title: Traditional serrated adenoma (TSA): morphological questions, queries and quandaries.
abstract: OBJECTIVE
  Traditional serrated adenoma (TSA) is an uncommon type of serrated adenoma that can be a precursor to biologically aggressive colorectal cancer that invokes the serrated (accelerated) pathway. The purpose of this review is to address some of the more contentious issues around nomenclature, diagnostic criteria, histological variants, coexistence with other polyp types, the occurrence of dysplasia and the differential diagnosis.
  
  
  RESULTS
  While the vast majority of TSAs are exophytic villiform polyps composed of deeply eosinophilic cells, flat top luminal serrations and numerous ectopic crypt foci, histological variants include flat TSA, filiform TSA and one composed of large numbers of mucin-containing cells. It is unlikely that there is any biological difference between the histological variants. There is a contention that TSAs are not dysplastic ab initio and that the majority do not show cytological atypia. Two types of dysplasia are associated with TSA. Serrated dysplasia is less well recognised and less commonly encountered than adenomatous dysplasia. TSA with dysplasia must be separated from TSA with coexisting conventional adenoma.
  
  
  CONCLUSIONS
  TSA is a characteristic polyp that may be extremely exophytic, flat or composed of mucin-rich cells and is typified by numerous ectopic crypt foci. They may coexist with other serrated polyps and conventional adenomas. Approximately 20-25% will be accompanied by adenomatous dysplasia.
authors.affiliation: Laboratory Medicine Program, Department of Pathology, University Health Network and University of Toronto, Toronto, Canada.
authors.forename: Runjan
authors.initials: R
authors.lastname: Chetty
mesh_terms: D018256:Adenomatous Polyps / Q000145:classification / Q000473:pathology*; D001706:Biopsy; D003111:Colonic Polyps / Q000145:classification / Q000473:pathology*; D015179:Colorectal Neoplasms / Q000145:classification / Q000473:pathology*; D003937:Diagnosis, Differential; D006801:Humans; D009378:Neoplasms, Multiple Primary / Q000145:classification / Q000473:pathology*; D011237:Predictive Value of Tests; D011379:Prognosis; D009626:Terminology as Topic
keywords: COLON; GASTROINTESTINAL DISEASE; NEOPLASMS