The hepato-biliary and pancreatic system consists of the intrahepatic and extrahepatic bile ducts, gallbladder, and pancreatic ductal system, which converge at the ampulla of Vater under sphincter of Oddi control to deliver bile and pancreatic enzymes into the second part of the duodenum.

Fig1 demonstrates the normal anatomy and some anatomical variants increasing predisposition to fistula formation.

Pancreatico-biliary  fistulas are classified into external fistulas, where the pancreatic duct/bile duct communicates with the skin (cutaneous), and internal fistulas, where secretions drain into internal compartments-Intrabadominally including the peritoneal cavity (ascites), retroperitoneum space gastrointestinal tract (involving stomach, duodenum, jejunum, or colon), vascular structures (arterial,venous ), and extraabdominally into pleura (pleural effusion), bronchial tree, pericardium and mediastinum. Fig2 demonstrates the classification.

The intrahepatic bile ducts and common bile duct normally function under low intraluminal pressure, directing bile flow toward the duodenum. During fasting, sphincter of Oddi contraction increases distal biliary pressure, diverting bile into the gallbladder for storage. With food intake, cholecystokinin (CCK) induces gallbladder contraction and sphincter relaxation, restoring a favorable pressure gradient and allowing bile to enter the duodenum. The pancreatic ductal system similarly operates under low basal pressure, with pancreatic secretions flowing from tail to head and draining into the duodenum through coordinated sphincter relaxation.Fig3 illustrates the normal direction of bile and pancreatic flow governed by physiological pressure gradients.

Disruption of this finely regulated pressure balance underlies the formation of pancreatico-biliary fistulas. Conditions causing elevated intraductal pressure—including stones, strictures, tumors, inflammation, or sphincter dysfunction—result in ductal dilatation, stasis, and enzyme activation. Sustained high-pressure leakage leads to autodigestion, tissue necrosis, and progressive erosion into adjacent structures. Secretions then track along tissue planes, forming abnormal communications with the peritoneum, pleura, bowel, or skin, as depicted in Fig3. Fig4 and Fig5 show the pathophysiology of biliary and pancreatic fistulas.

IMAGING MODALITIES

Imaging evaluation of pancreatico-biliary fistulas includes X-ray and ultrasound for initial clues, CT for detection and complications, MRI/MRCP for ductal delineation, and ERCP as the diagnostic and therapeutic gold standard (Fig6)

CLASSIFICATION

HEPATOBILIARY FISTULAS: Fig 7 demonstrates the various possible biliary fistulas . They develop mostly in long standing cholelithiasis.

Classical Imaging Features of Biliary Fistulas

Direct Signs:

• Visualization of an abnormal communication between bile ducts or gallbladder and adjacent structures on MRCP .
• Contrast extravasation from bile ducts on CT, MRCP, or cholangiography.
• Opacification of bowel, pleural space, or peritoneum during biliary contrast studies.

Indirect Signs:

• Pneumobilia
• Unexplained biliary dilatation proximal to obstruction.
• Periductal inflammatory changes or wall thickening.
• Adjacent fluid collections or abscesses, often bilious in nature.

CHOLECYSTO-CHOLEDOCHAL FISTULA :

 It is caused by extrinsic compression of the common hepatic duct by an impacted stone in the Hartmann’s pouch or cystic duct, leading to Persistent inflammation and erosion of the bile duct and formation of a cholecysto-biliary fistula (Type II Mirizzi syndrome).

Fig8 shows a Choledocho- cholecystic fistula in a patient presenting with obstructive jaundice.

CHOLECYSTO-PYLORIC FISTULA

 An abnormal biliary fistula connecting the gallbladder to the pylorus. Rarest of all enteric fistulas. Rigler’s triad: Ectopic gallstone, pneumobilia, bowel obstruction.

Fig9 shows a case of of cholecysto-pyloric fistula in a patient who presented with cholecystitis

CHOLECYSTO- DUODENAL FISTULA

Communication between gall bladder and duodenum. It is the most common type of enteric fistula.

Fig11 demonstrates Cholecysto-duodenal and peritoneal fistula in a patient who is a known case of cholelithiasis with pain abdomen

CHOLECYSTO-COLONIC FISTULA

An abnormal communication between the gallbladder and the colon, most commonly the hepatic flexure. Triad:  Cholelithiasis, chronic watery diarrhea, pneumobilia.

Fig31 demonstrates Cholecysto-colonic fistula in a patient who presented with acute pain in right upper quadrant.

HEPATIC DUCT PYLORIC FISTULA

Exceptionally rare, Accounts for far <1% of all internal biliary–enteric fistulas. Involves left hepatic duct branches more than right

Fig12 demonstrates Left sectoral hepatic duct – pyloric fistula in a 11 year old who presented with multiple episodes of colicky abdominal pain.

CHOLEDOCHO-JEJUNAL FISTULA

Abnormal communication between jejunum and common bile duct

Fig13 demonstrates choledocho-jejunal fistula in a case of post porto-enterotomy for biliary atresia, presenting with pain abdomen

CHOLEDOCHO-COLONIC FISTULA

An abnormal communication between the common bile duct and the colon, most commonly the hepatic flexure or transverse colon. Triad: Massive pneumobilia, chronic bile acid-induced diarrhea and vitamin K malabsorption.

