Endometrial stromal nodule embedded into term placenta.

A 28-year-old patient presented with a 5 cm endometrial stromal tumor situated at the uteroplacental interface, which was diagnosed ultrasonographically at the 28th week of pregnancy. The tumor was asymptomatic and closely attached to the decidua; after a normal term delivery, it was revealed to be embedded within the placenta. Microscopically, the neoplasm had a high mitotic rate and characteristic features of endometrial stromal tumor, such as CD10, progesterone receptor positivity, and an expansile linear, non-infiltrative pushing border. There were also pregnancy-related changes such as decidualization and myxoid change. In conclusion, the lesion was considered a benign endometrial stromal nodule with an unusual morphology and increased proliferation rate due to the hormonal stimuli of pregnancy.