Cesarean scar pregnancy (CSP) is a special type of ectopic pregnancy in which the gestational sac, fertilized egg or embryo is deposited on the previous isthmus of the anterior uterine wall. It is a special type of ectopic pregnancy. If the clinical diagnosis is unknown, blind surgical or pharmacological abortion may lead to hemorrhage, and in serious cases, it may lead to disseminated intravascular coagulation and even endanger the life of the pregnant woman, so the early diagnosis of the disease is the key to determine the prognosis.
In recent years, with the increasing rate of cesarean section, the incidence of hysterotomy pregnancy is on the rise. In this paper, we summarize the MRI data of 8 patients with clinicopathologically confirmed CSP and discuss their MRI performance characteristics to improve the understanding of the MRI performance of this disease.
1.Materials and methods
Retrospective analysis of 8 patients with clinicopathologically confirmed CSP in Anhui Medical University Affiliated Provincial Hospital, the patients’ ages ranged from 29 to 37 years, with an average of 33.2 years. The patients all had a history of cesarean delivery, and this pregnancy was 1 to 6 years from the time of cesarean surgery. The main clinical manifestations were menopause of 44 to 58 days, positive urinary chorionic gonadotropin (HCG), abdominal pain, and vaginal bleeding.
A Siemens Magnetom Trio Tim 3.0T superconducting MRI was used, and the patient was placed in the supine position with a body phased array coil. Routine scan: cross-sectional TSE T1WI: TR/TE 400-500ms/8-12ms, field of view (FOV) 250mm×280mm, layer thickness 5mm, layer spacing 1mm, excitation number (NEX) 1.
Axial TSET2WI fat suppression sequence: TR/TE (3000～3500ms/90～110ms); FOV250mm×280mm, layer thickness 5mm, layer spacing 1mm, NEX2. Sagittal TSET2WI sequence: TR/TE3000～3500ms/90～100ms, FOV250mm×280mm Sagittal TSET2WI fat suppression sequence: TR/TE 3200-3500ms/90-100ms, FOV250mm×280mm, layer thickness 5mm, layer spacing 0.8mm, NEX 2.
Coronal TSET2 WI: TR/TE4000～4200ms /100～120ms, FOV250mm×280mm, layer thickness 4mm, layer spacing 0.8mm, NEX 2.
2, Results
All 8 cases of CSP MRI clearly showed the morphology, size, position of the gestational sac and the situation with the uterine wall, with the best display in sagittal position.
The size of the gestational sac in the 8 cases of CSP ranged from 1.8 cm×1.1 cm×0.8 cm to 4.6 cm×4.5 cm×4.1 cm, and was located at the scar of the anterior wall incision in the lower uterine segment, with the gestational sac infiltrating into the myometrium and growing into the uterine cavity at the same time, and the anterior wall of the local uterine isthmus was significantly thinner, with the thickness of the isthmus ranging from 0.2 to 0.5 cm, averaging (0.25±0.15) cm. 7 of the 8 cases of CSP In 7 of the 8 CSP cases, the gestational sac was round or oval, with low signal in T1WI and high signal in T2WI, uniform wall thickness and smooth margins, and in 2 of these cases, blood was accumulated in the uterine cavity, with short T1 and short T2 signals;
In one of the eight cases of CSP, the gestational sac showed an irregular mass with predominantly iso-signal T1WI and mixed signal T2WI, while a small amount of blood was seen in the mass and in the uterine cavity.
In 6 of the 8 patients, transvaginal hysterectomy was performed to remove the atomic hysterectomy with a purple-blue color, and typical chorionic tissue was removed by incision, and in 2 cases, blood was seen; in 2 cases, ultrasound-guided aspiration was performed, and meconium-like tissue with typical chorionic tissue was scraped out, and in 1 case, blood was also aspirated. The postoperative pathology of all 8 cases confirmed that they were uterine incision pregnancies, consistent with the preoperative MRI diagnosis.
3. Discussion
3.1 Pathogenesis of CSP
The etiology and pathogenesis of CSP have not been completely elucidated. Most scholars agree that the most likely explanation for fertilized egg implantation in the uterine incision scar is that the endometrial basal layer was damaged during cesarean section, forming a sinus tract or fissure that communicates with the uterine cavity, and the fertilized egg invades the uterine incision scar through the sinus tract or fissure and implants into the myometrium.
