A 32-year-old woman with a history of pelvic inflammatory disease presents with amenorrhea and mild lower abdominal pain. Serum β-hCG is 1200 mIU/mL. Transvaginal ultrasound shows no intrauterine gestational sac, but a 2 cm echoic mass is seen in the right fallopian tube with a live fetal pole and cardiac activity. Which feature best distinguishes a tubal ectopic pregnancy from a cornual ectopic pregnancy?

Explanation

## Tubal vs. Cornual Ectopic Pregnancy ### Anatomical and Ultrasound Distinction | Feature | Tubal Ectopic | Cornual Ectopic | |---------|---------------|------------------| | **Location** | Within fallopian tube lumen | Within cornual portion of uterus (intramural) | | **Myometrial coverage** | No myometrial tissue | Myometrium intact on 3 sides | | **Ultrasound finding** | Gestational sac in adnexa, separate from uterus | Gestational sac eccentrically located, surrounded by myometrium | | **Rupture timing** | 8–12 weeks (thin tubal wall) | 12–16 weeks (thicker myometrium) | | **Viability** | Rarely viable beyond 12 weeks | May progress further (rare continuation) | **Key Point:** The **presence of intact myometrium on three sides** of the gestational sac is the pathognomonic ultrasound feature of cornual pregnancy. This distinguishes it from a tubal pregnancy, which lies entirely outside the uterus. ### Clinical Significance **High-Yield:** Cornual ectopics are more dangerous because: 1. The thicker myometrial wall delays rupture (12–16 weeks vs. 8–12 weeks for tubal). 2. Rupture causes massive hemorrhage from the cornual branch of the uterine artery. 3. They may rarely continue to viability if not detected early. **Clinical Pearl:** On transvaginal ultrasound, a cornual pregnancy appears as an eccentric gestational sac within the uterine cavity, with myometrium visible on all sides. A tubal pregnancy is clearly separate from the uterus, lying in the adnexa. ### Why the Other Options Are Non-Discriminating - **Fetal cardiac activity:** Both tubal and cornual ectopics can show cardiac activity if viable. - **β-hCG level:** Both produce hCG; level does not predict anatomical location. - **Unilateral pain:** Both present with lower abdominal pain on the affected side. [cite:Jeffcoate's Principles of Gynaecology Ch 8; Novak's Gynecology 16e Ch 19]