The Clinical Significance of Placental Site Nodule and Plaque in Women with Secondary Infertility Treated with Office Hysteroscopic Surgery: The Case Series of Retrospective Cohort Study.

Placental site nodule and plaque (PSNP) is a type of gestational trophoblastic disease, part of the subcategory of nonneoplastic trophoblastic lesions or tumor-like conditions,[ 1 ] found in women of reproductive age. The condition is often detected at the time of endometrial ablation, histologic examination of the endocervix, or pathologic examination after total hysterectomy, often in association with prior pregnancy.[ 2 3 4 ] The gross findings of PSNP that differentiate it from other uterine lesions have not been determined.[ 3 ] It is mainly diagnosed by histopathological examination of the endometrium using hematoxylin and eosin (H and E) staining: small, well-circumscribed, nodular aggregates of chorionic-type intermediate trophoblastic cells are embedded in a hyalinized stroma.[ 5 ] PSNP is a benign disease with few specific symptoms, and its clinical significance has not been well characterized.[ 1 ] There have been reports of PSNP diagnosed during the evaluation of patients with infertility,[ 6 ] but the influence of PSNP on infertility and recurrent pregnancy loss is not well understood. Hysteroscopy is useful in the diagnosis of intrauterine lesions and has been widely used as a diagnostic and therapeutic technique for infertility in recent years, as resolution has improved and the hysteroscope diameter has decreased. Intracavitary residual mass after pregnancy is the good indication of hysteroscopic diagnosis and treatment.[ 7 ] In addition, rare pathology resembling common intrauterine mass lesion may need careful observation and accurate diagnostic procedures.[ 8 ] Because PSNP is relatively rare, there have been few reports of the condition being observed and diagnosed by hysteroscopy. However, there are two such case reports. In the first, hysteroscopy was performed for persistent uterine bleeding after delivery and the authors noted that “the nodule was about 2 cm in diameter, had an irregular surface and a variegated appearance, and was white-red in color with hemorrhagic and necrotic areas.”[ 9 ] In the second report, hysteroscopy was performed for secondary infertility and the authors described “a small yellow-white, necrotic-appearing nodule.”[ 10 ] Other than these two reports, information on the specific hysteroscopic appearance of PSNP has not been well documented. However, there are no established hysteroscopic findings specific for PSNP. Chronic endometritis (CE) is an endometrial disorder diagnosed when there is increased infiltration of plasma cells that express CD138. Recently, much attention has been paid to CE as a cause of implantation failure and miscarriage in patients undergoing assisted reproductive technology (ART).[ 11 ] A relationship between CE and intrauterine lesions such as endometrial polyps and adhesions in the uterine cavity has been reported,[ 11 12 13 ] and the gross appearance of CE by hysteroscopy has been previously reported;[ 11 ] however, any relationship between CE and PSNP has not been well elucidated. In this study, we review the clinical characteristics of seven patients in whom PSNP was diagnosed by histopathological examination. All patients have no abnormal findings on ultrasonographic examination of the uterine cavity and underwent office hysteroscopy to search for the cause of secondary infertility. We also examine the relationship between PSNP and the presence of CE by CD138 immunostaining and discuss the effect of PSNP on fertility.

