Multimodal Imaging of a Giant Ovarian Mature Cystic Teratoma Featuring the Floating Ball Sign: A Case Report

Background: Ovarian Mature Cystic Teratomas (MCTs), the most common type of ovarian teratoma, contain tissues from all three germ layers. The “floating ball sign,” which consists of mobile spherules of sebum and keratin, is a characteristic feature seen on Computed Tomography (CT) and Magnetic Resonance Imaging (MRI). However, the imaging features can overlap with other cystic lesions, leading to potential misdiagnosis. This case report focuses on a giant MCT initially misdiagnosed as hydatid disease on CT. Its value lies in highlighting the diagnostic pitfall of over-relying on CT and demonstrating how a systematic, multimodal approach resolves uncertainty. Case Presentation: A 40-year-old female presented to our hospital due to a 3-month history of progressive, painless abdominal distension and recent urinary frequency/urgency. On physical examination, a soft, non-tender mass was palpated in the umbilical region. Initial abdominal-pelvic contrastenhanced CT revealed a huge cystic lesion with multiple internal cystic structures resembling “daughter cysts”, a feature suggestive of hydatid disease. However, preoperative parasite tests returned negative, creating a conflict with this initial suspicion, and the mass effect caused by the lesion obscured its origin on CT. This discrepancy prompted further evaluation, which revealed mobile intracystic spherical structures via targeted ultrasound, confirming their mobility and floatability. Meanwhile, MRI identified characteristic fat content through fat-saturated sequences. These findings confirm the “floating ball sign,” which collectively supported the possible diagnosis of MCT. The diagnosis was confirmed by exploratory laparotomy and subsequent histopathological analysis. Conclusion: This case illustrates that while CT is useful for initial evaluation of giant abdominopelvic masses, its findings can be misleading. When imaging and clinical data conflict, a deliberate diagnostic reconsideration pathway using targeted ultrasound and MRI is key to avoiding misdiagnosis.