Figure 12b. Mature ovarian cystic teratoma at 9 weeks gestation. Routine obstetric US demonstrated a large right adnexal mass. (a) Axial T1-weighted image shows a heterogeneous right adnexal mass with predominantly high signal intensity (arrow). A normal right ovary was not identified with any sequence. (b) Axial T1-weighted image obtained with fat suppression shows suppression of the high-signal-intensity areas within the mass (arrow), confirming the diagnosis of teratoma. We do not routinely perform MR imaging during the first trimester. In this case, the referring obstetrician thought the clinical indication was sufficiently compelling, and consent was obtained from the patient. The mass was surgically removed during pregnancy.