Chorionic bump: Progression to a subamniotic hematoma

Abstract

Introduction

A chorionic bump is an increasingly recognized ultrasound finding in first-trimester scans, which has been associated with early pregnancy loss. In ongoing second-trimester pregnancies, however, chorionic bumps usually resolve over time with no deleterious effect on the fetus. In this report, we describe the incidental ultrasound detection of a chorionic bump in early pregnancy and its progression to a subamniotic hematoma in the second trimester of pregnancy that persisted as such until delivery.

Case Report

A round, echogenic mass protruding from the choriodecidual surface measuring 13 × 11 × 8 mm was first identified during a transvaginal scan at 6.3 weeks’ gestation. Subsequent follow-up scan at 8.3 weeks revealed an increase in the size of the chorionic bump to 25 × 20 × 19 mm, which remained stable as determined by the routine late first-trimester scan. At the second-trimester scan, a subamniotic hematoma was identified in the surface of the placenta, close to the insertion of the umbilical cord. Subsequently, the pregnancy proceeded uneventfully.

Discussion

The etiopathology and clinical significance of a chorionic bump remain unclear. The case herein reported demonstrates that a chorionic bump can grow considerably without having a deleterious effect on the early embryo and, occasionally, can persist throughout pregnancy as a subamniotic hematoma.

Conclusion

A chorionic bump can occasionally progress to a subamniotic hematoma from the second trimester onwards. This observation further supports the hypothesis that a chorionic bump is the result of choriodecidual bleeding. An alternative explanation for the development of subamniotic hematomas is proposed.

Introduction

The first trimester of pregnancy is a fragile period in terms of viability, with up to 25% of pregnancies ending in miscarriage. Some of the ultrasound signs that can predict a poor outcome in early pregnancy are widely recognized, such as irregularities of the gestational sac, abnormal size and echogenicity of the yolk sac, and fetal bradycardia. ¹ A relatively lesser known indicator of early pregnancy outcome is the detection of a chorionic bump (CB), which is a distinct ultrasound feature of first-trimester pregnancies originally described as ‘an irregular, convex bulge from the choriodecidual surface into the first-trimester gestational sac’. ² In the original series of 15 cases, eight (53%) pregnancies ended in first- or second-trimester miscarriage, suggesting a strong association with poor pregnancy outcome. ² This association has been subsequently confirmed by several other clinical series.^3–5 During very early pregnancy, the recognition and correct diagnosis of CBs are also important as they can look like a malformed area of embryonic tissue with no cardiac activity adhered to the amnion and, therefore, they can sometimes mimic a missed miscarriage.³ From an etiologic point of view, there is some evidence to suggest that a CB represents a hematoma, with bleeding from the trophoblast and decidua occurring during placental development. ⁶ , ⁷ This is consistent with the appearance observed at follow-up scans, as the CB usually changes in its echogenic pattern and resolves over time, like a hematoma. In this report, we describe the incidental detection of a CB in early pregnancy and its ultrasound progression to a subamniotic hematoma in the second trimester of pregnancy.

Case report

A 31-year-old woman, gravida 2, para 1, underwent an early scan, as is our protocol, at 7.4 weeks’ gestation, menstrual age, to determine location of the pregnancy, rule out multiple pregnancy, confirm cardiac activity, and establish accurately the gestational age. Her family and medical history were non-contributory and her obstetric history was significant due to a previous Cesarean section following gestational hypertension. Transvaginal ultrasound revealed a single intrauterine gestational sac containing a live embryo with a crown-rump length (CRL) of 6 mm, consistent with a gestational age of 6.3 weeks. A round, echogenic mass protruding from the choriodecidual surface measuring 13 × 11 × 8 mm was identified in close proximity to the embryo and yolk sac (Figure 1(a)). In view of the reported association between CBs and early pregnancy loss,^3–5 the patient agreed to a follow-up transvaginal scan two weeks later to confirm an ongoing pregnancy. This revealed normal embryonic growth with a CRL of 18 mm and an increase in the size of the CB to 25 × 20 × 19 mm (Figure 1(b)). The patient was scheduled for a routine first-trimester scan for screening of chromosomal defects and major structural anomalies, which was performed at 13.4 weeks. At this scan, the CB remained stable in size, measuring 23 × 18 × 18 mm (Figure 1(c)). The CRL, fetal heart rate, nuchal translucency thickness, assessment of the nasal bone, and fetal and maternal Doppler studies were within the expected range for the gestational age. It is worth noting that the patient presented to the emergency room with spotting at 11 and 14 weeks. This was treated with a few days of bed rest after each episode, as well as vaginal micronized progesterone, 200 mg per day for 14 days, with a good clinical response. A routine second-trimester scan at 22 weeks revealed normal fetal anatomy and adequate growth. In addition, the CB was no longer identified but instead there was a cystic lesion in the surface of the placenta close to the umbilical cord insertion site measuring 31 × 15 mm and containing an echogenic mass of 18 × 13 mm, consistent with a subamniotic hematoma (Figure 1(d)). A follow-up scan at 28 weeks showed that the subamniotic hematoma remained stable in size, measuring 30 mm in diameter. Third-trimester growth scans were arranged, which showed suboptimal fetal growth intervals. At 39 weeks, labour was induced delivering a female infant weighing 2830 g in good condition. Examination of the placenta revealed a small subamniotic hematoma close to the umbilical cord insertion site (Figure 2).

