the first case was reported in the english medical literature by larsen and solomon in 1978 . 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 . 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 ) . 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 . 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 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 . ( 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 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 . ( 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 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 ) 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 m microspheres and stasis of blood flow was achieved . the left uterine artery was embolized using four vials of 500 - 700 m microspheres and an additional vial of 700 - 900 m 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 ] . ( 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 ) . ( 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 . 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 . women who undergo multiple cesarean sections develop scars with larger surface areas , which may in turn increase the risk of a scar implantation . , : ( 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 . the former type may progress to a viable pregnancy with significant risk of hemorrhage , while the latter type is at greater risk of rupture . diagnosis of a cesarean scar pregnancy requires a high index of clinical suspicion , as up to 40% of patients may be asymptomatic . symptoms of severe acute abdominal pain with heavy vaginal bleeding should raise concerns for impending rupture while hemodynamic instability indicates rupture of a csp . ultrasound is the first - line imaging modality for evaluation of a potential csp , with the majority of csps diagnosed on the basis of tvus . transvaginal ultrasound has a reported sensitivity of 84.6% , and has become the imaging examination of choice for diagnosis . sonographic criteria initially proposed by vial et al . , have been adopted by others to aid in the diagnosis of a csp : ( i ) a trophoblast located between the bladder and anterior uterine wall at the presumed site of the cesarean section scar , ( ii ) a gestational sac which is ovoid and regular in shape , as opposed to distorted and collapsed as can be seen in miscarriages , and ( iii ) a thin or discontinuous myometrium between the gestational sac and urinary bladder wall on sagittal images of the uterus through the amniotic sac . for example , vascularity of the sac on color doppler interrogation can aid in distinguishing a csp from the avascular sac of an aborting pregnancy . alternatively , a negative  sliding organ sign  when gentle pressure is applied to a sac seen at the level of the internal orifice of the uterus using the endovaginal probe can help differentiate a csp from a spontaneous abortion in progress . findings of high velocity ( peak velocity > 20 cm / sec ) and low impedance ( pulsatility index < 1 ) waveforms on pulsed doppler have been described with scar implantation . since transvaginal ultrasound combined with color and pulsed doppler evaluation is relatively reliable in diagnosing csps , most authors suggest limiting the use of mri to cases in which tvus findings are equivocal , or when the obstetrician requires additional information in preparation for surgery . one drawback to evaluation of csps with mri is the long acquisition time ; thus , patients need be hemodynamically stable . despite this limitation , mri has been used previously in a small number of patients as an adjunct to ultrasound evaluation . though not essential for diagnosis , mri can have an impact on patient management in rare or complicated forms of ectopic pregnancy , as with our patient . the decision to institute medical therapy versus sagittal and axial t1- and t2-weighted sequences can depict the gestational sac implanted in the anterior lower uterine segment and more clearly define involvement of adjacent organs ( e.g. urinary bladder ) . in addition , the multiplanar imaging capability of mr may be helpful in orienting the surgeon , should operative management be required . the ultrasound findings in our patient were highly suspicious of a cesarean scar pregnancy ; however , the low position of the gestational sac and its proximity to the urinary bladder presented a problem in light of the patient 's desire for future fertility . while the ultrasound images did not clearly demonstrate urinary bladder involvement , the mr images were more conclusive and showed the intrauterine pregnancy bulging through the myometrium of the lower uterine segment , immediately adjacent to and exerting mass effect on the superior aspect of the urinary bladder without invasion of the bladder wall . though the patient ultimately required a hysterectomy , an attempt was made to preserve fertility according to the patient 's wishes . in the case of our patient , additional evaluation with mri played a role in the decision to institute conservative medical management and may have also helped with surgical planning . while there is no standardized approach for the treatment of this condition to our knowledge , the general consensus is that cesarean scar pregnancies should