Aims: Serrated polyps of the colorectum are a heterogenous group of mucosal lesions including hyperplastic polyps (HP) and sessile serrated adenomas (SSA), but their morphologic distinction is not always straightforward. However, it is important for the pathologist to identify SSA because recent data show that they might be the precursors of serrated adenocarcinomas which are probably involved in the serrated pathway.
Material and methods: We selected 102 serrated colorectal polyps resected by colonoscopy and evaluated the following parameters: location, size, number of biopsies per polyp, superficial or tangential biopsies, type of resection, location of the serrated feature, branching, horizontalisation, dilatation and herniation of crypts through the muscularis mucosae, cellular type, epithelial tufts, cytoplasmic eosinophilia and dysplasia.
Results: There were 81 HP (79%), seven SSA (7%) of which one showed foci of dysplasia, five traditional serrated adenomas (5%) and three mixed polyps (HP and tubulous adenoma: 3%). Only six serrated polyps could not be classified. The main architectural criterion for diagnosing SSA was a serrated pattern throughout the crypt axis and the rarity of undifferentiated cells at the base of the crypts. Moreover, clinical characteristics were also helpful, since sessile serrated adenomas were significantly more often located in the right colon and larger (median: 11mm versus 4mm) than HP.
Conclusion: SSA can be distinguished morphologically from HP in a daily practice. The presence of foci of dysplasia in one case of SSA supports the hypothesis that these polyps have a carcinogenetic potential and should have the same clinical follow-up as traditional adenomas.