Fooled twice by an acute abdomen

The rarity of an unruptured tubal pregnancy in the second trimester makes it all the more difficult to diagnose sonographically. We report such a case presenting with signs and symptoms of acute abdomen. Ultrasound examinations at separate institutions at 12 weeks and immediately before surgery at 17 weeks failed to make the diagnosis.

Case report

A 40-year-old gravida 3, para 2002, with two prior cesarean deliveries, presented to our institution with sudden onset of diffuse and constant abdominal pain, 10 out of 10 in severity, and aggravated whenever she moved. The woman had no urinary or gastrointestinal symptoms and was thought to be at 17 weeks' gestational age, based on previous U/S diagnosis of a 13-weeks' intrauterine pregnancy at another institution 4 weeks earlier.

Upon presentation, she was afebrile and hemodynamically stable. Her abdomen was diffusely tender, with peritoneal signs. Vaginal examination revealed no cervical changes and no bleeding or abnormal discharge. Hemoglobin level was 11.8 g/dL. U/S revealed a 17-week-sized fetus located on the left side of an empty uterus displaying a 6-cm fundal myoma.

We suspected hemoperitoneum. After we'd narrowed the diagnosis to abdominal pregnancy versus ruptured uterus, the patient consented to an exploratory laparotomy with possible hysterectomy and was taken to the operating room. She didn't wish to have any more children.

Upon entering the abdomen, we found an enlarged uterus, 17×12×8 cm, and a left fallopian tube that was markedly distended, 16×10 cm. The very wide and edematous insertion of the dilated left tube into the uterus would have made it difficult to create adequate surgical pedicles for hemostasis. We therefore decided to perform a total hysterectomy with left salpingectomy. The left tube contained an intact gestational sac with placenta and fetus. Multiple myomas explained the enlarged uterus.

A rare complication indeed

In 1951, McElin and Randall defined advanced tubal pregnancy as a fetus and placenta enclosed within the fallopian tube with no other pelvic or intraabdominal organs involved in forming the sac and without signs of rupture.¹ According to these researchers, 45 cases of tubal pregnancies progressing to or close to term had been documented between 1746 and 1948, with a 75% rate of fetal demise. The absence of such cases in more recent literature reflects improved access to medical care and better practice standards in ob/gyn, including the use of U/S imaging. Early pelvic ultrasonography would presumably make the second-trimester presentation of an advanced tubal pregnancy unlikely.

Our case, however, illustrates the potential for confusion when a large ectopic pregnancy is not properly localized. When the sonographer fails to observe the line of demarcation between the ectopic gestation and the uterine fundus, the sonographer may mistakenly "see" the ectopic gestation as being incorporated into the uterus. Careful scanning, including imaging of the lower uterine segment and cervix, should allow sonographers to recognize an ectopic conceptus.

In our case, this distinction was not made on the first U/S at 13 weeks, and the enlarged uterine size may have added to the confusion. Later in pregnancy, the typical sonographic features of advanced tubal pregnancy include the identification of the uterus separate from the fetus, extrauterine placental location, and the absence of a myometrial rim around the gestational sac.

DR. VIDAEFF is Associate Professor, and DR. RAMIN is Professor and Chair, Division of Maternal-Fetal Medicine, Department of Obstetrics, Gynecology and Reproductive Sciences, University of Texas-Houston Medical School, Houston, TX.

REFERENCE

1. McElin TW, Randall LM. Intratubal term pregnancy without rupture: review of the literature and presentation of diagnostic criteria. Am J Obstet Gynecol. 1951;61:130-138.

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