Cesarean scar pregnancy

Bhusal Miluna

(Medical School of Yangtze University，Jingzhou 434023，China)

Wei Hua，Yi Cunjian

(Department of Gynaecology and Obstetrics the First Hospital of Yangtze University，Jingzhou 434000，China )

Implantation of a pregnancy within the previous cesarean section scar is Cesarean Scar Pregnancy(CSP).It is the rarest form of ectopic pregnancy.Cesarean scar is a rare site for implantation of a pregnancy.With increasing rates of abdominal delivery worldwide，this complication is likely to become more common.Early and accurate diagnosis of CSP is essential to avoid catastrophic complication such as severe hemorrhage，which may require hysterectomy and endanger the woman’s life，and to preserve future fertility.Only 19 cases were reported in the English literature from 1966-2002［1］，rising to 268 in a span of just 7-8 years［2］.However，with rising cesarean section rates and widespread access to imaging modalities such as sonography and magnetic resonance imaging(MRI)，its incidence has been rising［3］.Cesarean scar pregnancy is the increasingly common problem.This article aim is to give review on CSP and its current management.The exact incidence of CSP is unknown ，the incidence of cesarean scar pregnancy(CSP)is about 1 in 2000 pregnancies，which represents 6.15%of all ectopic pregnancies in women with a prior cesarean delivery［4］.in 2004 case series［2］，estimates an incidence of 1:2226 of all pregnancies，with a rate of 0.15%in women with a previous CSand a rate of 6.1%of all ectopic pregnancies in women who had at least one caesarean delivery［5］.The incidence is likely to rise substantially in the near future as cesarean delivery rates continue to increase.

1 Natural history and pathophysiology

In cesarean scar pregnancy sac is embedded in a previous cesarean scar and completely surrounded by myometrium and fibrous tissue of the scar，quite separate from the endometrial cavity.It has been proposed that the implantation invades the myometrium through a microtubular tract between the cesarean scar and endometrial cavity［1，6］.Damage to the decidua basalis during uterine surgery can persist in the endometrium in the form of tiny dehiscent tracts or minute wedge defects.CSP is more aggressive in its behaviour than placenta praevia and placenta accreta because of its early invasion of the myometrium［5］.Pathological findings after a total hysterectomy suggest that the villi are not merely penetrating the myometrium but are bound with or implanted in it.Vial Y proposed two different types of CSPs.The first is an implantation on the prior CSwith progression towards the cervicoisthmic space or the uterine cavity.Such a CSP may progress to a viable birth but with the risk of a lifethreatening bleeding.The second is a deep implantation into a CSdefect growing towards the bladder and abdominal cavity，a type that is more prone to rupture［7］.Very few of these pregnancies reported in the literature progressed beyond first trimester［8］.Almost all are terminated during first trimester.It is likely that if a developing pregnancy in a cesarean section scar were to continue to the second or third trimesters，there would be a substantial risk of uterine rupture with catastrophic hemorrhage.CSP progressing to 35 weeks of gestation has been described，but this case was complicated by massive haemorrhage and disseminated intravascular coagulopathy at CS，requiring a life-saving hysterectomy.

2 Clinical Presentation

CSP may present from as early as 5-6 weeks［5］.A light，painless vaginal bleeding is usually the early presenting symptom in 39%.Approximately 16%of women complain of accompanying mild to moderate pain.9%complain of only abdominal pain and can be an incidental finding in an asymptomatic woman(37%)［4］.Severe acute pain with profuse bleeding implies an impending rupture.Collapse or haemodynamic instability strongly indicates a ruptured CSP.Clinical examination in stable women is usually unremarkable.The uterus may be tender if the CSPis in the process of rupture.Research done on 28 CSPdiagnosed patients were found that persistent vaginal bleeding after early intrauterine pregnancy interruption(10 cases)，failure of medical abortion(6 cases)，amenorrhea followed by irregular vaginal bleeding(5 cases)，amenorrhea without vaginal bleeding(3 cases)，slow fall or even rise in serumβ-human chorionic gonadotropin(β-hCG)level after suction curettage(3 cases)，and irregular vaginal bleeding lacking of amenorrhea(1 case).The most frequent symptoms were amenorrhea and vaginal bleeding.Amenorrhea varying from39 to 80 days occurred in 27(96%)cases，and severe vaginal bleeding in 11(39%)cases［9］.

