A Placental Conundrum: Exaggerated Placental Site Tumor

Exaggerated placental site (EPS) is defined as a non-neoplastic condition in which there is proliferation of number of implantation site intermediate trophoblastic cells that infiltrates the endometrium and myometrium. This is a benign lesion and it’s an exaggeration of normal physiological process as the intermediate trophoblastic cells present in EPS are similar morphologically and immunophenotypically to those found in the normal implantation site. An exaggerated placental site may occur in association with normal pregnancy or an abortion. The significance of reporting this lesion lies in the fact that the cells of this lesion display an identical morphological features to the intermediate trophoblastic cells found in placental site trophoblastic tumour, placental site nodule & epithelioid trophoblastic tumour. To confirm the morphological analysis, we used immunohistochemistry panel comprising of Cytokeratin 18, p63and ki-67(MIB-1). We here present a rare case of an exaggerated placental site in a 30-year-old female who was in her first trimester of pregnancy and presented with signs of incomplete abortion.


Introduction
Exaggerated placental site (EPS) is defined as a nonneoplastic condition in which there is proliferation of number of implantation site intermediate trophoblastic cells that infiltrates the endometrium and myometrium. This is a benign lesion and it's an exaggeration of normal physiological process as the intermediate trophoblastic cells present in EPS are similar morphologically and immunophenotypically to those found in the normal implantation site. It was previously named syncytial endometritis but due to its non-inflammatory, non-syncytial nature and its extention beyond endometrium, the World Health Organization renamed it Exaggerated placental site. (1) It is therefore must to uncover such lesions as it is difficult to distinguish it from other trophoblastic neoplastic lesions, which validates early diagnosis and better prognosis. EPS is a benign lesion but awareness of the constellation of its clinical, morphological and immunohistochemical features aids in establishing the correct diagnosis and distinguishing this neoplasm from other benign and borderline lesions of similar morphology but different treatment modalities.

Case Report
A 30-year-old female, 14 weeks pregnant, presented to gynaecology department with bleeding per vagina, lower abdominal pain along with high fever. On examination, her fever was 38°C (100.4°F), her pulse rate was increased and blood pressure was falling. Her haemoglobin was low and total leucocyte count was raised. She had a previous history of abortion. Emergency curettage was performed as there were signs of incomplete abortion which was sent for histopathology.
Microscopic examination showed intermediate trophoblastic cells along with variable number of multinucleated trophoblastic cells which infiltrated the endometrium and myometrium. Endometrial glands were surrounded by trophoblastic cells and the smooth muscles of myometrium was separated by nests, cords and individual implantation site trophoblastic cells. At places there was decidual reaction with evidence of necrosis and inflammation. Focal areas of hyalinisation were also noted. However, no chorionic villi/ increased mitotic activity was noted in the sections examined. (Figure 1,2,3) It is difficult to distinguish it from placental site trophoblastic tumour(PSTT), placental site nodule(PSN)and epithelioid trophoblastic tumour(ETT) morphologically, hence immunohistochemical markers like CK 18, p63 and Ki-67 proliferation index was done for this distinction.  Considering this we kept EPS and PSTT in our differential.
It is important to make the differential diagnosis as the PSTT cells of the neoplastic proliferation of intermediate trophoblasts and the EPS cells have similar cytological and immunophenotypical features. Cases in which distinction is hard to make, Ki 67 proliferation index is considerably useful. While Ki 67 proliferation index being less than 1% is in favour of EPS, levels more than 5% support PSTT. Our Ki-67 index came out be less than 1%. (Figure 6)

Conclusion
EPS is a benign trophoblastic lesion, having no risk of persistent gestational trophoblastic diseases. However, the awareness of this rare entity is paramount as it must be distinguished from other borderline and malignant lesions like PSTT, PSN and Choriocarcinoma which require different and aggressive treatment protocol unlike this lesion. There is utmost need for more literature and documentation of such cases to establish the criteria of diagnosing this lesion confidently on the basis of morphology alone. We would like to attract attention to EPS which is not frequently seen and it must be carefully ruled out with the help of its histopathological features followed by immunohistochemistry.