Imaging in gynecological disease: ultrasound features of malignant ovarian yolk sac tumors (endodermal sinus tumors)

Objectives To describe the clinical and sonographic characteristics of malignant ovarian yolk sac tumors. Methods In this retrospective multicenter‐study we included 21 patients with a histological diagnosis of ovarian yolk sac tumor where still images and/or videoclips were available. Ten patients collected from the IOTA‐studies, had undergone a standardized preoperative ultrasound examination by an experienced ultrasound examiner between 1999 and 2016. The remaining eleven were identified through medical files, where images were retrieved from local image work stations and PACs systems. All tumors were described using IOTA terminology. The collected images and video clips were used for additional characterization by two observers. Results All cases were pure yolk sac tumors except for one, that was a mixed tumor (80% yolk sac tumor and 20% embryonic carcinoma). Median age at diagnosis was 25 (Interquartile range, IQR 19.5‐30.5) years. Seventy‐six percent (16/21) were FIGO stage I‐II when diagnosed. 58% (11/19) women felt pain during examination and one patient presented with ovarian torsion. Median S‐AFP level was 4755 μg/L (IQR, 1071 ‐ 25303) and CA‐125 126 kU/L (IQR, 35‐227). On ultrasound assessment 95% (20/21) of tumors were unilateral. The median of the maximal tumor diameter was 157 mm (IQR 107‐181), and the largest solid component 110 mm (IQR 66‐159). Tumors were classified either as multilocular‐solid (10/21, 48%), or as solid (11/21, 52%). Papillary projections were found in 10% (2/21) of the cases. Most tumors (20/21, 95%) were well vascularized (color score 3‐4) and none of the tumors had acoustic shadowing. Malignancy was suspected in all cases except for the patient with torsion, which presented with a color score of 1 and was classified as probably benign. Image and video clip quality was considered as adequate in 18/21 cases. Reviewing the images and videoclips we found that all tumors contained both solid components and cystic spaces, and that 89% (16/18) of the tumors had an irregular, still fine‐textured, and slightly hyperechoic solid tissue, giving them a characteristic appearance. Conclusion Malignant ovarian yolk sac tumors are often detected at an early stage, in young women usually in the second or third decade of life, presenting with pain and markedly elevated S‐AFP. On ultrasound yolk sac tumors are mostly unilateral, large, multilocular‐solid or solid, with fine‐textured slightly hyperechoic solid tissue, and rich vascularization.