A case of an endometriosis associated ovarian carcinoma that could not be diagnosed by preoperative MRI

We report a case of endometriosis associated ovarian carcinoma that could not be diagnosed using preoperative magnetic resonance imaging (MRI). A 29-year-old woman presented with a 3-year history of acute abdominal pain. MRI revealed a left-sided endometrial cyst measuring 4.5 cm, and she had a history of low-dose estrogen-progestin (LEP) therapy for a left ovarian endometrial cyst. The cyst showed a slight increase in size to 5 cm, 1 year after it was diagnosed; therefore, she underwent pelvic MRI, which did not reveal evidence of malignancy but only showed intracystic nodules, which were suspected to be clots. She continued to receive LEP therapy; however, transvaginal ultrasonography performed 2 years and 6 months after the detection of the cyst revealed an increase in the size of the cyst to 7 cm, and pelvic MRI performed at that time revealed an increase in the size of the nodules, which were suspected to be clots without any evidence of malignancy. Contrast-enhanced pelvic MRI performed 2 years and 10 months after initial diagnosis revealed further growth of both the cyst and nodules; therefore, she underwent surgery. The nodule was enlarged; however, we observed no contrast effect, and the position appeared to have shifted from the ventral to the dorsal aspect. Therefore, we speculated that the nodule was most likely a benign lesion, and performed laparoscopic left ovarian cystectomy. We did not observe any increase in tumor markers during the course of the study. Intraoperatively, the cyst ruptured; however, we could visualize a clear boundary between the cyst and the surrounding parenchyma, and the lesion was easily removed. We detected no abnormalities in the contralateral ovary or the pelvis. Histopathological evaluation of the resected specimen revealed clear cell carcinoma, and we performed, abdominal left adnexectomy and omental biopsy, 1 month after the initial operation. Clear cell carcinoma was not detected in the resected ovary, and she was administered 3 cycles of a combination of carboplatin plus paclitaxel. She has shown no recurrence over 4 months postoperatively.