Biliary tract infections encompass a wide spectrum of conditions ranging from acute bacterial infections to chronic parasitic infestations. Ultrasound serves as the primary imaging modality due to its excellent soft tissue differentiation, real-time imaging capability, and lack of ionizing radiation. This article details the sonographic appearance of five clinically significant biliary infections:

1. Ascending cholangitis - Bacterial infection of obstructed bile ducts
2. Liver fluke infections - Parasitic infestations (Clonorchis, Opisthorchis, Fasciola)
3. Recurrent pyogenic cholangitis - Oriental cholangiohepatitis
4. Biliary ascariasis - Worm infestation of biliary tree
5. HIV cholangiopathy - AIDS-related biliary disease

1. Ascending cholangitis

Acute bacterial infection secondary to biliary obstruction, most commonly from stones (70%), followed by strictures and tumors.

Pathophysiology

Obstruction → bacterial overgrowth (E. coli, Klebsiella, Enterococcus) → increased ductal pressure → systemic infection.

Ultrasound Findings

• Bile duct dilation (CBD > 8mm, intrahepatic > 2mm)
• Echogenic debris within ducts (pus/sludge)
• Pneumobilia (20% of cases) - bright echoes with “dirty” shadowing
• Gallstones or other obstructive lesions
• Portal vein thrombosis in severe cases

2. Liver Fluke Infections

Chronic parasitic infestations caused by Clonorchis sinensis, Opisthorchis viverrini (Asian liver flukes), and Fasciola hepatica (sheep liver fluke).

Epidemiology & Life Cycle

Endemic in Southeast Asia. Humans ingest metacercariae in raw fish (Clonorchis) or water plants (Fasciola) → larvae migrate to bile ducts → mature into adult flukes.

Ultrasound Findings

• Ductal wall thickening (fibrosis from chronic irritation)
• Intrahepatic duct dilation with normal CBD (60% of cases)
• Fluke visualization (2–10mm echogenic foci in ducts)
• Periductal fibrosis (hyperechoic streaks)
• Gallbladder sludge/stones (common complication)

3. Recurrent Pyogenic Cholangitis (RPC)

Also called Oriental cholangiohepatitis, common in Southeast Asia. Characterized by recurrent bacterial cholangitis with intrahepatic pigment stones.

Pathogenesis

Chronic parasitic infection (flukes/ascaris) → bile stasis → bacterial colonization → stone formation → recurrent infection cycles.

Ultrasound Findings

• Segmental intrahepatic duct dilation (left lobe predominance)
• Intraductal stones (cast-like, non-shadowing)
• Ductal strictures with abrupt caliber changes
• Parenchymal atrophy of affected segments
• Portal vein thrombosis in advanced cases

4. Biliary Ascariasis

Infestation by Ascaris lumbricoides, the largest intestinal nematode (15–35cm long).

Ultrasound Findings

• Long tubular structure in bile ducts (4–6mm diameter)
• Parallel echogenic lines (worm’s digestive tract)
• Spaghetti sign - coiled worms in gallbladder
• Real-time movement of worms (diagnostic)
• Ductal dilation proximal to obstruction

Clinical Management

Albendazole/mebendazole therapy. ERCP for extraction if worms don’t retreat to intestine within 3 days.

5. HIV Cholangiopathy

AIDS-related biliary disease occurring when CD4 counts < 100 cells/mm³, caused by opportunistic infections (Cryptosporidium, CMV, Microsporidia).

Ultrasound Findings

• Ductal wall thickening (>1.5mm)
• Strictures (focal or diffuse)
• Papillary stenosis (CBD dilation > 12mm)
• Intrahepatic duct irregularity (beaded appearance)
• Gallbladder wall thickening (acalculous cholecystitis)

Treatment Approach

Antiretroviral therapy (ART) is primary treatment. ERCP with sphincterotomy for symptomatic relief.

Comparative Ultrasound Features

Condition	Key Ultrasound Feature	Pathognomonic Sign
Ascending cholangitis	Dilated ducts + echogenic debris	Pneumobilia
Liver flukes	Ductal wall thickening	Visible flukes in ducts
RPC	Left lobe ductal dilation	Cast-like intraductal stones
Ascariasis	Long tubular structure	Parallel echogenic lines
HIV cholangiopathy	Ductal wall thickening	Beaded intrahepatic ducts

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