RESUMEN
INTRODUCTION: Increased progesterone levels during pregnancy may cause decidualisation of endometriomas mimicking malignancies on radiology and causing management dilemmas. CASE: An ovarian cyst was detected in a 33-year-old woman at her routine 12-week gestation ultrasound scan. By 18 weeks, the unilocular mass was increasing in size with features suggestive of early ovarian malignancy. The cyst was monitored throughout pregnancy and caesarean section at 38 weeks delivered a healthy male. Histology confirmed a decidualised endometrioma and benign dermoid cyst with no evidence of malignancy. LITERATURE REVIEW: The evidence for decidualised ovarian endometriomas in pregnancy was explored; 14 papers were identified, which reported 26 cases, excluding our index case. Of the 27 cases, 19 (70%) were managed surgically, 4 of which were delayed till caesarean section with concomitant cyst excision; 8 cases were managed conservatively through serial monitoring of the cyst, which spontaneously regressed following delivery. CONCLUSION: Surgical management of the cyst provides histological diagnosis but may introduce risks to mother and fetus; a conservative approach may cause anxiety but limits interventions. Elective caesarean section following monitoring throughout pregnancy may bridge the gap between surgical and purely conservative approaches if appropriate. Limited available evidence makes a definitive decision regarding management difficult. Decidualisation should be considered as a differential for suspicious ovarian lesions in pregnancy.