Cesarean Scar Pregnancy: Diagnosis and Management
Ilan E. Timor-Tritsch
Andrea Kaelin Agten
Cesarean scar pregnancy (CSP) is defined as a pregnancy implanted in the lower anterior segment of the uterus, either on the scar (also termed type 1) or in the “niche/dehiscence” (also termed type 2) left behind the incision of a previous cesarean delivery (CD). It is a potentially dangerous gestation that, treated or untreated, can lead to complications in all three trimesters of the pregnancy.
Differential diagnoses are miscarriage in progress or cervical pregnancy and rarely myomectomy scar pregnancy when the placenta implants at or on the site of a previous myomectomy.
Terms and Nomenclature
Over the years and since its first description by Vial et al. (1), various terms were and are still used. Most frequent are “cesarean scar ectopic,” “cesarean ectopic pregnancy,” “isthmocele,” “ectopic,” and “cesarean delivery scar pregnancy.”
We use the simple term “cesarean scar pregnancy” because, although implanted in lower part of the uterine cavity, the gestation is and remains contiguous with the cavity. If left to continue, the gestational sac expands/morphs into the upper part of the cavity leaving the placenta behind embedded on the scar or the “niche.” In addition, as opposed to the “real ectopic pregnancies,” if left to continue CSP can result in a liveborn offspring. As it will be discussed later, lately it is widely accepted that CSP is an early form of the placenta accreta spectrum [PAS]).
It is recognized that CSP is intimately related to previous CDs. The latest estimated rate of CDs published by the Centers for Disease Control and Prevention estimated in 2017 was 32.0% (2) and it seems to have stopped increasing and steadied at 32% from 2009 to 2011.
The true incidence of CSP is unknown. Almost all articles and related articles quote the only available estimates that the range is from 1/1,800 to 1/2,656 of all CDs performed (3,4). It may be higher because there may be some underreported, missed, or misdiagnosed cases. One could increase the reported incidence by increasing awareness and more precise diagnosis by transvaginal ultrasound (US) as well as by offering routine screening of every pregnancy after the previous CDs (5).
The only risk factor for CSP is one or more previous CDs.
During a normal pregnancy, the vascular bed is “remodeled” as the trophoblast enters the myometrium enabling a rich blood supply flowing through a low-resistance/high-velocity blood flow supplying the conceptus. A dedicated fibrinoid layer (Nitabuch) present between the endometrium and the cytotrophoblast of the normally attached placenta stops this physiologic “invasion.” Previous CD or uterine interventions compromise the healing myometrium an unopposed penetration of the trophoblast thought to create placental accretism.
There are several terminologies used to describe the different placental implantation patterns in the area of the healing previous CD incision. The original term used for the two types of implantation by Vial et al. (1) was “endogenous” if the pregnancy was deeply implanted in the myometrium and “exogenous” if the attachment was superficial. Subsequent respective terminologies used are type 1 versus type 2 (6,7), “Low lying” versus “surrounded by myometrium” (7), “in-niche” versus “on the scar” (8).
Pain is usually not a common presenting symptom of CSP.
It is more common to see that asymptomatic cases are being diagnosed by the booking US. Again, this may be a good reason to offer pregnant patients after a CD a routine very early (5-7 weeks) US evaluation. Such a scan is important because many CSPs are frequently misdiagnosed as miscarriages or threatened abortions leading to dilation and curettage (D&C) causing profuse bleeding and emergency surgical interventions ending up with an avoidable hysterectomy.
IMAGING AND OTHER DIAGNOSTICS
Three Dimensional US
Three-dimensional US is at times used for the diagnosis of CSO; however, it provides only marginal additional information (10,11,12).
The main imaging modality is transvaginal US.
The scan should always be performed with a partially filled bladder to examine the boundary between the bladder and the lower anterior wall of the uterus.
The diagnosis of CSP should be based on a positive pregnancy test in addition to the following sonographic criteria:
Empty uterine cavity and closed, empty endocervical canal
In very early pregnancies (5-6 weeks), the detection of a gestational sac in close proximity of the low anterior segment of the uterus
After 6 to 7 postmenstrual weeks, a gestational sac and the placenta located close to the hysterotomy scar or protruding into the niche created by the CD
Thin or absent myometrial layer between the gestational sac and the anterior uterine wall or the posterior bladder wall
Subjectively rich blood flow around the gestational sac determined by Doppler 6; interrogation using the most sensitive settings possible
Finding of placenta previa, one of the most important diagnostic markers of a CSP (also predictive of a second and third trimester PAS)
A simple and practical way to diagnose an early (5-6 and at times even a 7-week) CSP is to display a longitudinal, sagittal US picture of the uterus in question and draw an imaginary line across its middle to divide the uterus in half. If the center of the gestational sac is below that line and closer to the cervix, it is a CSP. If the center of the gestational sac is above that line, closer to the uterine fundus, it is an intrauterine pregnancy (Figure 3.1.4) (14).
Figure 3.1.3. The typical anteverted retroflexed uterus of a patient with the low, anterior, early first-trimester gestational sac of a CSP. B, bladder; CSP, cesarean scar pregnancy.
