MRI Features of Ovarian Fibroma and Fibrothecoma With Histopathologic Correlation

OBJECTIVE. The purpose of this article is to evaluate MRI features of ovarian fibroma and fibrothecoma with histopathologic correlation. MATERIALS AND METHODS. In this retrospective study, preoperative MRI examinations of 35 women (mean age, 49 years; range, 24-86 years) with pathologically proven ovarian fibroma (n = 25) or fibrothecoma (n = 10) were reviewed by two radiologists in consensus. MRI features, including visibility of ovaries, presence of capsule, degeneration, T1 and T2 signal, and enhancement pattern, were recorded and correlated with histopathologic features. After administration of gadopentetate dimeglumine, the maximum percentages of enhancement of fibroma or fibrothecoma, myometrium, and, if present, uterine fibroids (11/35 patients) were compared. RESULTS. All fibromas and fibrothecomas appeared well defined, with a mean size of 6.36 x 4.81 cm. Ipsilateral and contralateral ovaries were each seen in 89% (31/35) of patients. Most fibromas and fibrothecomas were isointense to hypointense compared with myometrium on T1-weighted (91% [32/35]) and T2-weighted (77% [27/35]) images. Capsule was noted in 63% (22/35) and degenerative changes were noted in 66% (23/35) of patients. Fibromas and fibrothecomas larger than 6 cm more likely showed capsule (p < 0.0001, Fisher exact probability test), degenerative changes (p = 0.003), peripheral subcapsular cystic areas (p < 0.0001), heterogeneous T2 signal (p = 0.001), and heterogeneous enhancement (p = 0.005). At least four of the above five characteristics were present in 93% (14/15) of fibromas and fibrothecomas larger than 6 cm (p < 0.0001). The maximum percentage of enhancement for fibromas and fibrothecomas (63%) was significantly lower than those for myometrium (131%; p < 0.0001) and fibroids (103%; p < 0.0001), without a statistically significant difference between the maximum percentage enhancement of myometrium and fibroids. A maximum percentage of enhancement less than 75% yielded 92% positive predictive value in differentiating fibromas and fibrothecomas from fibroids. Fibrothecomas had a higher maximum percentage of enhancement than did fibromas (p = 0.01). CONCLUSION. MRI features of ovarian fibromas and fibrothecomas depend on size, with capsule and degenerative changes common with fibromas and fibrothecomas larger than 6 cm. Fibromas and fibrothecomas enhance less than myometrium and fibroids do, and less than 75% maximum percentage enhancement can help in differentiating fibromas and fibrothecomas from fibroids.