Germcelltumorsmaydifferentiatetowardoogonia(dysgerminoma),primitiveembryonaltissue(embryonal),yolksac(endodermalsinustumor),placentaltissue(choriocarcinoma),ormultipletissuetypes(teratoma).
Diseases of pregnancy and pathologic conditions of the placenta are important contributors to morbidity and mortality for both mother and child. Discussed in this section are a limited number of disorders in which knowledge of the morphologic lesions contributes to an understanding of clinical disease.
Infections may reach the placenta by either of two paths: (1) ascension through the birth canal or (2) hematogenous (transplacental) spread.
Ascending infections are by far the more common; in most instances they are bacterial and are associated with premature rupture of the fetal membranes. On microscopic examination, the chorioamnion shows neutrophilic infiltration associated with edema and congestion (acute chorioamnionitis). With extension beyond the membranes, the infection may involve the umbilical cord and placental villi, resulting in acute vasculitis of the cord (funisitis). Ascending infections are caused by Mycoplasma, Candida, and bacteria of the vaginal flora.
Uncommonly, placental infections may arise by hematogenous spread of bacteria and other organisms; on histologic examination, placental villi are the most frequently affected structures (villitis). Syphilis, tuberculosis, listeriosis, toxoplasmosis, and various viruses (rubella, cytomegalovirus, herpes simplex virus) all can cause placental villitis. Transplacental infections can affect the fetus and give rise to the so-called “TORCH” complex (toxoplasmosis, other infections, rubella, cytomegalovirus infection, herpes) (Chapter 7).
Ectopic pregnancy is defined as implantation of a fertilized ovum in any site other than the uterus, which may occur in as many as 1% of pregnancies. In more than 90% of these cases, implantation occurs in the fallopian tube (tubal pregnancy); other sites include the ovaries and the abdominal cavity. Any factor that retards passage of the ovum through the fallopian tube predisposes to ectopic pregnancy. In about half of the cases, slowed passage results from chronic inflammation and scarring in the oviduct; intrauterine tumors and endometriosis may also hamper passage of the ovum. In the other 50% of tubal pregnancies, no anatomic cause is evident. Ovarian pregnancies probably result from rare instances in which the ovum is fertilized just as the follicle ruptures. Gestation within the abdominal cavity occurs when the fertilized egg drops out of the fimbriated end of the fallopian tube and implants on the peritoneum.
MORPHOLOGYInallsites,earlydevelopmentofectopicpregnanciesproceedsnormally,withformationofplacentaltissue,theamnioticsac,anddecidualchanges.Withtubalpregnancies,theinvadingplacentaeventuallyburrowsthroughthewallofthefallopiantube,causing intratubalhematoma(hematosalpinx),intraperitonealhemorrhage,orboth.Thetubeisusuallydistendedbyfreshlyclottedbloodcontainingbitsofgrayplacentaltissueandfetalparts.Thehistologicdiagnosisdependsonvisualizationofplacentalvillior,rarely,oftheembryo.