Ectopic placental site reaction in the Fallopian tube

Abstract

Although decidual change in the Fallopian tube following either intra-uterine or ectopic pregnancy is not uncommon, ectopic placental site reactions from prior unrecognized ectopic pregnancy are extremely rare. We describe the occurrence of an ectopic placental site reaction in a Fallopian lube, previously occluded by a Falope ring, which was subsequently re-anastomosed at salpingoplasty. The patient, a 37 year old women, subsequently had a partial salpingectomy performed a year after an intra-uterine pregnancy. Bela-HCG levels had consistently remained in the normal range. However, histological examination of the excised segments of Fallopian tube revealed an ectopic placental site reaction in the right Fallopian tube. Large mononuclear cells with bizarre atypical nuclei were present in the plicae, arranged in a nodular fashion, resembling placental site reactions as seen in the uterus. Immunohistochemical staining revealed negative staining for beta-HCG but focal positive staining for placental alkaline phosphatase and generalized positive staining for low molecular weight cytokeratin, (CAM 5.2) in keeping with intermediate trophoblast. Some suture material was present on the serosal surface of the Fallopian tube, surrounded by concentric layers of fibrosis and a focal foreign body type giant cell reaction; a marker of the previous surgery. It is possible that the previous surgery on the Fallopian tube may have played a role in the occurrence of the placental site reaction. The differential diagnosis of these histological appearances includes degenerate decidua and metastatic carcinoma. The possibility of a placental site trophoblastic tumour should also be considered but this lesion was too small to produce a tumour like mass and no mitoses were identified. The bizarre appearance of the cells may give rise to an erroneous diagnosis of malignancy, especially on small laparoscopic biopsies of the Fallopian tubes.