Ectopic Pregnancy

"Ring of Fire"


Ectopic "tubal ring" with peritrophoblastic flow
Low-impedance, high-diastolic (arrows) flow in ectopic
Increased vascularity around a corpus luteum cyst

Findings:

Color Doppler flow is identified surrounding a ring-like structure in the adnexa. This flow was typical of placental, low impedance flow, however extrauterine in location. Notice the similarities in the color Doppler appearance of the ectopic pregancy and a patient with a corpus luteum cyst (image on far right) and no evidence of ectopic pregnancy.

Discussion:

Ectopic pregnancies represent between 1-2% of all reported pregnancies. Despite the improved diagnosis of ectopic pregnancy, utilizing a variety of diagnostic methods including serial quantitative measurements of the ß subunit of human chorionic gonadotropin and high resolution transabdominal and transvaginal ultrasound, patients still present with ruptured ectopic pregnancy which may result in severe hemorrhage and even maternal death. Ectopic pregnancy accounts for 12%-18% of all maternal deaths annually. The ultrasound findings of ectopic pregnancy are based upon two major observations 1) Identification of an extrauterine gestational sac ("tubal ring") containing either a yolk sac or embryo or 2) Identification of indirect signs ie. no evidence of intrauterine pregnancy in the face of a positive pregnancy test with an adnexal or cul de sac mass or fluid. Even with high resolution ultrasound equipment and transvaginal scanning diagnostic accuracies of only 60-80% have been reported in most centers with this technology alone.

In the past decade, a number of investigators have utilized pulsed and color Doppler ultrasound in the evaluation of the pregnant patient. Taylor and his group described a flow pattern in placental tissues that was typically high-velocity, low impedance flow. This was thought to be related to invasion of the maternal tissues by trophoblastic villi. This characteristic flow can be identified using color Doppler imaging as an area of increased vascularity surrounding the gestational sac. Dillon et al demonstrated that this placental flow pattern can be seen in an intrauterine pregnancy approximately 36 days after the last menstrual period, reaching a peak at 50 days. As these flow patterns were seen with trophoblastic tissue they could be identified whether the pregnancy was within, or outside of the uterus. Subsequently, investigators have interrogated the adnexa in high risk patients for this characteristic flow pattern as a means of improving the diagnostic accuracy. Several centers have claimed accuracies of 80-95% with the addition of this technique. In addition to searching for a vascular ring in the adnexa, some have utilized measurements of the spectral Doppler pattern to diagnose the presence of an ectopic gestation. A resistive index value < 0.40 is said to be characteristic of an ectopic gestation.

There are two potential pitfalls that should be taken into account when utilizing Doppler evaluation: 1) Cases of either dead or early ectopic pregnancies may demonstrate no evidence of peritrophoblastic flow. A large mass, representing hematoma from a ruptured ectopic pregnancy may have little to no flow whereas a small "tubal ring" may have easily demonstrable flow. Several groups have correlated the measurements of the serum ß-hCG with the likelihood of peritrophoblastic flow. When the ß-hCG was less than 6,000 mIU/ml (1st International Ref. Standard) most ectopic gestations were avascular. Thus, the absence of placental flow does not exclude the diagnosis of ectopic pregnancy and 2) There is considerable overlap between the appearance and resistive index values of flow seen in an ectopic pregancy and the flow seen around a corpus luteum cyst. This is also true for some ovarian malignancies. As such, attempts should be made to identify the adnexal mass as being separate from the ovary. Less than 1% of ectopic pregnancies are intraovarian. In addition, low impedance flow has also been reported with tubo-ovarian abscesses.

There is hope that the results of Doppler interrogation of an ectopic pregnancy might aid in managing these cases. Cases in which the flow is markedly diminished or absent could theoretically be managed expectantly without surgical intervention.

References:

Pellerito JS, Taylor KJW, Quedens-Case C, Hammers LW et al. Ectopic pregnancy:evaluation with endovaginal color flow imaging. Radiology 183:407-411, 1992

Emerson DS, Cartier MS, Altieri LA, Felker RE et al. Diagnostic efficacy of endovaginal color Doppler flow imaging in an ectopic pregnancy screening program. Radiology 183:413-420, 1992

Tekay A and Jouppila P. Color Doppler flow as an indicator of trophoblastic activity in tubal pregnancies detected by transvaginal ultrasound. Obstet Gynecol 80:995-999, 1992

Kurjak A, Zalud I, Schulman. Ectopic pregnancy: transvaginal color Doppler of trophoblastic flow in questionable adnexa. J Ultrasound Med 10:685-689, 1991

Frates MC, Laing FC. Sonographic evaluation of ectopic pregnancy: an update. Amer J Roentgenol 165:251-259, 1995

Dillon EH, Feyock AL, Taylor KJW. Pseudogestaional sacs: Doppler ultrasound differentiation from normal or abnormal intrauterine pregnancies. Radiology 176:359-364, 1990

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