INTRODUCTION

Cesarean scar pregnancies (CSPs) are a relatively rare form of ectopic pregnancy. The first case was reported in the English medical literature by Larsen and Solomon in 1978.[1] Implantation of a pregnancy within the fibrous scar of a previous cesarean section is being reported more frequently, and the incidence is now higher than that of cervical ectopic pregnancies.[2] There has been a substantial increase in published cases of CSPs in the medical literature since its first reporting. While this may reflect a “true” increase in incidence given the rise in cesarean section rates over the years, it may also be attributed to improved detection of this condition, with routine use of transvaginal ultrasound (TVUS).[3] Early detection of a CSP is critical, as delayed diagnosis and management of this potentially life-threatening condition may result in complications, such as uterine rupture and hemorrhage with serious maternal morbidity and potential hysterectomy.

Diagnosis of such a condition should be made based on a high index of suspicion from clinical and imaging investigations combined with the patient's history and clinical manifestations. Improvements in ultrasound and magnetic resonance (MR) technology may enable earlier detection of a CSP, thus facilitating prompt intervention to avoid potential complications. To our knowledge, there is no standardized approach to treat this condition at present; however, various treatment options are available and should be tailored to meet the needs of each individual case. Further characterization of a CSP using magnetic resonance imaging (MRI) after initial ultrasonography may provide additional information useful for directing patient management and therapy (e.g. conservative versus surgical management).

We describe a case of an ectopic pregnancy implanted in the fibrous scar of a previous cesarean section, which led to vaginal bleeding. The patient was initially managed conservatively with systemic intramuscular methotrexate and bilateral uterine artery embolization, but ultimately required hysterectomy.

CASE REPORT

A 36-year-old woman (gravida 5, para 2) at approximately 8 weeks and 6 days gestation presented to her obstetrician complaining of heavy vaginal bleeding that had started 3 days prior. At the time of presentation, the vaginal bleeding had decreased to occasional spotting. The patient did not have abdominal pain or other constitutional symptoms. She also had no history of fibroids, endometriosis, or abnormal pap smears. She did report a medical history significant for beta thalassemia minor and a past surgical history of two prior cesarean sections for macrosomia. Serum beta-human chorionic gonadotropin (beta-hCG) level at the time of presentation measured 199,760 mIU/mL. A subsequent pelvic ultrasound showed a retroflexed gravid uterus with a single viable pregnancy in the lower uterine segment abutting the urinary bladder [Figure 1a–d]. Two- and 3-dimensional multiplanar views on the TVUS demonstrated a normal uterine fundus superior to the gestational sac. Fetal measurements were consistent with an estimated gestational age of 8 weeks and 5 days. Fetal cardiac activity measured 159 beats per minute (bpm). Given the position of the gestation in the lower uterine segment and the history of two prior cesarean sections, the findings on initial ultrasound examination raised the suspicion of a cesarean scar ectopic pregnancy with possible isthmic-cervical involvement [Figure 1a–d]. In addition, the proximity of the gestation to the urinary bladder raised the possibility of urinary bladder involvement; however, ultrasound examination could not exclude this possibility with certainty. The patient was referred to the hospital for admission, further evaluation with MRI, and medical management with the possibility of surgical intervention.

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Figure 1

(a) Sagittal and (b) transverse images from a pelvic ultrasound show a gravid retroflexed uterus measuring 12.4 × 6.5 × 7.1 cm corresponding to a volume of 299.3 cc. (c, d) Additional transabdominal images show a single intrauterine gestation with positive fetal cardiac activity measuring 159 beats per minute and a crown-rump length measuring 2.1 cm corresponding to an estimated gestational age of 8 weeks and 5 days

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MRI confirmed an intrauterine pregnancy bulging through the myometrium of the lower uterine segment with resultant mass effect on the superior right parasagittal aspect of the urinary bladder [Figure 2a–d] without direct invasion of the urinary bladder wall. The developing placenta was positioned inferiorly in this region with little or no surrounding myometrium. The findings on MRI were diagnostic of an ectopic pregnancy in the lower uterine segment, within the known cesarean scar, and confirmed the absence of urinary bladder involvement.

