Liver, biliary tract and pancreas

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Chapter 4 Liver, biliary tract and pancreas

Methods of imaging the hepatobiliary system

2. Ultrasound (US):

a Transcutaneous

b Intraoperative

3. CT including:

a Routine ‘staging’ (portal venous phase) CT

b Triple phase ‘characterization’ CT

c CT cholangiography.

5. Endoscopic retrograde cholangiopancreatography (ERCP)

6. Percutaneous transhepatic cholangiography (PTC)

7. Operative cholangiography

8. Post-Operative (t-tube) Cholangiography

9. Angiography – diagnostic and interventional

10. Radionuclide imaging:

a Static, with colloid

b Dynamic, with iminodiacetic acid derivatives.

PLAIN FILMS

May be useful to demonstrate air within the biliary tree or portal venous system, opaque calculi or pancreatic calcification.

ULTRASOUND OF THE LIVER

Contraindications

Patient preparation

Not imperative, but fasting or restriction to clear fluids only required if the gallbladder is also to be studied.

Equipment

3–5-MHz transducer and contact gel. Selection of the appropriate pre-set protocol and positioning of focal zone will depend upon the type of machine, manufacturer and patient habitus.

Technique

1. Patient supine

2. Time-gain compensation set to give uniform reflectivity throughout the right lobe of the liver

3. Suspended inspiration

4. Longitudinal scans from epigastrium or left subcostal region across to right subcostal region. The transducer should be angled up to include the whole of the left and right lobes

5. Transverse scans, subcostally, to visualize the whole liver

6. If visualization is incomplete, due to a small or high liver, then right intercostal, longitudinal, transverse and oblique scans may be useful. Suspended respiration without deep inspiration may suffice for intercostal scanning. In patients who are unable to hold their breath, real-time scanning during quiet respiration is often adequate. Upright or left lateral decubitus positions are alternatives if visualization is still incomplete

7. Doppler studies:

a Pulsed Doppler

b Colour Doppler

c Power Doppler

d Doppler with US contrast media or ‘US echo-enhancing agents’

e Second harmonic Doppler with contrast

f Pulse inversion Doppler with contrast.

Additional views

Hepatic veins

These are best seen using a transverse intercostal or epigastric approach. During inspiration, in real time, these can be seen traversing the liver to enter the inferior vena cava (IVC). Hepatic vein walls do not have increased reflectivity in comparison to normal liver parenchyma. The normal hepatic vein waveform on Doppler is tri-phasic reflecting right atrial pressures. Power Doppler may be useful to examine flow within the hepatic segment of the IVC since it is angle-independent.

Portal vein

The longitudinal view of the portal vein is shown by an oblique subcostal or intercostal approach. Portal vein walls are of increased reflectivity in comparison to parenchyma. The normal portal vein blood flow is towards the liver. There is usually continuous flow but the velocity may vary with respiration.

Hepatic artery

This may be traced from the coeliac axis, which is recognized by the ‘seagull’ appearance of the origins of the common hepatic artery and splenic artery. There is normally forward flow throughout systole and diastole with a sharp systolic peak.

Common bile duct

See below in ‘Ultrasound of the gallbladder and biliary system’

Spleen

The spleen size should be measured in all cases of suspected liver disease or portal hypertension. 95% of normal adult spleens measure 12 cm or less in length, and less than 7×5 cm in thickness. The spleen size is commonly assessed by ‘eyeballing’ and measurement of the longest diameter.¹ In children, splenomegaly should be suspected if the spleen is more than 1.25 times the length of the adjacent kidney,¹ normal ranges have also been tabulated according to age and sex.²

1 Loftus W.K., Metreweli C. Ultrasound assessment of mild splenomegaly: spleen/kidney ratio. Pediatr. Radiol.. 1998;28(2):98-100.

2 Megremis S.D., Vlachonikolis I.G., Tsilimigaki A.M. Spleen length in childhood with US: normal values based on age, sex, and somatometric parameters. Radiology. 2004;231(1):129-134.

Further reading

Albrecht T., Hohmann J., Oldenburg A., et al. Detection and characterisation of liver metastases. Eur. Radiol.. 2004;8(14 Suppl):25-33.

Kim T.K., Jang H.J., Burns P.N., et al. Focal nodular hyperplasia and hepatic adenoma: differentiation with low-mechanical-index contrast-enhanced sonography. Am. J. Roentgenol.. 2008;190(1):58-66.

Kono Y., Mattrey R.F. Ultrasound of the liver. Radiol. Clin. North Am.. 2005;43(5):815-826.

Shapiro R.S., Wagreich J., Parsons R.B., et al. Tissue harmonic imaging sonography: evaluation of image quality compared with conventional sonography. Am. J. Roentgenol.. 1998;171:1203-1206.

Wilson S.R., Burns P.N. An algorithm for the diagnosis of focal liver masses using microbubble contrast-enhanced pulse-inversion sonography. Am. J. Roentgenol. 2006;186(5):1401-1412.

