MORPHOLOGYTypicaladenomasrangefrom0.3to10cmindiameterandcanbepedunculated (
Fig.15.33A )orsessile, withthesurfaceofbothtypeshavingatextureresemblingvelvet(
Fig.15.33B )oraraspberry,duetotheabnormalepithelialgrowthpattern.Histologically,thecytologichallmarkofepithelial dysplasia (
Fig.15.34C )isnuclearhyperchromasia,elongation,andstratification.Thesechangesaremosteasilyappreciatedatthesurfaceoftheadenoma,becausetheepitheliumfailstomatureascellsmigrateoutofthecrypt.Pedunculatedadenomashaveslenderfibromuscularstalks(see
Fig.15.33C )containingprominentbloodvesselsderivedfromthesubmucosa.Thestalkusuallyiscoveredbynonneoplasticepithelium,butdysplasticepitheliumissometimespresent.
Adenomascanbeclassifiedastubular, tubulovillous, orvillous onthebasisoftheirarchitecture.Thesecategories,however,havelittleclinicalsignificanceinisolation.Tubularadenomastendtobesmall,pedunculatedpolypscomposedofsmall,rounded,ortubularglands(
Fig.15.34A ).Bycontrast,villousadenomas,whichoftenarelargerandsessile,arecoveredbyslendervilli(
Fig.15.34B ).Tubulovillousadenomashaveamixtureoftubularandvillouselements.Althoughfociofinvasionaremorefrequentinvillousadenomasthanintubularadenomas,villousarchitecturealonedoesnotincreasecancerriskwhenpolypsizeisconsidered.
Thehistologicfeaturesofsessile serrated adenomas, whicharealsoreferredtoassessileserratedpolyps,overlapwiththoseofhyperplasticpolypsandlacktypicalcytologicfeaturesofdysplasia(
Fig.15.34D ).Nevertheless,sessileserratedadenomas,whicharemostcommonintherightcolon,haveamalignantpotentialsimilartothatofconventionaladenomas.Themostusefulhistologicfeaturethatdistinguishessessileserratedadenomasfromhyperplasticpolypsisthepresenceofserratedarchitecturethroughoutthefulllengthoftheglands,includingthecryptbase,associatedwithcryptdilationandlateralgrowth,intheformer(
Fig.15.34D ).Bycontrast,serratedarchitecturetypicallyisconfinedtothesurfaceofhyperplasticpolyps.
Althoughmostcolorectaladenomasbehaveinabenignfashion,asmallproportionharborinvasivecanceratthetimeofdetection.Size is the most important characteristic that correlates with risk for malignancy. Forexample,while
Fig. 15.32 Hyperplasticpolyp.(A)Polypsurfacewithirregulartuftingofepithelialcells.(B)Tuftingresultsfromepithelialovercrowding.(C)Epithelialcrowdingproducesaserratedarchitecturewhenglandsarecutincross-section.
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Fig. 15.33 Colonicadenomas.(A)Pedunculatedadenoma(endoscopicview).(B)Adenomawithavelvetysurface.(C)Low-magnificationphotomicrograph ofapedunculatedtubularadenoma.