To our knowledge, this is the first report on the use of HIFU combined with suction curettage for treating exogenous CSP. The success rate in this study was 92.68% and no patient was converted to laparoscopy or hysterectomy. The median intraoperative blood loss during suction curettage was 99 ml. The average time for serum β-HCG level normalization was 23.18 ± 3.13 days, and the median time for menstruation recovery was 29.38 ± 3.34 days. Although there are some deficiencies in HCG levels and menstrual recovery compared with those after laparoscopy [11, 12], our protocol provides the possibility of one conservative treatment for exogenous CSP patients. We also reviewed the literature about the treatment of UAE combined with suction curettage for CSP. Introspective blood loss ranged from 14 ml to 114 ml, and serum β-HCG returned to normal levels within 15 to 29 days [26, 28, 29]. Our study obtained the similar results as those from the treatment of UAE combined with suction curettage and avoided the complications of UAE.
Theoretically, HIFU mainly uses high intensity ultrasound to focus on the internal target of the body in vitro. We speculate that HIFU contributes to the treatment of exogenous CSP in three ways. First, HIFU ablation can cause necrosis of the corresponding lesion cells. Through the mechanical effect of high intensity ultrasound, the high-temperature thermal effect formed an instantaneous high temperature > 60℃, which led to necrosis in the pregnancy tissue. Second, the cavitation effect of HIFU could loosen the adhesion between the myometrium at the uterine scar and the gestational sac, which would be helpful for removing the pregnancy tissue . Finally, HIFU has been reported to be used for the ablation of small vessels with a diameter < 2 mm . The thermal energy deposited in the pregnancy tissue can destroy small blood vessels. As seen on color Doppler assessment, the blood perfusion in the pregnancy tissue disappeared. For the reasons mentioned above, HIFU could make suction curettage a smoother process for removing the pregnancy tissue and reduce the risk of heavy hemorrhage. As reported before, adverse effects, such as sciatic and lower abdominal pain, injury to the bowel and bladder, fever, and skin burns, occur during HIFU ablation [32–34]. In the ablation for exogenous CSP, the target site was located at the anterior wall of the cervix, which was located away from the bowl in the pelvic cavity. Ablation began from the innermost part, which was not near the bladder. With simultaneous ultrasound monitoring, HIFU ablation in our study caused no damage to surrounding organs. Although all patients complained of abdominal or sacral pain during the HIFU ablation, no patients needed further treatment.
Due to the characteristics of exogenous CSP, there is a risk of uterine perforation and substantial hemorrhage during suction curettage. To avoid uterine perforation during suction curettage, we first carried out vacuum suction. If an ultrasound check showed residual tissue, curettage was performed very gently. In our study, no uterine perforations occurred. A previous study reported that perforation of the uterus occurred in a CSP patient during suction curettage after HIFU ablation . The author attributed this event to the 2 mm thickness of the interval myometrium between the bladder and gestation sac. In our study, the thickness of the thinnest interval myometrium was 1.5 mm, but no uterine perforation occurred. Therefore, we deduce that uterine perforation is a result of comprehensive factors. For patients with bleeding greater than 200 ml, we used a Foley balloon catheter to compress the hemorrhage, which avoided the possibility of conversion to laparotomy. However, there were still 3 patients who had to undergo a second suction curettage. We found that all three of these patients were administered Foley balloon catheters during the suction curettage. Thus, the suction curettage was interrupted, which resulted in residual pregnancy tissue.
We also found that the size of the gestational sac and the thickness of the interval myometrium between the bladder and gestational sac were correlated with blood loss during suction curettage. Our results were consistent with those of previous studies [36, 37]. Adhesion between the myometrium at the uterine scar and the gestational sac will form bleeding wounds as the pregnancy tissue is removed . The wound will expand with the increase in the gestational sac, which also elevates the risk of hemorrhage. The weakness of the myometrium is accompanied by poor contractility, which makes it difficult to close the bleeding vessels [39, 40]. We also found no significant difference in terms of age, BMI, gestational age, interval time from last CS, or β-HCG level before treatment between the two groups. We noticed that a previous study considered the β-HCG level to be a risk factor for massive hemorrhage . As a biochemical index representing trophoblastic cell activity, the β-HCG level of exogenous CSP may not be high due to the muscular layer defects and insufficiency of the blood supply. The inconsistency might result from the different grouping standards adopted in different studies.
In conclusion, our results indicate that HIFU combined with suction curettage is effective and safe in the treatment of exogenous CSP of < 9 weeks. We also found that the size of the gestational sac and the thickness of the interval myometrium between the bladder and gestational sac might be high-risk factors for blood loss during this treatment. Limited by the retrospective analysis and the sample number, we should validate our findings by carrying out prospective and large-scale multicenter studies in the future.