Definitively diagnosing primary fallopian tube carcinoma (PFTC) prior to surgery is difficult. In the first working diagnosis, PFTC is often misdiagnosed as ovarian cancer. Preoperative workups using magnetic resonance imaging (MRI) are capable of differentiating PFTC from epithelial ovarian carcinomas (EOCs). Both the sensitivity and the specificity of MRI for identifying PFTC are high. The presence of a hydrosalpinx is a hallmark of PFTC. On MRI, hydrosalpinges have characteristic sausage-shaped appearances due to intrauterine fluid accumulation and fallopian tube distention. Additionally, MRI scans are superior to computed tomography (CT) scans or ultrasound images in detecting tumor infiltration into surrounding organs. Here, we report a case in which PFTC was pre-operatively misdiagnosed as EOC.