Roel Bogie

Chapter 1

Laterally Spreading Tumors and Large Non-Polypoid Colorectal Polyps Laterally Spreading Tumors, further abbreviated as LSTs, are large, flat appearing neoplasms in the colon and rectum. They have firstly been described in Japan by prof. Kudo as lesions challenging to detect while posing a hazard to rapid progression into CRC. 17 LSTs are defined as lesions growing superficially (laterally) along the mucosa instead of growing upwards (luminal) or downwards (submucosal), of minimal 10 mm in diameter. 11 Although polypoid components can be present in LSTs, they are regarded as non-polypoid colorectal neoplasms. 17 LST is a endoscopic, morphological classification, regardless of histology. LSTs are of special interest because of the occurrence of different surface structures and specific corresponding clinical features. The surface can consist of granules or can be completely flat ( Figure 1.2 ). Both LST subtypes can be subclassified into two subtypes; the endoscopic Kudo LST classification. LSTs consisting of evenly sized granules are called LST granular homogenous (LST G-H). When one or more dominant granules (large, sessile like components) exist in a granular LST, it is called a LST granular nodular-mixed (LST-G-NM). These dominant granules are minimal 10 mm in size. LSTs with flat surface are called non-granular LSTs and can contain a pseudo-depression (subtle dentation) on the surface. Non-granular LSTs without pseudo-depression are called LST non granular flat elevated (LST-NG-FE) and those with pseudo-depression LST non-granular pseudo depressed (LST-NG-PD). 11 In contrast to pseudo-depressions, depressions have more abrupt walls and are an indication of deep mucosal invasion. These can occur in all premalignant neoplasms, regardless of morphology. The risk of containing submucosal invasion (SMI, i.e. colorectal cancer) in LSTs differs per subtype. Overall, LSTs have a lower to similar risk of SMI than pedunculated and sessile neoplasms of equal size. 18, 19 However, some subtypes may have a higher than average risk of SMI. 11, 20 LSTs are more challenging to resect than large polypoid polyps and require additional experience. 21 The combination of large size and a non-polypoid morphology, often with a proximal colonic location, makes endoscopic mucosal resection challenging. 10 The BSG guidelines proposed the term Large Non-Pedunculated Colorectal Polyps (LNPCPs) for all non-pedunculated colorectal neoplasms of minimal 20 mm in size. 10 Besides LSTs of 20mm or larger, also sessile neoplasms of 20 mm or larger are included.

Granular LSTs

Non-granular LSTs

Figure 1.2: Endoscopic Kudo LST classification. | Illustration of the four known subtypes of LSTs.

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