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Obstetrics » Obstetrics 1st Trimester
Ectopic pregnancy
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Presentation A 20 year old woman presents with right adnexal tenderness and positive urinary beta- HCG test.
Caption: Sagittal transvaginal uterine scan.
Description: A normal uterine stripe is seen. A small, rounded anechoic area, adjacent to the endometrial canal is noted; this is too small to represent an 8 week gestational sac. Also, no appreciable decidual reaction is seen, so it is not a decidual cyst
Caption: Transvaginal scan of the right adnexa.
Description: Sagittal view demonstrating a gestational sac with an embryo [of 8 weeks size]. No cardiac activity was noted. Complex free fluid was identified.
Caption: Power Doppler study of right adnexa.
Description: Increased vascularity is noted around the gestation sac- the classical "ring of fire" sign. The embryo is seen in the gestational sac.
Caption: Power Doppler study.
Description: Increased vascularity noted in the echogenic rim of the ectopic gestational sac.
Differential Diagnosis Ectopic pregnancy.
Final Diagnosis Ruptured ectopic pregnancy.
Discussion A number of ultrasound findings have been described in the setting of an ectopic pregnancy. These have been discussed in a previous case (click here to view this case in a new window). Vascular flow around an ectopic is variable and depends on the amount of trophoblastic tissue. The case shown here demonstrates the classical "ring of fire" sign seen on color Doppler studies in cases of ectopic gestation. Trophoblastic flow is characterized by high velocity systolic flow, and low resistance diastolic flow when seen in an extrauterine location. However, most studies now conclude that color Doppler does not significantly increase the diagnostic accuracy in cases of ectopic gestation, but can be used as a supplemental test to detect ectopic trophoblastic flow.

The closest differential of an ectopic is a corpus luteum cyst. Identification of a tubal ring that displays an echogenic chorionic rim with low resistance flow surrounding a hypoechoic structure, favors an ectopic pregnancy over a corpus luteum cyst. However, sometimes the corpus luteum can have highly vascular walls, which may simulate the ring of fire sign. According to a study by Rottem, et al, three criteria can aid in distinguishing between an ectopic gestation and corpus luteum cyst:
1.The echogenicity of a suspected finding relative to the ovary
2.The presence or absence of flow
3.The relationship of the sign to an intentionally displaced ovary

According to published reports, the tubal ring of an ectopic is usually more echogenic than the ovarian parenchyma, and may be more echogenic than the endometrium. In contrast, the walls of the corpus luteum usually appear less echogenic or about the same as the ovarian parenchyma. This can be used as an ancillary sonographic finding.

Also demonstrated in this case is the presence of a small anechoic area with barely perceptible walls, adjacent to the endometrial cavity. This may represent a simple endometrial cyst or a decidual cyst. The presence of decidual cysts is now known to be associated with ectopic pregnancy. Since no appreciable decidual reaction is seen, decidual cyst is less likely and it may be a simple endometrial cyst.

Case References 1. Rottem S, Thaler I, Levron J, et al. Criteria for transvaginal sonographic diagnosis of ectopic pregnancy. J Clin Ultrasound. 1990 May;18(4):274-9.
2. Ardaens Y, et al. Contribution of ultrasonography in the diagnosis of ectopic pregnancy. J Gynecol Obstet Biol Reprod (Paris). 2003 Nov;32(7 Suppl):S28-38.
3. Chew S, et al. The role of transvaginal ultrasonography and colour Doppler imaging in the detection of ectopic pregnancy. J Obstet Gynaecol Res. 1996 Oct;22(5):455-60.
4. Stein MW, Ricci ZJ, et al. Sonographic comparison of the tubal ring of ectopic pregnancy with the corpus luteum. JUM. 2004 Jan; 23(1):57-62.
5. Frates MC, Visweswaran A, Laing FC. Comparison of tubal ring and corpus luteum echogenicities: a useful differentiating characteristic. JUM. 2001 Jan; 20(1):27-31; quiz 33.
6. Ackerman TE, et al. Decidual cyst: endovaginal sonographic sign of ectopic pregnancy. Radiology. 1993 189(3): 727-731.
Follow Up At surgery a right tubal gestation was found.
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