Introduction Atypical placental site nodule is a rare histological intermediate between benign placental site nodule and malignant epithelial trophoblastic tumour . It may progress to placental site trophoblastic tumour or ETT over time. Patients diagnosed with APSN are offered a hysterectomy due to the 15% risk of progression to these malignant conditions- if this is not accepted, interval monitoring with hysteroscopy and endometrial biopsy. The objective of this study was to assess if hysteroscopic findings matched those of ultrasound or MRI in APSN patients declining hysterectomy.

Methods A retrospective review of all cases of APSN referred to a Tertiary Gestational Trophoblastic Centre in London between May 2017 and December 2023 was conducted. Women diagnosed with APSN were offered a hysteroscopy and endometrial biopsy at the centre, along with ultrasound and MRI.

Results 24 women were diagnosed during the afore-mentioned interval with APSN. Of these, on subjective hysteroscopic assessment, 44% had a normal endometrial cavity, 11% had endometrial polyps, 22% had a focal endometrial lesion, 11% had residual dead placental tissue and 11% had a thickened endometrium. Histology showed 50% had benign endometrial tissue, 29% had APSN, 4% had ETT, 8% had residual trophoblastic tissue, and 4% had a hyalinised placental site nodule. Ultrasound in these patients reported no endometrial/myometrial pathology in 92% of cases. All pelvic MRIs were normal. 75% of women had not completed their family at diagnosis.

Conclusion/Implications This study suggests that current ultrasound imaging techniques can be falsely reassuring and do not replace histological diagnosis in cases of APSN.