Estimated incidence rates of CSP range between 1/1800 and 1/2500 of all CDs performed [7–10]. Seow et al. [11] states that CSP was seen in 0.15 % of all pregnancies with a history of a previous CD. The above numbers appear unrealistic; however, their true incidence is unknown due to the lack of population based statistics (registries).

The only risk factor for CSP is a previous CD. However, since we found about eight cases of recurrent CSP in the literature, including our own case with four recurrences [12], we have to consider a previous CSP as a rare but possible risk factor for this entity.

Later in this chapter, we will provide evidence that the histology of the tiny placental insertion or myometrial invasion of a CSP in the first trimester of the gestation is identical with the histologic findings of a MAP in the second and third trimester of pregnancy. The only scientifically proven fact is that, in both diseases (CSP and MAP), intervening fibrinoid layer between the myometrium and the cytotrophoblastic shell in the placenta is naturally present between the endometrium in normally attached placentae when thinned or missing. This fibrin layer (fibrinoid material) is known by the name of Nitabuch layer. Previous uterine surgery or uterine interventions lead to thin or absent decidua basalis in scarred areas, as well as the abovementioned protective layer of the lower uterine segment. In CSP and in MAP this membrane is missing and the placental villi attach themselves and penetrate between the myometrial fibers into the depth of the uterine wall.

Other theories, such as the role of a low oxygen tension at the area of the scar providing a stimulus to help the invading cytotrophoblast [13, 14], as well as the in vitro studies of Kliman et al. [15] with trophoblast and EM explants, showing a strong propensity for attaching to exposed extracellular matrix and then to endometrial epithelial cells, are the most frequently quoted. Both theories support the observation that the more CDs a patient has, the higher risk of placenta previa and a MAP.

The two diagnostic modalities used are ultrasound and MRI; however, ultrasound is the best modality. Transvaginal sonography (TVS) presents an advantage over transabdominal ultrasound (TAS), since it has a higher resolution and can be placed in close proximity to the low, anterior gestational sac. MRI has been used for imaging and is expensive. In addition, it requires moving the patient to a radiology site. Also, MRI lacks the color Doppler flow that provides a high resolution image, which is important in establishing a correct diagnosis.

The diagnosis of CSP requires a high clinical index of suspicion. We reiterate, that every woman with a history of a previous CD and a positive pregnancy test, presenting in the first trimester of the pregnancy, should be considered a “rule out CSP” until proven otherwise. Stirnemann et al. [16, 17] published studies to lay the basics for such screening if proven significant. Until that time, this should be strongly considered, since there is no downside to that first early scan. Godin et al. [18], Vial et al. [19], and Seow et al. [20] published similar sonographic criteria they used to define a CSP; however, other authors used additional characteristics, relying mostly on single cases.

Our diagnostic criteria of CSP [4, 21] took in consideration a history of previous CD, a positive pregnancy test and the following sonographic criteria (Fig. 17.3):

If an AVM was suspected (at times, this may be the presenting sonographic picture), Doppler measurements of the blood velocity were measured and expressed by the peak systolic velocity (PSV) in cm/s. Velocities above 39 cm/s were considered for uterine artery embolization (UAE) by the interventional radiologist. This evaluation is best done when the region of interest of the Doppler interrogation is constricted to the questionable area, using the appropriate pulse repetition frequency and filter settings.

These are pathological, high velocity, low resistance “short circuits” of the blood stream between an organ’s arterial and venous supply. Ultrasound presents a valuable tool for the diagnosis of AVM and guideline for their treatment [22]. Although uncommon, they may cause dangerous hemorrhages due to disrupted blood vessels, after miscarriage or uterine instrumentation [23]. The acquired form, seen in CSP, is usually traumatic, resulting from prior dilation and curettage (D&C), therapeutic abortion, uterine surgery, or direct uterine trauma. Their incidence is about 1 % of CSPs. In our series of 60 CSPs five, patients had AVM [24].

