Differential Diagnosis
- Single most likely diagnosis
- Ectopic pregnancy (specifically, an interstitial ectopic pregnancy): This diagnosis is most likely due to the presence of a complex mass with fetal cardiac activity within the interstitial segment of the proximal fallopian tube, as seen on the transvaginal ultrasound. The patient's symptoms of nausea and vomiting, combined with a positive home pregnancy test and elevated serum β-hCG level, further support this diagnosis.
- Other Likely diagnoses
- Intrauterine pregnancy with a coexisting corpus luteum cyst or other adnexal mass: Although the ultrasound shows a complex mass within the fallopian tube, it's possible that the patient could have a normal intrauterine pregnancy with a separate adnexal mass. However, the presence of fetal cardiac activity within the mass makes this less likely.
- Molar pregnancy with an interstitial component: A molar pregnancy could potentially present with a complex mass and elevated β-hCG levels. However, the presence of fetal cardiac activity makes this diagnosis less likely.
- Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
- Ruptured ectopic pregnancy: Although the patient is currently stable, a ruptured ectopic pregnancy could occur at any time, leading to severe hemorrhage and potentially life-threatening complications. The presence of a moderate amount of free fluid in the pelvis increases the suspicion for a potential rupture.
- Uterine rupture: Given the patient's history of two cesarean deliveries, there is a risk of uterine rupture, especially with the presence of an interstitial ectopic pregnancy. This could lead to severe bleeding and complications for both the patient and the fetus.
- Rare diagnoses
- Heterotopic pregnancy: This is a rare condition where there is both an intrauterine and an ectopic pregnancy. Given the patient's history of fertility and the presence of an ectopic pregnancy, this diagnosis is possible but unlikely.
- Abdominal pregnancy: This is a rare type of ectopic pregnancy where the embryo implants in the abdominal cavity. Although the ultrasound shows the mass to be within the fallopian tube, it's possible that the pregnancy could be abdominal in nature. However, this would be an extremely rare occurrence.