Introduction: Placental site nodules (PSNs) are uncommon lesions typically found in uterine specimens and extremely rarely in extrauterine locations such as the fallopian tubes. PSNs are usually discovered incidentally and result from prior implantation sites. This case report describes an unexpected PSN found in a fallopian tube during a cesarean section with concurrent tubal sterilization.

Case Presentation: A 38-year-old multiparous woman (gravida 4, para 2) with a previous vaginal delivery underwent tubal sterilization during a cesarean section. The surgical procedure was uneventful, with no macroscopic abnormalities noted. The patient's medical history included treatment for an ectopic pregnancy with methotrexate. Pathological examination revealed the right fallopian tube to be unremarkable. However, the left fallopian tube contained a 0.3 cm nodule within its wall, characterized by central hyalinization, dystrophic calcifications, and peripheral intermediate trophoblast cells. Immunohistochemical analysis demonstrated GATA3 positivity and a low proliferative index (MIB-1). The absence of mitotic activity, necrosis, and typical morphology confirmed the diagnosis of a PSN.

Discussion: PSNs are benign lesions derived from intermediate extravillous trophoblasts. Their identification relies on both morphological characteristics and immunohistochemical staining. The differential diagnosis includes various trophoblastic diseases, which can be distinguished from PSNs by their specific features. This case contributes to the limited literature on extrauterine PSNs, highlighting the importance of recognizing these lesions in atypical locations and differentiating them from pathologies that are more aggressive.

Conclusion: This case highlights the rarity of PSNs in the fallopian tubes and underscores the importance of comprehensive pathological analysis for an accurate diagnosis.