A 28-year-old woman G2P1 with prior pelvic inflammatory disease and tubal ligation reversal presents with 6 weeks of amenorrhea, vaginal spotting, and right lower quadrant pain. Vitals are stable; serum β-hCG is 4,200 mIU/mL (above the discriminatory zone). Transvaginal ultrasound shows an empty uterine cavity, a small amount of echogenic free fluid in the cul-de-sac, and the finding marked **B** in the diagram — a hyperechoic ring surrounding a small anechoic sac in the right adnexa, separate from the ovary. Which of the following best describes the ultrasound finding at **B** and its clinical significance?
A. Intrauterine gestational sac with eccentric implantation — a normal early pregnancy that should be managed expectantly with serial ultrasound and β-hCG monitoring
B. Corpus luteum cyst — a normal ovarian finding that can mimic early pregnancy and requires serial β-hCG to exclude ectopic pregnancy
C. Tubal ring sign — a gestational sac implanted in the fallopian tube, representing an ectopic pregnancy that requires urgent management given the β-hCG level and clinical presentation
D. Hemorrhagic ovarian cyst — typically self-limited and does not require intervention unless rupture occurs with hemodynamic instability
Explanation
Why "Tubal ring sign — a gestational sac implanted in the fallopian tube, representing an ectopic pregnancy that requires urgent management given the β-hCG level and clinical presentation" is right
The structure marked B is the adnexal "tubal ring" — a hyperechoic ring surrounding a small anechoic sac, located in the adnexa separate from the ovary. This is the pathognomonic ultrasound finding for tubal ectopic pregnancy. According to ACOG Practice Bulletin 193, the tubal ring sign represents a gestational sac implanted within the fallopian tube. In this case, the combination of an empty uterine cavity, β-hCG above the discriminatory zone (1,500–2,000 mIU/mL), and the presence of a tubal ring with echogenic free fluid (hemoperitoneum) confirms tubal ectopic pregnancy. The patient's risk factors (prior PID, tubal surgery) and clinical presentation (amenorrhea, unilateral pain, vaginal bleeding) align with the classic triad. This finding mandates urgent management — either medical (methotrexate if unruptured and hemodynamically stable) or surgical (laparoscopic salpingectomy if ruptured or unstable).
Why each distractor is wrong
Corpus luteum cyst: While corpus luteum cysts can appear as adnexal rings, they are ovarian structures with a different ultrasound appearance (typically more cystic, arising from ovarian tissue). The tubal ring is specifically a gestational sac within the fallopian tube, separate from the ovary, and is associated with positive β-hCG and clinical symptoms of pregnancy — not a normal physiologic finding.
Hemorrhagic ovarian cyst: A hemorrhagic ovarian cyst would not explain the elevated β-hCG, amenorrhea, or vaginal bleeding. Additionally, the location of B is explicitly separate from the ovary, and the presence of echogenic free fluid suggests active bleeding from a ruptured or rupturing pregnancy, not a simple ovarian cyst.
Intrauterine gestational sac with eccentric implantation: This option contradicts the primary ultrasound finding — the uterine cavity is empty. The tubal ring is located in the adnexa, not within the uterus. A true intrauterine gestational sac would show the double-decidual sign and eccentric location within the endometrial cavity; a pseudosac (decidual reaction without true sac elements) may mimic early pregnancy but lacks the embryonic elements and is centrally located. The tubal ring is definitively extrauterine.
High-YieldNEET PG
The tubal ring sign (hyperechoic rim around an anechoic sac in the adnexa, separate from the ovary) is the most specific ultrasound finding for tubal ectopic pregnancy; combined with empty uterus, β-hCG >discriminatory zone, and clinical symptoms, it confirms ectopic pregnancy and guides urgent management decisions.
ACOG Practice Bulletin 193: Tubal Ectopic Pregnancy
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