Retained Products of Conception

About 1% of pregnancies are complicated by retained products of conception, more commonly after termination of pregnancy. Patients present with vaginal bleeding and abdominal or pelvic pain.

Ultrasound is the first-line imaging study for evaluation of retained products of conception. The classic appearance is heterogeneously echogenic material in the endometrial cavity that demonstrates blood flow. Increased blood flow can be seen in regions of retained tissue and in diffuse areas of the myometrium.

It must be noted that the absence of blood flow does not exclude the presence of retained products of conception. Our case, for example, did not present with a clear endometrial mass (just some endometrial thickening), and no definite flow could be identified within the endometrial cavity. A region of increased flow could be seen in the anterior wall of the uterus, with a mosaic pattern that was mistaken for the tissue vibration and turbulence of an arteriovenous fistula.

The retained products may demonstrate shadowing from calcium. There is typically an irregular interface between the endometrium and myometrium.

The endometrial cavity can appear normal on ultrasound or there may be endometrial fluid without a mass. In such cases, sonohysterography or MRI can be used to clarify the diagnosis.

MRI may demonstrate "an intracavitary uterine soft-tissue mass with variable T1 and T2 signal intensities, variable amounts of enhancing tissue, and variable degrees of myometrial thinning and obliteration of the junctional zone." These findings are seen in the MR images above.

Differential considerations:

• Gestational trophoblastic disease: MR and clinical features may overlap with those of retained products of conception, and a definitive diagnosis may not be possible. Patients with gestational trophoblastic disease characteristically have elevated beta-HCG levels, while patients with retained products of conception have dropping levels.
• Arteriovenous fistula/malformation: Blood flow patterns in retained products of conception may simulate an arteriovenous fistula, as in our case.
• Endometritis: Heterogeneous infected material in the endometrial cavity may simulate retained products of conception. Endometritis may also coexist with retained products of conception.
• Missed abortion: Look for a gestational sac with remaining fetal tissue and no cardiac activity (after the embryonic pole > 5 mm).

References

• Durfee SM, Frates MC, Luong A, Benson CB. The sonographic and color Doppler features of retained products of conception. J Ultrasound Med. 2005 Sep;24(9):1181-6.
• Noonan JB, Coakley FV, Qayyum A, Yeh BM, Wu L, Chen LM. MR imaging of retained products of conception. AJR Am J Roentgenol. 2003 Aug;181(2):435-9.
• Polat P, Suma S, Kantarcý M, Alper F, Levent A. Color Doppler US in the evaluation of uterine vascular abnormalities. Radiographics. 2002 Jan-Feb;22(1):47-53.