After 7 weeks, in continuing pregnancies, the chorionic/gestational sac with the embryo/fetus “moves” toward the fundus populating the uterine cavity (see Figure 3.1.3); however, the placenta with its vascularity remains anchored in its original site of implantation preserving one of the most diagnostic features of CSP (Figure 3.1.5).
It is important to determine the distance between the anterior uterine surface (or for that matter the posterior bladder wall) and the implanted placenta because the amount of intervening myometrium seems to predict the outcome. A study suggested that a deeply embedded gestational sac and placenta “in the niche” or dehiscence will result in a more ominous outcome than if it is implanted “on the scar” that has some thickness to it (8) (Figures 3.1.1 and 3.1.2). There are several
sonographic markers of CSP in the first trimester. Some are seen better in the late first trimester—for example, 8 to 11 weeks. Figure 3.1.6 demonstrates these sonographic markers comprehensively.
Magnetic Resonance Imaging (MRI)
Most authors versed in scar pregnancies do not recommend routine or additional MRI because transvaginal grayscale and color Doppler US imaging is considered to be reliable in establishing the correct diagnosis.
Recurrent CSPs are more frequent than intuitively thought. It is important to know that the diagnosis of CSP must also take into consideration the threat and realistic possibility of a recurrence. This fact was ignored for some time based upon sporadic single case reports. At this time, reviewing the literature of the last several years, it was clear that the rate of recurrence may reach 15% or more (15,16). We reported of a single patient with four recurrent CSPs. After the first four live CSPs were injected with local intragestational methotrexate (MTX), the last recurrent fifth CSP resulted in the delivery of a near-term offspring by repeat CD followed by hysterectomy confirming placenta percreta (17) (Figure 3.1.7).
Heterotopic pregnancies were also diagnosed and reported. In this case, the center of the gestational sac of the scar pregnancy will be closer to the cervix, whereas the center of the other sac is usually within the uterine cavity (Figure 3.1.8).
They deserve special attention because if the correct treatment is selected for the CSP, the intrauterine pregnancy can result in live offspring (18,19,20,21,22,23,24,25,26,27,28).
The best review containing detailed information seems to be by Ugurlucan et al. (27).
Evidence-based counseling of the patient and most importantly to her partner/husband or at times other family members accompanying her.
Always emphasize the fact that this is a rare as well as an extremely dangerous pregnancy and regardless of the management, it presents diagnostic and treatment challenges.
No decision regarding termination or continuation of the gestation is easy. Patients need time to arrive at a decision.
Termination of a CSP is time sensitive. Every day the decision is delayed, the gestation is growing hand in hand with its blood supply. Every day the chances of encountering a complication and its extent are increasing.
It should be clear that even in the best of circumstances, treatments may endanger the patient’s life.
Expectant management of CSP with positive heart activity is associated with a high burden of maternal morbidities such as severe hemorrhage, early uterine rupture, hysterectomy and severe PAS, and even maternal mortality. Despite the possible dangers, some CSPs may progress to, or close to, the term. It is therefore fair to question whether termination of the pregnancy should be the only therapeutic option offered to these women (29). Therefore, if continuation of the pregnancy is entertained, a perspective of the period until desired delivery is achieved describing the possible complications specific to each trimester (Figure 3.1.9).
The complications are mainly resulting from the fact that these will probably all be within the PAS, such as pregnancies with placenta accreta, increta, and percreta.
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Termination of CSP should be performed as soon as possible to minimize the risk of complications.
Minimally invasive approaches such as the double-balloon treatment can be performed under local anesthesia, whereas more invasive treatment methods, such as laparoscopy, require general anesthesia.
Most managements can be classified as one of the following and their combinations thereof:
Surgery (requiring general anesthesia)
Laparotomy (hysterectomy or local excision)
Excision by laparoscopy, hysteroscopy, or transvaginal approach
Dilatation of the cervix followed by sharp or blunt curetting
Suction aspiration without dilatation of the cervix
Minimally invasive procedure/US guided
Minimally invasive surgery without general anesthesia, such as local injection of MTX or KCl with or without local vasopressin
Systemic medication single or multidose intramuscular or intravenous administration of MTX
Uterine artery embolization (UAE)
Combination of the above treatments
Several articles reported on combining treatments in a planned, simultaneous, or sequential fashion.
Treatments are also changed, mostly after the first-line therapy failed.
Local pressure by inflatable balloons
Procedures and Technique
Choosing the Primary Treatment Options
There is no agreed-upon treatment protocol for CSP. Even “official” guidelines of pertinent societies involved in this area post rather ambiguous lists of treatment modalities and stay away from endorsing specific treatment/s. Recently, the Society of Maternal Fetal Medicine posted its suggested guidelines for diagnosing and treating CSPs (32). When practice and management patterns are reviewed, it is obvious that gynecologic surgeons generally use mostly D&C, laparoscopy, and hysteroscopy or laparotomy. Obstetricians, radiologists, and in vitro fertilization specialists prefer systemic, parenteral administration of MTX or US-guided local intragestational sac MTX (or potassium chloride). Interventional radiologists are asked to embolize the CSP. We reviewed the treatments, their efficacy, and complications published ending in the year 2012 (32). However, since then, other additional treatment protocols and their combinations were reported (31,33,34).
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