Among 1260 women who received office hysteroscopy at our faculty during the study period, a total of 400 patients with secondary infertility underwent hysteroscopy and endometrial aspiration. CD138 immunostaining was performed in 296 patients. Of these, 247 patients had no particular imaging findings in the uterine cavity. A total of seven patients (2.8%) were diagnosed with PSNP [ Figure 1 ]. Cohort of women with secondary infertility received hysteroscopy during study period They were diagnosed between 15 and 36 months (mean ± standard deviation [SD], 24.4 ± 10.3 month) after the patient’s preceding pregnancy. The mean (SD) patient age at diagnosis was 33.9 ± 3.3 years (range, 31–41 years). No patients had any symptoms such as abnormal uterine bleeding or lower abdominal pain. The cause of infertility, associated complications, and indication of assisted reproduction among the subjects showed wide variety. Women received hysteroscopy were advised avoiding pregnancy until final histopathological diagnosis were made after the procedures. The clinical backgrounds of seven women are summarized in Table 1 . Clinical backgrounds TVD: Transvaginal delivery, FET: Frozen-thawed embryo transfer, SA: Spontaneous abortion, PCOS: Polycystic ovary syndrome In 7 women diagnosed with PSNP, the findings of first hysteroscopy were described as follows. Case no. 1 presented with multiple micropolyps without hyperemia [ Figure 2g ]. Case No. 2 showed multiple yellow-white-colored protuberant lesions with irregular margins contained sandy particles at lower part of the uterine wall [ Figure 2a ]. Case No. 3 showed a yellow-white colored protuberant lesion with irregular margins at the lower part of the uterine wall and a micro polyp throughout the lumen [ Figure 2c ]. Case No. 4 showed a yellow-colored protuberant lesion at the uterine fundus with intrauterine adhesions [ Figure 2d ]. Case No. 5 showed a yellow-white colored membranous material and intense erythema of the endometrium (photo not available). Case No. 6 showed a yellow-white-colored protuberant lesion with irregular margins on the body [ Figure 2f ]. Case No. 7 had a stalkless polyp in the left uterine horn and intense erythema strong [ Figure 2k ]. Specific hysteroscopic findings of placental site nodule and plaque (PSNP) and associated nonspecific hysteroscopic findings. PSNP was detected in the MHR samples of upper panels (a-e), and PSNP was not detected in the MHR samples of lower panels (f-k). Pathologically confirmed PSNP specific hysteroscopic findings are indicated by black arrowheads, other non-PSNP findings by white arrowheads In 5 patients who received hysteroscopy at least twice for follow-up, the findings of secondary hysteroscopy were described as follows. Case No. 2 showed a yellow-white-colored protuberant lesion with irregular margins at the upper part of the uterine wall in the second look hysteroscopy [ Figure 2b ] and accumulation of yellow-white colored protuberant lesions with irregular margins at the lower part of the uterine wall and bluish-purple hemorrhagic plaques at the uterine fundus in the third look hysteroscopy [ Figure 2h ]. Case No. 3 showed a planar polyp at the anterior wall of the body and multiple micro polyps on the uterine corpus [ Figure 2i and j ]. In case No. 4, white colored protuberant lesion remained in the same location as the lesion in the first look in the second look hysteroscopy [ Figure 2e ], and the endometrium was normalized with only slight membranous adhesions in the third and fourth look hysteroscopy (photo not available). Case No. 5 showed a small amount of white membranous material in the lower part of the uterine wall (photo not available). Histopathological examination by H and E staining revealed hyalinized nodules with chorionic-type intermediate trophoblastic cells in all patients, resulting in a diagnosis of PSNP [ Figure 3a ]. In 2 patients, localization of cytokeratin AE1/AE3 in intermediate-type trophoblasts was confirmed [ Figure 3b ]. The PSNP nodules were embedded within the endometrial stroma and covered with endometrial tissue. There was no evidence of infection (e.g. neutrophilic infiltration). Histological characteristics of placental site nodule and plaque (PSNP). Representative photomicrographs of hyalinized PSNP nodule obtained from an endometrial biopsy of Patient No. 2 (×100), (a) Hematoxylin and eosin staining, (b) Immunohistochemical staining for cytokeratin AE1/AE3, (c) Immunohistochemical staining for CD138 According to the association between sampling methods and histological detection, PSNP was detected in both the MHR and