Figure 1: Longitudinal scans demonstrating a breech fetus and the superior aspect of the placenta with hypoechoic areas near the chorionic plate (top), and the inferior aspect of the placenta with hypoechoic areas throughout the entire thickness of the placenta (bottom).

Normal fetal morphology was visualized. Fetal biometry was consistent with dates. At this time the patient was counseled on the possibility of a molar pregnancy. An amniocentesis revealed a normal female karyotype, 46XX. The placental findings were attributed to hydropic degeneration.

A repeat ultrasound exam at 30 weeks gestation demonstrated fewer hypoechoic areas and small hyperechoic dots believed to represent areas of calcification (fig. 2). An ultrasound at 35 weeks gestation revealed the fetus to be growth retarded with a fetal age of 30 weeks. The placenta continued to look the same, with minute echogenic foci and multiple cystic spaces (fig. 2).

Figure 2: Transverse scans of the inferior portion of the placenta demonstrating fewer hypoechoic areas and small hyperechoic dots at 30 weeks gestation (top) and at 35 weeks gestation (bottom).

At 38 weeks gestation there was minimal fetal growth. Doppler studies were performed on the umbilical artery (S/D = 2.1), uterine arteries (S/D = 1.6), descending aorta (S/D = 8.4), middle cerebral artery (S/D = 5.8), and were considered to be within the normal limits. The biophysical profile score was 10. An amniocentesis was performed to determine lung maturity (L/S = 3.0, PG present). An oxytocin labor induction was initiated.

During labor she had an episode of vaginal bleeding. Artificial rupture of membranes revealed bloody amniotic fluid suggestive of abruptio placenta. Subsequently the fetal monitor displayed repetitive variable decelerations associated with more vaginal bleeding. She underwent a cesarean delivery. A female infant was born weighing 2490g with Apgar scores of 5 and 9. The umbilical cord gases were within normal limits. Blood clots were noted between the anterior uterine wall and the maternal surface of the placenta. Approximately 30% of the placental surface was considered to have separated prematurely. Her postoperative course was unremarkable, and she was discharged home on the fourth postoperative day.

Pathological examination of the placenta

There was a velamentous attachment of the 3 vessel umbilical cord with dimensions of 12cm in length and 1 cm. in diameter. The placenta weighed 950g, with dimensions of 20 x 15 x 3 cm. The membranes were marginally implanted, translucent, soft and thin. The fetal surface was purple in color with numerous tortuous vessels. The maternal surface was hemorrhagic. The cut section showed numerous cystic spaces which appeared to be dilated vascular channels (fig. 3).

Figure 3: Gross photograph of cut placental surface showing cavernous type of vascular channels.

These channels were more pronounced close to the fetal surface. The cystic spaces varied in size from 1‑10mm. There were no discrete tumors. Microscopically many large vascular channels were seen surrounded by fibrous tissue and flattened syncytial cells (fig. 4).

Figure 4: A giant placental villus with large, thick- walled vessels.

There were no cellular nodules with ill‑ formed vessels, and a cavernous appearance was present throughout the placenta. This cavernous appearance correlates well with the multiple hypoechoic areas visualized on ultrasound.

Discussion

Definition

A chorioangioma is a benign tumor of the placenta consisting of blood vessels and stroma that proliferates beyond normally developing chorionic villi.

Incidence

This is the most common primary tumor of the placenta, followed by hydatidiform mole and choriocarcinoma. The incidence has been reported between 0.2‑139:10,000 births. ^9,10 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. These smaller choriangiomas are often not diagnosed because they are not visible to the eye, and placentas are usually not examined by a pathologist. The overall accepted incidence in the literature is 1 in 100 births. The recurrence risk is not yet known but appears to be very small. ¹¹

Pathogenesis

A chorioangioma originates from primitive chorionic mesenchyme. It develops when blood vessels and stroma proliferate independently of the surrounding tissue. Marchetti describes three histological tumor types which are believed to represent various phases of tumor development¹². 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 16^th day after fertilization, although there has been no documentation of chorioangiomas during the first trimester. In our case, the patient did not have a first trimester ultrasound; the placental findings were noted during the second trimester. As more women have ultrasound studies during the first trimester, it is plausible that placental changes that may indicate a chorioangioma will be noted during this period.

