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Obstetrics » Obstetrics 1st Trimester
Molar pregnancy
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Author(s) :
Chaitali Shah, FRCR
Presentation A 54 year old woman presents with a 2 month history of amenorrhea. She now complains of severe vaginal bleeding and abdominal pain. She has a beta HCG level of approximately 200,000 units.
Caption: Sagittal sonogram of the uterus.
Description: Sagittal sonogram of the uterus, demonstrating an enlarged uterus [18.0x 8.0x 10.0 cms] with a heterogeneous soft tissue mass within the endometrial cavity with anechoic spaces within. The myometrium appears to be normal.
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.
Caption: Transverse color Doppler view of the uterus.
Description: Transverse color Doppler view of the uterus demonstrates increased flow within the myometrium. There is lack of flow within the mass suggesting that there is degeneration of the molar pregnancy.
Caption: Sagittal view of the uterus.
Description: Sagittal view of the uterus demonstrating the molar pregnancy in the process of expulsion.
Differential Diagnosis Molar pregnancy.
Final Diagnosis Non-invasive molar pregnancy.
Discussion Molar gestation can be a frightening complication of pregnancy. Gestational trophoblastic disease encompasses a wide spectrum of entities ranging from hydatidiform mole [complete or partial], invasive mole, choriocarcinoma and a not so common entity, the placental site trophoblastic tumor [PSST]. 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. A complete molar pregnancy occurs when a sperm fertilizes an empty ovum resulting in the development of only placental parts. A partial mole results when two sperm fertilize a single ovum. Thus, a complete mole is completely paternal in origin, with a karyotype of usually 46 XX and a partial mole has a triploid karyotype of 69XXX or 69 XXY or 69 XYY.

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.

The diagnosis of molar pregnancy can nearly always be made by ultrasound, because the chorionic villi of a typical complete mole proliferate with vascular 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.

Color Doppler is mainly useful in identifying aggressive lesions, as it defines focal regions of increased vascularity [often associated with high diastolic flow], within the myometrium representing invasion. MRI can also be used to detect invasion. This case showed increased vascular flow in the myometrium, with an avascular mass within the endometrial canal, indicating the loss of blood supply to the molar tissue, consistent with its partial expulsion as shown in image 4. Ovarian enlargement with bilateral theca – lutein cysts may also be seen.

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 can establish the differential diagnosis in utero of the various forms of placental molar transformations.

Case 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.
Follow Up This patient underwent a dilatation and curettage and histopathology findings were consistent with a complete hydatidiform mole showing marked degenerative changes.
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