NON TROPHOBLASTIC PLACENTAL TUMORS 

 

Chorioangioma - Teratoma - Metastasis

 

CHORIOANGIOMA (1-5)
  • The chorioangioma or placental hemangioma is the most common benign tumor of the placenta, followed by hydatidiform mole and choriocarcinoma..
  • Most common non trophoblastic placental tumor and has a reported incidence of between 0.2‑139:10,000 births (Large tumors, those greater than 5 cm, have been reported to occur from 0.2‑4:10,000 births. Smaller chorioangiomas occur more frequently with an incidence of 14‑139:10,000 deliveries) (22,23).
  • Reported incidence in pathological series is as high as 1%, however not all tumors are sonographically visible (24).
  • The recurrence risk is not yet known but appears to be very small.
  • Chorioangiomas are hamartoma, which arise as a malformation of the primitive angioblastic tissue of the placenta.
  • Small tumors are essentially asymptomatic.
  • Large, clinically significant chorioangiomas occur much less frequently, with a reported incidence ranging from 1 in 3500 to 1 in 9000 births.
  • Large chorioangiomas (>5cm) are thought to act as peripheral arteriovenous shunts resulting in cardiac overload, complications associated with them include congestive heart failure, polyhydramnios, hydrops fetalis, premature labor, maternal and fetal coagulopathies and hemolytic anemia (5,8,40,41).

 

PATHOGENESIS

 

A chorioangioma originates from primitive chorionic mesenchyme. It develops when blood vessels and stroma proliferate independently of the surrounding tissue.

Marchetti (25) describes three histological tumor types (believed to represent various phases of tumor development)

·         One type is less differentiated or more immature with a compact structure of mostly cellular elements.

·         The second type is the mature angiomatous or vascular type. This is the most common type of chorioangioma composed of numerous small blood vessels and capillaries.

·         The last type is characterized by degenerative changes.

Although tumors tend to be of one type, some may exhibit a combination of the characteristics described above.

Chorioangiomas are believed to originate at about the 16th day after fertilization, although there has been no documentation of chorioangiomas during the first trimester.

 

ULTRASOUND

 

The specific findings of chorioangioma are variable, and depend largely on the histological composition of the tumor (angiomatous, cellular or degenerative).

Histological classification correlates well with the sonographic features.

·         If the mass is predominantly vascular, color flow imaging reveals a hypervascularization pattern.

·         Cellular and degenerative types are solid or cystic tumors with little vascularity and the gray-scale appearance ranges from echogenic to hypoechogenic.
 

  • Rounded, primarily hypoechoic or mixed echogenic mass. It is well circumscribed and has a different echogenicity from the rest of the placental tissue.

 

 

  • Most chorioangiomas are small, single, circular, encapsulated and intraplacental. Ultrasound appearances that have been described include:
    • Multicystic (12) – the case below demonstrates the rare multicentric angiomatous form (target lesions with hypoechoic central portion and echogenic rim). All lesions demonstrated peripheral arterial inflow and venous outflow on color doppler.

    • Echogenic mass with dilated vascular channels (13).
    • Complex (14,15).
    • Uniformly and non-uniformly solid (16-18).
    • Multitumoral (19).
  • Usually situated near the umbilical cord insertion site.
  • They are surrounded by a capsule or pseudocapsule.
  • Location:
    • These tumors are usually a single, well-circumscribed mass within the placental substance, but they can present as multiple separate masses that usually bulge into the amniotic cavity.
    • Less often they can be located in the membranes and attached to the placenta by a vascular pedicle.
    • They have also been described on the umbilical cord  (22).

 

  • Rarely they may present as diffuse mass lesions. Our case presented as “target lesions” with a hyperechogenic periphery and central hypoechoic central portion.
  • Usually on the surface of the placenta.
  • Usually 1-5 cm in size.
  • Mild to moderate blood flow on color doppler (helps distinguish chorioangioma from an intraplacental hematoma).
  • Non-immune hydrops (6), thought to be caused by shunting of blood through a large arteriovenous malformation (seen with large tumors)
  • Calcification seen sonographically has not been reported (7).
  • Polyhydramnios (14-33%) independent of tumor size and is probably related to the vascularity of the tumor and fluid leakage. Polyhydramnios and fetal hydrops may spontaneously regress when the chorioangioma degerates (8,20,21).
  • Color doppler pattern is dependent on the histological type of the tumor. Cellular tumors consisting of mixed mesenchymal tissue are relatively avascular whereas the angiomatous type is vascular. Lesions above 7-8 cm may get shunting of fetal blood through the tumor (arterio-venous fistula). Janiaux and Ogle (8) suggest that vascularization of the tumor is an important determining factor of pregnancy outcome. No specific complications should be expected in avascular tumors whereas vascular tumors containing numerous large vessels may result in polyhydramnios and fetal congestive cardiac failure.
  • CDI plays an essential role in the differential diagnosis and management of chorioangiomas. Where the tumor is avascular, no specific complications should be expected. Where the tumor is vascularized, and in particular if it contains numerous large vessels, serial ultrasound and Doppler examinations is warranted to detect fetal complications and polyhydramnios (8).
  • Color Doppler imaging has contributed greatly to the prenatal differentiation between placental chorioangiomas and other nonvascular tumors such as hematoma, infarcts, intervillous thrombosis, teratoma and partial mole (42,43).
    • The angioarchitecture revealed by 3D power Doppler confirms that the vascular channels in the tumor were continuous with the fetal circulation. This rules out other vascularized lesions such as placental hemorrhage (44), maternal lakes, degenerated myoma or placenta accrete (45,46).
    • Using color Doppler ultrasound, Jauniaux and Ogle (47) categorized various vascular patterns of chorioangiomas and further identified that tumor vascularization is a pivotal determinant factor of pregnancy outcome.
    • Hsieh and Soong (48) illustrated how changes on intracardiac Doppler, rather than a change in tumor size, could reflect the pathophysiological situation in the presence of a chorioangioma. However, detection of such subtle changes requires a high level of expertise.

