Serrated Lesions of Colorectum: A New Pathway in Colorectal Carcinogenesis

Colorectal polyps were traditionally classified as hyperplastic or adenomatous polyps. Adenomatous polyps were thought to be the precursor lesions of most of the colorectal cancers, but later serrated lesions were recognized as precursors of nearly one-third of colorectal cancers. Serrated lesions are a distinct group of polyps with special morphologic and histologic properties and a different carcinogenesis pathway to colorectal cancers. They are pale, flat or depressed lesions which may result in failure of detection on colonoscopy. So the endoscopist should be aware of these lesions and should follow the patients according to the surveillance guidelines. DOI : 10.14302/issn.2471-7061.jcrc-13-375 Corresponding author: Nurten Savas, e-mail: nakyurek2000@yahoo.com, Phone: 0090 216 5541500 Fax:0090 216 474 95 96 Running Title: Serrated adenoma Received : Dec 13, 2013 Accepted : Jan 01, 2015 Published : Jan 20, 2015 Freely Available Online www.openaccesspub. org | JCRC CC-license DOI : 10.14302/issn.2471-7061.jcrc-13-375 Vol-1 Issue 1 Pg. no.2 Introduction Traditionally colorectal polyps were classified as either hyperplastic or adenomatous polyps and adenomatous polyps were thought to be the precursor of most of the colorectal cancers (CRC). Later serrated adenoma was described by Longacre and Fenoglio-Preiser in 1990 [1] for a subset of polyps that had both a serrated hyperplastic-like architecture and adenomatous changes or dysplasia, thereafter Torlakovic and Snover characterized a group of patients with serrated adenomatous polyposis, which showed similar features to hyperplastic polyps but with a sessile pattern of growth. [2]. Serrated lesions of colorectum are currently classified into three general categories [3]; hyperplastic polyp (HP), sessile serrated adenoma / polyp (SSA/P) with or without cytological dysplasia, and traditional serrated adenoma (TSA). The terms SSA and SSP are considered synonyms and both are acceptable (Table1). In general the subtypes of serrated lesions are identified by cytological and architectural features also by location and extent of proliferative zone. Hyperplastic Polyp (HP) True HP compromise 80-90% of all serrated lesions, and likely have no neoplastic risk. They are typically small (<5mm), appear slightly raised and occur more frequently in the rectosigmoid region. It is difficult to differentiate hyperplastic polyps from other polyps by conventional light endoscopy and histology is needed for diagnosis [3,4]. HP occur most fresquently in the fifth and sixth decades of life. HP’s are characterized by variably prominent serrations occuring in the upper one-third to one half of crypts that are generally straight and demonstrate more or less normal localization of the proliferative zone to the base of the crypts. The superficial saw-tooth outline feature is a consequence of simultaneous increase of proliferation as well as inhibition of programmed cellular apoptosis. The degree of serration is more pronounced in the upper half and surface of the polyps than at the base. According to the morphological growth pattern, lack of proliferative abnormalities and the mucin content of the epithelial cells, 3 subtypes of HP are described [4,5,6]. The most frequent subtype of HP is the one with microvesicular mucinous cells named mivrovesicular hyperplastic polyp (MVHP) this type is characterized with the presence of small droplet mucin in cytoplasm of the Table 1. Classification of serrated lesions of colorectum Prevalence Shape Distribution Malignant potential Hyperplastic polyp Very common Sessile/flat Mostly distal Very low Sessile serrated adenoma/polyp Common Sessile/flat 80% proximal