The implantation of a pregnancy in the cesarean scar is considered the rarest presentation of ectopic pregnancy and high morbidity and mortality. Little is known about the natural history of this condition, but allowing the pregnancy to progress carries the risk of rupture of the uterine scar, possibly requiring hysterectomy [1]. Of the various theories to explain this type of ectopic pregnancy, the most reasonable seems to be that the blastocyst enters the myometrium through a microscopic scar dehiscence, which may have been created by trauma from a previous segmental cesarean section or any other surgery.

Since the advent of transvaginal ultrasound (TUS) and magnetic resonance imaging (MRI), this type of ectopic pregnancy could be diagnosed early in pregnancy and treated conservatively, preserving fertility. This article reports two cases of ectopic pregnancy in the cesarean scar, illustrating the main aspects in TUS and MRI.

Case 1

A 44-year-old patient, without comorbidities, G2P1cA0. On 03/08/2016, with a pregnancy of 9w4d, she was admitted with a report of bleeding for 03 days. Transvaginal ultrasound showed a single gestational sac with an embryo of anomalous morphology, no heartbeats were identified (a miscarriage in progress), located in an isthmic topography, in an exophytic position, on the topography of a scar from a previous cesarean section, not being possible to identify the trophoblasto-myometrial interface properly. It is also evident an intense vascularization in the Doppler study, being the initial diagnosis of placental accreta. An MRI of the pelvis was performed, which showed an ectopic pregnancy with a gestational sac implanted in the cesarean section scar (type II—exogenous), with signs of trophoblast/placenta accreta (Figure 1). The patient underwent laparotomy, where the gestational sac was identified, mobilized and separated from the vesicouterine planes.

Case 2

A 30-year-old patient, without comorbidities, G2P1C, admitted on 06/10/2016, with a 7w3d pregnancy, with a report of abdominal pain. Transvaginal ultrasound showed a single gestational sac with a gestational sac implanted in the cesarean section scar, transmural type I (endogenous). An MRI of the pelvis was performed on 8/17/2016, demonstrating an ectopic pregnancy with the gestational sac implanted in the cesarean section scar, transmural, type I—endogenic (Figure 2). The patient was treated conservatively with methotrexate and had a good response, with no complications.

Ectopic pregnancy in cesarean scar (EPCS) is a relatively rare phenomenon and can occur not only due to cesarean section, but also related to any other type of trauma to the uterine wall, such as myomectomy, manual removal of placenta, dilation, and curettage and even in vitro fertilization [2],[3].

Due to the increase in cesarean deliveries, EPCS has become increasingly common, occurring 1 in 500 pregnancies among women who have already undergone cesarean delivery and accounting for 4% of ectopic pregnancies [4].

The pathogenesis has not been well defined, but the most likely theory is impaired wound healing after previous trauma with consequent myometrial defect where the blastocyst will implant. This impaired healing may be due to poor blood flow due to systemic diseases such as diabetes, collagen diseases, postoperative wound infection, short-term pregnancies, or inadequate suturing [2],[5].

They are caused by the migration of the blastocyst into the myometrium through a dehiscence in the cesarean scar [4],[6],[7]. This condition differs from intrauterine pregnancy with placenta accreta because the gestational sac is completely surrounded by the myometrium and fibrotic scar tissue, separate from the endometrial cavity or fallopian tube [3],[5].

Two types are described depending on the depth of implantation, with type I progressing toward the uterine cavity (endogenous) and type II progressing toward the bladder and abdominal wall (exogenic) [2],[4].

A quarter of women are asymptomatic at diagnosis; but the rest may present with vaginal bleeding or abdominal pain [2], making the differential diagnosis between miscarriage and cervico-isthmic pregnancy difficult [3],[5],[7].

Every patient with EPCS has a positive pregnancy test measured through β-hCG [2],[8]. If diagnosed early, the uterus can be preserved [3] and possible complications such as placenta accreta, uterine rupture, disseminated intravascular coagulopathy, hypovolemic shock, and even death can be avoided [2],[4].

Transvaginal ultrasound is the test of first choice and the findings are evaluated according to the criteria of Vial [6]: empty uterine cavity and cervical canal, gestational sac at the hysterostomy site, thinning or absence of myometrial tissue between the bladder and the gestational sac, a sign of negative “organ slippage” translated by the non-displacement of the gestational sac when applying pressure with the transducer [5] and a peritrophoblastic hypervascularization identified with the use of Doppler [2],[7],[8].

In cases of doubt or difficulty in transvaginal ultrasound, the magnetic resonance with images in the 3 orthogonal planes and T1 and T2-weighted sequences allows a more detailed assessment of the anatomy, such as the depth of invasion of the trophoblast into the myometrium, involvement of the serosa or bladder, the exact position, and volume of the gestational sac [6].

Outcomes of an ectopic pregnancy in cesarean section scar are variable. Its prognosis is related to gestational age and β-hCG levels, regardless of type I or II. The risk of rupture in ectopic pregnancy increases as gestational age and β-hCG levels increase. In cases of ruptured ectopic pregnancy, the patient may progress to bleeding, shock, and even death. Therefore, it is important that the diagnosis is made early, avoiding further complications [9],[10].

The treatment of ectopic pregnancy aims to prevent bleeding and other complications, in addition to seeking to preserve the patient's uterus. There are several proposals for interventions; however, there is no consensus on the ideal approach in cicatricial ectopic pregnancy. The definition of the conduct depends on several factors, among them the gestational age, the levels of β-hCG, and the hemodynamic stability of the patient. Thus, there is no specific treatment for type I or type II [9].

Treatment should be individualized and consideration should be given to the gestational age, the desire for future pregnancies, the length of gestation, the therapeutic possibilities available, and the experience of the medical team [6],[8],[11].

Numerous treatment modalities have been recorded, including expectant management when the patient is hemodynamically stable and decides to wait for a spontaneous abortion; systemic or local drug treatment with direct application to the gestational sac, with methotrexate being the most commonly used substance; uterine artery embolization; surgical procedures such as hysteroscopy with resection of the gestational sac/curettage and hysterectomy or combination of medical and surgical treatments [2],[4].

If the option is drug treatment, surveillance of the drop in β-hCG value until it becomes negative, as well as ultrasound control until the gestational sac disappears [6],[12].

Ectopic pregnancy in a cesarean scar is a rare condition that can develop into a serious condition, leading to maternal death. The interest of an early diagnosis lies in the possibility of making an appropriate therapeutic decision based on the clinical context, imaging information, the patient’s wishes and technical conditions; in order to reduce possible complications.