 
  • Pulsed doppler – waveform usually shows a typical fetal pattern.
  • An increase in the echogenicity of the tumor as pregnancy advances is a good prognosis as this appearance is related to fibrotic degeneration of the lesion, reducing the amount of fetal blood shunted through the tumor (8).

 

COMPLICATIONS
  • Chorioangiomas >5 cm are more frequently associated with fetal and maternal complications (hydrops, thrombocytopenia, elevated maternal serum Afp. Large tumors require 1-2 week serial ultrasounds to monitor growth and the development of hydrops.
  • Fetal anemia with or without associated hydrops (7).
  • Polyhydramnios - incidence of polyhydramnios has been found to be related to the size of the tumor. It occurs in 18‑35% of patients with large tumors (26).
  • Oligohydramnios has been reported to be associated with chorio­angioma. This diagnosis was made subjectively at the time of birth in a term gestation without the benefit of sonography. This association has not been confirmed by subsequent literature (27).
  • Obstructed labor, which were attributed to the size and location of the chorioangioma (25). These reports have not been substantiated by more recent literature and appear to have been a coincidental rather than a causal finding.
  • The incidence of preeclampsia is believed to be increased by some (23,28), but others (22,26,29) believe the incidence is similar to that of the general population. Froehlich, using ColLaborative Research Study data, has documented an increased incidence of preeclampsia of 16.4% vs 4.8% when comparing a group of 76 women with chorioangioma to a control group of 44,994 women (28).
  • Antepartum bleeding is believed to be caused by a premature separation of the placenta as a result of bleeding from the tumor bed or a rupture of the vascular pedicle.
    • Froehlich reported a 4.0% incidence of abruptio placenta in the group with chorioangioma vs 1.2% in the control group (28).
  • Postpartum hemorrhage has been reported to occur on occasions secondary to the over‑distension of the uterus and subsequent uterine atony. Rarely the tumor has been reported to remain in the uterine cavity after delivery of the placenta and has caused postpartum hemorrhage (22).
  • There is a case report of ovarian theca lutein cysts and high levels of hCG being associated with chorioangioma (30). The cause of these cysts is unknown but may occur either as a result of high hCG levels or as an abnormal ovarian response to normal hCG levels. The authors believe that the source of hCG in their case may be either the enlarged placenta or the chorioangioma itself.
  • Elevated serum alpha‑fetoprotein levels associated with chorio­angioma. It is believed that this elevation is caused by feto‑maternal hemorrhage.
  • Arteriovenous shunts have been reported in large chorioanfiomas, which can result in fetal tachycardia, cardiomegaly and hypervolemia (31). As a result, there is the possibility of high output cardiac failure, edema, hydrops, and stillbirth (32-34). Fetal anemia can also lead to hydrops through compensatory production of red cells by the liver, which causes hepatomegaly, portal hypertension, and hepatic cell dysfunction, resulting in hypoproteinemia.
  • The abnormal tortuous vascular channels in these tumors may cause red cell destruction and platelet sequestration, resulting in thrombocytopenia, microangiopathic hemolytic anemia, and disseminated intravascular coagulation (35). Feto‑maternal hemorrhage may also cause fetal anemia (36,37).
  • There appears to be a connection between chorioangiomas and other vascular anomalies such as skin hemangiomas and single umbilical artery. The incidence of single umbilical artery in pregnancies complicated by chorioangioma is 2.7% compared to 0.7% in the control group, and the incidence of skin lesions is 12.2% versus 2.1% in the control group (28).
  • Although there have been some reports of chromosome abnormalities associated with chorioangiomas (28,38,39), this does not seem to be a true association.
  • Higher incidence of velamentous insertion of the cord (4.1% vs 1.5%) (28). 
  • Chazotte and colleagues (48) first reported a case of spontaneous infarction of a chorioangioma, which was evident from decreasing tumor size and gradual transition to an echolucent appearance on ultrasound.

 

DIFFERENTIAL DIAGNOSIS
  • Placental hemorrhage may be sonographically indistinguishable (6). Placental hemorrhage may show some diminution in size over a period.
  • Placental metastasis from a primary maternal tumor (very rare).
  • Submucus fibroids – located on the maternal side rather than the placental side.

·         Partial hydatidiform moles are characterized by localized swelling of chorionic villi with focal trophoblastic hyperplasia and, on ultrasound, appear as multiple diffuse sonoluscent intraplacental areas.

 

 

TERATOMA
  • Rare tumor.
  • There is a controversy as to whether they actually arise from abnormal fetal development in a twin pregnancy. The distinction between placental teratoma and fetus amorphous (blighted fetus in a twin pregnancy) is controversial (9).
  • Fox's criteria (10) - teratomas are characterized by a lack of development of skeletal parts and absence of an umbilical cord. Fox postulates that because germ cells are capable of multifarious differentiation and have migratory capabilities, they are able to implant at various sites and can develop into teratomas.
  • During the first three months of fetal development, primordial germ cells migrate out through the wall of the envaginated gut into the umbilical cord. With further migrations these cells could land up in the placenta and thus form a nidus for placental teratoma. Therefore histological analysis is required to differentiate a teratoma from fetus amorphous (9).

 

ULTRASOUND


 

  • Mixed cystic and solid masses that resemble a chorioangioma.
  • 10-20% are purely cystic (10).
  • Calcification occurs in 40% of cases.

 

 

 

PLACENTAL METASTASIS

 

 

Link to Placental metastasis

 

 

 

REFERENCES
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