The "Ring of Fire": Corpus Luteum vs Ectopic Pregnancy

Both a normal corpus luteum and an ectopic pregnancy can demonstrate the vascular "Ring of Fire" sign on ultrasound.

These features favor an ectopic pregnancy

• will move separately from the ovary when pushed

• has a thicker, more echogenic rim

• typically displays either a low resistive index (RI) of < 0.4 or high RI of > 0.7

A corpus luteum cyst will have:

• low-resistance flow (high diastolic flow)

• a thin wall

• may contain "crenulated" (scalloped) borders or internal lacy echoes from hemorrhage.