Fig14 demonstrates a choledocho-colonic fistula in a 60 year old patient,who underwent  cholecystectomy presents with biliary stricture and recurrent cholangitis.

BILIARY PERITONEAL FISTULA

Bile leaks most commonly occur post hepatic and biliary interventions like ERCP,PTBD. HIDA scan is most effective modality to demonstrate bile leaks

Fig15 demonstrates cases of biliary peritoneal fistula in a posttransplant patient and in a post cholecystectomy patient

BILIO-VASCULAR FISTULA

It defined as the presence of blood within the biliary tract due to an abnormal communication between the bile ducts and the surrounding vasculature. Quincke’s triad: right upper quadrant pain, jaundice, gastrointestinal bleeding.

Fig16 demonstrates Hepatic arterial biliary fistula in a 45 year old male patient, status post cholecystectomy presented with hematemesis.

HEPATO PLEURO BRONCHIAL FISTULA

 Abnormal communication between the biliary tract and the tracheobronchial tree . Most commonly associated with ruptured hydatid cyst, amoebic/pyogenic liver abcess.

The presence of bilioptysis is pathognomonic for a bronchobiliary fistula

Fig17 demonstrates Hepato biliary fistula in a patient who presented who  presented cough and breathing difficulty and biliopstysis

BILIO-CUTANEOUS FISTULA

Abnormal connection of biliary tree to skin. Most commonly due to iatrogenic causes.

Fig18 demonstrates Bilio cutaneous fistulas in two cases, one post PTBD removal and other due to spontaneous occurrence.

PANCREATIC FISTULAS

 Fig19 demonstrates the various possible pancreatic fistulas . They develop mostly in long pancreatitis with pseudocyst and walled off necrosis formations.

IMAGING SIGNS:

DIRECT SIGNS

• Direct contrast extravasation from the pancreatic duct into an adjacent organ or cavity.
• Visible continuous fistulous tract from the pancreatic duct or pseudocyst to peritoneum, pleura, bowel, or skin.
• Gas within a pancreatic pseudocyst indicating communication with bowel.

INDIRECT SIGNS:

• Unexplained or recurrent peripancreatic fluid collections or pseudocysts.
• Disproportionately large pleural effusion or ascites without primary cardiopulmonary or hepatic cause.
• Dilated or abruptly cut-off pancreatic duct suggesting upstream ductal disruption.
• Fluid tracking along retroperitoneal or mediastinal planes from the pancreas.

PANCREATICO-GASTRIC FISTULA

Abnormal communication between pancreatic duct/ psuedocyst with stomach. Can result in formation of bouveret syndrome

Fig20 demonstrates pancreatico-gastric fistula in a case of pancreatitis who presented with spontaneous psuedocysto- gastrostomy.

PANCREATICO-DUODENAL FISTULA

An abnormal communication between pancreas and duodenum.

Fig21 demonstrates Pancreatico-duodenal fistula in 70 year old patient who presents with abdominal pain and belching

PANCREATICO-COLONIC FISTULA

An abnormal communication between the pancreas and mainly the splenic flexure of colon. Most common enteric fistula in pancreas.

Fig22 shows Pancreatico-colonic fistula in a 45 year old female patient,   who is a follow up case of necrotizing pancreatitis

PANCREATICO-PERITONEAL FISTULA

Abnormal communication with the peritoneum resulting in pancreatic ascities, with high amylase levels is diagnostic

Fig23 demonstrates Pancreatico-peritoneal fistula in case of Post traumatic transection of pancreas.

PANCREATICO-RETROPERITONEAL FISTULA

Tracking of peripancreatic fluid into the retroperitoneum, most likely in cases of necrotic pancreatitis.

Fig23 demonstrates Pancreatico-retroperitoneal fistula in patient who presented with pancreatitis.

PANCREATICO-VASCULAR

An abnormal communication between pancreatic duct/psuedocyst with blood vessels .Most commonly associated with psuedoaneurysm of splenic artery.

Fig25 demonstrates Pancreatico-vascular fistula in a patient, who is known case of pancreatitis presented with upper GI bleed

PANCREATICO MEDISTINAL FISTULA

Abnormal connection of pancreas to the mediastinum.Triad: Massive pleural effusions, elevated pleural fluid amylase and protein levels.

Fig26 demonstrates pancreatico-mediastinal fistula in a case of recurrent pancreatitis

PANCREATICO-PLEURAL FISTULA

Abnormal communication of pancreas with pleura resulting in recurrent left sided pleural effusion with elevated amylase levels

Fig27 demonstrates pancreatico-pleural fistula in a known case of chronic pancreatitis who presented with recurrent left sided pleural effusion

PANCREATICO CUTANEOUS FISTULA

Persistent drainage of pancreatic secretions through the skin. Usually following iatrogenic injuries to duct.

Fig28 demonstrates Pancreatico-pleural-cutaneous fistula in a patient,who is a known case of necrotizing pancreatitis

MANAGEMENT

• To reduce ductal pressure and divert secretions into the duodenum to allow spontaneous healing – ERCP with stenting +/- sphincterotomy
• To control infections:Percutaneous drainage and antibiotics
• To remove the primary disease
• Surgery is reserved for refractory or complicated fistulas like colonic fistulas
• Embolisation and coiling done in vascular fistulas.

Fig29 and 30 shows the management of fistulas.