Figure 1.

Sequential ultrasound views of the chorionic bump. (a) At the time of the dating scan (6.3 weeks’ gestation according to crown-rump length), a chorionic bump (arrow) measuring 13 × 11 × 8 mm close to the embryo (E) and yolk sac (YS) is identified. (b) At 8.5 weeks, the chorionic bump (arrow) is larger, measuring 25 × 20 × 19 mm. A: amnion; E: embryo. (c) At 13.4 weeks, the size of the chorionic bump (arrow) is stable, measuring 23 × 18 × 18 mm. Note that the chorionic bump is clearly located underneath the amnion (A). (d) Subamniotic hematoma at 22 weeks’ gestation. Note the placental cyst close to the insertion of the umbilical cord (UC) insertion site. The retracting clot representing the hematoma is indicated by the arrow. A: amnion.

Figure 2.

Postpartum appearance of the subamniotic hematoma on the fetal surface of the placenta (arrows). Note its close proximity to the umbilical cord insertion site.

Discussion

The case presented here provides additional evidence on the prenatal course of the ultrasound finding known as a CB. ² Firstly, we present serial information regarding its ultrasound appearance throughout the first and second trimesters of pregnancy. To date, most reports have described spontaneous resolution of the CB in the vast majority of cases, supporting the hypothesis that this finding represents a choriodecidual hematoma that subsequently resolves. Our case, however, demonstrates that, in some cases, a CB can grow considerably without having a deleterious effect on the early embryo. In this regard, follow-up scans are indicated in order to monitor the size of the CB, especially if detected in very early pregnancy or if they are large or multiple at presentation. ⁵ If normal fetal growth is confirmed at follow-up scans, the risk of pregnancy loss decreases considerably. Indeed, once the pregnancy reaches the late first trimester, the prognosis of the pregnancy in such cases is generally good. ⁸

Secondly, our case describes an unusual prenatal evolution for a CB, which progressed from a first-trimester heterogeneous bulge to a second-trimester subamniotic hematoma. The latter condition is described as a cystic lesion protruding from the fetal surface of the placenta, surrounded by a thin membrane and containing areas of echogenic material. ⁹ It is thought to be the result of bleeding from the area close to the umbilical cord insertion site, secondary to traction and rupture of fetal vessels running underneath the amniotic membrane. ⁹ In these cases, bleeding is self-limited as the clot is firmly contained by the amnion. Retraction of the clot occurs over time, producing the characteristic ultrasound features of a subamniotic hematoma with the echoic, retracting clot at its base surrounded by the anechoic serum layer. Our case therefore suggests another pathophysiologic mechanism for a subamniotic hematoma, which can be the result of a choriodecidual hematoma occurring early in pregnancy. Such a hematoma remains covered by the amnion and does not usually grow for the remainder of the pregnancy. Nevertheless, adequate surveillance should be undertaken in selected cases, as large subamniotic hematomas can be associated with fetal growth restriction. ⁹ An additional associated risk is related to their location; if near the umbilical cord insertion site and especially if they are large in size, they can occasionally compress placental vessels and umbilical cord leading to adverse fetal outcome.

A potential limitation of our observation was the fact that the precise umbilical cord insertion site was not determined in the first trimester and the subamniotic hematoma might have developed later unrelated to the presence of the CB. However, at the time the subamniotic hematoma was detected, there was no other finding on the surface of the placenta that suggested coexisting conditions. Based on a review of the literature, only one report of a CB progressing to a subamniotic hematoma has been described previously. ¹⁰ In that case, the CB evolved into a large cystic mass on the fetal surface of the placenta, which was diagnosed as a septal cyst. ¹⁰ However, the available documentation in that case suggests that the CB was indeed a subamniotic hematoma, thus supporting our observation that a large CB can progress to a subamniotic hematoma in the second trimester of gestation, usually without additional risks to the fetal wellbeing and outcome of the pregnancy. A true placental cyst, another differential diagnosis, is a rare condition that seems to be an intrinsic primary lesion of the placenta and, therefore, with no relationship to a CB.

Conclusion

A chorionic bump identified on first-trimester ultrasound can be associated with early pregnancy loss, therefore follow-up first-trimester scans should be considered, especially in those pregnancies with an increased risk of miscarriage. Nevertheless, CBs can also grow and progress to a subamniotic hematoma, with no consequence to the fetus.