Histological characterization of traditional serrated Adenomas compared to conventional Adenomas

Background: Among the recently described and more rapidly progressing colorectal serrated lesions traditional serrated adenoma (TSA) is the rarest subtype. The morphologic distinction between TSA and conventional adenoma, especially villous/tubulovillous adenoma (VA/TVA), may be difficult, because there is a significant histological overlap between these lesions. According to the literature, there are three characteristic features usually present in TSAs: ectopic crypt foci (ECF), luminal serration and typical cytology with columnar epithelial cells with eosinophilic cytoplasm and elongated, centrally placed nuclei. Currently, TSA diagnosis needs at least two of the three features above with at least one present in 50% of the polyp. Aims: The aim of our study was to evaluate the presence of these morphological features in TSAs and TVAs, and define which features are most helpful in distinguishing TSA from TVA. Results: A total of 115 polyps diagnosed as TSA or TVA were reviewed and 11 polyps were selected and classified as TSA on the basis of the current diagnostic criteria. As a control group, we studied 104 TVAs and determined the same features. Both ECF and typical cytology were seen in 10 of the 11 TSAs (91%), luminal serration was present in 73%. To the extent of more than 50% of the polyp, typical cytology was noted in 7 cases (64%), ECF and luminal serration was seen in 3 TSAs (27%). Of the 104 TVAs, typical cytology was present in 35 cases (34%), ECF was found in 9% and luminal serration was noted in 20%. Typical cytological features were seen only in 3 TVAs (3%) to the extent of more than 50% of the adenoma. Luminal serration in more than half of the specimen was seen only in one TVA. The presence of all three morphological features simultaneously was observed in 6 of the 11 TSAs (55%), and only in 3 of the 104 TVAs (3%). Two TVAs showed typical TSA-like patterns to a considerable degree. Conclusions: In conclusion, ECF proved to be the most helpful morphological feature regarding the diagnosis of TSA, although it is not specific to TSA and is not seen in every case of TSA. Luminal serration and TSA-like cytology are frequently present in TVAs, but they are only visible in extreme cases in more than 50% of the adenoma. Some polyps show a mixed morphology, with TSA-like and conventional adenoma-like areas. These cases may be regarded as „mixed polyps”. This study was supported by the Hungarian Scientific Research Fund (OTKA-K111743 grant).