Biliary Imaging Flashcards
MCRP Overview
Heavily weighted T1 or T2?
Contrast-enhanced MRCP - What’s all this about?
- MRCPis an abdominal MRI acquired with heavily T2-weighted sequences that increase the contrast between T2 hyperintense stationary fluid in the biliary tract and surrounding structures.
- Fast spin echo sequences are most commonly used for MRCP acquisition. various techniques can be employed to optimize imaging including breath-hold sequences and respiratory-triggered sequences.
- Heavily T2-weighted sequences primarily image the biliary tree.
- Sequences with intermediate T2 (TE 80-100 ms) are best suited for visualization of the biliary ductal system and surrounding tissue, in particular, to evaluate extraluminal structures.
- Contrast-enhanced MRCP can also be performed with fat-saturated T1-weighted imaging after injection of gadolinium contrast agents that have biliary excretion, such as gadoxetic acid disodium Eovist and gadobenate dimeglumine Multihance. These agents shorten T1 relaxation, resulting in T1 hyperintense biliary fluid, but require a 20-45 minute delay prior to imaging to allow time for biliary excretion.
Advantages of MRCP over ERCP
- MRCP has the ability to see extra-luminal findings.
- MRCP can visualize excluded (obstructed) ducts.
- MRCP is non-invasive.
Disadvantages of MRCP compared to ERCP
- MRCP does not allow for concurrent therapeutic intervention.
- MRCP does not actively distend the biliary ductal system with contrast.
- MRCP has worse spatial resolution compared to ERCP.
Choledochal Cysts
What are they?
What is the classification system?
When do they usually get diagnosed? Clinical presentation?
Treatment?
Contrast to biliary hamartomas.
- Choledochal cysts are thought to represent a heterogeneous group of diseases with a common end pathway of intrahepatic or extrahepatic biliary ductal dilation.
- The Todani system divides the cysts into types I-V based on their number, distribution, and morphology.
- Most choledochal cysts are diagnosed in childhood, but less commonly may be a new diagnosis for an adult. Clinically, choledochal cysts can present with nonspecific abdominal pain or may be found incidentally.
- Choledochal cysts are often resected due to increased cholangiocarcinoma risk, which can be as high as 25%.
- In contrast to biliary hamartomas, choledochal cysts do communicate with the biliary tree.
Todani Classification for Choledochal Cysts
type I: most common, accounting for 80-90% 1 (this type can present in utero)
Ia: dilatation of extrahepatic bile duct (entire)
Ib: dilatation of extrahepatic bile duct (focal segment)
Ic: dilatation of the common bile duct portion of extrahepatic bile duct
type II: true diverticulum from extrahepatic bile duct
type III: dilatation of extrahepatic bile duct within the duodenal wall (choledochocoele)
type IV: next most common
IVa: cysts involving both intra and extrahepatic ducts
IVb: multiple dilatations/cysts of extrahepatic ducts only
type V: multiple dilatations/cysts of intrahepatic ducts only (Caroli disease)
What is the most common type of choledochal cyst?
- A type I choledochal cyst, representing extrahepatic dilation of the common bile duct, is the most common type of extrahepatic cyst.
Caroli Disease
What is it? Possible association?
What is Carolie syndrome?
Imaging characteristic?
- Caroli disease represents saccular dilation of the intrahepatic bile ducts, which may be segmental or diffuse.
- Caroli disease may be associated with polycystic kidneys.
- Caroli syndrome is Caroli disease plus hepatic fibrosis.
- The central-dot sign describes the small branches of the portal vein and hepatic artery bridging the dilated bile ducts, which look like a central dot on contrast-enhanced CT.
Biliary anatomic variants
What are the significance of:
Low insertion of cystic duct?
Aberrant right posterior duct?
- Low insertion of the cystic duct
- With a low insertion of the cystic duct, the surgeon may misidentify the common duct as the cystic duct if the patient undergoes cholecystectomy, possibly leading to inadvertent common duct ligation.
- Aberrant right posterior duct
- An aberrant right posterior duct is only important if the patient is a right hepatic lobe liver donor, as the two right hepatic ducts need to be anastomosed separately in the recipient.
Criteria for acute cholecystitis
- Gallbladder wall thickening >3 mm (a nonspecific finding).
