**7. Placental mesenchymal dysplasia**

Placental mesenchymal dysplasia is a rare vascular anomaly of the placenta characterized by mesenchymal stem villous hyperplasia [1]. The ultrasound diagnosis includes placentomegaly and a "grape-like" placental appearance, both mistaken clinically and macroscopically for a partial hydatidiform molar pregnancy [44]. The differential diagnosis is important, because it may result in termination of pregnancy. Still, the final diagnosis is made by means of placental histology. The disorder also has been reported to be associated with both intrauterine growth restriction (IUGR) and fetal death [45]. In many cases, the cause of fetal death is fetal vascular obstructive pathology, causing longstanding, severe fetal hypoxia, due to chorionic vessel thrombosis [46]. Beckwith-Wiedemann syndrome has been linked to placental mesenchymal dysplasia. Invasive testing is advisable to confirm a normal karyotype and exclude partial molar pregnancy [47].

dimensions. However, large chorioangiomas have been associated with a range of fetal conditions (fetal anemia, thrombocytopenia, hydrops, hydramnios, intrauterine growth retardation), including prematurity and stillbirth [1]. Also, large tumors can degenerate in necrosis, calcification, hyalinization, or myxomatous degeneration. Typically, on the ultrasound, a chorioangioma is located near the insertion of the cord into the amniotic cavity, as a hypoechoic, rounded mass with usually anechoic cystic areas with low resistance pulsatile flow (e.g., **Figure 6**) [52]. In rare cases the tumors are pedunculated. As differential diagnosis, subamniotic hematoma, partial hydatidiform mole, submucosal uterine fibroid, placenta tera-

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Most infections arise from several infective agents that may cross into the placenta from the maternal circulation [1]. These kinds of infections can be associated with a variety of developmental effects, from virtually insignificant to major maternal and fetal developmental complications. Placental examination by a pathologist should be considered in every case of preterm delivery, fetal tachycardia, maternal signs of endomyometritis (e.g., fever, uterine tenderness, leukocytosis, tachycardia), neonatal intensive care unit admission, malodorous placenta, retained placenta or postpartum hemorrhage, and stillbirth [54]. However, a specific infectious agent is rarely diagnosed by placental examination. Still, the placental histology may confirm the clinical diagnosis of an infectious etiology in some cases of nonreassuring fetal heart rate patterns or neonatal morbidity/mortality. The most common

• Malaria: characterized by the pigment-laden maternal red blood cells and macrophages

• Cytomegalovirus is the most common congenital viral infection, mostly subclinical at birth in cases of intrauterine growth restriction and stillbirths [56]. The classic histopathological finding in the placenta includes viral inclusions. These may be detected only if using im-

• Herpes simplex virus: the histopathological features of the placenta may include lymphoplasmacytic villitis. The demonstration of the virus by immunohistochemistry or by molecular techniques allows the diagnosis, since the above findings are nonspecific [57].

• *Listeria monocytogenes* is characterized by acute villitis, with abscess formation and fetal

• Streptococcal infection: both group B and group A streptococci can produce placental

• Syphilis: *Treponema pallidum* infections determine a chronic villitis (plasma cells, mixed

toma, and atypical placental venous lake should be considered [53].

**10. Placental infections**

placental infections are:

aggregate in the intervillous space [55].

munohistochemistry techniques.

central nervous system damage [58].

acute and chronic infiltrate).

infection.
