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• SECTION 1: SKINSPONGIOTIC AND PSORIASIFORM DERMATOSES4 Pityriasis RoseaChristopher Lum, MD, Amity Tran, BA, and Emily Leibovitch, BA6 Contact DermatitisGeorge R. Collins, DO10 Atopic DermatitisWang L. Cheung, MD, PhD and Karen S. Thompson, MD12 Perniosis14 Seborrheic DermatitisKaren S. Thompson, MD, Angelica R. Putnam, MD, and Wang L. Cheung, MD, PhDINFLAMMATORY/INTERFACE DERMATOSES16 Erythema Multiforme and Related Disorders20 Pityriasis LichenoidesVESICOBULLOUS DERMATOSES24 Acropustulosis of InfancyLarissa V. Furtado, MD26 Dermatitis Herpetiformis28 Epidermolysis Bullosa, Inherited32 Erythema Toxicum Neonatorum34 Hailey-Hailey Disease36 Chronic Bullous Disease of Childhood38 Transient Neonatal Pustular MelanosisVASCULAR AND RELATED DISEASES40 Urticaria and Variants44 Leukocytoclastic VasculitisPANNICULITIDES48 Erythema Nodosum52 Subcutaneous Fat Necrosis of NewbornJessica M. Comstock, MD and Angelica R. Putnam, MD54 Sclerema NeonatorumCONNECTIVE TISSUE56 Lupus Erythematosus62 Morphea/Scleroderma66 DermatomyositisMETABOLIC/DEPOSITION DISEASES70 Calcinosis CutisDirk Elston, MD and Carly A. Elston, MDNONINFECTIOUS GRANULOMATOUS DISEASES74 Chalazion76 Granuloma AnnulareAngelica R. Putnam, MDPILOSEBACEOUS DISEASE78 Acne VulgarisViseslav Tonkovic-Capin, MDALOPECIAS80 TrichotillomaniaGarth Fraga, MDDISORDERS OF EPIDERMAL MATURATION AND KERATINIZATION84 IchthyosisMichael W. Peterson, DO86 Darier Disease88 Porokeratosis92 Incontinentia PigmentiChristine J. Ko, MDDISORDER OF COLLAGEN94 Aplasia Cutis CongenitaMichael W. Peterson, DO, Nathan Peterson, DO, and Karen S. Thompson, MDBACTERIAL INFECTIONS96 Impetigo100 Staphylococcal Scalded Skin Syndrome102 Ecthyma and Ecthyma Gangrenosum104 Cat-Scratch DiseaseIrina Margaritescu, MD, PhD and Bruce R. Smoller, MD110 Atypical Mycobacterial InfectionsCary Chisholm, MD and Karen S. Thompson, MDVIRAL INFECTIONS112 Molluscum ContagiosumTalley Whang, MD114 HerpesvirusFUNGAL INFECTIONS116 CandidiasisARTHROPODS/PARASITES120 Bite ReactionsAtsuko Kodama, MD124 ScabiesGonzalo De Toro, MDCYSTS126 Epidermal Inclusion Cyst128 Dermoid CystSECTION 2: SOFT TISSUE134 Necrotizing FasciitisBrian J. Hall, MD136 Tumoral CalcinosisKaren S. Thompson, MDSECTION 3: BONE AND JOINTCONGENITAL/GENETIC/HEREDITARY140 Osteogenesis Imperfecta144 Chondrodysplasia Punctata148 Thanatophoric DysplasiaTRAUMA/INJURY/REACTIVE150 Bone Fracture and Repair154 OsteomyelitisKaren S. Thompson, MD and Angelica R. Putnam, MD158 Stress and Costochondral Junction160 Juvenile Idiopathic ArthritisSECTION 4: SKELETAL MUSCLE166 Spinal Muscular AtrophyHannes Vogel, MD168 X-Linked Muscular Dystrophy: Duchenne and Becker172 Congenital MyopathiesSECTION 5: CENTRAL NERVOUS SYSTEM176 Cerebral Heterotopia and Ectopia178 Focal Cortical DysplasiaB. K. Kleinschmidt-DeMasters, MD192 MyelomeningoceleBrock Kaya, MD194 Encephalocele196 Tethered Cord198 Cerebral Arteriovenous MalformationsBrock Kaya, MD and Angelica R. Putnam, MD202 Cerebral Cavernous Malformation206 Hypoxic-Ischemic EncephalopathyBahig M. Shehata, MD, Cynthia T. Bunting, BS, and Phillip Quigley, BS210 Periventricular LeukomalaciaBahig M. Shehata, MD, Nancy Elawabdeh, BS, and Caitlin Cundiff, BS214 Arachnoid CystsTarik Tihan, MD, PhD and Karen S. Thompson, MD216 Meningioangiomatosis222 Germinal Matrix-Intraventricular HemorrhageBahig M. Shehata, MD and Nancy Elawabdeh, BSINFECTIOUS226 Bacterial Meningoencephalitis232 Fungal Meningoencephalitis238 Viral Meningoencephalitis242 Protozoal MeningoencephalitisSECTION 6: ENDOCRINE248 Adrenal CytomegalyArthur S. Tischler, MD250 Adrenal Heterotopia252 Adrenal Hypoplasia and MalformationsArthur S. Tischler, MD and Karen S. Thompson, MD254 Adrenal Cortical Hyperplasia258 Dyshormonogenetic GoiterVania Nosé, MD, PhD264 Ectopic Thyroid266 Thyroglossal Duct Cyst268 Cystic Fibrosis, PancreasMari Mino-Kenudson, MD270 Stress Reactions in Adrenal GlandBahig M. Shehata, MD, Holly C. Jordan, BS, and Erica J. Colvin, MD272 Hemorrhagic Necrosis of Adrenal GlandBahig M. Shehata, MD, Holly C. Jordan, BS, and Sydney R. Archer, BS274 Chronic Lymphocytic ThyroiditisBahig M. Shehata, MD, Brent M. Cone, BS, and Cynthia T. Bunting, BS278 Graves Disease284 Hypertrophy of Pancreatic IsletsJessica M. Comstock, MDSECTION 7: RESPIRATORY288 Bronchogenic CystBahig M. Shehata, MD, Nancy Elawabdeh, BS, and Charlotte A. Cooper, BS290 Congenital Alveolar Capillary DysplasiaBahig M. Shehata, MD, Ryan J. Cone, BS, and Charlotte A. Cooper, BS294 Congenital Lobar EmphysemaJessica M. Comstock, MD and Karen S. Thompson, MD296 Congenital Pulmonary LymphangiectasisBillie Fyfe, MD298 Diffuse Pulmonary LymphangiomatosisMonica P. Revelo, MD, PhD and Brandon T. Larsen, MD, PhD302 Congenital Pulmonary Airway Malformation306 Congenital Surfactant DeficiencyBillie Fyfe, MD and Eileen Margaret McKay, MD310 Cystic Fibrosis314 Sequestrations316 Aspiration320 Asthma322 Bronchopulmonary DysplasiaLarissa V. Furtado, MD and Karen S. Thompson, MD326 Hyaline Membrane Disease328 Interstitial Pulmonary EmphysemaLarissa V. Furtado, MD and Angelica R. Putnam, MD330 Persistent Pulmonary Hypertension332 Idiopathic Pulmonary HemosiderosisSaul Suster, MD334 Pulmonary Venoocclusive Disease/PulmonaryCapillary HemangiomatosisBahig M. Shehata, MD, Angelica R. Putnam, MD, and