EAB samples from 5 patients, Case No. 2, 3, 4, 5 and 6, with yellow-white-colored protuberant lesion. Of these, case No. 5 had erythema on hysteroscopy. In 2 patients with multiple micro polyps and endometrial polyps, case No. 1 and 6, PSNP was detected only in the EAB sample, but not in the MHR sample. Of the 5 patients who underwent second look hysteroscopy, 2 patients, case No. 2 and 4, showed yellow-white colored protuberant lesion as in the first hysteroscopy, and pathologically PSNP remained in both MHR and EAB samples. In case No. 3, in which multiple micro polyps and endometrial polyps were found at the second hysteroscopy, PSNP remained in the EAB sample. According to our diagnostic criteria using CD138 immunopositivity, 5 patients were diagnosed as CE after the first hysteroscopy. Of these, in case No. 5, DOXY was administered immediately after the first hysteroscopy, and subsequent hysteroscopy and histological examination confirmed that the patient was negative for CE. The other 3 patients, case No. 2, 3, and 4, underwent second look hysteroscopy without administration of DOXY after first hysteroscopy. Case No. 2 and 3 were judged to have persistent CE based on CD138 staining, and were received DOXY after second look hysteroscopy, and confirmed to be negative for CE after medical treatment. Case No. 4 had adhesions in the uterine cavity, so the second look hysteroscopy was performed only to detach the adhesions, and the CD138 staining obtained during the third look hysteroscopy confirmed that the patient was CE negative without DOXY administration. The remaining patient, case No. 6, received only EAB after first hysteroscopy and was confirmed CE negative. Case No. 7 was diagnosed as CE negative after first hysteroscopy, and we performed EAB without hysteroscopy for histological confirmation, but it revealed CE without PSNP. We performed second look hysteroscopy, and DOXY was started immediately after the procedure, but CE was absent by final pathological diagnosis. In these five CE-positive patients, CD138-positive plasma cell infiltration was observed around the PSNP lesion [ Figure 3c ], and four women (Case No. 3, 4, 5 and 6) showed concomitant plasma cell infiltration in endometrial stroma distant from PSNP lesion. One of the two CE-negative patients, case No. 7, also showed plasma cells infiltration around the PSNP nodules by CD138 immunostaining. The only case with no evidence of plasma cell infiltration was case No. 1. Hysteroscopic and pathological findings and adjunct examination and treatment after hysteroscopy were summarized in Table 2 . Hysteroscopic and pathological findings and adjunct examination and treatment after hysteroscopy *Since this lesion was determined to be a remnant of the previous lesion, it was re-excised and no pathological examination was performed, † We performed EAB alone after the 1 st hysteroscopy to confirm the eradication of lesions and unexpectedly pathological diagnosis revealed CE without PSNP, then we performed 2 nd hysteroscopy to search for residual lesions, but since there were no specific findings, we started doxycycline before the final determination of pathological diagnosis. However, the patient was later found to be CE-negative. CE: Chronic endometritis, MHR: Office mini-hysteroscopy with resection, EAB: Endometrial aspiration biopsy, PSNP: Placenta site nodule and plaque, DOXY: Doxycycline The median time to confirmation of disappearance of PSNP and CE (i.e. cure) was 2 months (range, 1–6 month). All of the patients became pregnant after hysteroscopic treatment. Four patients became pregnant on the first frozen-thawed embryo transfer after the intervention, and 2 patients conceived spontaneously during the cycle immediately after the intervention. The other woman conceived on the third embryo transfer attempt. Three pregnancies resulted in full-term delivery, 4 ended in spontaneous abortion. In these four women, two women gave live birth in subsequent pregnancy after miscarriage. In other two women, one woman was complicated with recurrent Asherman’s syndrome and other woman had resulted in repeated miscarriage. Both women could not give livebirth during the observation period. In women gave live birth, there were no complications during pregnancy or delivery, including any evidence of the placenta accreta spectrum. Treatment outcomes after hysteroscopy are summarized in Table 3 . Treatment outcomes *Second inspection could not perform due to pregnancy confirmed before examination, † Livebirth in subsequent spontaneous pregnancy, ‡ Livebirth in subsequent FET pregnancy. NA: Not applicable, FET: Frozen-thawed embryo transfer

