Fig.20.20 ).Arimofcompressed,non-neoplasticparathyroidtissue,generallyseparatedbyafibrouscapsule,oftenisvisibleattheedgeoftheadenoma.Thechiefcellsoftheadenomaarelargerandshowgreaternuclearsizevariabilitythannormalchiefcells.Cellswithbizarreandpleomorphicnucleiareoftenseenwithinadenomas(so-called“endocrineatypia”)andmustnotbetakenasasignofmalignancy.Mitoticfiguresarerare.Incontrastwiththenormalparathyroidparenchyma,adiposetissueisinconspicuouswithinadenomas.
Fig.20.19Technetium-99radionuclidescandemonstratesanareaofincreaseduptakecorrespondingtotheleftinferiorparathyroidgland(arrow). Thisprovedtobeaparathyroidadenoma.Preoperativescintigraphyisusefulinlocalizinganddistinguishingadenomasfromparathyroidhyperplasia,inwhichmorethanoneglandwilldemonstrateincreaseduptake.
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Fig.20.20Chiefcellparathyroidadenoma.(A)Inthislow-powerview,asolitaryhypercellularadenomaisdelineatedfromtheresidualnormocellularglandontheupperright.(B)High-powerdetailshowsminimalvariationinnuclearsizeandoccasionalfollicleformation.(Courtesy of Dr. Nicole Cipriani, Department of Pathology, University of Chicago, Chicago, Illinois.)
Parathyroidhyperplasiaistypicallyamultiglandularprocess.Insomecases,however,enlargementmaybegrosslyapparentinonlyoneortwoglands,complicatingthedistinctionbetweenhyperplasiaandadenoma.Microscopically,themostcommonpatternseenisthatofchiefcellhyperplasia,whichmayinvolvetheglandsinadiffuseormultinodularpattern.Lesscommonly,theconstituentcellscontainabundantclearcytoplasmasaconsequenceoftheaccumulationofglycogen—aconditiondesignatedwater-clearcellhyperplasia.Asinthecaseofadenomas,stromalfatisinconspicuouswithinfociofhyperplasia.
Parathyroidcarcinomasmaybecircumscribedlesionsthataredifficulttodistinguishfromadenomas,ortheymaybeclearlyinvasiveneoplasms.Thesetumorsenlargeoneparathyroidglandandconsistofgray-white,irregularmassesthatsometimesexceed10ginweight.Thecellsusuallyareuniformandresemblenormalparathyroidcells.Theyarearrayedinnodularortrabecularpatterns.Thetumormassisusuallyenclosedbyadense,fibrouscapsule.Thereisgeneralagreementthatadiagnosisofcarcinomabasedoncytologicdetailisunreliable;invasionofsurroundingtissuesandmetastasisaretheonlydefinitivecriteria.Localrecurrenceoccursinone-thirdofcases,andmoredistantdisseminationoccursinanotherone-third.
Morphologicchangesinotherorgans: •Skeletalchangesincludeincreasedosteoclasticactivity,whichresultsinerosionofbonematrixandmobilizationofcalciumsalts,particularlyinthemetaphysesoflongtubularbones.Boneresorptionisaccompaniedbyincreasedosteoblasticactivityandtheformationofnewbonetrabeculae.Inmoreseverecases,thecortexisgrosslythinnedandthebonemarrowcontainsincreasedamountsoffibroustissueaccompaniedbyfociofhemorrhageandcysts(osteitisfibrosacystica)(Chapter21).Aggregatesofosteoclasts,reactivegiantcells,andhemorrhagicdebrisoccasionallyformmassesthatmaybemistakenforneoplasms(browntumorsofhyperparathyroidism).