Chorioangiomas vary in size from a few millimeters to several centimeters in diameter. These tumors are usually a single mass, but they can present as multiple separate masses. They are surrounded by a capsule or pseudocapsule. They are usually located on the fetal surface of the placenta and are visualized as a mass bulging into the amniotic cavity. They can occur in the substance of the placenta or can protrude from the maternal side. Less often they can be located in the membranes and attached to the placenta by a vascular pedicle. Chorioangiomas have also been described on the umbilical cord. A variation of these findings has been described in a review article where the placenta was diffusely infiltrated by angiomatous tumor tissue⁹. Our case illustrates similar gross and histological findings. In addition, our case provides real time ultrasound photography of a diffuse chorioangioma.

Ultrasound diagnosis

The first report of a chorioangioma diagnosed by antepartum ultrasound was in 1978¹. Chorio­angioma is usually depicted as a well circumscribed intraplacental mass with a complex echo pattern. Uniform and nonuniform echogenic appearances and multicystic masses have also been representative of this tumor. The echo density of the well‑delineated tumor differs from that of the placenta, allowing for its prompt recognition. Caldwell et al. described the ultrasound appearance of a diffuse chorioangioma using ultrasound equipment available in 1977¹³. The ultrasound was performed at 32 weeks to investigate the cause of a large‑for‑date uterus. They visualized an enlarged placenta that weighed 1,770g but missed the hydramnios that was diagnosed at birth.

Until the advent of current ultrasound technology, the description of a diffuse chorioangioma was that of an enlarged placenta. We describe a diffuse angiomatous lesion of the placenta which differs from the usual sonographic characteristics of chorioangiomas. On sonography the placenta in our case also appeared enlarged with multiple hypoechoic areas which were thought to represent cystic molar tissue or hydropic degeneration. At birth, the placenta weighed 950g.

Differential diagnosis

Angiomatous lesions should be differentiated from organizing blood clots and submucous myomas. The echo pattern of a blood clot tends to change over time, while the chorioangioma tends to remain unchanged. Myomas are usually located near the maternal surface of the placenta, while most large chorioangiomas are found on the fetal surface of the placenta. Other tumors of the placenta, such as a partial hydatidiform mole, must enter into the differential since the chorioangioma is not always well delineated. 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. In our case there was no evidence of a circumscribed tumor, but we found diffuse enlarged villi with cavernous type vascular channels. These giant villi were more pronounced close to the fetal surface, and, on ultrasound, the dilated, thick‑walled vessels mimicked vesicles of a hydatidiform mole.

Associated findings

The most common clinical complication associated with chorio­angioma is hydramnios. The incidence of hydramnios has been found to be related to the size of the tumor. It occurs in 18‑35% of patients with large tumors¹⁴. A complication of hydramnios is an increased incidence of preterm labor, premature rupture of membranes, and preterm delivery.

Oligohydramnios has been reported to be associated with chorio­angioma¹⁵. 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. There have also been reports of obstructed labor which were attributed to the size and location of the chorioangioma¹². 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^10,16, but others^9,14,17 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 women¹⁶.

Various articles note the occurrence of antepartum and postpartum hemorrhage associated with chorio­angioma^9,14,16. The 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 group¹⁶. Abruptio placenta was evident in our case, even though we did not have a discrete tumor bed. 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 hemorrhage⁹.

There is a case report of ovarian theca lutein cysts and high levels of hCG being associated with chorioangioma¹⁸. 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.

There have been case reports of elevated serum alpha‑fetoprotein levels associated with chorio­angioma. It is believed that this elevation is caused by feto‑maternal hemorrhage. In the cases reported by Thomas and Blakemore, the amniotic fluid alpha‑fetoprotein levels were within normal limits³². In our case, serum alpha‑fetoprotein was not performed, and the amniotic fluid alpha‑fetoprotein level was normal.