- Pericholecystic fluid or inflammatory changes in the pericholecystic fat.
- Gallbladder hyperemia.
- Gallbladder calculi (although not all gallstones are radiopaque; ultrasound is more sensitive).
This is typically diagnosed with US and the criteria is similar
What are the complications of acute cholecystitis?
- gangrenous cholecystitis
- gallbladder perforation
- emphysematous cholecystitis.
Gangrenous cholecystitis
How does it occur?
Imaging?
Treatment?
- Due to increased intraluminal pressure, leading to gallbladder wall ischemia.
- On imaging, the gallbladder wall thickening may be notably asymmetric and intraluminal membranes may be present.
- Due to the increased risk of perforation, treatment is emergent cholecystectomy or cholecystostomy.
Acute Gallbladder Perf
Mortality?
What can occur in subacute perf?
- Very high mortality due to generalized bile peritonitis.
- Subacute perforation may lead to a pericholecystic abscess and chronic perforation may cause a cholecystoenteric fistula.
Emphysematous Cholecystitis
Etiology?
Typical patient?
Treatment?
- It is a severe complication of acute cholecystitis caused by gas-forming bacteria. gas may be present either within the lumen or the wall of the gallbladder.
- The typical patient susceptible to emphysematous cholecystitis is an elderly diabetic.
- Treatment of emphysematous cholecystitis is most often emergent cholecystectomy or cholecystostomy, although treatment can be conservative in patients with a very high surgical risk.
Ascending Cholangitis
Classic presentation?
Imaging appearance?
Treatment?
- Obstruction of the biliary tree, most commonly due to choledocholithiasis, may cause ascending cholangitis, which presents with the clinical triad of fever, abdominal pain, and jaundice -Charcot’s triad.
- On imaging, the key finding is hyperenhancement and thickening of the walls of the bile ducts, often with a common bile duct stone present. On ultrasound, debris within the biliary system may be apparent.
- Initial treatment is antibiotics and fluid resuscitation. Endoscopic biliary intervention may be necessary if the patient does not respond to conservative management.
Primary Sclerosing Cholangitis
What is it?
Association? Epidemiology?
Imaging? What else does it look like?
Long-term complications?
Raffi Mnemonic: primary sClerosing CHolangitis - associated with CHolangioCA and ulcerative Colitis - Lead Pipe (mPoP-anca)
- Primary sclerosing cholangitis is idiopathic inflammation and destruction of bile ducts.
- PSC is associated with ulcerative colitis UC and is more common in males.
- Most (~75%) patients with PSC have UC, while only a few 4-5% of patients with UC have PSC.
- Biliary imaging shows a characteristic beaded, irregular appearance of the common bile duct and intrahepatic bile ducts.
- PSC appears similar to HIV-cholangiopathy, although cholangitis in HIV patients is more commonly associated with papillary stenosis.
- Long-term complications of PSC include cirrhosis, cholangiocarcinoma, and recurrent biliary infections. Cross-sectional imaging is better at evaluating for these complications compared to ERCP.
Biliary Cystadenoma
What is it? Presentation?
Does it communicate with the biliary system?
Imaging?
Malignant transformation? Presence of what should raise concern for a more dire dx?
- Biliary cystadenoma is a benign cystic neoplasm, occurring predominantly in middle-aged women. Biliary cystadenoma may be quite large at presentation and cause nonspecific symptoms such as abdominal pain, nausea, vomiting, and obstructive jaundice.
- Biliary cystadenoma does not communicate with the biliary system.
- On imaging, biliary cystadenoma appears as a large, multiloculated, cystic mass. The presence of septations distinguishes cystadenoma from a simple cyst. The septations may mimic an echinococcal cyst. In contrast to hepatic abscess or necrotic metastasis, a thick enhancing wall is not a feature of cystadenoma.
- Although benign, cystadenoma may uncommonly recur after resection.
- Malignant degeneration to biliary cystadenocarcinoma has been reported but is rare.
- The presence of a large solid component or thick calcification should raise concern for cystadenocarcinoma.
Normal Bild Duct Anatomy
Right hepatic + Left hepatic ducts -> Common hepatic duct + cystic duct -> common bilde duct + ventral pancreatic duct of Wirsung -> Ampulla of Vater and sphinctor of Oddi
