Résumé : The authors report and discuss an exceedingly rare case of a unilocular macrocystic serous cystadenomas diagnosed in a 63-year-old female patient, which was preoperatively misdiagnosed as a mucinous cystic neoplasm, due to the atypical magnetic resonance (MR) imaging features shown at presentation and the misleading results obtained through cystic fluid analysis. This manuscript overviews the typical and atypical manifestations of this entity and highlights the advantages, potential limitations and pitfalls of both MR imaging and cystic fluid analysis.