Ovarian microcystic stromal tumor with significant bizarre nuclei

Rationale: Ovarian microcystic stromal tumor is a relatively rare tumor type, which is characterized by morphology with microcyst structure, solid cellular areas, and hyalinized fibrous stroma. The most reported tumors were stage I with good prognosis. Patient concerns: We report a case of a 33-year-old woman with primary ovarian microcystic stromal tumor with significant bizarre nuclei. We describe the clinical, histopathological, and immunohistochemical findings and review the English literatures. So far, as we know, the patient presented here is a rare case of ovarian microcystic stromal tumor with prominent bizarre nuclei accounting for about 50% of the tumor cells. Diagnoses: She was diagnosed with ovarian microcystic stromal tumor with significant bizarre nuclei. Interventions: The right ovarian tumor was resected laparoscopically on October 19, 2018. Outcomes: Up to now, the patient is free of disease at 19 months of follow-up. Lessons: This is a rare case of ovarian microcystic stromal tumor with obvious bizarre nuclei. This report will contribute to expand the morphological spectrum of ovarian microcystic stromal tumor.