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Figure 2

(a) Sagittal T1-weighted fat-saturated contrast-enhanced image of the uterus just off midline demonstrates an intrauterine gestational sac distending the endometrial cavity. The sac produces an outward bulge in the lower uterine segment at the site of cesarean section scar (white arrowheads) and is intimately related to the urinary bladder roof. Enhancing trophoblastic tissue/placenta (red arrow) is present at the bulging site. (b) Sagittal T2-weighted image of the uterus again shows the outward bulging gestational sac through the cesarean scar. Marked thinning of the myometrium is seen at the base/periphery of the bulging gestational sac. The central portion of the bulging gestation sac appears to be covered only by thin hypointense serosa (yellow arrowheads). Of note on this image is the preserved urinary bladder wall with a separating hyperintense fat plane (white arrows). (c) Coronal T2-weighted and (d) coronal T2-weighted fat-saturated images demonstrate the preserved hypointense urinary bladder wall at the level where the gestational sac bulging through the scar sits atop the urinary bladder. Note also the marked thinning of the overlying myometrium (black and white arrowheads)

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Upon admission, conservative management was initiated. The patient underwent a successful bilateral uterine artery embolization via a right common femoral artery approach. The right uterine artery was embolized using five vials of 500-700 μm microspheres and stasis of blood flow was achieved. The left uterine artery was embolized using four vials of 500-700 μm microspheres and an additional vial of 700-900 μm microspheres with near stasis of flow. The patient also received systemic intramuscular methotrexate therapy (80 mg administered via the left gluteus muscle). Quantitative serum beta-hCG levels began to decrease, though fetal cardiac activity remained present and measured in the range of 160 bpm. A second dose of 80 mg intramuscular methotrexate was administered 3 days later with serum beta-hCG levels continuing to decline; however, follow-up serial ultrasound examinations continued to demonstrate fetal cardiac activity in the 160 bpm range. The patient was deemed to have failed initial conservative therapy and was given the option of an intra-amniotic injection of potassium chloride with methotrexate or a hysterectomy. The patient ultimately decided on surgical management and underwent a total abdominal hysterectomy with extensive lysis of adhesions. Intraoperative findings revealed the urinary bladder to be densely adherent to the lower uterine segment and the unruptured pregnancy, primarily on the right as demonstrated on the MRI. Pathologic evaluation of the hysterectomy specimen revealed a gravid leiomyomatous uterus with decidua in the uterine corpus as well as serosal adhesions to adipose tissue and skeletal muscle at the prior cesarean section scar. A portion of spongy, placental tissue measuring 5.0 × 4.0 × 2.7 cm was attached to the anterior lower uterine segment with extension to the upper endocervical canal. An embryo with four limb buds and ambiguous genitalia was present within the gestational sac [Figure 3a–c]. No cytotoxic effects related to the embolization or chemotherapy were reported.

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Figure 3

(a, b) Photographs of the gross specimen post-hysterectomy show a gestational sac with a single embryo (dashed yellow arrow) measuring 2.4 cm in length attached by a 2.6 cm long umbilical cord (not shown). Four limb buds (red arrows) are present with ambiguous genitalia. (c) Microscopic evaluation of the sample from the scarred portion of the lower uterine segment in the implantation site shows myometrium ranging from 0.1 cm to 1.8 cm in thickness (black arrowheads) and chorionic villi with trophoblasts (black arrows) invading into 1 mm of fibroadipose tissue, suggesting impending rupture. (Hematoxylin and eosin stain, ×20)

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DISCUSSION

Once considered an extremely rare entity, cesarean scar pregnancies are becoming a more common occurrence with the increase in elective cesarean procedures and improvement in detection of CSPs with TVUS. While the cause and pathophysiology are still not well understood, to our knowledge, many theories regarding the mechanism of a CSP have been proposed. It has been hypothesized that poor vascularity in the anterior lower uterine segment impairs healing after cesarean procedures in some women, rendering this area vulnerable to formation of small dehiscent tracts or defects into which a trophoblast can implant.[3] Women who undergo multiple cesarean sections develop scars with larger surface areas, which may in turn increase the risk of a scar implantation. Two types of CSPs have been proposed by Vial et al.,: (i) implantation of the trophoblast on a prior cesarean scar with growth toward the uterine cavity and (ii) implantation deep in the scar defect with progression toward the bladder and abdominal cavity.[4] The former type may progress to a viable pregnancy with significant risk of hemorrhage, while the latter type is at greater risk of rupture.

CONCLUSION

Cesarean scar ectopic pregnancy remains a relatively rare entity; however, this potentially life-threatening condition is being reported more often as greater numbers of elective cesarean procedures are performed worldwide. TVUS remains the imaging modality of choice for diagnosis, though MRI may play a greater role in evaluating CSPs. The superior soft tissue characterization and anatomical information provided by MRI allows patients and clinicians to consider conservative management as initial therapy, especially with the increasing availability of minimally invasive UAE. Combined with conservative medical therapy, minimally invasive UAE makes preserving fertility in the face of a CSP more achievable. While there is no standardized approach at present, intervention must be instituted early to minimize complications and maternal morbidity regardless of which therapeutic option is decided upon. Treatment must be tailored to each individual case and requires careful discussion between the patient and clinician. In the end, the decision should be made based on the patient's clinical presentation, age of the gestation, desire for future fertility, and clinician's experience in managing this condition.