ThemicroscopicfeaturesofactiveCrohndiseaseincludeabundantneutrophilsthatinfiltrateanddamagecryptepithelium.Clustersofneutrophilswithinacryptarereferredtoasacrypt abscess andoftenareassociatedwithcryptdestruction.UlcerationiscommoninCrohndisease,andtheremaybeanabrupttransitionbetweenulceratedandnormalmucosa.Repeatedcyclesofcryptdestructionandregenerationleadtodistortion of mucosal architecture; thenormallystraightandparallelcryptstakeonbizarrebranchingshapesandunusualorientationstooneanother(
Fig.15.29A ).Epithelialmetaplasia,anotherconsequenceofchronicrelapsinginjury,oftentakestheformofgastricantral-appearingglands(pseudopyloricmetaplasia).Paneth cell metaplasia mayoccurintheleftcolon,wherePanethcellsarenormallyabsent.Thesearchitecturalandmetaplasticchangesmaypersist,evenwhenactiveinflammationhasresolved.Mucosalatrophy,withlossofcrypts,mayfollowyearsofdisease.Noncaseating granulomas (
Fig.15.29B ),ahallmarkofCrohndisease,arefoundinapproximately35%ofcasesandmayariseinareasofactivediseaseoruninvolvedregionsinanylayeroftheintestinalwall(
Fig.
15.29C ).Granulomasalsomaybefoundinmesentericlymphnodes.Cutaneousgranulomasformnodulesthatarereferredto(misleadingly)asmetastatic Crohn disease.The absence of granulomas does not preclude a diagnosis of Crohn disease.
http://ebooksmedicine.net
Fig. 15.28 GrosspathologyofCrohndisease.(A)Small-intestinalstricture.(B)Linearmucosalulcersandthickenedintestinalwall.(C)Creepingfat.
Fig. 15.29 MicroscopicpathologyofCrohndisease.(A)HaphazardcryptUlcerativecolitisalwaysinvolvestherectumandextendsproxiorganizationresultsfromrepeatedinjuryandregeneration.(B)Noncaseatingmallyinacontinuousfashiontoinvolvepartortheentirecolongranuloma.(C)TransmuralCrohndiseasewithsubmucosalandserosal
The clinical manifestations of Crohn disease are extremely variable. In most patients, disease begins with intermittent attacks of relatively mild diarrhea, fever, and abdominal pain. Approximately 20% of patients present acutely with right lower-quadrant pain and fever, which may mimic acute appendicitis or bowel perforation. Patients with colonic involvement may present with bloody diarrhea and abdominal pain, creating a differential diagnosis with some colonic infections. Periods of disease activity typically are interrupted by asymptomatic intervals that last for weeks to many months. Disease reactivation can be associated with a variety of external triggers, including physical or emotional stress, specific dietary items, NSAID use, and cigarette smoking.
Iron-deficiency anemia may develop in individuals with colonic disease, while extensive small-bowel disease may result in serum protein loss and hypoalbuminemia, generalized nutrient malabsorption, or malabsorption of vitamin B12 and bile salts. Fibrosing strictures, particularly of the terminal ileum, are common and require surgical resection. Disease often recurs at the site of anastomosis, and as many as 40% of patients require additional resections within 10 years. Fistulas develop between loops of bowel and may also involve the urinary bladder, vagina, and abdominal or perianal skin. Perforations and peritoneal abscesses can also occur.