My Most Unusual Case: Cesarean Scar Ectopic Pregnancy

After a repeat ultrasound (Figures 1 and 2), this patient was diagnosed with a CSEP and admitted to OB-GYN services. A confirmatory computed tomography scan noted a cesarean delivery scar diverticulum with a pregnancy located in the diverticulum. The patient then received a potassium chloride injection into the gestational sac and intramuscular methotrexate. Prior to discharge, she was instructed to follow up with the OB-GYN service to trend quantitative β-HCG levels.

Discussion

Cesarean scar ectopic pregnancy was first described in the obstetric literature in 1978 and originally thought to be an exceedingly rare occurrence.^5,6 With both the increasing number of cesarean deliveries performed and improvement in imaging technology, it is now believed that uterine scar ectopic pregnancy makes up as much as 6.1% of ectopic pregnancies in patients with a prior cesarean delivery.⁷ This diagnosis is well-documented in the obstetric and radiology literature, yet has never been discussed in an emergency medicine publication. Searching through both Pubmed and EMBase using the terms “cesarean” and “ectopic” yields no EM literature on the topic of CSEP. This is concerning because ultrasound of the pregnant patient is now a routine function of EPs.

Clinical history can be helpful in differentiating CSEP from alternative diagnoses. Patients undergoing spontaneous abortion are more likely to have lower abdominal cramping and experience greater loss of blood. While there is no correlation between the number of cesarean deliveries a woman has had and the likelihood of developing a CSEP, factors that impede myometrial healing (eg, preterm cesarean, cesarean after arrest of first stage of labor, chorioamnionitis) do, however, increase a patient’s risk of developing CSEP.⁵

Similar to tubal ectopic pregnancy, CSEP oftentimes presents early with mild, nonspecific symptoms. Thirty-nine percent of cases present with light, painless vaginal bleeding while only 25% present with abdominal pain. Moreover, 37% of cases are asymptomatic at the time of diagnosis.⁵

One study by found the mean gestational age at diagnosis to be 7.5 weeks.⁵ Delayed diagnosis places the patient at risk for uterine rupture, hemorrhage, and maternal death, making suspicion and prompt diagnosis by bedside ED ultrasound essential.^7,8

Regardless of one’s clinical suspicion, the diagnosis is made (or ruled out) through ultrasound. Uterine scar ectopic pregnancy is suspected when ballooning of the lower uterine segment is noted,¹ when a trophoblast is seen at a presumed cesarean scar beneath the utero-vesicular fold, and when myometrium between the gestational sac and bladder wall is thin (<8 mm).² As seen with this patient, the diagnosis is challenging as a uterine scar ectopic pregnancy can easily be mistaken for an intrauterine pregnancy. The clinician must make every effort to ensure that the pregnancy is surrounded by appropriate myometrium. It is much easier to diagnose an ectopic pregnancy far removed from the uterus, where the uterus and pregnancy are easily visualized and independent. 

Management of patients with CSEP remains outside of the scope of EM, and there is no consensus among our colleagues in OB-GYN on optimal management of these patients. Options include systemic or local injection of methotrexate and potassium chloride, or minimally invasive surgery for removal.⁵

As bedside ultrasound by EPs becomes standard of care for first-trimester pregnancies, a greater awareness of emergent obstetric pathologies becomes necessary. Vigilance and proper ultrasound technique will enable the EP to make the diagnosis of CSEP, minimizing maternal morbidity and mortality.

Drs Haight and Watkins are residents in the division of emergency medicine, Washington University School of Medicine, Saint Louis, Missouri. Dr Kane is a clinical instructor in the division of emergency medicine, Washington University School of Medicine, Saint Louis, Missouri.