not be managed expectantly due to the risk of uterine rupture and hemorrhage . conservative medical management includes systemic or local administration of methotrexate , local injection of embryocides ( e.g. potassium chloride , hyperosmolar glucose , or crystalline trichosanthin ) into the gestational sac , or a combination of both . the likelihood of treatment success with methotrexate is greatest when the serum beta - hcg level is less than 5,000 miu / ml , during the first 6 weeks of pregnancy , or when the embryo exhibits no cardiac activity . of note , our patient had an admission serum beta - hcg level of 199,760 miu / ml and the embryo did demonstrate cardiac activity . if conservative management is instituted , close follow - up of the pregnancy with tvus is warranted . while serial tvus with color doppler evaluation has been shown to correlate well with serum beta - hcg levels , it has been suggested that the high - velocity , low - impedance flow associated with the gestation may not change despite intervention until the serum beta - hcg levels return to normal . patients who demonstrate such flow characteristics on follow - up tvus despite progressively declining serum beta - hcg levels on follow - up may be at increased risk of catastrophic uterine rupture and hemorrhage , as was the case in our patient . surgical options include combined medical treatment with surgical sac aspiration , uterine curettage , hysteroscopic evacuation , laparoscopic removal , primary open hysterotomy , or hysterectomy . the patient 's clinical symptoms and desire for future fertility , age and size of the gestation , and the clinician 's experience dictates which treatment option is most appropriate . patients who choose conservative medical management should be counseled regarding the possibility of requiring definitive surgical treatment in the event of failed medical therapy . in addition , it has been suggested that the risk of spontaneous uterine rupture is 17 times more likely in women with a prior cesarean section compared to those with an unscarred uterus . this statistic , combined with the increased risk of uterine rupture after implantation of a pregnancy in the thin cesarean scar , should be taken into consideration when contemplating conservative versus surgical management . an alternative to the more traditional treatment options presented is combined medical management with uterine artery embolization ( uae ) , which was the therapy initially instituted in our patient . uae is minimally invasive , and may be an attractive option should patients present with vaginal bleeding yet maintain a desire to preserve fertility . one study of 66 patients found uae combined with local methotrexate administration to be more effective in treating csps compared to traditional methods and had increased success rate , fewer complications , and a reduced risk for hysterectomy . in our patient , uae was combined with systemic methotrexate administration rather than local injection into the gestational sac . it has been suggested that absorption of systemic methotrexate by the conceptus may be limited due to poor vascularization of the fibrous cesarean scar . this may have been a contributing factor in the failure of conservative therapy in our patient , who ultimately required treatment with hysterectomy . diagnosis of a cesarean scar pregnancy requires a high index of clinical suspicion , as up to 40% of patients may be asymptomatic . symptoms of severe acute abdominal pain with heavy vaginal bleeding should raise concerns for impending rupture while hemodynamic instability indicates rupture of a csp . ultrasound is the first - line imaging modality for evaluation of a potential csp , with the majority of csps diagnosed on the basis of tvus . transvaginal ultrasound has a reported sensitivity of 84.6% , and has become the imaging examination of choice for diagnosis . , have been adopted by others to aid in the diagnosis of a csp : ( i ) a trophoblast located between the bladder and anterior uterine wall at the presumed site of the cesarean section scar , ( ii ) a gestational sac which is ovoid and regular in shape , as opposed to distorted and collapsed as can be seen in miscarriages , and ( iii ) a thin or discontinuous myometrium between the gestational sac and urinary bladder wall on sagittal images of the uterus through the amniotic sac . for example , vascularity of the sac on color doppler interrogation can aid in distinguishing a csp from the avascular sac of an aborting pregnancy . alternatively , a negative  sliding organ sign  when gentle pressure is applied to a sac seen at the level of the internal orifice of the uterus using the endovaginal probe can help differentiate a csp from a spontaneous abortion in progress . findings of high velocity ( peak velocity > 20 cm / sec ) and low impedance ( pulsatility index < 1 ) waveforms on pulsed doppler have been described with scar implantation . since transvaginal ultrasound combined with color and pulsed doppler evaluation is relatively reliable in diagnosing csps , most authors suggest limiting the use of mri to cases in which tvus findings are equivocal , or when the obstetrician requires additional information in preparation for surgery . one drawback