Charlotte A. Cooper, BS338 Nonspecific Interstitial Pneumonia340 Hypersensitivity PneumonitisCesar A. Moran, MD, Neda Kalhor, MD, and Karen S. Thompson, MD342 Eosinophilic PneumoniaCesar A. Moran, MD and Neda Kalhor, MD346 AdenovirusSaul Suster, MD and Karen S. Thompson, MD348 Human MetapneumovirusBahig M. Shehata, MD, Samuel N. Jactel, BS, and Nancy Elawabdeh, BS352 Respiratory Syncytial VirusMISCELLANEOUS354 Neuroendocrine Cell Hyperplasia of InfancySECTION 8: CARDIOVASCULAR358 Arrhythmogenic Right Ventricular CardiomyopathyJagdish Butany, MBBS, MS, FRCPC and Karen S. Thompson, MD362 Hypertrophic CardiomyopathyVidhya Nair, MBBS, MD, FRCPC364 Dilated CardiomyopathyJennifer Pogoriler, MD, PhD368 Fabry DiseaseMonica P. Revelo, MD, PhD372 Fatty Acid Metabolic Disorders374 Glycogen Storage Diseases376 Mitochondrial Myopathies380 Capillary Malformations384 Lymphatic Malformations388 Venous Malformations392 Arteriovenous Malformations and Fistulas396 Endocardial Fibroelastosis398 Lymphocytic Myocarditis402 Acute Pericarditis406 Acute Rheumatic Fever410 Kawasaki Disease414 COVID-19-Related Pathology and PediatricMultisystem Inflammatory SyndromeSECTION 9: ALIMENTARY CANALESOPHAGUS426 Inlet PatchAlexandros D. Polydorides, MD, PhD430 Tracheoesophageal Fistula and Esophageal Atresia434 Esophageal Duplication Cyst438 Gastroesophageal Reflux Disease444 Eosinophilic Esophagitis448 Herpes Simplex Virus EsophagitisLaura W. Lamps, MD450 CandidaSTOMACH452 Chemical GastropathyGregory Y. Lauwers, MD and Alexandros D. Polydorides, MD, PhD456 Chronic GastritisAlexandros D. Polydorides, MD, PhD and Staci Bryson, MD458 Granulomatous GastritisAlexandros D. Polydorides, MD, PhD and Gregory Y. Lauwers, MD462 Lymphocytic Gastritis468 Eosinophilic GastroenteritisGregory Y. Lauwers, MD and Karen S. Thompson, MD470 Fundic Gland Polyp472 Collagenous Gastritis476 Helicobacter heilmannii GastritisJoel K. Greenson, MD and Alexandros D. Polydorides, MD, PhD478 Helicobacter pylori GastritisSMALL BOWEL482 Small Intestine Duplication Cyst484 Ectopic PancreasAlexandros D. Polydorides, MD, PhD and Joel K. Greenson, MD488 Gastric Heterotopia490 Meckel Diverticulum492 Microvillous Inclusion Disease494 Primary Intestinal LymphangiectasiaJoel K. Greenson, MD and Karen S. Thompson, MD496 AbetalipoproteinemiaFlorette K. Gray Hazard, MD and Karen S. Thompson, MD500 Tufting EnteropathyAlexandros D. Polydorides, MD, PhD and Florette K. Gray Hazard, MD504 Autoimmune EnteropathyINFLAMMATORY/IMMUNE DYSFUNCTION508 Celiac Disease514 Common Variable ImmunodeficiencyJoel K. Greenson, MD, Laura W. Lamps, MD, and Alexandros D. Polydorides, MD, PhD518 Giardia520 CryptosporidiumAPPENDIX522 Acute AppendicitisLaura W. Lamps, MD and Karen S. Thompson, MD526 Granulomatous Appendicitis528 Enterobius Vermicularis Appendicitis530 Fibrous ObliterationScott R. Owens, MDCOLON532 Cystic Fibrosis, IntestinalKajsa Affolter, MD and Alexandros D. Polydorides, MD, PhD534 Colonic Duplications, Cysts, and CongenitalDiverticula538 Hirschsprung Disease544 Intestinal Motility Disorders546 Diversion Colitis548 Pneumatosis Intestinalis554 Solitary Rectal Ulcer Syndrome/Mucosal Prolapse560 Necrotizing Enterocolitis562 Eosinophilic/Allergic Colitis568 Focal Active Colitis570 Crohn Disease582 Ulcerative ColitisAlexandros D. Polydorides, MD, PhD and Scott R. Owens, MD590 Collagenous Colitis598 Cytomegalovirus604 Entamoeba Histolytica606 AdenovirusKaren S. Thompson, MD and Laura W. Lamps, MD608 Acute Infectious Colitis610 Pseudomembranous ColitisStaci Bryson, MD and Angelica R. Putnam, MDSECTION 10: LIVER/GALLBLADDER616 Congenital Hepatic FibrosisRomil Saxena, MBBS, MD, FRCPath and Hanlin L. Wang, MD, PhD618 Caroli DiseaseRomil Saxena, MBBS, MD, FRCPath and Joseph Misdraji, MD620 Cystic Fibrosis, HepaticJoseph Misdraji, MD624 Dubin-Johnson Syndrome626 Gilbert Disease628 Progressive Familial Intrahepatic Cholestasis636 Biliary AtresiaRomil Saxena, MBBS, MD, FRCPath and Grace E. Kim, MD642 Syndromic Paucity of Intrahepatic Bile Ducts(Alagille Syndrome)646 Paucity of Intrahepatic Bile Ducts (Nonsyndromic)650 Autoimmune HepatitisLisa Yerian, MD and Karen S. Thompson, MD656 ?-1-Antitrypsin DeficiencyKari D. Caradine, MD and Angelica R. Putnam, MD660 Glycogen Storage DiseaseJoseph Misdraji, MD, Lisa Yerian, MD, and Grace E. Kim, MD666 Niemann-Pick Disease668 Tyrosinemia670 Gaucher Disease672 Neonatal HemochromatosisMatthew M. Yeh, MD, PhD674 Wilson Disease680 Choledochal Cyst682 Intestinal Failure-Associated Liver Disease (TotalParenteral Nutrition Injury)Florette K. Gray Hazard, MD and Angelica R. Putnam, MD686 Neonatal Hepatitis690 Reye SyndromeRomil Saxena, MBBS, MD, FRCPath and Laura W. Lamps, MD692 Nonalcoholic Fatty Liver Disease and NonalcoholicSteatohepatitisMatthew M. Yeh, MD, PhD and Karen S. Thompson, MD696 Primary Sclerosing CholangitisHanlin L. Wang, MD, PhD700 Venoocclusive DiseaseSanjay Kakar, MD702 Drug-Related Acute HepatitisSanjay Kakar, MD and Angelica R. Putnam, MD706 Viral HepatitisLisa Yerian, MD710 Epstein-Barr VirusHanlin L. Wang, MD, PhD and Angelica R. Putnam, MD714 Herpes Simplex Virus Hepatitis716 CytomegalovirusKari D. Caradine, MDSECTION 11: GENITOURINARYKIDNEY/URINARY TRACTGLOMERULAR DISEASES720 Congenital Nephrotic SyndromeMikako Warren, MD726 Diffuse Mesangial Sclerosis732 Minimal Change