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Obstetrics » Obstetrics 1st Trimester
Complete Molar Gestation: Role of Ultrasound
Author(s): Chaitali Shah, FRCR | Pamela T. Johnson, MD | Ashok Bhanushali, MD | Phyllis Glanc, MD, FRCPC
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Introduction

Molar gestation is a complication of pregnancy and occurs due to an abnormal fertilization process.

Types of Gestational Trophoblastic Neoplasia [GTD]

A wide spectrum of entities characterized by abnormal proliferation of pregnancy-related trophoblasts with variable malignant potential:
1. Non-invasive hydatidiform mole [complete or partial],
2. Invasive mole,
3. Choriocarcinoma,
4. Placental site trophoblastic tumor [PSST] and
5. Epithelioid trophoblastic tumor [a newer entity].


Etio-pathogenesis

Molar gestations are increased in older and very young females of reproductive age and in those with a history of prior molar pregnancy. Advanced paternal age may be a risk factor for a complete molar pregnancy
1. A complete molar pregnancy occurs when a sperm fertilizes an empty ovum, resulting in the development of only placental parts. A complete mole is completely paternal in origin, with a karyotype of usually 46 XX.
2. A partial mole results when two sperms fertilize a single ovum and results in development of certain or all fetal parts. A partial mole predominantly has a triploid karyotype of 69XXX or 69 XXY or 69 XYY; however, a diploid karyotype may also exist.


Clinical Presentation

Patients with a complete molar pregnancy usually present with the classical symptoms of vaginal bleeding, hyperemesis, passage of grape like vesicles per vagina and a uterus larger than dates [although some may present with a smaller than dates uterus]. A few patients may show evidence of preeclampsia and features of hyperthyroidism. However, with the advent of high-resolution transvaginal ultrasound imaging, molar pregnancy is now being diagnosed at a much earlier stage before all the classical symptoms develop. With a partial molar pregnancy, patients are usually asymptomatic or may present with symptoms of a missed or incomplete abortion.

Imaging

The diagnosis of molar pregnancy can nearly always be made by ultrasound, because the chorionic villi of a typical complete mole proliferate with vacuolar swelling and produce a characteristic vesicular sonographic pattern.
• Previously when the diagnosis was made at a later stage, the classical ‘snowstorm’ pattern of the
  uterus was described; however this is not commonly seen now.
• Benson et al reported that the majority of first trimester complete moles demonstrated a typical
  sonographic appearance of a complex and echogenic intrauterine mass containing many small
  cystic spaces {which correspond to the hydropic villi on gross pathology}.
• One may see a large, central fluid collection that mimics an anembryonic gestation or abortion.


• Occasionally, there is merely a central mass of variable echogenicity, presumably because the villi
   are too small to be seen with sonography at that time.

Caption : Scan of the uterus

Description : The classical bunch-of-grapes appearance or snow-storm appearance in the uterine cavity is noted. This is the typical appearance of a gestational trophoblastic disease.

Please click here to view the source of this image.

Caption : Transverse sonogram of the uterus

Description : Transverse sonogram of the uterus demonstrates the heterogeneous mass within the endometrial cavity. The visualized anterior and posterior myometrium appear to be normal and uninvolved.

Please click here to view the source of this image.

Caption : Sagittal scan of the uterus

Description : This is the sagittal view of the uterus demonstrating that the endometrial cavity is filled with an echogenic mass containing cystic spaces.


Studies have shown color Doppler to be useful in the evaluation and follow up of gestational trophoblastic tumors. Angiogenesis is an integral part of any tumor development and color Doppler usually reveals increased vascularity in the mole, followed by a decrease with treatment. Low resistance blood vessels with low pulsatility and resistance indices have been noted in malignant and aggressive gestational trophoblastic tumors. These may also be useful in predicting the response to treatment in addition to diagnosis.


Caption : Color Doppler scan in a patient with a molar gestation

Description : The hyperechoic mass in the uterus demonstrates areas of increased vascularity.



