Pancreatic hydatid cyst with a characteristic "water-lily" sign

Cystic echinococcosis rarely involves the pancreas and may mimic common cystic neoplasms. Recognition of characteristic imaging signs is central to diagnosis; the "water-lily" sign (floating detached endocyst) is a rare and highly characteristic finding in favor of transitional-stage hydatid cyst and, when recognized, can prevent inappropriate cyst puncture and guide stage- and anatomy-based management.

A 34-year-old woman from Iran, an endemic region for cystic echinococcosis, presented with intermittent epigastric/right upper quadrant pain. At an outside institution, endoscopic ultrasound-guided fine-needle aspiration had been performed before referral; cyst-fluid amylase was 20 U/L and carcinoembryonic antigen was not detected, arguing against pseudocyst and mucinous neoplasm. Ultrasound and MRI/MRCP performed after EUS showed a unilocular pancreatic head cyst with a floating internal membrane ("water-lily"/"serpent" appearance) and mild upstream pancreatic duct dilatation. Our multidisciplinary team favored pancreatic cystic echinococcosis. The patient underwent surgical cyst excision with avoidance of scolicidal instillation into the biliary tree. Albendazole (400 mg twice daily, ∼ 10-15 mg/kg/day) was given perioperatively and continued for 6 months. Pathology confirmed laminated membranes and protoscolices. She remains asymptomatic on surveillance MRI without recurrence.

In an endemic region, a pancreatic cyst with a floating membrane and low cyst-fluid amylase should raise suspicion for cystic echinococcosis. Anchoring the diagnosis to WHO staging and resisting routine EUS-FNA can avert spillage and caustic cholangiopathy from scolicidal agents. Radiologists play the key role in making this distinction.