Causes of Placentomegaly
Placentomegaly in the context of maternal syphilis exposure is most commonly caused by congenital syphilis infection, which triggers a fetal inflammatory response characterized by villous stromal hypercellularity, chronic villitis with plasma cells, and necrotizing funisitis. 1, 2
Syphilis-Related Placental Pathology
In congenital syphilis, the placenta becomes enlarged and thickened due to specific histopathologic changes:
- Villous enlargement and hypercellular areas in terminal and stem villi, characterized by increased mesenchymal cells and Hofbauer cells 3, 4
- Chronic villitis with plasma cell infiltration, representing the fetal immunological response to treponemal infection 3, 4
- Necrotizing funisitis (inflammation and necrosis of the umbilical cord), which is strongly associated with congenital syphilis when controlling for gestational age 3
- Acute villitis with focal peri- and intravillous polymorphonuclear concentration, sometimes with necrosis 4
- Erythroblastosis (increased nucleated red blood cells), particularly prominent in stillborn infants with congenital syphilis 3
Clinical Context and Ultrasound Findings
When placentomegaly is detected on ultrasound in a pregnant woman whose partner has syphilis, this represents a sonographic sign of fetal or placental syphilis and indicates greater risk for fetal treatment failure:
- Thickened placenta is specifically listed as a sonographic marker of fetal/placental syphilis alongside hepatomegaly, ascites, hydrops, and fetal anemia 1, 2
- Placentomegaly commonly occurs with hepatomegaly as the most frequent ultrasound findings in congenital syphilis 5, 6
- These ultrasound abnormalities warrant consultation with obstetric specialists and indicate higher-risk pregnancies that may require enhanced monitoring 1, 2
Other Causes of Placentomegaly (General Medical Knowledge Context)
While the question focuses on syphilis exposure, placentomegaly has multiple etiologies including:
- Infectious causes: TORCH infections (Toxoplasmosis, Other [including syphilis], Rubella, Cytomegalovirus, Herpes), parvovirus B19, malaria 6
- Fetal anemia: from any cause including hemolytic disease, chronic fetomaternal hemorrhage
- Maternal diabetes mellitus: causing placental edema and enlargement
- Chromosomal abnormalities: triploidy, trisomy 13,18,21
- Twin-twin transfusion syndrome: in monochorionic pregnancies
- Placental tumors: chorioangiomas, partial molar pregnancy
Critical Management Implications
Given the partner's syphilis diagnosis, immediate maternal serologic testing is mandatory:
- All pregnant women should be screened for syphilis at the first prenatal visit, and high-risk women require additional screening at 28-32 weeks and at delivery 1, 2, 7, 8
- If maternal syphilis is confirmed, treatment with benzathine penicillin G is the only proven therapy to prevent congenital syphilis and must be administered according to disease stage 2, 7, 8
- Pretreatment ultrasound should be performed in viable pregnancies when feasible, particularly after 20 weeks gestation, to assess for fetal involvement 2, 8, 5
- Pregnancies with ultrasound abnormalities including placentomegaly are at higher risk for compromise during treatment and fetal treatment failure, requiring obstetric specialist consultation 1, 2, 5
Diagnostic Pitfall to Avoid
Do not assume the placenta is normal based on gross appearance alone - five of six placentas in one series of proven congenital syphilis had no remarkable gross features, yet all showed characteristic histologic lesions on microscopic examination 4. Histopathologic examination improves detection rates for congenital syphilis from 67% to 89% in live-born infants and 91% to 97% in stillborn infants 3.