PSNP should be recognized as a cause of secondary infertility. This is the first report of case series of hysteroscopic targeted biopsy and histological confirmation, which revealed specific clinicopathological features of PSNP related to secondary infertility. The lesion can be specifically identified under hysteroscopy as multiple yellow-white-colored protuberant lesions with irregular margins. The combination of hysteroscopic resection and EAB may offer complete removal of the latent lesion and fertility restoration can be expected. Although possible clinical relationship between PSNP and CE has been shown in this report, therapeutic effects of hysteroscopic eradication of PSNP to subside CE may need further investigations. In women with secondary infertility, it is important to pay attention to the findings of PSNP on hysteroscopy. The combination of aggressive resection and histopathologic examination with CD138 immunostaining may result in accurate diagnosis, rapid treatment decisions, and restoration of fertility. Conceptualization and Methodology, Mari Nomiyama and Michio Kitajima; Investigation, Rika Yamamichi, Kaoru Arima, Mari Nomiyama, Kayoko Kojima and Fumio Yamasaki; Data Collection, Rika Yamamichi and Mari Nomiyama; Writing – Original Draft Preparation, Rika Yamamichi; Writing – Review and Editing, Michio Kitajima; Supervision, Mari Nomiyama and Fumio Yamasaki; Funding Acquisition, Mari Nomiyama and Michio Kitajima. All authors have read and agreed to the final version of the manuscript. The datasets generated during and/or analyzed during the current study are available from the corresponding author on reasonable request There are no conflicts of interest.

In 1990, Young et al . first reported the clinical and pathologic features of 20 patients with PSNP.[ 2 ] Thereafter, Santos et al . reported the clinicopathological features and immunohistological findings in 25 patients with PSNP.[ 3 ] In Young’s report, 17 of the 20 patients had a history of pregnancy, and in the Santos report, all patients had a history of pregnancy; the time from prior pregnancy to diagnosis ranged from 1 to 8 years and 1–10 years, respectively.[ 2 3 ] In our present report, all 7 patients had a history of pregnancy, and the median time from prior pregnancy to diagnosis was 16 months. In the previous literature, most patients with PSNP were diagnosed incidentally after endometrial ablation or hysterectomy that was performed for subjective symptoms such as menorrhagia or other types of abnormal uterine bleeding.[ 2 3 ] Shih et al . reported that women with PSNP had preceding abnormal cervical cytology (35%), dysmenorrhea or hypermenorrhea (30%), recurrent pregnancy loss (5%), retained products of conception (5%), postcoital bleeding (2.5%), and infertility (2.5%).[ 15 ] However, none of the women with PSNP in our study were symptomatic and have no imaging findings; our study population comprised 2.8% of the patients examined for secondary infertility at our center. Our results suggest that PSNP, even when asymptomatic, may be associated with secondary infertility. Kaur described the gross findings of PSNP as, “no lesion may be visible to the naked eye or single/multiple lesions that range in size from 4 to 10 mm (average 2 mm) may be identified. It is usually yellow to tan in color.”[ 1 ] In Kaur’s study, PSNP was diagnosed in a patient who underwent hysteroscopic examination,[ 1 ] but there have been few reports on the hysteroscopic findings of PSNP, and no classic findings have been definitely established. Kim et al . described the hysteroscopic findings of PSNP as “a small yellow-white, necrotic-appearing nodule.”[ 10 ] However, Zupi et al . reported that “the nodule was about 2 cm in diameter, had an irregular surface and a variegated appearance, and was white-red in color with hemorrhagic and necrotic areas.”[ 9 ] In the current study utilizing hysteroscopy, in addition to multiple yellow-white-colored protuberant lesion, micro polyps and endometrial polyps were also found, and were resected under direct hysteroscopic observation. In 5 patients where PSNP was detected in both MHR and EAB samples, targeted biopsy using MHR within yellow-white colored protuberant lesion detected PSNP. This suggests that yellow-white colored protuberant lesion is likely to be specific hysteroscopic findings of PSNP. However, PSNP were also detected in two EAB samples without specific hysteroscopic findings, suggesting the possibility of buried PSNP covered by superficial endometrium, which is difficult to observe by hysteroscopy, and other possibility of PSNP with nonspecific appearances. The gross and hysteroscopic findings described in the previous literature are consistent with our present findings confirmed in multiple patients.