Fig. 9.10 Mononuclearandgranulomatousinflammation.(A)Acuteviralhepatitischaracterizedbyapredominantlylymphocyticinfiltrate.(B)Secondarysyphilisinthedermiswithperivascularlymphoplasmacyticinfiltrateandendothelialproliferation.(C)Granulomatousinflammationinresponsetotuberculosis.Notethezoneofcaseation(asterisk), whichnormallyformsthecenterofthegranuloma,withasurroundingrimofactivatedepithelioidmacrophages,someofwhichhavefusedtoformgiantcells(arrows); thisinturnissurroundedbyazoneofactivatedTlymphocytes.Thishigh-magnificationviewhighlightsthehistologicfeatures;thegranulomatousresponsetypicallytakestheformofathree-dimensionalspherewiththeoffendingorganisminthecentralarea.
http://ebooksmedicine.net
MORPHOLOGYSomevirusesreplicatewithincellsandmakeviralaggregatesthatarevisibleasinclusionbodies(e.g.,herpesvirusesoradenovirus)orinducecellstofuseandformmultinucleatedcellscalledpolykaryons (e.g.,measlesvirusorherpesviruses)(see
Fig.9.1 ).Focalcelldamageintheskinmaycauseepithelialcellstobecomedetached,formingblisters.Somevirusescancauseepithelialcellstoproliferate(e.g.,venerealwartscausedbyHPVortheumbilicatedpapulesofmolluscumcontagiosumcausedbypoxviruses).Finally,virusescancontributetothedevelopmentofmalignantneoplasms(Chapter6).
Clostridium perfringens and other organisms that secrete powerful toxins can cause such rapid and severe necrosis that tissue damage is the dominant feature.
MORPHOLOGYBecausefewinflammatorycellsarepresent,necroticlesionsresembleinfarctswithdisruptionorlossofbasophilicnuclearstainingandpreservationofcellularoutlines.Clostridia oftenareopportunisticpathogensthatareintroducedintomuscletissuebypenetratingtraumaorinfectionofthebowelinaneutropenichost.Similarly,theparasiteE. histolytica causescoloniculcersandliverabscessescharacterizedbyextensivetissuedestructionandliquefactivenecrosiswithoutaprominentinflammatoryinfiltrate.Byentirelydifferentmechanisms,virusescancausewidespreadnecrosisofhostcellsassociatedwithinflammation,asexemplifiedbydestructionofthetemporallobesofthebrainbyHSVortheliverbyHBV.ThepowerfulexotoxinsofC. diphtheriae causenecrosisoflaryngealepitheliumgivingrisetoapseudo-membranecomprisedofnecroticcellsenmeshedinafibrinousexudate.Thiscancauseasphyxia.
Many infections elicit chronic inflammation, which can either resolve with complete healing or lead to extensive scarring.
Fig. 9.11 Schistosoma haematobium infectionofthebladderwithnumerouscalcifiedeggsandextensivescarring.
MORPHOLOGYSometimesanexuberantscarringresponseisthemajorcauseofdysfunction.Forexample,schistosomeeggscause“pipestem”fibrosisoftheliverorfibrosisofthebladderwall(
Fig.9.11 ).M. tuberculosis causesconstrictivefibrouspericarditis.ChronicHBVinfectionmaycausecirrhosisoftheliver,inwhichdensefibrousseptasurroundnodulesofregeneratinghepatocytes.