Depth of invasion
Lymphatic invasion
Maximum tumor diameter (cm)
≤1
1.1–2
2.1–3
3.1–4
4.1–5
≥5.1
pT1 SM1
No
3.0
3.6
4.4
5.4
6.6
8.1
Yes
5.2
6.4
7.7
9.4
11.4
13.7
pT1 SM2–3
No
10.5
12.7
15.3
18.5
22.1
26.4
Yes
17.8
21.4
25.5
30.3
35.7
41.8
pT2
No
9.8
11.9
14.3
17.3
20.7
24.7
Yes
16.7
20.0
23.9
28.5
33.7
39.5
pT3
No
19.7
23.6
28.0
33.2
39.0
45.4
Yes
32.2
37.9
44.1
51.0
58.3
65.7
Relative risk (95% confidence intervals) of lymph node metastasis in pT1 rectal cancers. SM1, invasion into superficial third of submucosa. SM2/SM3, invasion into middle and deep third of the submucosa. (Used with permission of Georg Thieme Verlag KG from Bosch et al. [6])
Depth of Invasion
When considering adverse histologic features for early rectal cancer, depth of tumor invasion is the most familiar and commonly referenced factor. T1 cancers are associated with a 10–15% incidence of occult lymph node metastases, and T2 cancers are associated with a 20–28% risk of lymph node metastasis [7–10]. Kikuchi and coauthors demonstrated the importance of depth of invasion within subclasses of submucosa invasion on the node metastasis and local recurrence in T1 cancers. By dividing submucosal invasion in the upper, middle, and lower thirds of the submucosa (SM1, SM2, SM3), an incremental increase in the risk of nodal metastases with a deeper depth of invasion is observed. SM3 level of invasion conferred a similar risk of nodal metastases as did a T2 cancer [11, 12]. Ding and coauthors described a similar phenomenon for T2 cancers whereby risk of lymph node metastasis increases with deeper penetration of the tumor into the muscularis propria [13].
Colonoscopic polypectomy specimens are usually partial thickness, so without the complete submucosal layer to visualize, the Kikuchi submucosal level of invasion cannot be determined. Under these circumstances, another predictive measurement system for depth submucosal invasion is needed. A Japanese collaborative study led by Kitajima reported that sessile polyps with depth of invasion <1 mm, as measured from the muscularis propria, and pedunculated polyps with <3 mm submucosal invasion into the polyp neck predicted for a very low risk of lymph node metastasis [14, 15].
Tumor Budding
There is increased recognition that tumor budding , defined as small nests of five or more cancer cells along the invasive front of the tumor, is a strong predictor of lymph node metastasis in colon and rectal cancer. Tumor budding is present in 16–25% of T1 cancers [16–18] and has an odds ratio of 5.1–5.8 at predicting lymph node metastases [6, 8].
Lymphovascular Invasion
Lymphovascular invasion (LVI) is present in 12–32% of T1 rectal cancers [7, 17]. LVI has long been recognized a predictor of lymph node metastasis with a reported odds ratio between 3.0 and 11.5 [6–8, 19].
Poor Differentiation
Poorly differentiated tumor histology has also long been a predictor of lymph node metastasis in early rectal cancer. However, this feature is seen rather infrequently and is only present in 2–4% of early rectal cancers [5, 6, 8, 20].
Preoperative Planning, Patient Workup, and Optimization
Once a patient has been diagnosed with rectal cancer, a standardized workup is initiated to exclude synchronous colorectal neoplasm and assess for locally advanced and metastatic disease [3]. Synchronous neoplasm is excluded via screening colonoscopy. Metastatic disease is evaluated using CT scan of the chest, abdomen, and pelvis. Local regional disease is evaluated using rectal cancer protocol MRI or endorectal ultrasound (EUS) . EUS is useful in evaluating candidates for local excision, as it is better than MRI and CT in visualizing the individual layers of the bowel wall and differentiating superficial T1 and T2 rectal cancers [19]. Rectal cancer protocol MRI is a useful adjunct in assessment and surveillance of mesorectal lymph nodes [21].
For optimal surgical planning , preoperative rigid or flexible sigmoidoscopy is necessary to assess the location and extent of the rectal tumor, the tumor height from the anal verge, anterior/posterior/lateral location, tumor bulk, extent of circumferential involvement, or other features which might hinder access to the proximal border of the tumor. This can affect choice of patient positioning, planned complexity and length of surgery, risk of intraperitoneal entry, and plan for closure strategy. Sometimes a “rectal” tumor is found up in the sigmoid, beyond the reach of transanal instruments.
Standard transanal excision has typically been restricted to tumors that are less than 40% of the circumference of the rectum and tumors within 8 cm of the anal verge. These limitations, however, arose not because these dimensions portend high risk of recurrence, but rather, they represented the restricted reach and visibility afforded through standard transanal instrumentation. TES – through improved lighting, visualization, advanced instrumentation, and the benefit of a stable pneumorectum – overcomes these size and location restrictions such that they are no longer considered a contraindication, provided the tumor can be removed en bloc with negative margins.
Operative Setup and Technique
The requisite equipment for transanal endoscopic surgery involves an operating transanal platform, laparoscopic or modified laparoscopic instruments, CO2 insufflation unit, laparoscope and light source, suction device, and monopolar and/or bipolar energy sources and handpieces depending on the surgeons’ preferences and a method to close the rectal wall defect such as suture or laparoscopic suture devices. Each TES platform will require a greater or lesser amount of disposable and reusable equipment. The initial TES platforms used rigid, reusable proctoscopes, transanal endoscopic microsurgery (TEM, Richard Wolf Medical Instruments, Knittlingen, Germany), and transanal endoscopic operating system (TEO®, Karl Storz, Tuttlingen, Germany). Transanal minimally invasive surgery (TAMIS), introduced in 2010, utilizes a disposable single-port platform placed transanally. The most common TAMIS platform is the GelPOINT® Path (Applied Medical, Rancho Santa Margarita, CA, USA).
As with all major surgeries, patient comorbidities and nutritional and smoking status should be optimized prior to elective surgery. Preoperative preparation involves a bowel preparation to ensure the rectal lumen and surgical field remain as clear as possible during the procedure. Most surgeons advocate for a full mechanical bowel preparation to achieve this goal, and some centers report clearance with enemas alone. Colorectal surgery prophylactic preprocedural intravenous antibiotics are administered in the operating room. Since spontaneous patient breathing can compromise adequate pneumorectum, general anesthesia with muscular relaxation is the preferred anesthetic modality.
Patient positioning is based on surgeon preference and surgical platform. TAMIS, using the disposable platform with straight instruments, can universally be done in lithotomy position. This also permits easy access to the abdomen for laparoscopy in the event of intraperitoneal entry and need for laparoscopic closure. TEM and TEO reusable platforms have beveled proctoscopes and angled instruments that facilitate operating on tumors located in the down position. Hence, patients with anterior tumors can be positioned prone split leg, posterior tumors in lithotomy, and lateral tumors in decubitus hip flex position. Intraperitoneal entry with TEM and TEO can usually be repaired transanally. Since TES patients have minimal postoperative discomfort , they can be managed as an outpatient or a 23-hour overnight stay.
Technique for TEM and TEO
Following positioning , the anus is gently dilated to facilitate insertion of the 4-cm-diameter proctoscope. The proctoscope is secured to the table with a U-shaped mounting arm. An airtight faceplate is secured, and tubing is connected to the suction insufflator unit. Pneumorectum is established and the video laparoscope adjusted to view the target lesion. Three instrument ports are available for use of the modified angled TEM/TEO laparoscopic instruments.
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