[ 1 9 10 ] The presence of PSNP should be considered in women with secondary infertility when these hysteroscopic findings are observed. In addition, as PSNP was detected in all EAB specimens along with hysteroscopic MHR sampling, auxiliary diagnostic and therapeutic role of EAB sampling may be emphasized. In this investigation, we also focused on the association between PSNP and CE. The association between CE and several types of intrauterine lesions has been previously reported.[ 11 12 13 ] In these studies, the CE-positive rate is high in patients with uterine disorders such as endometrial polyps and intrauterine adhesions, and the cure rate of CE is high after hysteroscopic surgery.[ 13 ] Considering the possibility that intrauterine lesions induce secondary CE, we speculated that CE may develop secondary to PSNP. In the present study, we detected CD138 in plasma cells surrounding the PSNP nodules in 6 of 7 patients. In addition to this, infiltration of CD138 immunoreactive plasma cells in endometrial stroma other than PSNP that compatible to CE detected in 4 patients (Case No. 3, 4, 5 and 6). Most PSNP nodule showed obvious innate inflammatory reactions, and these inflammations might have spread to endometrial stroma distant from PSNP. From this point of view, some women who were treated by DOXY before the definite pathological confirmation of CE might not need immediate antibiotics similar to endometrial polyps. On the other hand, since the majority of women diagnosed as having CE were treated with DOXY in this study, immediate DOXY administration may be more feasible in women with PSNP. Although the relationship between PSNP and CE may need further investigation, this study suggests that inflammatory reaction caused by PSNP may provoke secondary CE in surrounding endometrium. PSNP has been considered to be of low clinical significance.[ 1 ] Although there have been reports of PSNP being diagnosed during evaluation for infertility,[ 6 ] the association between PSNP and infertility has not been examined. In the seven patients included in this study, all of pregnancy was achieved after PSNP resection. Three of the seven pregnancies were achieved in women with repeated ART implantation failures. Although it is not clear whether PSNP or CE treatment (DOXY administration) contributed to the restoration of fertility, our study may indicate that the hysteroscopic procedure and concomitant EAB were effective, since pregnancy were achieved shortly after the hysteroscopic procedure. Based on the previous literature and our present findings, it is likely that PSNP is easily overlooked because patients may not have symptoms, and because there may be a long interval between PSNP and a prior pregnancy. It is worthwhile to perform hysteroscopy for secondary infertility to detect the disease, resect it, and confirmation with secondary aspiration biopsy and follow up hysteroscopy.

We conducted a retrospective cohort study of patients with secondary infertility who showed no abnormalities in the uterine cavity by transvaginal ultrasonography and/or magnetic resonance imaging (MRI) and picked up the subjects diagnosed as PSNP by histologic examination after office hysteroscopy between January 2017 and December 2022. The study was conducted at a Japanese fertility center that performs approximately 800 ART treatment cycles and 350 outpatient hysteroscopic examinations each year. This was a retrospective study involving patients who submitted written informed consent for undergoing fertility treatment in our department. All patients gave written informed consent for the publication of the data obtained during this study. This study was conducted in accordance with the Declaration of Helsinki and was approved by the Institutional Review Board of Takagi Hospital (Approval number: CL006, Approval date: August 28, 2024). The following information was obtained for each patient from their clinical records: age, number of previous pregnancies, method of achieving prior pregnancy (ART vs. spontaneous pregnancy), time from prior pregnancy to examination, number and location of hysteroscopic findings, presence of PSNP, the sampling method used to obtain the diagnostic specimens (office mini-hysteroscopy with resection [MHR] or blind aspiration using a plastic device, designated as an endometrial aspiration biopsy [EAB]), number and location of plasma cells detected by CD138 immunostaining, additional