There are two main differential diagnostic entities to consider: First, a cervical pregnancy, which is rare and has no history of prior CDs. Second, a miscarriage in progress, which can be seen in the cervical canal or close to the internal os and “on its way out” having no heart activity. Also, under pressure on the cervix with the vaginal probe, the sac will slide back-and-forth, while a true CSP will stay fixed. It should be noted that misdiagnosis has, at times, severe consequences. The proof is in the literature: 107 of the 751 cases of CSP reviewed (13.6 %) were missed or misdiagnosed leading to complications (e.g., hysterectomy and loss of fertility) [4]. Figure 17.7 demonstrates a simple method to distinguish between the two, abovementioned, differential diagnostic entities and a true CSP.

However, it is extremely important to realize that this simplified diagnostic aid is valid and reliable only while the gestational sac is small (e.g., 5–6 mm in diameter or 5–6 postmenstrual weeks) and remains “local,” close to the niche or above the scar. In other words, the sac did not start to elongate and move/expand cranially to fill the uterine cavity. In this case, the sac will be found increasingly in the uterine cavity misleading the uninitiated observer to think that it is an intrauterine sac. In such cases one should shift the attention from the sac and concentrate upon the blood vessels of the tiny placenta, which stay in their original site of implantation, thereby holding the most important diagnostic feature of CSP: the true site of placental implantation. Figures 17.2, 17.3, 17.4, and 17.5 clearly demonstrate the abovementioned diagnostic principle.

Lately, clinicians and clinical researchers have started to pay attention to the exact location of placental implantation in the area of the scar/niche left behind by the previous CD. Vial et al. [19] suggested that there are two kinds of CSPs, based on depth of implantation. The question is whether a deeply implanted chorionic sac in a niche or dehiscence, close to the bladder with very thin or no visible myometrium (Fig. 17.8a, b) will result in a worse outcome than if inserted on top of a scar that has some thickness (see Fig. 17.8c, d). Comstock et al. [25] and personal communication with Cali G. refer to “on-the-scar implantations” as “low lying sacs” and assume that these are the CSPs that may proceed to third trimester giving rise to MAP. Deeply implanted in the niche, surrounded by myometrium and seldom reach term is a “true” scar pregnancy. We slightly differ about the latter form of CSP since we have witnessed the reaching delivery of a live offspring.

Rac et al. [26] studied 39 patients, of which 14 had histologically confirmed MAP. The smallest myometrial thickness measurement was one of the variables associated with invasion. More research is needed before the gestational-sac-to-bladder distance (see Fig. 17.8) can become useful in counseling patients with CSP in the first trimester of pregnancy.

The connection or continuity between CSP and MAP has gradually become evident through clinical observation [27, 28]. We studied placental implantation in the early (second trimester) placenta accreta and in CSP, to find out if they represent different stages in the disease continuum leading to morbidly adherent placenta in the third trimester [29]. Two pathologists, blinded to the diagnosis, evaluated their histologic slides on the basis of these microscopic slides. They could not tell the difference between the two clinical entities and found that both had one thing in common: neither had intervening deciduas between the villi and the myometrium, consistent with the classic definition of morbidly adherent placenta. Therefore, our conclusion is that CSP and an early second trimester placenta accreta are histopathologically identical and represent different stages in the disease continuum leading to MAP in the third trimester.

The next logical question is whether, left untreated, a CSP would result in a live born offspring. We followed ten patients diagnosed with CSPs who opted to continue the pregnancy declining early termination [30]. The diagnosis of CSP was made before 10 weeks. All ten had sonographic signs of MAP by the second trimester. Nine of the ten patients delivered live born neonates, between 32 and 37 weeks. One patient had progressive intractable vaginal bleeding, leading to hysterectomy, at 20 weeks. The other nine patients underwent hysterectomy at the CD. Blood loss ranged from 300 to 6000 mL. Histopathological diagnoses of all placentae was: placenta percreta.

Above, we provided reliable data regarding two clinical issues: (1) CSP is a precursor of MAP, both sharing the same histopathology and (2) pregnancies diagnosed as CSP in the first trimester may proceed to deliver live offspring, risking premature delivery and loss of uterus and fertility. This data can be used to counsel patients with CSP, to make an evidence-based and informed choice between first-trimester termination of an early pregnancy or continuation, risking premature delivery and loss of uterus and fertility.

