Cesarean Scar Ectopic Pregnancy in the First Trimester

2016-07-11 19:01:31

Category: Abdominal Imaging, Region: Pelvis-Uterus, Plane: Sagittal

ABSTRACT: We report a case of ectopic pregnancy in a Cesarean section scar in a 29-year-old woman who presented with intermittent vaginal bleeding in early pregnancy. Cesarean scar pregnancy requires prompt recognition, as delay in diagnosis and treatment carries a high risk of uterine rupture and life-threatening hemorrhage. Early recognition and characterization of this entity is critical in preventing significant maternal morbidity and determining appropriate management. Proposed etiologies, risk factors, imaging features, and clinical management will be discussed. CASE HISTORY: A 29-year-old woman (G8P5A2) presented to the emergency department in early pregnancy with three days of intermittent vaginal bleeding. On presentation, she was hemodynamically stable and afebrile. She denied abdominal pain, fever, dysuria, or other constitutional symptoms. Serum beta-hCG measured 38,698 IU/mL. Remaining laboratory values were within normal limits. She had no history of uterine fibroids, endometriosis, or other gynecologic pathology. Obstetric history was significant for three prior Cesarean sections. Transvaginal ultrasound performed in the emergency department revealed an anteverted, anteflexed gravid uterus with single live intrauterine pregnancy. Fetal measurements corresponded to an estimated gestational age of 7 weeks 1 day. M-mode ultrasound showed fetal cardiac activity at 124 bpm. The gestational sac was located in the low anterior uterine segment, and there was marked thinning of overlying myometrium. The uterine fundus superior to the gestational sac was normal in appearance, as was the cervical canal. No adnexal abnormality was identified. The findings were considered highly suspicious for Cesarean scar ectopic pregnancy. The patient was seen the following day by her obstetrician, and MRI was requested for confirmation prior to termination of pregnancy. Sagittal and axial T1 and T2-weighted images demonstrated a gestational sac bulging through the myometrium of the lower uterine segment in the region of Cesarean section scar. There was thinning of the anterior myometrium, which remained intact, and no bladder wall invasion. The posterior aspect of the gestational sac extended into the endometrial cavity of the lower uterine segment. The posterior myometrium was normal in thickness. Findings confirmed ectopic pregnancy in a lower uterine segment Cesarean scar. Due to clinical stability, lack of associated complications, and early stage of pregnancy, the patient was successfully treated on an outpatient basis with intra-amniotic instillation of methotrexate and intramuscular methotrexate injection. IMAGES FIGURE 1: Longitudinal grayscale transvaginal ultrasound obtained with a MHz transducer shows an anteverted, anteflexed uterus. The uterine cavity (red arrow) and cervical canal (white arrow) are empty. There is a gestational sac (yellow arrow) in the anterior myometrium of the lower uterine segment, with marked thinning of the overlying myometrium. FIGURE 2: Transverse grayscale transvaginal ultrasound images show a gestational sac (yellow arrow) with yolk sac (white arrow) and fetal pole (red arrow) in the anterior myometrium of the lower uterine segment. FIGURE 3: M-mode transvaginal ultrasound of the fetal pole demonstrates fetal cardiac activity at 124 bpm. FIGURE 4: Midline sagittal T2W MR image through the pelvis shows a gestational sac within the myometrium of the anterior lower uterine segment, in the region of Cesarean section scar. The posterior aspect of the sac extends into the endometrial cavity of the lower uterine segment (red arrow). Anterior to the gestational sac, the myometrium is thinned (yellow arrow). Myometrium along the posterior lower uterine segment is normal in thickness. There is no placental invasion of the urinary bladder (white arrow), which is collapsed. FIGURE 5: Axial T2W (figure 5a) and T1W fat-suppressed (figure5b) MR images through the pelvis show the gestational sac implanted within the anterior myometrium of the lower uterine segment, with surrounding decidual reaction (white arrow). A thin layer of myometrium covers the anterior aspect of the gestational sac (white arrow). CONCLUSION: Since the first case was reported in the English medical literature in 1978, the apparent incidence of Cesarean scar pregnancies has continued to rise, likely due to increasing numbers of elective Cesarean sections as well as improved detection with transvaginal ultrasound. Estimated incidence is now 1 per 1,800-2,226 pregnancies, exceeding than that of cervical ectopic pregnancies. Cesarean scar pregnancies present unique diagnostic and therapeutic challenges. TVUS remains the first-line imaging modality in the diagnosis of CSP, with reported sensitivity of 84.6%. Key imaging findings include an empty uterine cavity and cervix, gestational sac in the low anterior uterine segment, and thinned or absent overlying myometrium; MRI may provide useful anatomic information in equivocal cases or prior to surgical intervention. This case illustrates the key imaging features of early Cesarean scar pregnancy. A full case report will provide discussion of proposed etiologies, risk factors, imaging features, and clinical management of Cesarean scar pregnancy.