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Making Mountains out of Moles: The molar pregnancy

November 30, 2013

I was called into an exam room by our physician assistant  the other day.  She had just done a POCUS on a 43 year old female, gravida 5, 10 weeks pregnant, with vaginal spotting and no significant pain.  We are lucky to have some keen PA’s who are completing their certification in basic POCUS.  This has two immediate benefits:  they can diagnose important findings rapidly and notify the attending ER doc but as a bonus they are also quick to know which patients the doc will want to scan and get everything set up to go, saving lots of time.

So our patient with first trimester bleeding was showing a confusing image.  The PA was unable to identify an intrauterine pregnancy by transabdominal approach so she came to get me and had the transvaginal probe ready to go.  Now before I do a TV scan, I always do a quick TA scan to make sure of the anatomy and prevent that embarrassing situation where the patient is much further along than she thinks and the fetus won’t be visible by TV.

When I applied the probe this is what I saw::

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10 week gestational age molar pregnancy

An echogenic mass in the uterus filled with multiple cystic structures.  The patient had a betaHCG of 30000 and no other symptoms other than mild vaginal bleeding.  Her previous pregnancies were unremarkable and the current one was a bit of a surprise.

I felt the imaging was consistent with an early molar pregnancy and obtained a comprehensive ultrasound from the radiology department.  The report described thickened inhomogeneous appearing soft tissue material within the region of the central canal with a few scattered cystic regions.  A portion of debris material possibly on the basis of clots.  Opinion was possible retained products of conception on basis of a recent spontaneous miscarriage but essentially nonspecific and ectopic can’t be ruled out. No mention of molar pregnancy.

Despite the lack of typical clinical symptoms I thought the ultrasound image concerning enough to get an OB-GYNE consult.  The attending agreed that it looked like a molar pregnancy and took the patient to the OR that evening for a D&C.

Pathology came back confirming abnormal chorionic villi with marked atypical trophoblastic proliferation favouring a complete mole.

Gestational Trophoblastic Neoplasias or molar pregnancies occur when the fertilization process goes wrong.  There are many different types including partial or complete, invasive, and choriocarcinoma.  Approximately 1 in 1000 pregnancies in the USA is molar pregnancy and up to 1 in 100 pregnancies in Indonesia has this condition.

Molar pregnancies tend to be found in the older or very young female.  Previous molar pregnancy is the biggest risk factor.

While complete molar pregnancies can present with vaginal bleeding, hyperemesis, larger than gestational age uterus and even passage of grape like vesicles. many patients with partial molar pregnancies can be asymptomatic or present just like a missed/incomplete abortion.

The diagnosis is most often made by ultrasound because the chorionic villi proliferate with vacuolar swelling that leads to a characteristic vesicular pattern.

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Possible 7 week molar pregnancy in young teenage patient lost to followup

Before high resolution ultrasound the diagnosis was often made later in the pregnancy and a snow-storm appearance within the uterus was described.

The majority of molar pregnancies are now diagnosed in the first trimester showing a complex, echogenic intrauterine mass containing multiple small cystic spaces.  Sometimes there is a larger central fluid collection or mass that can look like a miscarriage.

While emergency physicians have always been told to avoid doppler in early pregnancy scans, it is interesting to note that studies show colour doppler is useful in evaluating molar pregnancies as tumour angiogenesis results in increased low pulsatility, low resistance flow within the mass.  Response to therapy can be estimated from a decrease in blood flow on repeat ultrasound.

I am lucky enough to be married to a brilliant pathologist.  (Well she married me so perhaps her intelligence can be questioned.)  She tells me that the tissue diagnosis of molar pregnancies can be challenging and the more tissue available the better.  Thus if you think your patient may have a GTN, better to get an early OB-GYNE consult as the recommended treatment is evacuation of the uterus as soon as possible followed by weekly serum betaHCGs.

For a nice summary of molar pregnancy and ultrasound:

Sonoworld Molar Pregnancy Review

Good review article:

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

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