Passage of decidual cast following poor compliance with oral contraceptive pill

Background: Decidual cast describes the spontaneous sloughing of endometrium as an entire piece while retaining the shape of the endometrial cavity. It may be associated with increased serum progesterone levels and must be considered as a differential diagnosis in a patient who passes tissue per vagina while on progesterone containing hormonal contraception.

Case: A 13-year-old adolescent with a history of menorrhagia since menarche, presented to the pediatric emergency room with worsening abdominal pain and heavy vaginal bleeding stopping her oral contraceptive pill 10 days prior to presentation. Her symptoms resolved spontaneously following passage of tissue per vagina which was later by histopathology to be a decidual cast.

Conclusion: Decidual cast is a rare pathological entity that may be a side effect of progesterone-containing hormonal contraceptives, requiring patient education before use.