3 Diagnosis

3.1 Ultrasound

It is the first-line diagnostic tool for CSP.Majority of the CSPs have been diagnosed by transvaginal scan(TVS)in the early weeks of pregnancy.A recent literature search identified 751 cases of CSP.Of interest is that 13.6%(107/751)had been misdiagnosed as cervical pregnancies，spontaneous abortions in progress(on its way to expulsion)，or low intrauterine pregnancies.Given the potential serious complications of a CSP，reliable diagnostic criteria are required for the differential diagnosis.In the presence of a positive pregnancy test，a CSP was diagnosed by transvaginal Ultrasound using the following criteria:①Visualization of an empty uterine cavity as well as an empty endocervical canal.②Detection of the placenta and/or a gestational sac embedded in the hysterotomy scar.③In early gestations(＜8 weeks)，a triangular gestational sac that fills the niche of the scar，at＞8 postmenstrual weeks this shape may become rounded or even oval.④A thin(1-3 mm)or absent myometrial layer between the gestational sac and the bladder.⑤A closed and empty cervical canal.⑥The presence of embryonic/fetal pole and/or yolk sac with or without hear activity.⑦The presence of a prominent and at times rich vascular pattern at or in the area of a CD scar in the presence of a positive pregnancy test.All these criteria had to be present to diagnose CSP.Some of the above criteria(items①，④and⑤)were derived from the literature［7，10］.And(items ②，③，⑥ and ⑦)are modified by the other literature.Transvaginal three-dimensional(3-D)power Doppler ultrasound has been used to enhance the diagnostic accuracy of a CSP.

3.2 Doppler

It will show distinct circular peritrophoblastic perfusion surrounding the gestation sac that can help delineate the CSP sac with location of the placenta in relation to the scar and proximity to the bladder［8］.With pulsed Doppler functions，more information on the flow pattern of the peritrophoblastic vasculature can be obtained.Typically，a prominent high-velocity(peak velocity＞20 cm/second)，low impedance(pulsatility index ＜1)flow velocity waveforms can be demonstrated，consistent with normal early pregnancy［5］.

3.3 Magnetic resonance imaging

Both sagittal and transverse T1-and T2-weighted MRI sequences can clearly show the gestational sac embedded in the anterior lower uterus.MRI is superior in the assessment of the pelvic structures because of improved differentiation of soft tissue，spatial resolution and the possibility of a multiplanar imaging and it can measure the volume of the lesion.

3.4 Diagnostic laparoscopy

Laparoscopy has been used for diagnosis of CSP.The uterus is usually seen normal sized or bulky(depending on the gestation age)with the CSParising as a hillock with a‘salmon red’ecchymotic appearance，bulging the uterine serosa from the previous cesarean section scar behind the bladder.The fallopian tubes and the ovaries are seen normal［11-13］.

3.5 Diagnostic hysteroscopy

It allows the cervix and the uterine cavity to be distended，with relatively little trauma，with the finding of a normal and empty uterine cavity together with the pregnancy tissues at the lower corpus［12］.

4 Treatment

Because of the rarity of the condition，majority of CSPs are case reports or small case series reported in the literature，with no consensus on the preferred mode of treatment.In the first trimester strongly recommended termination of pregnancy as there is a high risk of subsequent uterine rupture，massive bleeding and life-threatening complications.Treatment options include medical treatment with local or systemic Methotrexate(MTX)injection and surgical treatment via hysteroscopy or laparoscopy［14］.Several medical and surgical modalities are available for the treatment of cesarean scar pregnancy，but most authors have reported the combination of 2-3 different techniques more useful than any method used alone.Especially，curettage alone without a prior uterine artery embolization or local MTX injection may lead to life threatening bleeding［15］.Treatment objectives should be to perform feticide prior to rupture，to remove the gestation sac and to retain patient’s future fertility.