Disease740 Focal Segmental GlomerulosclerosisMikako Warren, MD and A. Brad Farris, III, MD752 Acute Postinfectious Glomerulonephritis760 Membranoproliferative Glomerulonephritis768 C3 GlomerulonephritisLynn D. Cornell, MD774 Dense Deposit DiseaseA. Brad Farris, III, MD780 Systemic Lupus ErythematosusShane Meehan, MB, BCh, Robert B. Colvin, MD, andIngeborg Bajema, MD798 IgA Nephropathy808 Henoch-Schönlein Purpura Nephritis816 Thin Basement Membrane Nephropathy820 Alport SyndromeTUBULOINTERSTITIAL DISEASES830 Acute Tubular InjuryShane Meehan, MB, BCh836 Acute PyelonephritisNeeraja Kambham, MD844 Tubulointerstitial Nephritis With Uveitis848 Primary HyperoxaluriaVASCULAR DISEASES850 Fibromuscular Dysplasia (Renal Artery Stenosis)856 Hemolytic Uremic Syndrome, Infection Related and AtypicalNeeraja Kambham, MD and Ivy A. Rosales, MD862 Vasculitis, ANCA RelatedCYSTIC AND DEVELOPMENTAL DISEASES868 Reflux NephropathySanjay Jain, MD, PhD872 Polycystic Kidney Disease, Autosomal RecessiveStephen M. Bonsib, MD876 Polycystic Kidney Disease, Autosomal DominantAnthony Chang, MD880 Medullary Cystic Kidney Disease/NephronophthisisHelen Liapis, MD882 Renal DysplasiaSanjay Jain, MD, PhD and Karen S. Thompson, MD886 Renal Tubular Dysgenesis888 Ask-Upmark KidneyREPRODUCTIVE SYSTEM890 Accessory Breast TissueJeffrey L. Killeen, MD892 CryptorchidismSteven S. Shen, MD, PhD896 Testicular Regression Syndrome898 Disorders of Sexual Development906 Hidradenitis SuppurativaJason C. Reutter, MD and Angelica R. Putnam, MD908 Childhood Behçet DiseaseMaria Angelica Selim, MD and Karen S. Thompson, MD912 Adnexal (Ovarian) TorsionBlaise Clarke, MD and Angelica R. Putnam, MD914 Meconium Periorchitis916 Testicular Torsion918 Ovarian CystsSECTION 12: HEMATOPOIETICLYMPH NODESREACTIVE LYMPHADENOPATHIES924 Reactive Follicular HyperplasiaC. Cameron Yin, MD, PhD and Andrea N. Marcogliese, MD930 Reactive Paracortical Hyperplasia938 Progressive Transformation of Germinal CentersL. Jeffrey Medeiros, MD and Roberto N. Miranda, MD944 Hyaline-Vascular Castleman DiseasePei Lin, MD and Andrea N. Marcogliese, MD950 Dermatopathic LymphadenitisSa A. Wang, MD and Andrea N. Marcogliese, MD956 Kimura DiseaseRoberto N. Miranda, MD, L. Jeffrey Medeiros, MD, and C.Cameron Yin, MD, PhD964 Kikuchi-Fujimoto Disease974 Rosai-Dorfman DiseaseINFECTIOUS LYMPHADENOPATHIES984 Infectious Mononucleosis LymphadenitisPei Lin, MD988 Cat-Scratch DiseaseRoberto N. Miranda, MD, L. Jeffrey Medeiros, MD, and Andrea N. Marcogliese, MD994 Mycobacterial InfectionTariq Muzzafar, MBBS1002 Chronic Granulomatous Lymphadenitis1010 Toxoplasma LymphadenitisCarlos E. Bueso-Ramos, MD, PhD and Andrea N. Marcogliese, MDBLOOD AND BONE MARROW1016 Chediak-Higashi SyndromeDavid R. Czuchlewski, MD and Andrea N. Marcogliese, MD1020 Congenital Amegakaryocytic Thrombocytopenia1024 Congenital Thrombotic Thrombocytopenic Purpura1028 Congenital Erythrocytosis1032 Diamond-Blackfan Anemia1036 Hereditary SpherocytosisCarla S. Wilson, MD, PhD and Andrea N. Marcogliese, MD1042 Hereditary ElliptocytosisKaaren K. Reichard, MD and Andrea N. Marcogliese, MD1046 Fanconi Anemia1050 Pyruvate Kinase DeficiencyKristin Hunt Karner, MD1052 Shwachman-Diamond Syndrome1056 Severe Congenital Neutropenia and CyclicNeutropenia1060 Sickle Cell Anemia1064 Hemophagocytic Lymphohistiocytosis1074 Thalassemia1080 Infectious Mononucleosis SyndromesCarla S. Wilson, MD, PhD1090 Parvovirus B19 Infection1094 Transient Erythroblastopenia of ChildhoodKathryn Foucar, MD and Andrea N. Marcogliese, MDTHYMUS1096 Acute Thymic Involution

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• SECTION 1: SKINSPONGIOTIC AND PSORIASIFORM DERMATOSES4 Pityriasis RoseaChristopher Lum, MD, Amity Tran, BA, and Emily Leibovitch, BA6 Contact DermatitisGeorge R. Collins, DO10 Atopic DermatitisWang L. Cheung, MD, PhD and Karen S. Thompson, MD12 Perniosis14 Seborrheic DermatitisKaren S. Thompson, MD, Angelica R. Putnam, MD, and Wang L. Cheung, MD, PhDINFLAMMATORY/INTERFACE DERMATOSES16 Erythema Multiforme and Related Disorders20 Pityriasis LichenoidesVESICOBULLOUS DERMATOSES24 Acropustulosis of InfancyLarissa V. Furtado, MD26 Dermatitis Herpetiformis28 Epidermolysis Bullosa, Inherited32 Erythema Toxicum Neonatorum34 Hailey-Hailey Disease36 Chronic Bullous Disease of Childhood38 Transient Neonatal Pustular MelanosisVASCULAR AND RELATED DISEASES40 Urticaria and Variants44 Leukocytoclastic VasculitisPANNICULITIDES48 Erythema Nodosum52 Subcutaneous Fat Necrosis of NewbornJessica M. Comstock, MD and Angelica R. Putnam, MD54 Sclerema NeonatorumCONNECTIVE TISSUE56 Lupus Erythematosus62 Morphea/Scleroderma66 DermatomyositisMETABOLIC/DEPOSITION DISEASES70 Calcinosis CutisDirk Elston, MD and Carly A. Elston, MDNONINFECTIOUS GRANULOMATOUS DISEASES74 Chalazion76 Granuloma AnnulareAngelica R. Putnam, MDPILOSEBACEOUS DISEASE78 Acne VulgarisViseslav Tonkovic-Capin, MDALOPECIAS80 TrichotillomaniaGarth Fraga, MDDISORDERS OF EPIDERMAL MATURATION AND KERATINIZATION84 IchthyosisMichael W. Peterson, DO86 Darier Disease88 Porokeratosis92 Incontinentia PigmentiChristine J. Ko, MDDISORDER OF COLLAGEN94 Aplasia Cutis CongenitaMichael W. Peterson, DO, Nathan Peterson, DO, and Karen S. Thompson, MDBACTERIAL INFECTIONS96 Impetigo100 Staphylococcal Scalded Skin Syndrome102 Ecthyma and Ecthyma Gangrenosum104 Cat-Scratch DiseaseIrina Margaritescu, MD, PhD and Bruce R. Smoller, MD110 Atypical Mycobacterial InfectionsCary Chisholm, MD and Karen S. Thompson, MDVIRAL INFECTIONS112 Molluscum ContagiosumTalley Whang, MD114 HerpesvirusFUNGAL INFECTIONS116 CandidiasisARTHROPODS/PARASITES120 Bite ReactionsAtsuko Kodama, MD124 ScabiesGonzalo De Toro, MDCYSTS126 Epidermal Inclusion Cyst128 Dermoid CystSECTION 2: SOFT TISSUE134 Necrotizing FasciitisBrian J. Hall, MD136 Tumoral CalcinosisKaren S. Thompson, MDSECTION 3: BONE AND JOINTCONGENITAL/GENETIC/HEREDITARY140 Osteogenesis Imperfecta144 Chondrodysplasia Punctata148 Thanatophoric DysplasiaTRAUMA/INJURY/REACTIVE150 Bone Fracture and Repair154 OsteomyelitisKaren S. Thompson, MD and Angelica R. Putnam, MD158 Stress and Costochondral Junction160 Juvenile Idiopathic ArthritisSECTION 4: SKELETAL MUSCLE166 Spinal Muscular AtrophyHannes Vogel, MD168 X-Linked Muscular Dystrophy: Duchenne and Becker172 Congenital MyopathiesSECTION 5: CENTRAL NERVOUS SYSTEM176 Cerebral Heterotopia and Ectopia178 Focal Cortical DysplasiaB. K. Kleinschmidt-DeMasters, MD192 MyelomeningoceleBrock Kaya, MD194 Encephalocele196 Tethered Cord198 Cerebral Arteriovenous MalformationsBrock Kaya, MD and Angelica R. Putnam, MD202 Cerebral Cavernous Malformation206 Hypoxic-Ischemic EncephalopathyBahig M. Shehata, MD, Cynthia T. Bunting, BS, and Phillip Quigley, BS210 Periventricular LeukomalaciaBahig M. Shehata, MD, Nancy Elawabdeh, BS, and Caitlin Cundiff, BS214 Arachnoid CystsTarik Tihan, MD, PhD and Karen S. Thompson, MD216 Meningioangiomatosis222 Germinal Matrix-Intraventricular HemorrhageBahig M. Shehata, MD and Nancy Elawabdeh, BSINFECTIOUS226 Bacterial Meningoencephalitis232 Fungal Meningoencephalitis238 Viral Meningoencephalitis242 Protozoal MeningoencephalitisSECTION 6: ENDOCRINE248 Adrenal CytomegalyArthur S. Tischler, MD250 Adrenal Heterotopia252 Adrenal Hypoplasia and MalformationsArthur S. Tischler, MD and Karen S. Thompson, MD254 Adrenal Cortical Hyperplasia258 Dyshormonogenetic GoiterVania Nosé, MD, PhD264 Ectopic Thyroid266 Thyroglossal Duct Cyst268 Cystic Fibrosis, PancreasMari Mino-Kenudson, MD270 Stress Reactions in Adrenal GlandBahig M. Shehata, MD, Holly C. Jordan, BS, and Erica J. Colvin, MD272 Hemorrhagic Necrosis of Adrenal GlandBahig M. Shehata, MD, Holly C. Jordan, BS, and Sydney R. Archer, BS274 Chronic Lymphocytic ThyroiditisBahig M. Shehata, MD, Brent M. Cone, BS, and Cynthia T. Bunting, BS278 Graves Disease284 Hypertrophy of Pancreatic IsletsJessica M. Comstock, MDSECTION 7: RESPIRATORY288 Bronchogenic CystBahig M. Shehata, MD, Nancy Elawabdeh, BS, and Charlotte A. Cooper, BS290 Congenital Alveolar Capillary DysplasiaBahig M. Shehata, MD, Ryan J. Cone, BS, and Charlotte A. Cooper, BS294 Congenital Lobar EmphysemaJessica M. Comstock, MD and Karen S. Thompson, MD296 Congenital Pulmonary LymphangiectasisBillie Fyfe, MD298 Diffuse Pulmonary LymphangiomatosisMonica P. Revelo, MD, PhD and Brandon T. Larsen, MD, PhD302 Congenital Pulmonary Airway Malformation306 Congenital Surfactant DeficiencyBillie Fyfe, MD and Eileen Margaret McKay, MD310 Cystic Fibrosis314 Sequestrations316 Aspiration320 Asthma322 Bronchopulmonary DysplasiaLarissa V. Furtado, MD and Karen S. Thompson, MD326 Hyaline Membrane Disease328 Interstitial Pulmonary EmphysemaLarissa V. Furtado, MD and Angelica R. Putnam, MD330 Persistent Pulmonary Hypertension332 Idiopathic Pulmonary HemosiderosisSaul Suster, MD334 Pulmonary Venoocclusive Disease/PulmonaryCapillary HemangiomatosisBahig M. Shehata, MD, Angelica R. Putnam, MD, and Charlotte A. Cooper, BS338 Nonspecific Interstitial Pneumonia340 Hypersensitivity PneumonitisCesar A. Moran, MD, Neda Kalhor, MD, and Karen S. Thompson, MD342 Eosinophilic PneumoniaCesar A. Moran, MD and Neda Kalhor, MD346 AdenovirusSaul Suster, MD and Karen S. Thompson, MD348 Human MetapneumovirusBahig M. Shehata, MD, Samuel N. Jactel, BS, and Nancy Elawabdeh, BS352 Respiratory Syncytial VirusMISCELLANEOUS354 Neuroendocrine Cell Hyperplasia of InfancySECTION 8: CARDIOVASCULAR358 Arrhythmogenic Right Ventricular CardiomyopathyJagdish Butany, MBBS, MS, FRCPC and Karen S. Thompson, MD362 Hypertrophic CardiomyopathyVidhya Nair, MBBS, MD, FRCPC364 Dilated CardiomyopathyJennifer Pogoriler, MD, PhD368 Fabry DiseaseMonica P. Revelo, MD, PhD372 Fatty Acid Metabolic Disorders374 Glycogen Storage Diseases376 Mitochondrial Myopathies380 Capillary Malformations384 Lymphatic Malformations388 Venous Malformations392 Arteriovenous Malformations and Fistulas396 Endocardial Fibroelastosis398 Lymphocytic Myocarditis402 Acute Pericarditis406 Acute Rheumatic Fever410 Kawasaki Disease414 COVID-19-Related Pathology and PediatricMultisystem Inflammatory SyndromeSECTION 9: ALIMENTARY CANALESOPHAGUS426 Inlet PatchAlexandros D. Polydorides, MD, PhD430 Tracheoesophageal Fistula and Esophageal Atresia434 Esophageal Duplication Cyst438 Gastroesophageal Reflux Disease444 Eosinophilic Esophagitis448 Herpes Simplex Virus EsophagitisLaura W. Lamps, MD450 CandidaSTOMACH452 Chemical GastropathyGregory Y. Lauwers, MD and Alexandros D. Polydorides, MD, PhD456 Chronic GastritisAlexandros D. Polydorides, MD, PhD and Staci Bryson, MD458 Granulomatous GastritisAlexandros D. Polydorides, MD, PhD and Gregory Y. Lauwers, MD462 Lymphocytic Gastritis468 Eosinophilic GastroenteritisGregory Y. Lauwers, MD and Karen S. Thompson, MD470 Fundic Gland Polyp472 Collagenous Gastritis476 Helicobacter heilmannii GastritisJoel K. Greenson, MD and Alexandros D. Polydorides, MD, PhD478 Helicobacter pylori GastritisSMALL BOWEL482 Small Intestine Duplication Cyst484 Ectopic PancreasAlexandros D. Polydorides, MD, PhD and Joel K. Greenson, MD488 Gastric Heterotopia490 Meckel Diverticulum492 Microvillous Inclusion Disease494 Primary Intestinal LymphangiectasiaJoel K. Greenson, MD and Karen S. Thompson, MD496 AbetalipoproteinemiaFlorette K. Gray Hazard, MD and Karen S. Thompson, MD500 Tufting EnteropathyAlexandros D. Polydorides, MD, PhD and Florette K. Gray Hazard, MD504 Autoimmune EnteropathyINFLAMMATORY/IMMUNE DYSFUNCTION508 Celiac Disease514 Common Variable ImmunodeficiencyJoel K. Greenson, MD, Laura W. Lamps, MD, and Alexandros D. Polydorides, MD, PhD518 Giardia520 CryptosporidiumAPPENDIX522 Acute AppendicitisLaura W. Lamps, MD and Karen S. Thompson, MD526 Granulomatous Appendicitis528 Enterobius Vermicularis Appendicitis530 Fibrous ObliterationScott R. Owens, MDCOLON532 Cystic Fibrosis, IntestinalKajsa Affolter, MD and Alexandros D. Polydorides, MD, PhD534 Colonic Duplications, Cysts, and CongenitalDiverticula538 Hirschsprung Disease544 Intestinal Motility Disorders546 Diversion Colitis548 Pneumatosis Intestinalis554 Solitary Rectal Ulcer Syndrome/Mucosal Prolapse560 Necrotizing Enterocolitis562 Eosinophilic/Allergic Colitis568 Focal Active Colitis570 Crohn Disease582 Ulcerative ColitisAlexandros D. Polydorides, MD, PhD and Scott R. Owens, MD590 Collagenous Colitis598 Cytomegalovirus604 Entamoeba Histolytica606 AdenovirusKaren S. Thompson, MD and Laura W. Lamps, MD608 Acute Infectious Colitis610 Pseudomembranous ColitisStaci Bryson, MD and Angelica R. Putnam, MDSECTION 10: LIVER/GALLBLADDER616 Congenital Hepatic FibrosisRomil Saxena, MBBS, MD, FRCPath and Hanlin L. Wang, MD, PhD618 Caroli DiseaseRomil Saxena, MBBS, MD, FRCPath and Joseph Misdraji, MD620 Cystic Fibrosis, HepaticJoseph Misdraji, MD624 Dubin-Johnson Syndrome626 Gilbert Disease628 Progressive Familial Intrahepatic Cholestasis636 Biliary AtresiaRomil Saxena, MBBS, MD, FRCPath and Grace E. Kim, MD642 Syndromic Paucity of Intrahepatic Bile Ducts(Alagille Syndrome)646 Paucity of Intrahepatic Bile Ducts (Nonsyndromic)650 Autoimmune HepatitisLisa Yerian, MD and Karen S. Thompson, MD656 ?-1-Antitrypsin DeficiencyKari D. Caradine, MD and Angelica R. Putnam, MD660 Glycogen Storage DiseaseJoseph Misdraji, MD, Lisa Yerian, MD, and Grace E. Kim, MD666 Niemann-Pick Disease668 Tyrosinemia670 Gaucher Disease672 Neonatal HemochromatosisMatthew M. Yeh, MD, PhD674 Wilson Disease680 Choledochal Cyst682 Intestinal Failure-Associated Liver Disease (TotalParenteral Nutrition Injury)Florette K. Gray Hazard, MD and Angelica R. Putnam, MD686 Neonatal Hepatitis690 Reye SyndromeRomil Saxena, MBBS, MD, FRCPath and Laura W. Lamps, MD692 Nonalcoholic Fatty Liver Disease and NonalcoholicSteatohepatitisMatthew M. Yeh, MD, PhD and Karen S. Thompson, MD696 Primary Sclerosing CholangitisHanlin L. Wang, MD, PhD700 Venoocclusive DiseaseSanjay Kakar, MD702 Drug-Related Acute HepatitisSanjay Kakar, MD and Angelica R. Putnam, MD706 Viral HepatitisLisa Yerian, MD710 Epstein-Barr VirusHanlin L. Wang, MD, PhD and Angelica R. Putnam, MD714 Herpes Simplex Virus Hepatitis716 CytomegalovirusKari D. Caradine, MDSECTION 11: GENITOURINARYKIDNEY/URINARY TRACTGLOMERULAR DISEASES720 Congenital Nephrotic SyndromeMikako Warren, MD726 Diffuse Mesangial Sclerosis732 Minimal Change Disease740 Focal Segmental GlomerulosclerosisMikako Warren, MD and A. Brad Farris, III, MD752 Acute Postinfectious Glomerulonephritis760 Membranoproliferative Glomerulonephritis768 C3 GlomerulonephritisLynn D. Cornell, MD774 Dense Deposit DiseaseA. Brad Farris, III, MD780 Systemic Lupus ErythematosusShane Meehan, MB, BCh, Robert B. Colvin, MD, andIngeborg Bajema, MD798 IgA Nephropathy808 Henoch-Schönlein Purpura Nephritis816 Thin Basement Membrane Nephropathy820 Alport SyndromeTUBULOINTERSTITIAL DISEASES830 Acute Tubular InjuryShane Meehan, MB, BCh836 Acute PyelonephritisNeeraja Kambham, MD844 Tubulointerstitial Nephritis With Uveitis848 Primary HyperoxaluriaVASCULAR DISEASES850 Fibromuscular Dysplasia (Renal Artery Stenosis)856 Hemolytic Uremic Syndrome, Infection Related and AtypicalNeeraja Kambham, MD and Ivy A. Rosales, MD862 Vasculitis, ANCA RelatedCYSTIC AND DEVELOPMENTAL DISEASES868 Reflux NephropathySanjay Jain, MD, PhD872 Polycystic Kidney Disease, Autosomal RecessiveStephen M. Bonsib, MD876 Polycystic Kidney Disease, Autosomal DominantAnthony Chang, MD880 Medullary Cystic Kidney Disease/NephronophthisisHelen Liapis, MD882 Renal DysplasiaSanjay Jain, MD, PhD and Karen S. Thompson, MD886 Renal Tubular Dysgenesis888 Ask-Upmark KidneyREPRODUCTIVE SYSTEM890 Accessory Breast TissueJeffrey L. Killeen, MD892 CryptorchidismSteven S. Shen, MD, PhD896 Testicular Regression Syndrome898 Disorders of Sexual Development906 Hidradenitis SuppurativaJason C. Reutter, MD and Angelica R. Putnam, MD908 Childhood Behçet DiseaseMaria Angelica Selim, MD and Karen S. Thompson, MD912 Adnexal (Ovarian) TorsionBlaise Clarke, MD and Angelica R. Putnam, MD914 Meconium Periorchitis916 Testicular Torsion918 Ovarian CystsSECTION 12: HEMATOPOIETICLYMPH NODESREACTIVE LYMPHADENOPATHIES924 Reactive Follicular HyperplasiaC. Cameron Yin, MD, PhD and Andrea N. Marcogliese, MD930 Reactive Paracortical Hyperplasia938 Progressive Transformation of Germinal CentersL. Jeffrey Medeiros, MD and Roberto N. Miranda, MD944 Hyaline-Vascular Castleman DiseasePei Lin, MD and Andrea N. Marcogliese, MD950 Dermatopathic LymphadenitisSa A. Wang, MD and Andrea N. Marcogliese, MD956 Kimura DiseaseRoberto N. Miranda, MD, L. Jeffrey Medeiros, MD, and C.Cameron Yin, MD, PhD964 Kikuchi-Fujimoto Disease974 Rosai-Dorfman DiseaseINFECTIOUS LYMPHADENOPATHIES984 Infectious Mononucleosis LymphadenitisPei Lin, MD988 Cat-Scratch DiseaseRoberto N. Miranda, MD, L. Jeffrey Medeiros, MD, and Andrea N. Marcogliese, MD994 Mycobacterial InfectionTariq Muzzafar, MBBS1002 Chronic Granulomatous Lymphadenitis1010 Toxoplasma LymphadenitisCarlos E. Bueso-Ramos, MD, PhD and Andrea N. Marcogliese, MDBLOOD AND BONE MARROW1016 Chediak-Higashi SyndromeDavid R. Czuchlewski, MD and Andrea N. Marcogliese, MD1020 Congenital Amegakaryocytic Thrombocytopenia1024 Congenital Thrombotic Thrombocytopenic Purpura1028 Congenital Erythrocytosis1032 Diamond-Blackfan Anemia1036 Hereditary SpherocytosisCarla S. Wilson, MD, PhD and Andrea N. Marcogliese, MD1042 Hereditary ElliptocytosisKaaren K. Reichard, MD and Andrea N. Marcogliese, MD1046 Fanconi Anemia1050 Pyruvate Kinase DeficiencyKristin Hunt Karner, MD1052 Shwachman-Diamond Syndrome1056 Severe Congenital Neutropenia and CyclicNeutropenia1060 Sickle Cell Anemia1064 Hemophagocytic Lymphohistiocytosis1074 Thalassemia1080 Infectious Mononucleosis SyndromesCarla S. Wilson, MD, PhD1090 Parvovirus B19 Infection1094 Transient Erythroblastopenia of ChildhoodKathryn Foucar, MD and Andrea N. Marcogliese, MDTHYMUS1096 Acute Thymic Involution

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• SECTION 1: SKINSPONGIOTIC AND PSORIASIFORM DERMATOSES4 Pityriasis RoseaChristopher Lum, MD, Amity Tran, BA, and Emily Leibovitch, BA6 Contact DermatitisGeorge R. Collins, DO10 Atopic DermatitisWang L. Cheung, MD, PhD and Karen S. Thompson, MD12 Perniosis14 Seborrheic DermatitisKaren S. Thompson, MD, Angelica R. Putnam, MD, and Wang L. Cheung, MD, PhDINFLAMMATORY/INTERFACE DERMATOSES16 Erythema Multiforme and Related Disorders20 Pityriasis LichenoidesVESICOBULLOUS DERMATOSES24 Acropustulosis of InfancyLarissa V. Furtado, MD26 Dermatitis Herpetiformis28 Epidermolysis Bullosa, Inherited32 Erythema Toxicum Neonatorum34 Hailey-Hailey Disease36 Chronic Bullous Disease of Childhood38 Transient Neonatal Pustular MelanosisVASCULAR AND RELATED DISEASES40 Urticaria and Variants44 Leukocytoclastic VasculitisPANNICULITIDES48 Erythema Nodosum52 Subcutaneous Fat Necrosis of NewbornJessica M. Comstock, MD and Angelica R. Putnam, MD54 Sclerema NeonatorumCONNECTIVE TISSUE56 Lupus Erythematosus62 Morphea/Scleroderma66 DermatomyositisMETABOLIC/DEPOSITION DISEASES70 Calcinosis CutisDirk Elston, MD and Carly A. Elston, MDNONINFECTIOUS GRANULOMATOUS DISEASES74 Chalazion76 Granuloma AnnulareAngelica R. Putnam, MDPILOSEBACEOUS DISEASE78 Acne VulgarisViseslav Tonkovic-Capin, MDALOPECIAS80 TrichotillomaniaGarth Fraga, MDDISORDERS OF EPIDERMAL MATURATION AND KERATINIZATION84 IchthyosisMichael W. Peterson, DO86 Darier Disease88 Porokeratosis92 Incontinentia PigmentiChristine J. Ko, MDDISORDER OF COLLAGEN94 Aplasia Cutis CongenitaMichael W. Peterson, DO, Nathan Peterson, DO, and Karen S. Thompson, MDBACTERIAL INFECTIONS96 Impetigo100 Staphylococcal Scalded Skin Syndrome102 Ecthyma and Ecthyma Gangrenosum104 Cat-Scratch DiseaseIrina Margaritescu, MD, PhD and Bruce R. Smoller, MD110 Atypical Mycobacterial InfectionsCary Chisholm, MD and Karen S. Thompson, MDVIRAL INFECTIONS112 Molluscum ContagiosumTalley Whang, MD114 HerpesvirusFUNGAL INFECTIONS116 CandidiasisARTHROPODS/PARASITES120 Bite ReactionsAtsuko Kodama, MD124 ScabiesGonzalo De Toro, MDCYSTS126 Epidermal Inclusion Cyst128 Dermoid CystSECTION 2: SOFT TISSUE134 Necrotizing FasciitisBrian J. Hall, MD136 Tumoral CalcinosisKaren S. Thompson, MDSECTION 3: BONE AND JOINTCONGENITAL/GENETIC/HEREDITARY140 Osteogenesis Imperfecta144 Chondrodysplasia Punctata148 Thanatophoric DysplasiaTRAUMA/INJURY/REACTIVE150 Bone Fracture and Repair154 OsteomyelitisKaren S. Thompson, MD and Angelica R. Putnam, MD158 Stress and Costochondral Junction160 Juvenile Idiopathic ArthritisSECTION 4: SKELETAL MUSCLE166 Spinal Muscular AtrophyHannes Vogel, MD168 X-Linked Muscular Dystrophy: Duchenne and Becker172 Congenital MyopathiesSECTION 5: CENTRAL NERVOUS SYSTEM176 Cerebral Heterotopia and Ectopia178 Focal Cortical DysplasiaB. K. Kleinschmidt-DeMasters, MD192 MyelomeningoceleBrock Kaya, MD194 Encephalocele196 Tethered Cord198 Cerebral Arteriovenous MalformationsBrock Kaya, MD and Angelica R. Putnam, MD202 Cerebral Cavernous Malformation206 Hypoxic-Ischemic EncephalopathyBahig M. Shehata, MD, Cynthia T. Bunting, BS, and Phillip Quigley, BS210 Periventricular LeukomalaciaBahig M. Shehata, MD, Nancy Elawabdeh, BS, and Caitlin Cundiff, BS214 Arachnoid CystsTarik Tihan, MD, PhD and Karen S. Thompson, MD216 Meningioangiomatosis222 Germinal Matrix-Intraventricular HemorrhageBahig M. Shehata, MD and Nancy Elawabdeh, BSINFECTIOUS226 Bacterial Meningoencephalitis232 Fungal Meningoencephalitis238 Viral Meningoencephalitis242 Protozoal MeningoencephalitisSECTION 6: ENDOCRINE248 Adrenal CytomegalyArthur S. Tischler, MD250 Adrenal Heterotopia252 Adrenal Hypoplasia and MalformationsArthur S. Tischler, MD and Karen S. Thompson, MD254 Adrenal Cortical Hyperplasia258 Dyshormonogenetic GoiterVania Nosé, MD, PhD264 Ectopic Thyroid266 Thyroglossal Duct Cyst268 Cystic Fibrosis, PancreasMari Mino-Kenudson, MD270 Stress Reactions in Adrenal GlandBahig M. Shehata, MD, Holly C. Jordan, BS, and Erica J. Colvin, MD272 Hemorrhagic Necrosis of Adrenal GlandBahig M. Shehata, MD, Holly C. Jordan, BS, and Sydney R. Archer, BS274 Chronic Lymphocytic ThyroiditisBahig M. Shehata, MD, Brent M. Cone, BS, and Cynthia T. Bunting, BS278 Graves Disease284 Hypertrophy of Pancreatic IsletsJessica M. Comstock, MDSECTION 7: RESPIRATORY288 Bronchogenic CystBahig M. Shehata, MD, Nancy Elawabdeh, BS, and Charlotte A. Cooper, BS290 Congenital Alveolar Capillary DysplasiaBahig M. Shehata, MD, Ryan J. Cone, BS, and Charlotte A. Cooper, BS294 Congenital Lobar EmphysemaJessica M. Comstock, MD and Karen S. Thompson, MD296 Congenital Pulmonary LymphangiectasisBillie Fyfe, MD298 Diffuse Pulmonary LymphangiomatosisMonica P. Revelo, MD, PhD and Brandon T. Larsen, MD, PhD302 Congenital Pulmonary Airway Malformation306 Congenital Surfactant DeficiencyBillie Fyfe, MD and Eileen Margaret McKay, MD310 Cystic Fibrosis314 Sequestrations316 Aspiration320 Asthma322 Bronchopulmonary DysplasiaLarissa V. Furtado, MD and Karen S. Thompson, MD326 Hyaline Membrane Disease328 Interstitial Pulmonary EmphysemaLarissa V. Furtado, MD and Angelica R. Putnam, MD330 Persistent Pulmonary Hypertension332 Idiopathic Pulmonary HemosiderosisSaul Suster, MD334 Pulmonary Venoocclusive Disease/PulmonaryCapillary HemangiomatosisBahig M. Shehata, MD, Angelica R. Putnam, MD, and Charlotte A. Cooper, BS338 Nonspecific Interstitial Pneumonia340 Hypersensitivity PneumonitisCesar A. Moran, MD, Neda Kalhor, MD, and Karen S. Thompson, MD342 Eosinophilic PneumoniaCesar A. Moran, MD and Neda Kalhor, MD346 AdenovirusSaul Suster, MD and Karen S. Thompson, MD348 Human MetapneumovirusBahig M. Shehata, MD, Samuel N. Jactel, BS, and Nancy Elawabdeh, BS352 Respiratory Syncytial VirusMISCELLANEOUS354 Neuroendocrine Cell Hyperplasia of InfancySECTION 8: CARDIOVASCULAR358 Arrhythmogenic Right Ventricular CardiomyopathyJagdish Butany, MBBS, MS, FRCPC and Karen S. Thompson, MD362 Hypertrophic CardiomyopathyVidhya Nair, MBBS, MD, FRCPC364 Dilated CardiomyopathyJennifer Pogoriler, MD, PhD368 Fabry DiseaseMonica P. Revelo, MD, PhD372 Fatty Acid Metabolic Disorders374 Glycogen Storage Diseases376 Mitochondrial Myopathies380 Capillary Malformations384 Lymphatic Malformations388 Venous Malformations392 Arteriovenous Malformations and Fistulas396 Endocardial Fibroelastosis398 Lymphocytic Myocarditis402 Acute Pericarditis406 Acute Rheumatic Fever410 Kawasaki Disease414 COVID-19-Related Pathology and PediatricMultisystem Inflammatory SyndromeSECTION 9: ALIMENTARY CANALESOPHAGUS426 Inlet PatchAlexandros D. Polydorides, MD, PhD430 Tracheoesophageal Fistula and Esophageal Atresia434 Esophageal Duplication Cyst438 Gastroesophageal Reflux Disease444 Eosinophilic Esophagitis448 Herpes Simplex Virus EsophagitisLaura W. Lamps, MD450 CandidaSTOMACH452 Chemical GastropathyGregory Y. Lauwers, MD and Alexandros D. Polydorides, MD, PhD456 Chronic GastritisAlexandros D. Polydorides, MD, PhD and Staci Bryson, MD458 Granulomatous GastritisAlexandros D. Polydorides, MD, PhD and Gregory Y. Lauwers, MD462 Lymphocytic Gastritis468 Eosinophilic GastroenteritisGregory Y. Lauwers, MD and Karen S. Thompson, MD470 Fundic Gland Polyp472 Collagenous Gastritis476 Helicobacter heilmannii GastritisJoel K. Greenson, MD and Alexandros D. Polydorides, MD, PhD478 Helicobacter pylori GastritisSMALL BOWEL482 Small Intestine Duplication Cyst484 Ectopic PancreasAlexandros D. Polydorides, MD, PhD and Joel K. Greenson, MD488 Gastric Heterotopia490 Meckel Diverticulum492 Microvillous Inclusion Disease494 Primary Intestinal LymphangiectasiaJoel K. Greenson, MD and Karen S. Thompson, MD496 AbetalipoproteinemiaFlorette K. Gray Hazard, MD and Karen S. Thompson, MD500 Tufting EnteropathyAlexandros D. Polydorides, MD, PhD and Florette K. Gray Hazard, MD504 Autoimmune EnteropathyINFLAMMATORY/IMMUNE DYSFUNCTION508 Celiac Disease514 Common Variable ImmunodeficiencyJoel K. Greenson, MD, Laura W. Lamps, MD, and Alexandros D. Polydorides, MD, PhD518 Giardia520 CryptosporidiumAPPENDIX522 Acute AppendicitisLaura W. Lamps, MD and Karen S. Thompson, MD526 Granulomatous Appendicitis528 Enterobius Vermicularis Appendicitis530 Fibrous ObliterationScott R. Owens, MDCOLON532 Cystic Fibrosis, IntestinalKajsa Affolter, MD and Alexandros D. Polydorides, MD, PhD534 Colonic Duplications, Cysts, and CongenitalDiverticula538 Hirschsprung Disease544 Intestinal Motility Disorders546 Diversion Colitis548 Pneumatosis Intestinalis554 Solitary Rectal Ulcer Syndrome/Mucosal Prolapse560 Necrotizing Enterocolitis562 Eosinophilic/Allergic Colitis568 Focal Active Colitis570 Crohn Disease582 Ulcerative ColitisAlexandros D. Polydorides, MD, PhD and Scott R. Owens, MD590 Collagenous Colitis598 Cytomegalovirus604 Entamoeba Histolytica606 AdenovirusKaren S. Thompson, MD and Laura W. Lamps, MD608 Acute Infectious Colitis610 Pseudomembranous ColitisStaci Bryson, MD and Angelica R. Putnam, MDSECTION 10: LIVER/GALLBLADDER616 Congenital Hepatic FibrosisRomil Saxena, MBBS, MD, FRCPath and Hanlin L. Wang, MD, PhD618 Caroli DiseaseRomil Saxena, MBBS, MD, FRCPath and Joseph Misdraji, MD620 Cystic Fibrosis, HepaticJoseph Misdraji, MD624 Dubin-Johnson Syndrome626 Gilbert Disease628 Progressive Familial Intrahepatic Cholestasis636 Biliary AtresiaRomil Saxena, MBBS, MD, FRCPath and Grace E. Kim, MD642 Syndromic Paucity of Intrahepatic Bile Ducts(Alagille Syndrome)646 Paucity of Intrahepatic Bile Ducts (Nonsyndromic)650 Autoimmune HepatitisLisa Yerian, MD and Karen S. Thompson, MD656 ?