term oncologic outcomes of rTAMIS.
While rTAMIS is effective in the management of polyps and early-stage rectal malignancies, T2 lesions and other locally advanced tumors are recommended to undergo TME for curative-intent surgery. , Building on the foundations of TAMIS and TEM, taTME was developed in part to overcome limitations of transabdominal surgery in very low rectal cancers. Since Sylla et al. first described taTME in 2010, colorectal surgeons have had access to a new, minimally invasive technique to approach the TME of low rectal cancers. Naturally, with the development of robotic surgery, surgeons adopted the robotic platform for taTME.
To date, there has not been widespread acceptance of r-taTME or large studies to support its use. However, case series appear to have favorable results. In their initial series Ruiz et al. performed r-taTME in five patients with stage II/III rectal cancers less than 6 cm from the anal verge. All operations were completed with negative margins and complete TME specimens. Similarly, Ye et al. recently reported a series of 13 patients undergoing r-taTME for low rectal cancers. All patients had complete, or nearly complete TME specimens with similar total, and transanal operative times to conventional TAMIS.
The adoption of robotics in low rectal cancer has opened the door to perform increasingly complex operations from a transanal route. Both for local excision and TME, current data appear to support its use; however, further studies are needed to clarify role of robotic transanal surgery. Furthermore, currently available generations of robots are still limited by instrument collisions, challenges in docking, and port configuration through the transanal access port. In response to these challenges, new, lower-profile single-port robots have simultaneously evolved specifically to improve access in transanal applications. These new platforms are detailed below.
New robotic transanal platforms for low rectal cancer
Medrobotics flex colorectal drive
The Flex system was developed by Medrobotics as a semi-robotic platform for natural orifice surgery. The platform was initially used for transoral robotic surgery and was later approved for colorectal transanal applications. The system comprises two separate carts ( Fig. 53.1 ): the Flex Cart and the Flex Console. The Flex Cart is mounted to the bed for the procedure and contains a robotically controlled articulating endoscope capable of traversing a 180-degree nonlinear course ( Fig. 53.2 ). Once placed at the target lesion, the scope’s position can be locked. Two working channels accept 3.5 mm first- and third-party flexible instruments. The instruments are nonrobotic and provide tactile feedback to the operating surgeon. They are designed and delivered into the operating field to allow for triangulation within the colonic lumen. Insufflation is maintained using a proprietary reusable rectoscope that is locked to the bed. The Flex console provides 3D visualization and control of the flexible endoscope.
Several feasibility studies have shown potential for this platform in transanal surgery. Atallah et al. demonstrated the system is effective for endoluminal lesions up to 17 cm as well as taTME with some limitations in suturing and reach. Paull et al. compared the outcomes of the Medrobotics platform versus the da Vinci Si for rTAMIS and they found decreased operative times, decreased estimated blood loss, and fewer conversions to conventional TAMIS in the Flex cohort. Cadaveric studies by Carmichael et al. similarly demonstrate potential use of this platform in taTME; however, they note challenges in maneuvering the instruments for distal rectal lesions. Importantly, current generation instruments wore out and lost grasping strength with prolonged use during their study. Currently, there are no long-term or large-scale studies supporting the use of the Flex system in transanal surgery.
da Vinci single port (SP)
Although the da Vinci Si and Xi platforms have been used for robotic transanal surgery, they have inherent limitations. The long inflexible arms and tight working space of the anal canal can lead to frequent external clashing. Furthermore, the large 8 mm instruments can obscure visualization of the working space.
The da Vinci SP is a platform developed for single-port surgery in multiple applications. Its design inherently overcomes some of the limitations of the other da Vinci platforms regarding transanal surgery. The platform consists of a single 25 mm cannula through which three fully wristed instruments and a fully wristed endoscope are advanced ( Fig. 53.3 ). The instruments can be individually positioned or the platform itself can be rotated 360 degrees to allow for multiquadrant surgery within the rectum. The instruments can reach a distance of 24 cm and triangulate to allow for improved working space.
