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Spleen, Thymus, Thymus DEVELOPMENTAL DISORDERS THYMIC HYPOPLASIA/APLASIA in DiGeorge Syndrome -also parathyroid failure -can also have heart/great vessel malfcns ->lack of T-cell Immunity, hypoparathyroidism THYMIC CYSTS-uncommon, asymptomatic -serous or mucinous fluid, can be hemorrhage -no clinical significance, Spleen SPLENOMEGALY Congestive Splenomegaly- -persistent/chronic venous congestion -Causes: systemic, intrahepatic derangement of portal vein, obstructive venous disorders in splenic/portal vein ->all lead to portal or splenic vein HTN Systemic (central venous) congestion (500gm) in card. decompensation of right side of heart -from tricuspid/pulmonic valvular dz -chronic cor pulmonale -left-sided heart failure Alcoholic or Pigment cirrhosis-diffuse fibrous scarring ->most extreme enlargements Spontaneous Portal Vein Thrombosis Splenic Vein Thrombosis via pressure of nearby tumors -stomach or pancreas MORPHOLOGY Longstanding - 1000-5000, increasingly firm -capsule uninvolved -collagen deposits in BM of sinusoids->no passage ->hypersplenism -focal hemorrhages->Gandy-Gamna nodules-fibrosis -contains Fe, Ca deposits on CT, elastin, Thymus CAs Arising in Thymus Germ Cell Tumors Lymphomas HD Carcinoids, Thymus Normal Function Derived from 3rd, inconstantly 4th phar. puch -with lower parathyroid glands (can end up in thymic capsule) -thymus grows til puberty, then atrophies smaller than baby's -fibrofatty tissue replaces parenchyma -can also involute due to severe stress, HIV infx Pyramid shape, 2 fused lobes Thymic epith cells and T-lymphocytes predominate -packed along cortex, more structured lattice in medulla, deep cortex Cortex-epith cells w/ abundant cyto, pale nuc, small nucleoli, cytoplasmic extensions to other cells -Superficial Cortex-large prothymocytes w/ early T-cell markers-CD2 -Deeper Cortex-smaller, maturer thymocytes w/ CD1, CD2, CD3, CD4, CD8 Medulla-epith cells w/ scant cytosol, more oval, no cyto. extensions can be spindled, dark nuclei, whorls of these -> Hassall Corpuscles -larger thymocytes, CD1,2,3 and either CD4 or CD8 Also in thymus-macs, DCs, rare eos, neutrophils, B-cells, myoid (mm.) cells, Spleen RUPTURE Caused by crushing injury or severe blow -Rarely, a spontaneous rupture -most often in infx mononucleosis, malaria, typhoid fever, leukemia, other acute splenitis -->extensive, massive intraperitoneal hemorrhage -must be surgically removed to prevent blood loss/shock, Spleen SPLENOMEGALY General Features: -cause dragging sensation in left UQ -pressure on stomach->discomfort after eating Hypersplenism-unknown cause 1.Splenomegaly 2.One or pancytopenia b/c storage of cells 3.Correction via splenectomy, Spleen Anatomic Disorders Often secondary dz (not primary) due to: 1.Filtration of unwanted elements-1/120 RBCs/day -macs can remove RBCs or "pit" them by removing Heinz -also remove bac, cell debris, ABNL molecules (metabolic dz) -remove Ag-coated or ABNL RBCs (spheres, sickle cell) 2.Immune Function-major 2ndary organ -reticular network traps Ags->lymphocyte contact 3.Lymphoreticular Cell source, sometimes hematopoiesis -before birth, and takes over in severe anemia 4.Reserve Pool and Storage Site of RBCs-30-40mL -in splenomegaly->greatly increased -can store 80-90% total platelets, lots of WBCs ->leukopenia, Thymus THYMIC HYPERPLASIA -lymphoid follicles appear in thymus -'thymic follic hyperplasia' -follics like in LNs, w/ GCs, FDCs, and B-cells -mostly in MYASTHENIA GRAVIS (65-76% of MG) -also in other autoimmune dzs-Graves, SLE, SD, RA, Spleen SPLENOMEGALY Nonspecific Acute Splenitis -"acute splenic tumor" -via any blood-borne infx -via bac or inflam. agents MORPHOLOGY-200-400gm, soft -red pulp congestion can efface lym follicles -inflam infiltrate sometimes in red/white pulp -sometimes acute necrosis of center of follic. -esp in hemolytic streptococcus -rarely, abscess formation, Thymus THYMOMAS Tumors of Thymic Epith Cells ONLY -can have few or lots of bkgrd thymocytes -not monoclonal or tumorous 2 Types: BENIGN/ENCAPSULATED-majority -spindle-cell/medullary thymoma -few thymocytes MALIGNANT THYMOMA Type 1-INVASIVE-cytologically benign -but biologically aggressive -PENETRATE CAPSULE, INVADE -25% fo thymomas Type 2-THYMIC CARCINOMA-5% -cytologically malignant -anaplasia -fleshy and invasive -mostly SCCs, poorly diff'ated, EXPRESS CD5 -dense bkgrd of non-neo thymocytes -some lymphepitheliomas have EBV (Asians) Both in adults ᡠ MALE=FEMALE 20-30% of mediastinal CA (HD, some NHL) MORPHOLOGY-lobulated, firm -may have some necrosis, Calcification CLINICAL -40%-thymic masses on imaging/local pressure Sx -40-45%-myasthenia gravis -few discovered incidentally during cardiac surgery