liver & hepatobiliary.pdf

Imaging of the Liver and Biliary Tract DR.AISHA DABNOUN RADIODIAGNOSIS SIRTE UNIVERSITY Imaging of the Liver and Biliary Tract The hepatobiliary system is composed of the liver, gallbladder, and bile ducts. The liver produces bile, which is a fluid made of cho...

Imaging of the Liver and Biliary Tract DR.AISHA DABNOUN RADIODIAGNOSIS SIRTE UNIVERSITY Imaging of the Liver and Biliary Tract The hepatobiliary system is composed of the liver, gallbladder, and bile ducts. The liver produces bile, which is a fluid made of cholesterol, phospholipids, conjugated bilirubin, bile salts, electrolytes, and water. Bile, which assists in digestion and helps eliminate waste products, is stored in the gallbladder. The hepatobiliary system can be affected by infections, cysts, solid masses, ischemia, and mechanical flow obstruction, which mandate the presence of reliable imaging tests to determine the etiology. Imaging methods: The methods that evaluate structural changes in the liver and biliary tract includes: 1. Ultrasonography (U/S): Advantages: Low cost , No radiation dose , Widespread availability and Fast. 1. CT scan. 2. MRI including magnetic resonance cholangiopancreatography (MRCP).  Ultrasonography(U/S): 1. Trauma with concern for hepatobiliary injury. 2. Concern for biliary obstruction. 3. Concern for hepatic abscess. 4. Evaluation for cholecystitis. 5. Signs and symptoms of liver failure/chronic liver disease. 6. Evaluation of hepatic steatosis. 7. Screening for neonates with abnormalities noted on prenatal US (biliary atresia). 8. known cirrhosis to evaluate for hepatocellular carcinoma (HCC). Exam technique: Positioning: Individual: Access to the RUQ abdomen. 1. Size: Liver: Normal liver span is usually < 16 cm in the midclavicular line (may vary by sex and body size). Variant anatomy includes a Riedel lobe, caudate lobe papillary process, and accessory hepatic lobe(s). Gallbladder: Transverse dimension: 4 cm Length is more variable: generally ≤ 10 cm Wall thickness should be ≤ 3 mm. 2. Echogenicity: Liver parenchyma: Homogeneous in echotexture Usually isoechoic (same brightness) or slightly hyperechoic (brighter or white on the screen) as compared with the right kidney Gallbladder is anechoic (black on the screen). 3. Position: Liver: inferior to the right hemidiaphragm Gallbladder: found in gallbladder fossa (under the right lobe of the liver) Extrahepatic ducts: The common hepatic duct and the cystic duct (from the gallbladder) form the common bile duct. Common bile duct (CBD) : should be < 6 mm in diameter in those 60 years of age or younger. Add 1 mm for every decade after 60 years of age (e.g., 7 mm for 70s, 8 mm for 80s). Postcholecystectomy status can cause enlargement of the CBD, termed the "reservoir effect." Anatomy of the liver and the biliary system Normal liver ultrasound showing a homogeneous parenchyma Liver staetosis(fatty liver): increase echogenesity and attenuation(hyperechogenic), signal toward the fat. Liver Cirrohosis: surface nodularity, overall coarse and heterogeneous echotexture, and segmental hypertrophy/atrophy. Liver Trauma: showing a small hyperdense lesion in the liver indicating contusion. Normal Gallbladder ultrasound Gallbladder(stone): single large radiopaque stone with posterior acoustic shadowing. Cholecystitis: inflammation of gall bladder, increase wall thickness >3mm Biliary atresia:is a congenital biliary disorder, which is characterized by an absence or severe deficiency of the extrahepatic biliary tree. It is one of the most common causes of neonatal cholestasis, often causing cirrhosis immediately and leading to death and accounts for over half of children who undergo liver transplantation. By Ultrasound: echogenic fibrous tissue anterior to the portal vein: Triangular cord sign represents ductal remnant of extrahepatic bile duct.  Computed tomography(CT): Indications: Medical indications: 1. Follow-up of suspicious US imaging: 2. Hypoechoic/hyperechoic lesions 3. Concern for vascular pathology 4. Contour deformities 5. Bile duct dilation 6. Fluid collections Malignancy: 1. Evaluate initial staging of HCC 2. Surveillance for recurrence of disease  Major trauma: 1. Evaluation of hepatic parenchyma. 2. Evaluation for hepatic hemorrhage +/– active extravasation on delayed images. 3. Concern for subtle pathology not seen on US. Advantages: Excellent resolution of anatomical detail A normal contrast-enhanced CT scan of the liver: K: kidney L: liver P: pancreas St: stomach Sp: spleen Magnetic resonance imaging(MRI): Advantage: 1. Provides higher level of imaging and detail of fluid, enhancement, and soft tissue. 2. Can be used for evaluation of pregnant individuals. Sequences: -T1 weighted image -T2 weighted image -T1 fat saturation Axial T1 in phase Axial T1out phase Axial T2 Axial T1 fat sat Indications: Detailed evaluation of hepatic lesions: Hemangiomas Cysts HCC Metastasis Indeterminate lesions noted incidentally on US and CT Magnetic resonance cholangiopancreatography (MRCP) Used for those with suspected pancreaticobiliary disease and with conditions that preclude endoscopic retrograde cholangiopancreatography (ERCP) Fat-suppressed 2-D or 3-D heavily T2W sequences 3-D reconstruction by using a maximum intensity projection (MIP) patients fast for 3 hours before the MRCP MRCP MRI sequences: -T1 weighted image: fluid (e.g. urine, CSF): low signal intensity (black) muscle: intermediate signal intensity (grey) fat: high signal intensity (white) -T2weighted image: fluid (e.g. urine, CSF): high signal intensity (white) muscle: intermediate signal intensity (grey) fat: high signal intensity (white) -T1 fat SAT: Fat suppression (or attenuation or saturation) is a tweak performed on many T1 weighted sequences, to suppress the bright signal from fat.  MRI Abdominal views: Axial view: sagittal & coronal view: