Transanal Single Port Excision of Rectal Lesions
Avo Artinyan
Daniel Albo
DEFINITION
The first description of transanal excision (TAE) of rectal lesions is often attributed to Parks and colleagues. The classic technique described by Parks1 involves the excision of low rectal lesions under direct vision with the aid of transanal retractors and standard surgical instruments. Although relatively effective for low rectal lesions, TAE is extremely difficult for lesions in the midrectum and effectively impossible for lesions in the upper rectum.
The advantages associated with TAE versus radical surgery include the following: lower morbidity, less pain, shorter operating times, shorter hospital stays, no wound complications, faster/more complete recovery, and avoidance of permanent colostomy.
Transanal endoscopy microsurgery (TEM) generally refers to an approach for the local excision of lesions in the midto upper rectum first described by Buess et al.2 in the early 1980s.
Although several variations in technique and instrumentation have been described, common to all of these are the following: (1) endoscopic visualization of the rectum, (2) gas/CO2 insufflation, and (3) the use of laparoscopic and/or other specialized instrumentation that allows for bimanual surgical dissection and suture repair.
The procedure is notably distinct from endoscopic mucosal resection (EMR) and other techniques that rely on flexible gastrointestinal endoscopy with associated limited instrumentation introduced via the working channels of these scopes.
Other terms such as transanal minimally invasive surgery (TAMIS) describe the same procedure with slight variations in instruments, especially with respect to the transanal access platform. In this chapter, we use the term transanal endoscopy microsurgery to include all of these procedures and variations.
The procedure has recently seen an increase in popularity with the introduction of newer, less expensive instrument platforms as well as expanding interest in, and indications for, the local excision of rectal cancer.
DIFFERENTIAL DIAGNOSIS
TEM can be used to treat a wide variety of both malignant and benign rectal conditions, including but not limited to large rectal adenomas, early rectal cancers, neuroendocrine tumors, endometriomas, and rectal strictures.
These lesions encompass a wide variety of pathophysiologic entities with many common underlying complaints that alert the clinician to pathology within the distal large bowel and rectum.
TEM can serve as both a diagnostic procedure as well as an effective therapeutic procedure in the appropriate setting.
PATIENT HISTORY AND PHYSICAL FINDINGS
Patients with rectal lesions (usually rectal polyps and rectal cancers) generally present with occult or clinically evident rectal bleeding. Those with early or small lesions may be completely asymptomatic with rectal pathology discovered on screening colonoscopy.
A thorough history and physical examination should be performed, important components of which include the following:
Presence of rectal pain and/or tenesmus, which can often alert the surgeon to a more extensive lesion with sphincter/levator ani involvement
Presence of obstructive symptoms
Description of anorectal function, with any fecal incontinence or leakage documented preoperatively
Urinary and erectile function, with dysfunction documented preoperatively
A detailed oncologic history including both personal and family history of colorectal cancer, other malignancies, and hereditary cancer/polyposis syndromes
Physical examination should include the following:
Routine abdominal examination, with particular attention to the presence of any surgical incisions, which may become pertinent should laparoscopy or laparotomy be necessary.
Digital rectal examination with gross assessment of sphincter function
Bilateral inguinal nodal examination for clinically evident nodal metastases
Rigid proctoscopy by the surgeon to define the anatomic parameters of the lesion
Rigid proctoscopic examination is the most critical portion of the physical examination and is the key to proper selection of patients for TEM. Examination should be standardized and should document the following findings:
The distal and proximal extent of the lesion measured from the anal verge
Position of the lesion within the circumference of the rectum (anterior, posterior, or lateral)
Total circumference of the rectal wall involved by the lesion
IMAGING AND OTHER DIAGNOSTIC STUDIES
A complete colonoscopy should be performed on all patients preoperatively. In the setting of possible colorectal neoplastic disease, the location of all polyps should be described, and all suspicious lesions should be endoscopically excised or biopsied if excision is not feasible. Lesions that are unresectable or are suspicious for invasive adenocarcinoma should be tattooed to facilitate resection if necessary in the future.
For all suspicious rectal lesions (≤15 cm from anal verge on rigid proctoscopy), locoregional staging with endorectal ultrasound (EUS) or rectal magnetic resonance imaging (MRI) should be performed to define the depth of the lesion and the potential for nodal involvement.
