Acknowledgements
We would like to thank Enago (https://www.enago.com/) for their English language review. Kyoko Ono contributed to the work. She is a pathologist in our hospital. This case was presented at the 69th Annual Congress of the Japan Society of Obstetrics and Gynecology, Hiroshima, April 15, 2017.
Disclosure statement
No potential conflict of interest was reported by the author(s).