4.1 Conservative medical treatment

Conservative medical treatment is appropriate for a woman who is pain free and haemodynamically stable with an unruptured CSP of＜8 weeks of gestation and a myometrial thickness＞2 mm between the CSP and the bladder［16］.Several types of conservative treatment have been used:dilatation and curettage，excision of trophoblastic tissues(laparotomy or laparoscopy［17］，local and/or systemic administration of MTX，bilateral hypogastric artery ligation associated with trophoblastic evacuation，and selective uterine artery embolization combined with curettage and/or MTX administration.

4.1.1 Medical treatment CSPs have been shown well respence systemic administration of MTX(dose of 50mg/m2)，especially in those with β-hCGlevels ＜ 5000mIu/ml［18］.Medical management with local injection of MTX has been more successful，with success rates of 70%-80%when used as the initial treatment option［8］.This involves the direct injection of 25mg MTX into the pregnancy，performed transvaginally under ultrasound guidance.Local injections of potassium chloride have also been reported and were used［8］.MTX has also been used systemically in combination with dilation and evacuation with success［19］.Under ultrasound guidance，MTX can be injected locally to the gestation sac via transabdominal or via transvaginal route.The transvaginal approach allows for a shorter distance to the gestation sac with minimal risk of bladder injury.

4.1.2 Medical treatment combined with surgical sac aspiration It is difficult to rule out some scar dehiscence already developing at the time of treatment，as the very thin myometrium could be in a state of prerupture.Medical treatment has therefore been combined with surgical aspiration of the sac in some cases.Various sequences of combination have been described，e.g:local potassium chloride→TVS-guided sac aspiration→local MTX injection → intramuscular MTX injection［20］.systemic MTX → sac aspiration by vaginal route → local MTX［21］.Selective embryo reduction by potassium chloride and primary sac aspiration have been performed in heterotopic IVF twin and triplet pregnancies，respectively［15］.

Medical treatment alone or in conjunction with needle aspiration can avoid unnecessary laparotomy and preserve the woman’s fertility，but it requires time and patience.It may take 4-16 weeks forβ-hCGto drop to normal［11］.Close follow up with serialβ-hCGmonitoring is therefore essential.Serial transvaginal colour flow Doppler is useful for monitoring the response to medical treatment and appears to correlate well withβ-hCGlevels.

A review of the literature by Arslan et al［22］shows that uterine curettage was either unsuccessful or caused complications in eight out of nine women，requiring surgical treatment，and in a case series of eight CSPs，Wang［12］had four secondary referrals after failed curettage，thus indicating a failure rate of 70%(12/17).The gestation sac of a CSPis not actually within the uterine cavity，and the chorionic villi implant into the caesarean section scar of the lower segment.Therefore，not only the trophoblastic tissue is unreachable by the curette but also such attempts can potentially rupture the uterine scar leading to severe haemorrhage and cause more harm.Profuse bleeding during the procedure and absence of chorionic villi in the specimen obtained by curettage must prompt immediate laparoscopy/laparotomy.Blind uterine curettage as a primary treatment for CSP is therefore insufficient and should be discouraged.

4.2 Hysteroscopy evacuation

Hysteroscopy is a minimally invasive operative technique that offers direct visualization，low morbidity，and high primary success rates to date，although numbers are small and further experience would be helpful to determine the safest and most appropriate technique.It has the patient shorter follow-up time and a more rapid return to fertility.The short time interval to return of normalβ-hCG levels indicates that complete removal of all gestational material is likely even when visualization is not optimal.Hysteroscopic removal was first described by Wang et al.in 2005［8］，where the CSPwas removed without complication，and at 4 weeks after the procedure there was normal sonographic echotexture of the uterus and normal serumβ-hCG.A recent study showed that real-time ultrasound guidance during a hysteroscopic surgery resulted in a trend towards reducing the uterine perforation rate［23］.