With all suspected or confirmed colorectal neoplastic disease, complete staging computed tomography (CT) of the chest, abdomen, and pelvis should be performed to rule out metastatic disease.
Positron emission tomography (PET)/CT should be used selectively for patients with suspected metastatic disease or those that are poor candidates for intravenous (IV) contrast secondary to renal insufficiency or contrast allergy.
Anal physiologic studies with manometry should be strongly considered for patients with preoperative symptoms and signs of fecal incontinence to document preoperative sphincter function.
SURGICAL MANAGEMENT
Indications for Transanal Endoscopy Microsurgery
Large rectal polyps not amenable to colonoscopic resection (usually sessile adenomatous polyps)
Rectal adenocarcinoma—The indications for the local excision of rectal adenocarcinoma continue to evolve, particularly with the recent completion of multidisciplinary trials such as the American College of Surgeons Oncology Group (ACOSOG) Z6041 trial. Because TEM is used to excise local disease and does not adequately address nodal disease, the degree to which the procedure is appropriate and successful is directly proportional to the likelihood of nodal metastases. In the combined literature, the risk of nodal disease is best predicted by T stage and is on the order of 5% to 10% for T1 lesions, 15% to 25% for T2 disease, and 35% to 75% for T3 disease. Other pathologic factors are also useful in predicting risk of nodal disease and recurrence, and these are potentially applicable for patient selection (Table 1). The desire to perform/undergo a minimally invasive procedure should not supplant sound oncologic principles.
Low-risk T1 disease—Definitive therapy for rectal cancer should be reserved only for patients with low-risk T1 disease. This is also the current position of the National Comprehensive Cancer Network (NCCN). High-risk T1 or any T2 disease with combination therapy—Patients with high-risk T1 or any T2 disease who undergo TEM with curative intent should ideally be treated in a clinical trial setting with either preoperative or postoperative chemoradiation. Given that TEM is not the standard of care in this setting, the risks and benefits of TEM versus radical resection need to be carefully discussed with the patient and appropriate consent obtained and documented.
Lesions of any stage, technically amenable to TEM, in patients who refuse radical resection, appropriate discussion and consent must be documented
Lesions of any stage, technically amenable to TEM, for palliative purposes
Other less common indications that have been reported include rectal carcinoids, endometriomas, angiodysplasia, rectal ulcers, rectal strictures, and other benign pathologies. Just as with rectal adenocarcinoma, the decision to perform TEM in these settings should be based on sound clinical judgment.
Table 1: Additional Factors Associated with Increased/High Risk of Lymph Node Involvement/Local Recurrence | |||||
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Anatomic Considerations
TEM is ideally suited for lesions whose entire extent falls within 5 to 15 cm from the anal verge.
The technical “sweet spot” for TEM is between 6 and 10 cm (midrectum), beyond which the surgeon has to contend with instrument limitations, diminished visualization and exposure, and the potential for peritoneal entry.
TEM has been described for lesions proximal to 15 cm. However, peritoneal entry is much more likely with fullthickness excision in this setting, and extensive expertise is required to perform an adequate and safe suture repair.
The likelihood of peritoneal entry is dependent on the circumferential location of the lesion (Table 2). For example, the mean distance to the peritoneal reflection anteriorly in men is at 9.7 cm, compared to 15.5 cm posteriorly. Dissection in the posterior midline can also result in entry into the intraabdominal colonic mesentery, without frank intraperitoneal entry.3
Lesions distal to 5 cm are usually covered in part or completely by the transanal access device. These lesions are more suited for conventional TAE.
There is no absolute contraindication based on the total circumferential extent of the lesion, and complete circumferential excisions have been described. However, excision of lesions that occupy more than 40% of the circumference is technically much more challenging, may be associated with more advanced lesions, and can lead to compromised margins. Sound judgment and careful patient selection are required.
Table 2: Distance of Peritoneal Reflection from Anal Verge (Mean with Range, cm) | |||||||||||||||
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Preoperative Preparation
The key to the technical success of the TEM operation is adequate visualization and exposure. As a result, preoperative
mechanical bowel preparation is invaluable. We ask our patients to have a normal lunch and take a clear liquid diet with adequate hydration thereafter and nothing by mouth after midnight. We prefer a mechanical bowel preparation with two bottles of magnesium citrate in the afternoon the day before surgery, with a Fleet enema the night before and the morning of the procedure.
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