to evaluation of csps with mri is the long acquisition time ; thus , patients need be hemodynamically stable . despite this limitation , mri has been used previously in a small number of patients as an adjunct to ultrasound evaluation . though not essential for diagnosis , mri can have an impact on patient management in rare or complicated forms of ectopic pregnancy , as with our patient . the decision to institute medical therapy versus sagittal and axial t1- and t2-weighted sequences can depict the gestational sac implanted in the anterior lower uterine segment and more clearly define involvement of adjacent organs ( e.g. urinary bladder ) . in addition , the multiplanar imaging capability of mr may be helpful in orienting the surgeon , should operative management be required . the ultrasound findings in our patient were highly suspicious of a cesarean scar pregnancy ; however , the low position of the gestational sac and its proximity to the urinary bladder presented a problem in light of the patient 's desire for future fertility . while the ultrasound images did not clearly demonstrate urinary bladder involvement , the mr images were more conclusive and showed the intrauterine pregnancy bulging through the myometrium of the lower uterine segment , immediately adjacent to and exerting mass effect on the superior aspect of the urinary bladder without invasion of the bladder wall . though the patient ultimately required a hysterectomy , an attempt was made to preserve fertility according to the patient 's wishes . in the case of our patient , additional evaluation with mri played a role in the decision to institute conservative medical management and may have also helped with surgical planning . while there is no standardized approach for the treatment of this condition to our knowledge , the general consensus is that cesarean scar pregnancies should not be managed expectantly due to the risk of uterine rupture and hemorrhage . conservative medical management includes systemic or local administration of methotrexate , local injection of embryocides ( e.g. potassium chloride , hyperosmolar glucose , or crystalline trichosanthin ) into the gestational sac , or a combination of both . the likelihood of treatment success with methotrexate is greatest when the serum beta - hcg level is less than 5,000 miu / ml , during the first 6 weeks of pregnancy , or when the embryo exhibits no cardiac activity . of note , our patient had an admission serum beta - hcg level of 199,760 miu / ml and the embryo did demonstrate cardiac activity . if conservative management is instituted , close follow - up of the pregnancy with tvus is warranted . while serial tvus with color doppler evaluation has been shown to correlate well with serum beta - hcg levels , it has been suggested that the high - velocity , low - impedance flow associated with the gestation may not change despite intervention until the serum beta - hcg levels return to normal . patients who demonstrate such flow characteristics on follow - up tvus despite progressively declining serum beta - hcg levels on follow - up may be at increased risk of catastrophic uterine rupture and hemorrhage , as was the case in our patient . surgical options include combined medical treatment with surgical sac aspiration , uterine curettage , hysteroscopic evacuation , laparoscopic removal , primary open hysterotomy , or hysterectomy . the patient 's clinical symptoms and desire for future fertility , age and size of the gestation , and the clinician 's experience dictates which treatment option is most appropriate . patients who choose conservative medical management should be counseled regarding the possibility of requiring definitive surgical treatment in the event of failed medical therapy . in addition , it has been suggested that the risk of spontaneous uterine rupture is 17 times more likely in women with a prior cesarean section compared to those with an unscarred uterus . this statistic , combined with the increased risk of uterine rupture after implantation of a pregnancy in the thin cesarean scar , should be taken into consideration when contemplating conservative versus surgical management . an alternative to the more traditional treatment options presented is combined medical management with uterine artery embolization ( uae ) , which was the therapy initially instituted in our patient . uae is minimally invasive , and may be an attractive option should patients present with vaginal bleeding yet maintain a desire to preserve fertility . one study of 66 patients found uae combined with local methotrexate administration to be more effective in treating csps compared to traditional methods and had increased success rate , fewer complications , and a reduced risk for hysterectomy . in our patient , uae was combined with systemic methotrexate administration rather than local injection into the gestational sac . it has been suggested that absorption of systemic methotrexate by the conceptus may be limited due to poor vascularization of the fibrous cesarean scar . this may have been a contributing factor in the failure of conservative therapy in our patient , who ultimately required treatment with hysterectomy . 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 .