A puzzling ovarian tumour: pregnancy luteoma with diffuse endometriosis.

BACKGROUND: Pregnancy luteoma is a distinctive non-neoplastic hormone dependent lesion arising in pregnancy and mimicking an ovarian tumour. Fewer than 200 cases have been described in the English-language literature. Its clinical and morphological features are characteristic and must be considered in order to prevent diagnostic misinterpretation. To the best of our knowledge the association of pregnancy luteoma with endometriosis has not been reported in literature to date. CASE REPORT: A 30-year-old pregnant woman with no particular past medical history, consulted her gynaecologist at 17 weeks gestation for routine check-up. The patient was asymptomatic and did not show any signs of virilization. Ultrasonography disclosed a left adnexal heterogeneous mass measuring 7 cm in diameter with intramural vegetations. The right ovary was unremarkable. The patient underwent salpingo-oophorectomy considering the imaging findings were suspicious for malignancy. Histologically, the lesion was constituted of large sheets of luteinized polygonal cells with abundant eosinophilic cytoplasm and small round nuclei devoid of atypia and mitotic figures. In addition, there were several ectopic endometrial glands surrounded by abundant decidualized or edematous stroma. Immunohistochemically, these glands were immunoreactive for cytokeratin 7. The final pathological diagnosis was pregnancy luteoma associated with diffuse endometriosis. CONCLUSIONS: Because of its relative rarity, pregnancy luteoma is likely to be clinically misinterpreted and overtreated, as in the present case.