Impaired lymphatic drainage and consequent lymph-edema usually results from a localized obstruction caused by an inflammatory or neoplastic condition. For example, the parasitic infection filariasis can cause massive edema of the lower extremity and external genitalia (so-called “elephantiasis”) by producing inguinal lymphatic and lymph node fibrosis. Infiltration and obstruction of superficial lymphatics by breast cancer may cause edema of the overlying skin; the characteristic finely pitted appearance of the skin of the affected breast is called peau d’orange (orange peel). Lymphedema also may occur as a complication of therapy. One relatively common setting for this clinical entity is in women with breast cancer who undergo axillary lymph node resection and/or irradiation, both of which can disrupt and obstruct lymphatic drainage, resulting in severe lymphedema of the arm.
HEART FAILURE RENAL FAILURE MALNUTRITION, HEPATIC SYNTHESIS, NEPHROTIC SYNDROME Capillary hydrostatic pressure Renal blood flow Activation of the renin-angiotensin-aldosterone system Retention of Na+ and H2O EDEMA Blood volume Plasma albumin Plasma osmotic pressure
Fig. 4.3 Pathwaysleadingtosystemicedemaresultingfromheartfailure,renalfailure,orreducedplasmaosmoticpressure.
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Excessive retention of salt (and its obligate associated water) can lead to edema by increasing hydrostatic pressure (because of expansion of the intravascular volume) and reducing plasma osmotic pressure. Excessive salt and water retention are seen in a wide variety of diseases that compromise renal function, including poststreptococcal glomerulonephritis and acute renal failure (Chapter 14).
MORPHOLOGYEdemaiseasilyrecognizedongrossinspection;microscopicexaminationshowsclearingandseparationoftheextracellularmatrix(ECM)elements.Althoughanytissuecanbeinvolved,edemamostcommonlyisencounteredinsubcutaneoustissues,lungs,andbrain.
Subcutaneous edema canbediffusebutusuallyaccumulatespreferentiallyinpartsofthebodypositionedthegreatestdistancebelowtheheart,wherehydrostaticpressuresarehighest.Thus,edematypicallyismostpronouncedinthelegswithstandingandthesacrumwithrecumbency,arelationshiptermeddependent edema. Fingerpressureoveredematoussubcutaneoustissuedisplacestheinterstitialfluid,leavingafinger-shapeddepression;thisappearanceiscalledpitting edema. Edemaresultingfromrenal dysfunction ornephrotic syndrome oftenmanifestsfirstinlooseconnectivetissues(e.g.,theeyelids,causingperiorbitaledema).Withpulmonary edema, thelungsoftenaretwotothreetimestheirnormalweight,andsectioningshowsfrothy,sometimesblood-tingedfluidconsistingofamixtureofair,edemafluid,andextravasatedredcells.Brain edema (Chapter23)canbelocalized(e.g.,becauseofabscessortumor)orgeneralized,dependingonthenatureandextentofthepathologicprocessorinjury.Withgeneralizededema,thesulciarenarrowedasthegyriswellandbecomeflattenedagainsttheskull.