Ectopic Pregnancy
"Ring of Fire"
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Ectopic Pregnancy
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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.
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