MAP can exist in the first trimester of pregnancy. For beginners, Comstock et al. [25] described seven patients after sonographic examination at 10 weeks or earlier with placenta accreta, increta, percreta, not only by their clinical course but, more importantly, by pathologic examination of the uterus. In six, at the time of the early ultrasound, the chorionic sac was located in the lower uterine segment, in the scar area of the previous CD. Two patients underwent D&C, at which time severe bleeding led to hysterectomy. The remaining four had sonographic findings typical of placenta accreta during subsequent scans but delivered at term. The author’s conclusion suggested that, in a patient with a previous CD, a chorionic sac detected by a 10 week or less ultrasound, located in the lower uterine segment, suggests the possibility of placenta accreta. A similar article was published by Ballas et al. [27].

Using our material, Fig. 17.9 depicts the early sonographic markers of a MAP: placenta previa, focal loss of the clear space and focally increased vascularity. The patient in this example delivered at 34 weeks and had placenta accreta. In ten patients, we reported [30] the early sonographic markers of MAP could be detected at the end of the first and beginning of the second trimester.

In the case of positive heart activity, counseling should enumerate the two main, clinical management options to reach a decision as early as possible. The two options before further growth of the gestation are: (1) termination or (2) continuation of the pregnancy. Our counseling of patients with a CSP diagnosed in the first trimester of pregnancy underwent a fundamental change. Several years ago we would counsel toward termination of the pregnancy without delay. Recent studies on the natural history of the CSP, with the possibility of reaching term or near term delivery of a live offspring, has changed our counseling. We provide the patient with evidence that this is possible and that the patient should understand that a placenta accreta at the CD may necessitate hysterectomy. Management in the above case should be based on the patient’s age, number of previous CDs, desired number of children, and the expertise of the clinicians giving the care. If the patient decides to continue the pregnancy, bleeding precautions should be given. The management should be based upon serial ultrasounds, until a safe gestational age is reached. A multidisciplinary team should be involved in the delivery and blood products should be available, since ultrasound cannot predict the blood loss at surgery. Our general guidelines in counseling and managing the patient with a CSP are shown in Fig. 17.10.

Treatment regimens and their combinations can be classified as one of the following:

The last two can be guided by continuous, real-time ultrasound.

It is beneficial for the patient with CSP to be referred to a facility that provides evidence-based care as well as experienced in managing cases, in response to developing emergency situations. Such centers should be able to provide operating rooms, interventional radiology procedures and have available immediately blood transfusion/blood products. The latter, since bleeding complications is typical of this dangerous clinical entity.

Based upon the in-depth and available literature, analyzing the different aspects of CSP, in 2012 there were about 33 published treatment modalities with their results and complications [4]. No preferred treatment became apparent, however, of the 751 patients D&C (305), surgical excision (laparoscopic, hysteroscopic and transvaginal) (261), UAE (142), MTX (92), and local, intragestational sac injection (86) were the most used.

Between 2012 and 2014, no less than 1223 cases of CSP were published in about 61 peer-reviewed articles. Not surprising is the fact that Chinese authors contributed 91 % of the cases, describing their various and different treatment modalities/combinations of managing approximately 1115 patients. This is due to their large population and over 40 % CD rate. At least 36 primary or combination treatments were found; however, the number is not substantially different from the list of treatment approaches described in our review of 751 cases. No wonder one cannot draw a clear conclusion as to which treatment was the most effective, resulting in the least or no complications. This large number underlines the fact that, in 2015, there is no nationally/internationally agreed upon or suggested management protocol published with a set of guidelines to manage CSP or early first-trimester placenta accreta. While the distribution of the various treatments and their rates of use are found in the tables of our previous review [4], the somewhat different distribution of treatment choices are detailed in Table 17.1.

Despite several treatments for CSP our detailed discussion will be limited to the most used. A much more detailed analysis is found in our in-depth review [4], complete with their efficacy and complication rates. We now add the pertinent data resulting from the review of the 1223 cases published after 2012.