USMLE题库Genitourinary21-30

Genitourinary题库Q21A21-year-oldmaleisbeingevaluatedforrecurrentkidneystones.Sodiumcyanideisaddedtohisurine,followedbyasodiumnitroprussidesolution,andtheurinebecomesred-purpleincolor.Furtherquantitativelaboratoryevaluationismostlikelytodetectwhichofthefollowingabnormalitiesinthispatient?A.HypercalciuriaB.HyperoxaluriaC.HyperuricosuriaD.HypocitraturiaE.AminoaciduriaA21Correctanswer:ERecurrentnephrolithiasisinayoungpatientshouldalertthephysiciantothepossibilityofaninbornerrorofmetabolism.Cystinuriaresultsfromadefectintherenalproximaltubules,whichcausesdecreasedreabsorptionoftheaminoacidcystine.Theincreasedcystineexcretioncanprecipitatestoneformation.Thecystinetransporteralsocontributestothereabsorptionofotherdibasicaminoacids(arginine,ornithine,lysine).Increasedexcretionoftheseaminoacidsdoesnotresultinstoneformation,however,asthesearerelativelysoluble.Patientswithcystinuriaexperiencerecurrentkidneystones,beginningatayoungage.Hexagonalcystinecrystalsonurinalysisarepathognomonic.Thesecrystalsarerelativelyradiopaqueduetothedensityofsulfur-containingcompounds.Theyforminacidicurine(pH6).Thedetectionofcystineinurineisimportantnotonlyforestablishingadiagnosis,butalsoformonitoringtreatmenteffectsandforpredictingtherateofstoneformation.Thesodiumcyanide-nitroprussidetestdescribedinthevignettedetectssulfhydrylgroups,andisarapidqualitativedeterminantofthepresenceofurinecystine.Thecyanideaddedtotheurineconvertscystinetocysteine.Thenitroprussidethenbindscysteine,causingapurplediscolorationin2-10minutes.Treatmentofcystinuriainvolveshydrationandalkalinizationofurine.(ChoicesA,B,CandD)Hypercalciuria,hyperoxaluria,hyperuricosuriaandhypocitraturiaareriskfactorsforrecurrentcalciumstoneformation.However,theseabnormalitiesarenottypicallyfoundinpatientswithcystinuria.Q22A68-year-oldmalepresentstoyourofficecomplainingofurgency,frequency,aweakurinarystream,andstrainingonmicturition.Thesesymptomshavebeenpresentforthepastfewyears,buthavegraduallybecomemoresevere.Healsonotesnocturia,aswellasoliguriaalternatingwithpolyuria.Thepatient'skidneysaremostlikelytodemonstrate:A.GlomerularsclerosisandhyalinosisB.TubularepithelialdysplasiaC.HyperplasticarteriolarchangesD.IschemictubularnecrosisE.ParenchymalpressureatrophyA22Correctanswer:EStrainingonurinationinanelderlymalesuggestsbladderoutflowobstruction(BOO),aconditionusuallyduetoprostateenlargement.ThemostcommoncauseofBOOisbenignprostatichyperplasia(BPH),foundin90%ofallautopsiesofmenover70yearsofage.EarlysymptomsofBPHincludefrequency,urgency,nocturia,hesitancy,andweakurinarystream.Astheprostateenlargesfurtherandthebladderoutletobstructionworsens,patientsexperienceasensationofincompletebladderemptying.Thisusuallysignifiesurinaryretention.Overflowincontinenceisthenextclinicalstage.BPHischaracterizedbyacombinationofepithelialandstromalhyperplasia,predominantlyintheperiurethralandtransitionzones.Onpalpation,theprostatehasarubberyconsistency,incontrasttoprostatecancer,wheretheglandisnodularandveryfirm.Urinaryretentionleadstoincreasedpressureintheurinarytract,causingcharacteristicmorphologicalchanges.Thebladderwallhypertrophies,toincreaseitscontractileforce.Asurinaryretentionprogresses,theureters,renalpelvis,andcalycesdilateanddeform,leadingtohydronephrosis.Therenalparenchymaultimatelybecomesatrophicandscarredduetorefluxofurineanddamageofrenaltissue.(ChoiceA)Glomerularsclerosisandhyalinosisisoftenseenindiabeticnephrosclerosis.(ChoiceB)Epithelialdysplasiamarksanalterationincellarchitecture.Cellschangeinshape,size(pleomorphic),andstaining(hyperchromatic).Nucleienlargeaswell.Dysplasiaisconsideredaprecursorofmalignancy.Benignprostatichyperplasiadoesnotpredisposetorenaltubulardysplasia.(ChoiceC)Hyperplasticarteriolarchangesareinducedbylong-standingsystemichypertension.(ChoiceD)Ischemictubularnecrosisresultsfromhemorrhage,low-flowstates(suchasMl),orsystemicvasodilatation(suchassepsis).Itssymptomsarethoseofacuterenalfailure:oliguria,increasedserumBUNandcreatinine(azotemia),fluidoverload,andelectrolytedisturbances.Q23A3-month-oldboyisbroughttotheofficebyhismotherforaroutinecheckup.Heisfoundtohavearight-sidedwhitepupillaryreflex.Hisfatherwasdiagnosedwitharetinalneoplasmduringchildhoodandhadhislefteyeenucleated.Thischildisatthegreatestriskofdevelopingwhichofthefollowingneoplasms?A.AcutelymphoblasticleukemiaB.NeuroblastomaC.EwingsarcomaD.OsteosarcomaE.MedulloblastomaA23Correctanswer:DRetinoblastomaisthemostcommonoculartumorofchildhood.Itusuallypresentswithawhitepupillaryreflex(leukocoria)inchildren5yearsold.Approximately60%ofretinoblastomasaresporadic(usuallyunilateral),while40%arefamilial(often,butnotalways,bilateral).Childrenwithsporadicretinoblastomaarenotatriskforothermalignancies,whilepatientswithfamilialretinoblastomaoftendevelopothertumors,usuallysarcomas,laterinlife.Amongthesesecondarymalignancies,osteosarcoma(ChoiceD)occursmostoften.FamilialretinoblastomaoccursduetoagermlinemutationthataffectstheRbtumorsuppressorgeneonchromosome13.Allcellsinthebodyofanaffectedindividualcarrythismutation.Astherearetwoa