treatment (e.g. analgesia at the time of hysteroscopy or administration of antibiotics), time from initial examination to confirmation of cure, time to pregnancy after hysteroscopic treatment, and method of achieving pregnancy after treatment (ART or spontaneous pregnancy). Hysteroscopy was performed during each patient’s proliferative phase, shortly after cessation of menses, in an outpatient setting and without anesthesia. After completing hysteroscopic inspection of the uterine cavity, any suspected lesions were resected under hysteroscopic observation. Lesions were completely resected from the same horizontal plane as the surrounding normal endometrium using a shear forceps during MHR.[ 11 ] Clinical CE was suspected if there were endometrial polyps with an irregular surface, micropolyps, hyperemia, nonpolypoid endometrium with diffuse hyperemia, or multiple micropolyps. All patients underwent EAB after hysteroscopic examination were completed. When the examination time was limited due to pain, and abnormal lesions could not be completely resected, secondary outpatient hysteroscopic surgery was performed at following visit; in some patients, hysteroscopic surgery was performed under anesthesia with a brief hospitalization. All hysteroscopic procedures were performed using a 5-mm Bettocchi ® hysteroscope set (KARL STORZ, Tuttlingen, Germany), which has a rigid scope with a 30° lens and a 2.9-mm outer diameter. Endometrial aspiration was performed using an Endosuction ® catheter (Hakko Corporation, Chikuma, Japan).[ 11 ] Tissue samples resected by hysteroscopy and collected by EAB were placed in separate containers, fixed in 10% formalin, prepared thin sections from different paraffin blocks were HE stained, and sent for histopathological examination. Histopathological diagnoses were made by two independent pathological departments. Primary diagnosis was made by institutional general pathologist at our faculty. Then, experienced gynecologic pathologist (F.Y.) made final diagnosis using multiple H and E-stained sections. Both were blinded to hysteroscopic gross findings and final pathological diagnosis had agreed each other. Briefly, if well-circumscribed nodular aggregates of chorionic-type intermediate trophoblastic cells were present, embedded in a hyalinized stroma, the lesion was diagnosed with PSNP. Chorionic-type intermediate trophoblastic cells were defined as having abundant eosinophilic or vacuolated cytoplasm, well-defined cell membranes, small nuclei, increased chromatin, irregular nuclear membranes, and a tendency to degeneration. When these histologic features were embedded within the endometrial stroma, covered with endometrial tissue (i.e. superficial epithelium and stroma), and when superficial epithelium and stroma were observed between the endometrial surface of the uterus and the nodule, PSNP was confirmed. The final diagnosis was made when these pathologic features were consistently confirmed within the lesions. In some patients, cytokeratin AE1/AE3 immunostaining (cytokeratin AE1/AE3 antibody; Nichirei Bioscience, Tokyo, Japan) was used as an auxiliary diagnostic method for PSNP. The histologic diagnosis of CE was made by CD138 immunostaining (CD138 antibody; Dako, Glostrup, Denmark). As our intervention policy for infertile women with CE was changed during the study period, the diagnostic criteria for the presence of CE in women with PSNP were altered depending on the time. From January 2017 to December 2020, CE was diagnosed when the number of immunoreactive plasma cells was more than 10 in 20 high-power magnification fields irrespective of the presence of organic lesion like PSNP, based on diagnostic criteria previously reported.[ 11 14 ] As we changed our policy that we do not consider aggregation of CD138 immunoreactive plasma cells in organic lesion, such as PSNP, as CE after January 2021, CE was diagnosed when the number of immunoreactive plasma cells in the endometrial stroma without PSNP was more than 20 in 20 high-power magnification fields. In women with confirmed PSNP, we performed second-look hysteroscopy or endometrial sampling during the proliferative phase, approximately 2–3 months after the pathologic diagnosis. If residual lesions were suspected, the site was re-resected. If CE was detected, oral doxycycline (DOXY) was either administered immediately after the diagnosis or given if CE persisted after reexamination. The disappearance of PSNP and CE on histopathological re-examination was considered a cure, and the patient was instructed to resume fertility treatment or to discontinue contraceptive use.