-1-Antitrypsin DeficiencyKari D. Caradine, MD and Angelica R. Putnam, MD660 Glycogen Storage DiseaseJoseph Misdraji, MD, Lisa Yerian, MD, and Grace E. Kim, MD666 Niemann-Pick Disease668 Tyrosinemia670 Gaucher Disease672 Neonatal HemochromatosisMatthew M. Yeh, MD, PhD674 Wilson Disease680 Choledochal Cyst682 Intestinal Failure-Associated Liver Disease (TotalParenteral Nutrition Injury)Florette K. Gray Hazard, MD and Angelica R. Putnam, MD686 Neonatal Hepatitis690 Reye SyndromeRomil Saxena, MBBS, MD, FRCPath and Laura W. Lamps, MD692 Nonalcoholic Fatty Liver Disease and NonalcoholicSteatohepatitisMatthew M. Yeh, MD, PhD and Karen S. Thompson, MD696 Primary Sclerosing CholangitisHanlin L. Wang, MD, PhD700 Venoocclusive DiseaseSanjay Kakar, MD702 Drug-Related Acute HepatitisSanjay Kakar, MD and Angelica R. Putnam, MD706 Viral HepatitisLisa Yerian, MD710 Epstein-Barr VirusHanlin L. Wang, MD, PhD and Angelica R. Putnam, MD714 Herpes Simplex Virus Hepatitis716 CytomegalovirusKari D. Caradine, MDSECTION 11: GENITOURINARYKIDNEY/URINARY TRACTGLOMERULAR DISEASES720 Congenital Nephrotic SyndromeMikako Warren, MD726 Diffuse Mesangial Sclerosis732 Minimal Change Disease740 Focal Segmental GlomerulosclerosisMikako Warren, MD and A. Brad Farris, III, MD752 Acute Postinfectious Glomerulonephritis760 Membranoproliferative Glomerulonephritis768 C3 GlomerulonephritisLynn D. Cornell, MD774 Dense Deposit DiseaseA. Brad Farris, III, MD780 Systemic Lupus ErythematosusShane Meehan, MB, BCh, Robert B. Colvin, MD, andIngeborg Bajema, MD798 IgA Nephropathy808 Henoch-Schönlein Purpura Nephritis816 Thin Basement Membrane Nephropathy820 Alport SyndromeTUBULOINTERSTITIAL DISEASES830 Acute Tubular InjuryShane Meehan, MB, BCh836 Acute PyelonephritisNeeraja Kambham, MD844 Tubulointerstitial Nephritis With Uveitis848 Primary HyperoxaluriaVASCULAR DISEASES850 Fibromuscular Dysplasia (Renal Artery Stenosis)856 Hemolytic Uremic Syndrome, Infection Related and AtypicalNeeraja Kambham, MD and Ivy A. Rosales, MD862 Vasculitis, ANCA RelatedCYSTIC AND DEVELOPMENTAL DISEASES868 Reflux NephropathySanjay Jain, MD, PhD872 Polycystic Kidney Disease, Autosomal RecessiveStephen M. Bonsib, MD876 Polycystic Kidney Disease, Autosomal DominantAnthony Chang, MD880 Medullary Cystic Kidney Disease/NephronophthisisHelen Liapis, MD882 Renal DysplasiaSanjay Jain, MD, PhD and Karen S. Thompson, MD886 Renal Tubular Dysgenesis888 Ask-Upmark KidneyREPRODUCTIVE SYSTEM890 Accessory Breast TissueJeffrey L. Killeen, MD892 CryptorchidismSteven S. Shen, MD, PhD896 Testicular Regression Syndrome898 Disorders of Sexual Development906 Hidradenitis SuppurativaJason C. Reutter, MD and Angelica R. Putnam, MD908 Childhood Behçet DiseaseMaria Angelica Selim, MD and Karen S. Thompson, MD912 Adnexal (Ovarian) TorsionBlaise Clarke, MD and Angelica R. Putnam, MD914 Meconium Periorchitis916 Testicular Torsion918 Ovarian CystsSECTION 12: HEMATOPOIETICLYMPH NODESREACTIVE LYMPHADENOPATHIES924 Reactive Follicular HyperplasiaC. Cameron Yin, MD, PhD and Andrea N. Marcogliese, MD930 Reactive Paracortical Hyperplasia938 Progressive Transformation of Germinal CentersL. Jeffrey Medeiros, MD and Roberto N. Miranda, MD944 Hyaline-Vascular Castleman DiseasePei Lin, MD and Andrea N. Marcogliese, MD950 Dermatopathic LymphadenitisSa A. Wang, MD and Andrea N. Marcogliese, MD956 Kimura DiseaseRoberto N. Miranda, MD, L. Jeffrey Medeiros, MD, and C.Cameron Yin, MD, PhD964 Kikuchi-Fujimoto Disease974 Rosai-Dorfman DiseaseINFECTIOUS LYMPHADENOPATHIES984 Infectious Mononucleosis LymphadenitisPei Lin, MD988 Cat-Scratch DiseaseRoberto N. Miranda, MD, L. Jeffrey Medeiros, MD, and Andrea N. Marcogliese, MD994 Mycobacterial InfectionTariq Muzzafar, MBBS1002 Chronic Granulomatous Lymphadenitis1010 Toxoplasma LymphadenitisCarlos E. Bueso-Ramos, MD, PhD and Andrea N. Marcogliese, MDBLOOD AND BONE MARROW1016 Chediak-Higashi SyndromeDavid R. Czuchlewski, MD and Andrea N. Marcogliese, MD1020 Congenital Amegakaryocytic Thrombocytopenia1024 Congenital Thrombotic Thrombocytopenic Purpura1028 Congenital Erythrocytosis1032 Diamond-Blackfan Anemia1036 Hereditary SpherocytosisCarla S. Wilson, MD, PhD and Andrea N. Marcogliese, MD1042 Hereditary ElliptocytosisKaaren K. Reichard, MD and Andrea N. Marcogliese, MD1046 Fanconi Anemia1050 Pyruvate Kinase DeficiencyKristin Hunt Karner, MD1052 Shwachman-Diamond Syndrome1056 Severe Congenital Neutropenia and CyclicNeutropenia1060 Sickle Cell Anemia1064 Hemophagocytic Lymphohistiocytosis1074 Thalassemia1080 Infectious Mononucleosis SyndromesCarla S. Wilson, MD, PhD1090 Parvovirus B19 Infection1094 Transient Erythroblastopenia of ChildhoodKathryn Foucar, MD and Andrea N. Marcogliese, MDTHYMUS1096 Acute Thymic Involution