Vial et al. suggested that there are two ways of CSP growth, one is that the gestational sac is implanted at the previous cesarean incision scar and grows toward the bladder and abdominal cavity, and the trophoblast gradually invades the myometrium, and this way of growth usually results in early hemorrhage and even uterine rupture; the other way is that the gestational sac is implanted at the scar and grows toward the uterine cavity, and there is a possibility of continued pregnancy, but the uterus often occurs until the middle or late pregnancy The other way is that the gestational sac is implanted in the scar and grows in the direction of the uterine cavity, with the possibility of continuing the pregnancy, but the uterus often ruptures and serious bleeding and other complications until the middle or late pregnancy. In the eight cases of CSP in our group, the gestational sac was found to be located at the uterine incision scar and grew prominently towards the uterine cavity, while encroaching into the myometrium.
3.2 MRI presentation of CSP
The accurate diagnosis of uterine incisional pregnancy requires a combination of clinical and imaging data. Currently, the main imaging method used in clinical practice is color Doppler ultrasound, and MRI is relatively less used, but the clinical value of MRI is gradually being recognized. A study [6] showed that MRI can clearly distinguish the relationship between uterine cavity, cesarean scar and gestational sac through multidimensional images, which can be used for early diagnosis and treatment selection of CSP.
In China, by performing both color Doppler ultrasound and MRI in 40 patients and observing the results of both methods, some scholars concluded that the correct rates of both ultrasound and MRI in diagnosing cesarean incisional pregnancy were higher, and the differences were not statistically significant, but MRI could better show the relationship between the cesarean incisional pregnancy and the surrounding tissues. In addition to clearly showing the morphology and size of the gestational sac, all cases in this group also clearly showed the invasion of the gestational sac into the muscular layer, which allowed more accurate measurement of the thickness of the isthmus thinning and facilitated the choice of clinical treatment plan.
In two cases in our group, ultrasound-guided aspiration was performed based on MRI suggesting myometrial thickness >3.5 mm.
Most of the domestic and foreign literature reports on diagnostic imaging criteria for CSP are as follows.
(1) absence of intrauterine gestational sac;
(2) No gestational sac in the cervical canal;
(3) Gestational sac growing in the anterior wall of the uterine isthmus;
(4) weak muscle wall between the bladder and the gestational sac. However, it has been suggested that the absence of gestational mass in the cervical canal is the main point of differential diagnosis with cervical pregnancy, but not necessarily the absence of gestational mass in the uterine cavity, because in early pregnancy the gestational sac develops rapidly and the sac can extend into the uterine cavity. It is also believed that for the diagnosis of CSP, whether the gestational sac is located in the myometrium or invades the myometrium to grow is the key to the diagnosis of CSP.
The following features can suggest CSP: the lower part of the anterior uterine wall, the original cesarean section (isthmus) is significantly thinned and dilated, and the gestational sac is implanted in the thinned isthmus; the gestational sac is mostly round or oval; the signal of the gestational sac is variable, with low or equal signal on T1WI and low signal on T2WI. The signal of the gestational sac is variable, with low or equal signal in T1WI and high or mixed signal in T2WI;
The wall of the gestational sac is mostly visible around the gestational sac. The foci are circumferentially reinforced on enhancement scans, and some of them are reinforced within the sac and around the sac. A small number of gestational sacs appear as non-capsular mixed-signal soft tissue masses in the lower uterine segment, which can be combined with hemorrhagic signals. Some scholars believe that MR examination can clearly show the relationship between the cesarean scar and the gestational sac, and the scar shows a strip-shaped shadow with low signal in T1WI and T2WI, and a depression is visible in the local anterior uterine wall.
3.3 Differential diagnosis of CSP
CSP should be differentiated from cervical pregnancy and spontaneous abortion. Cervical pregnancy presents with a significantly enlarged and barrel-shaped cervix, but the uterine body and isthmus are usually not large, the uterine cavity is empty, the gestational sac or heterogeneous mass is visible in the enlarged cervical canal, the external cervical opening is dilated and the internal opening is tightly closed. In spontaneous abortion the gestational sac is located at the cervical canal and there are pregnancy masses and blood clots in the uterine cavity, indicating intrauterine fetal death, and a decrease in blood beta-HCG levels is also evident.
CSP presents with closure of the internal and external cervical os and the gestational sac is located at the incisional scar of the lower anterior uterine wall of the uterus. CSP can be correctly diagnosed by MRI features such as the incisional scar of the uterus, the location of the gestational sac and changes in the signal and thickness of the adjacent myometrium.
Cesarean incisional pregnancy is a relatively rare type of ectopic pregnancy, and with the increasing rate of cesarean delivery in China, the incidence of CSP is increasing year by year, and the condition is relatively aggressive. The MRI manifestation of uterine incisional pregnancy has certain characteristics and is of great value for early clinical diagnosis and treatment.