4.3 Laparoscopic removal

Laparoscopy has been described successfully in a small case series［12-13］and is appropriate if the pregnancy is seen to be protruding into the abdominal cavity or bladder，where the patient is hemodynamically stable，and there are appropriate facilities with experienced surgeons to undertake this procedure［7，13］.It have reported four such cases followed by a successful laparoscopic resection of a CSP［11，13］.Operative laparoscopy should be performed only after a prior TVSconfirms the diagnosis.The CSP mass is incised and the pregnancy tissue removed in an endobag.Bleeding can be minimized by local injection of vasopressin(1unit/ml，5-10ml)，haemostasis achieved by bipolar diathermy［12］and the uterine defect closed with endoscopic suturing.In trained hands，laparoscopic treatment is safe and less time consuming(mean 113.8 ± 32.0minutes，range 75-120minutes)［11-12］，blood loss is limited(mean 200.0 ±108.0ml，range 50-200ml)and recovery is fast with minimal hospital stay(mean 3.0days).

4.4 Primary open surgical treatment

Laparotomy followed by wedge resection of the lesion(hysterotomy)should be considered in women who do not respond to conservative medical and/or surgical treatments，present too late or if facilities and expertise for operative endoscopy are not available.Laparotomy is mandatory when uterine rupture is confirmed or strongly suspected［24］.This conventional low-tech surgery，which is available in all hospitals，has the advantage of complete removal of the CSP and simultaneous repair of the scar，followed by a quick return of the β-hCG to normal level within 1-2 weeks.

4.5 Expectant treatment

It can also be done but it may lead to uterine rupture with serious consequence.Expectant treatment of viable CSPs either fails or carries a significant risk of rupture requiring laparotomy and hysterectomy.In women having expectant treatment，emergency operative delivery must be instituted without delay in the event of any features indicating uterine rupture.Expectantly managed a CSPwhich was suspected at 7 weeks.An elective caesarean section was planned at 36 weeks，but severe abdominal pain necessitated an emergency caesarean section at 35 weeks followed by hysterotomy.We can describe a case，first diagnosed at 16 weeks and managed expectantly，as the woman refused a TOP.She required a laparotomy and hysterotomy because of a ruptured CSP at 20 weeks.Both these cases were complicated by massive haemorrhage requiring multiple units of blood transfusion.

5 Conclusion

The incidence of CSPis unknown，however，the estimated prevalence is reported to be between 1:1800 and 1:2226［25］.Little is understood about the natural history or the pathophysiology of the CSP.It has been proposed that the implantation invades the myometrium through a microtubular tract between the cesarean scar and endometrial cavity［1，6］.Such a tract can also develop from the trauma of other uterine surgery，e.g.curettage，myomectomy，metroplasty，hysteroscopy and even manual removal of placenta.CSP may present from as early as 5-6 weeks［5］.CSP is more aggressive in its behaviour than placenta praevia and placenta accreta because of its early invasion of the myometrium.Cesarean scar ectopic pregnancy is often misdiagnosed as incomplete abortion，in process of expulsion and patients mistakenly undergo curettage leading to life threatening hemorrhage.Diagnosis of cesarean scar pregnancy requires a high degree of suspicion，especially when no intrauterine gestational sac can be identified and a pregnancy of unknown location is suspected.Early diagnosis and early treatment of cesarean scar ectopic pregnancy is essential to prevent maternal morbidity and mortality.Light，painless vaginal bleeding is usually the early presenting symptom.It can be an incidental finding in an asymptomatic woman.Severe acute pain with profuse bleeding implies an impending rupture.Collapse or haemodynamic instability strongly indicates a ruptured CSP.First-line diagnostic tool for CSPis Ultrasound.Majority of the CSPs have been diagnosed by transvag-inal scan(TVS)in the early weeks of pregnancy.It can be diagnosed by Doppler，Three-dimensional ultrasound，Magnetic resonance imaging，Diagnostic hysteroscopy or Diagnostic laparoscopy.Treatment options include medical treatment with local or systemic MTX injection and surgical treatment via hysteroscopy or laparoscopy［14］.Several medical and surgical modalities are available for the treatment of cesarean scar pregnancy，but most authors have reported the combination of 2-3 different techniques more useful than any method used alone.This review is to，up to date and help women to raise awareness in this contemporary，potentially risky clinical condition.

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