Shinji Tanaka, MD, PhD
Definition of Colorectal Endoscopic Submucosal Dissection and Endoscopic Mucosal Resection Techniques
To comprehend the indications for endoscopic mucosal resection (EMR) and endoscopic submucosal dissection (ESD), we must first understand the definition of colorectal EMR and ESD. The definitions for both of these techniques are clearly outlined in the 2015 Colorectal ESD/EMR Guidelines from the Japan Gastroenterological Endoscopy Society (JGES).1 With EMR, a physiological saline solution or viscous solution is injected into the underlying submucosa of a colorectal lesion using the injection needle. Next, the lesion is entrapped with a snare and resected with electrocautery. While polyp resection during cold polypectomy is performed without applying high-frequency current, electrocautery is essential in EMR and is routinely used. Similarly, with ESD, a mucosal lifting solution is also locally injected into the underlying submucosa of a lesion to facilitate resection. Unlike EMR, however, the surrounding circumferential normal mucosa of the lesion is first incised using an ESD electrosurgical knife followed by submucosal dissection. This technique allows en bloc resection of lesions irrespective of size.
The JGES guidelines1 provide specific terminology to distinguish several variations of the ESD technique. “Pure ESD” is defined as a technique in which submucosal dissection is completed with the electrosurgical knife without using a snare. The guidelines define “precutting EMR” as a technique in which the outer circumferential margins of the lesion are incised followed by snare resection of the lesion without submucosal dissection. Conversely, “hybrid ESD” is defined as a technique in which the submucosal layer is dissected with a combination of the electrosurgical knife or tip of the snare followed by snare resection.
The Concept of Endoscopic Resection of Colorectal Lesions
Ideally, endoscopic en bloc resection is desirable for the removal of all lesions; but this is particularly important for lesions with a possibility of submucosal invasion (SMI) because en bloc resection provides precise prognostic histopathological information, such as invasion depth, histologic grade including its heterogeneity, vessel involvement, and tumor budding.1,2 EMR or ESD is not indicated for colorectal lesions with deep SMI, given the high risk for incomplete resection rate and that of lymph node metastasis (Figure 8-1). Lesions with high-grade dysplasia (classified as intramucosal cancer in Japan) also have the potential to invade the submucosal layer (Figure 8-2). As such, colorectal lesions with high-grade dysplasia ideally should also be resected en bloc for accurate histopathological staging.2 Conversely, colorectal polyps with low-grade dysplasia (corresponding to adenoma in Japan) can be resected in piecemeal fashion because these have a negligible risk of deeper invasion.1,2
Owing to the size limitation of snares, en bloc EMR is limited to lesions generally less than 20 mm in diameter, whereas ESD can potentially provide en bloc removal of any lesion regardless of size.1,2
Laterally Spreading Tumors
Laterally spreading tumors (LSTs)3 are defined as low-profile, superficially spreading tumors larger than 10 mm in diameter, with each subtype showing unique characteristics. Most colorectal lesions larger than 20 mm are usually LSTs. The different LST subtypes and their relationship with the Paris-Japanese classifications are shown in Figure 8-3.4,5 As described in the table, LST does not describe the morphological classification of the lesion but is rather a broad term used for categorizing all superficially spreading colorectal lesions.
Previous data6 have shown that granular-type LSTs (LST-G) with a homogenous appearance have a very low incidence of SMI regardless of its size. Most identified homogenous LST-Gs are benign adenomas with a low incidence of SMI or cancer (Table 8-1). Conversely, nodular mixed type LST-G may present with SMI, particularly in any predominant nodule within the lesion (Table 8-2). Hence, the potential foci of SMI (eg, large nodule) should be excised en bloc and evaluated separately from the remainder of the lesion.
Nongranular-type LST (LST-NG), especially, those with a pseudo-depressed morphology, show a high incidence of SMI, irrespective of their size (see Table 8-1). Endoscopic imaging with pit pattern analysis has been shown to assist in the differentiation between benign adenomatous lesions and those with potential for SMI.7 Generally, lesions with a regular Kudo/Tsuruta pit pattern (Types II, III, or IV) are restricted to the mucosa whereas those with a Type VN (nonstructured) pit pattern carry a higher risk for SMI. Given the higher risk of SMI in LST-NG when compared to LST-G, particularly in the pseudo-depressed type of LST-NG irrespective of size or pit pattern (Table 8-3), en bloc excision and not piecemeal EMR should be performed to secure an optimal histopathological specimen (Figure 8-4).
* P < 0.01 Jan. 1990—Sep. 2008, Department of Endoscopy, Hiroshima University Hospital.