Caption : Spectral waveform analysis in a case of gestational trophoblastic neoplasm

Description : The spectral waveform within the cystic mass in the uterus reveals a mixed arterial and venous waveform, with low resistance arterial flow.

Non-invasive GTD may appear avascular and contain many cystic spaces within, which correspond to the swollen chorionic villi. Invasive GTD including choriocarcinomas however show increased intratumoral blood flow, and focal areas of increased flow in the myometrium as well, if there is local invasion. Presence of extrauterine gestational disease confirms the aggressive nature of the GTD. In borderline cases, the final diagnosis of invasion versus non-invasion is confirmed only by histopathology and hence all the evacuated moles need to undergo a complete pathological workup.

Ovarian enlargement with bilateral theca – lutein cysts is a common association.

Studies have concluded that it is not always possible to make a diagnosis of early molar pregnancy by ultrasonography and therefore, histological examination of the aborted or evacuated specimens remains important and DNA analysis should be carried out for the final diagnosis, if histology is inconclusive. Genetic marker analysis using polymerase chain reaction is rapid and accurate in identifying and classifying complete and partial moles. A complete mole has about a 15% chance of recurrence, while a partial mole has about a 3% chance.

Serum quantitative beta HCG levels provide important information for deciding on the likelihood of a molar pregnancy. These levels are usually very high for the given gestational period, although early stages may have normal levels. Failure of these levels to return to a normal value, post treatment, is a prognostic indicator of retained molar tissue. The present data indicates that ultrasound can correctly identify molar changes in early pregnancy and together with HCG levels and uterine Doppler measurements may establish the differential diagnosis in utero of the various forms of placental molar transformations.
Patients are often counseled to avoid pregnancy for at least one year to minimize the risk of missing persistent trophoblastic neoplasia.


References

1. Shigeru Sasaki. Clinical presentation and management of molar pregnancy. Best Practice and Research Clinical Obstetrics and Gynecology. 17 (6), December 2003, Pages 885-892.

2. Batorfi J, Vegh G, et al. How long should patients be followed after molar pregnancy? Analysis of serum hCG follow-up data. Eur J Obstet Gynecol Reprod Biol. 2004 Jan 15; 112(1): 95-7.

3. Benson C, et al. Sonographic appearance of first trimester complete hydatidiform moles. Ultrasound in Obstetrics and Gynecology. 16 (2000), pp. 188–191.

4. Lazarus E, et al. Sonographic appearance of early complete molar pregnancies. Journal of Ultrasound in Medicine 18 (1999), 589–593.

5. Sebire N, et al. The diagnostic implications of routine ultrasound examination in histologically confirmed early molar pregnancies. Ultrasound in Obstetrics and Gynecology 18 (2001), 662–665.

6. Wagner B, et al.Gestational trophoblastic disease: Radiologic- Pathologic correlation. Radiographics. January 1996, Volume 16, Number 1.

7. Benson C, et al. Sonographic appearance of first trimester complete hydatidiform moles. Ultrasound in Obstetrics and Gynecology. 16 (2000), pp. 188–191.

8. Kawano M, et al.Transvaginal color Doppler studies in gestational trophoblastic disease. Ultrasound Obstet Gynecol. 1996 Mar; 7(3): 197-200.

9. Yalcin OT, Ozalp SS, Tanir HM. Assessment of gestational trophoblastic disease by Doppler ultrasonography. Eur J Obstet Gynecol Reprod Biol. 2002 Jun 10; 103(1): 83-7.

10. Bidzinski M, et al. Clinical usefulness of color doppler flow examination during treatment of gestational trophoblastic disease. Ginekol Pol. 1999 Feb; 70(2): 88-92.

11. Sebire NJ, Rees H, et al. The diagnostic implications of routine ultrasound examination in histologically confirmed early molar pregnancies. Ultrasound Obstet Gynecol. 2001 Dec; 18(6): 662-5.

12. Woo JS, et al. Partial hydatidiform mole: ultrasonographic features. Aust N Z J Obstet Gynaecol. 1983 May;23(2):103-7.