 Large chorioangiomas have the potential to become arteriovenous shunts which can compromise the fetal circulation by increasing the venous return to the heart, thereby causing tachycardia, cardiomegaly and hypervolemia¹⁹. As a result, there is the possibility of high output cardiac failure, edema, hydrops, and stillbirth^20,21,22. 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 coagulation²³. Feto‑maternal hemorrhage may also cause fetal anemia^24,25. The sinusoidal heart rate pattern has been noted to be present in some cases of severe anemia and chorioangioma^24,26. The abnormal vascular channels are non‑functional placental tissue which do not allow for proper nutrient delivery and oxygenation of fetal blood. The decrease in functional placental tissue can lead to intrauterine growth retardation²⁷. In our case the infant was growth retarded, probably due to some degree of placental insufficiency.

 In the older literature, chorio­angioma has been associated with congenital anomalies, but there has never been a cause and effect relationship established with any of these anomalies. An analysis of the Collaborative Research Study data reveals an increased incidence of various malformations in infants with intrauterine chorioangioma when compared to controls¹⁶. This finding is probably due to a statistical aberration, since there is no valid reason for the supposed increases in malformations such as hip deformity, inguinal hernia, talipes, ear deformity, metatarsus deformity, and pigmented nevus. Additionally, there is no connection between these deformities to allow for grouping them all with one condition. There does appear to be, however, 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 hemangioma is 12.2% vs 2.1% in the control group¹⁶.

There have been some reports of chromosome abnormalities associated with chorioangiomas^16,28,29. There does not seem to be a true association between these chromosomal abnormalities and chorioangioma since all three cases are of different karyotypes.

Pregnancies with chorio­angiomas have been noted to have a higher incidence of velamentous insertion of the cord (4.1% vs 1.5%)¹⁶. Velamentous insertion of the cord was noted in the case we report. There have been reports of circumvallate placenta associated with chorioangioma; however, the overall incidence appears to be the same as that in the general population^{9, 16}. Placenta previa is also a condition that has been loosely associated with chorioangioma, but a true correlation has never been established.  

Table 1: Associated functional and structural abnormalities

Doppler ultrasound

Grundy et al., using Doppler ultrasound obtained, a flow pattern from the vascular channels of a chorioangioma similar to that of the umbilical cord³⁰. This demonstrated to the authors that the vascular channels in the tumor were involved with the fetal circulation. They proposed using Doppler ultrasound of the tumor vessels to aid in making the diagnosis of choriangioma. Schulman et al. have suggested that the degree of fistulous involvement of the tumor with the fetal circulation can be determined by the umbilical artery Doppler indices³¹. They believe that normal Doppler indices imply non‑involvement of the fetal circulation with the tumor. The findings in our case appear to contradict Schulman"s theory since we had normal Doppler studies associated with a growth‑retarded fetus. We propose that the large vascular channels in the placental tumor lower the vascular resistance in the umbilical circulation. Until we have Doppler data on fetuses with hydrops secondary to chorioangioma, we will not know what happens to the umbilical circulation when there is extensive arteriovenous shunting.

Management

Outcome is dependent on the size of the tumor. Smaller tumors have been found to be inconsequential. Large and diffuse tumors have been associated with pregnancy complications and therefore merit closer surveillance. A thorough ultrasound examination of the fetus should be performed to exclude any anomaly. Fetal karyotyping should be considered based on the few case reports of associated chromosomal abnormalities. In all cases, serial sonograms should be performed to assess the growth of the tumor, growth of the fetus, and development of hydrops. During the third trimester, fetal well‑being should be monitored with fetal movement counts, heart rate monitoring and biophysical profiles, as deemed necessary. The role of Doppler ultrasound for surveillance remains uncertain but should be performed to add to the information available and allow for future determination of its value in this setting.

References

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