A fishy situation – expanding the differential diagnosis of the fish-mouth papilla

Hydatid disease (echinococcosis) is a parasitic infection that presents with hepatic cysts and pulmonary involvement. Hepatic hydatid disease can lead to an obstruction of the biliary tree in the case of cyst rupture [1]. This case report provides endoscopic images of a hepatic hydatid cyst mimicking the fish-mouth appearance of papilla, usually pathognomonic for main duct intraductal papillary mucinous neoplasm (MD-IPMN [2]).

A 35-year-old man, from North Africa, presented with acute on chronic epigastric pain. Initial work-up revealed increased alanine aminotransferase (648 IU/L) and total bilirubin (99 μmol/L) levels. A computed tomographic scan showed a multilobulated, septated, calcified lesion in the inferior left liver, suggestive of a hepatic cyst ([Fig. 1]). He was later lost to follow-up.

Fig. 1 A CT scan showed a multi-lobulated, septated, calcified lesion in the inferior left liver, suggestive of a hepatic cyst. CT, computed tomography.

Nine years later, he returned to the emergency room with work-up confirming cholangitis. MRCP showed poorly defined obstructive filling defects within a slightly dilated bile of 8 mm in diameter ([Fig. 2]). Interval growth of the hepatic cyst and left intrahepatic biliary ductal dilatation was noted.

Fig. 2 MRI revealed interval growth of the hepatic cyst and left intra-hepatic biliary ductal dilatation. MRI, magnetic resonance imaging.

ERCP demonstrated a white, soft, mucinous substance protruding from the ampulla ([Video 1]). The endoscopic images were suggestive of a fish-mouth papilla ([Fig. 3]). After biliary sphincterotomy, the spontaneous discharge of thick, white membranes occurred.

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Fish-mouth papilla appearance of the ampulla, and discharge of thick, white membranes after sphincterotomy.Video 1

Fig. 3 ERCP: a white, soft, mucinous substance protruding from the ampulla, suggestive of a fish-mouth papilla.

Evaluation of the biliary aspirate with wet mount iodine microscopy identified numerous hooklets ([Fig. 4]) and confirmed the diagnosis of a compressive echinococcal cyst. He was first treated with albendazole and then referred to hepatobiliary surgery for resection. Both ERCP and left hepatectomy conferred a significant clinical and biochemical improvement.

Fig. 4 Wet mount iodine microscopy: biliary aspirate with numerous hooklets, confirming echinococcosis.

A ruptured hydatid cyst can lead to the fish-mouth papilla, which is typically pathognomonic for MD-IPMN. ERCP was effective in the treatment of cholangitis in the context of biliary obstruction from hydatid cyst rupture and biliary aspirate confirmed the diagnosis.

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Contributorsʼ Statement

Omar El Ouarzadi: Conceptualization, Data curation, Investigation, Methodology, Project administration, Writing – original draft, Writing – review & editing. Reda Goudrar: Conceptualization, Data curation, Writing – original draft, Writing – review & editing. Marc-André Smith: Data curation, Formal analysis, Investigation, Resources, Validation, Visualization, Writing – review & editing. Marcel Tomaszewski: Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Project administration, Resources, Supervision, Validation, Writing – review & editing.

Conflict of Interest

Dr. Marcel Tomaszewski is a consultant for Boston Scientific and Pendopharm. All other authors have no conflicts of interests to declare.

• References

• 1 Bhalla VP, Paul S, Klar E. Hydatid Disease of the Liver. Visc Med 2023; 39: 112-120
• 2 Asokkumar R, Chin YK. Fish-Mouth Papilla. Clin Gastroenterol Hepatol 2018; 16: A34

Publication History

Article published online:
08 January 2026