Ultrasound of the Gallbladder and Biliary System

Indications

1. Suspected gallstones

2. Right upper quadrant pain

4. Fever of unknown origin

5. Acute pancreatitis

6. To assess gallbladder function

7. Guided percutaneous procedures.

Contraindications

Patient preparation

Fasting for at least 6 h, preferably overnight. Water may be permitted.

Equipment

3–5-MHz transducer and contact gel. Selection of the appropriate pre-set protocol and positioning of focal zone will depend upon the type of machine, manufacturer and patient habitus. A stand-off may be used for a very anterior gallbladder.

Technique

1. The patient is supine.

2. The gallbladder can be located by following the reflective main lobar fissure from the right portal vein to the gallbladder fossa

3. Developmental anomalies are rare but the gallbladder may be intrahepatic or on a long mesentery

4. The gallbladder is scanned slowly along its long axis and transversely from the fundus to the neck leading to the cystic duct.

5. It must be re-scanned in the left lateral decubitus or erect positions because stones may be missed if only supine scans are used.

6. Visualization of the neck and cystic ducts may be improved by head down tilt.

The normal gallbladder wall is never more than 3-mm thick.

Additional views

Assessment of gallbladder function

1. Fasting gallbladder volume may be assessed by measuring longitudinal, transverse and antero-posterior (AP) diameters.

2. Normal gallbladder contraction reduces the volume by more than 25%, 30 min after a standard fatty meal. Somatostatin, calcitonin, indometacin and nifedipine antagonize this contraction.

Intrahepatic bile ducts

1. Left lobe: transverse epigastric scan

2. Right lobe: subcostal or intercostal longitudinal oblique.

Normal intrahepatic ducts are visualized with modern scanners. Intrahepatic ducts are dilated if their diameter is more than 40% of the accompanying portal vein branch. There is normally acoustic enhancement posterior to dilated ducts but not portal veins. Dilated ducts have a beaded branching appearance.

Extrahepatic bile ducts

1. The patient is supine or in the right anterior oblique position.

2. The upper common duct is demonstrated on a longitudinal oblique, subcostal or intercostal scan running anterior to the portal vein. The right hepatic artery is often seen crossing transversely between the two.

3. The common duct may be followed downwards along its length through the head of the pancreas to the ampulla and, when visualized, transverse scans should also be performed to improve detection of intraduct stones.

The segment of bile duct proximal to the junction with the cystic duct (the common hepatic duct) is 4 mm or less in a normal adult; 5 mm is borderline and 6 mm is considered dilated. The lower bile duct (common bile duct) is normally 6 mm or less. Distinction of the common hepatic duct from the common bile duct depends on identification of the junction with the cystic duct. This is usually not possible with US. Colour-flow Doppler enables quick distinction of bile duct from ectatic hepatic artery. In less than one-fifth of patients the artery lies anterior to the bile duct.

Post-cholecystectomy

There is disagreement as to whether the normal common duct dilates after cholecystectomy. Symptomatic patients and those with abnormal liver function tests should have further investigations if the common duct measures more than 6 mm.

Further reading

Foley W.D., Quiroz F.A. The role of sonography in imaging of the biliary tract. Ultrasound Q.. 2007;23(2):123-135.

Ultrasound of the Pancreas

Indications

1. Suspected pancreatic tumour

2. Pancreatitis or its complications

3. Epigastric mass

4. Epigastric pain

6. To facilitate guided biopsy and/or drainage.

Contraindications

Patient preparation

Nil by mouth, preferably overnight.

Equipment

3–5-MHz transducer and contact gel. Selection of the appropriate pre-set protocol and positioning of focal zone will depend upon the type of machine, manufacturer and patient habitus. A stand-off may be required in thin patients.

Technique

1. The patient is supine.

2. The body of the pancreas is located anterior to the splenic vein in a transverse epigastric scan.

3. The transducer is angled transversely and obliquely to visualize the head and tail.

4. The tail may be demonstrated from a left intercostal view using the spleen as an acoustic window.

5. Longitudinal epigastric scans may be useful.

6. The pancreatic parenchyma increases in reflectivity with age, being equal to liver reflectivity in young adults.

7. Gastric or colonic gas may prevent complete visualization. This may be overcome by left and right oblique decubitus scans or by scanning with the patient erect. Water may be drunk to improve the window through the stomach and the scans repeated in all positions. One cup is usually sufficient. Degassed water is preferable.

The pancreatic duct should not measure more than 3 mm in the head or 2 mm in the body.

Endoscopic US (see p. 81) and intra-operative US are useful adjuncts to transabdominal US. EUS may be used to further characterize and biopsy pancreatic mass lesions. Intra-operative US is used to localize small lesions (e.g. islet cell tumours prior to resection).

Further reading

Eloubeidi M.A., Jhala D., Chhieng D.C., et al. Yield of endoscopic ultrasound-guided fine-needle aspiration biopsy in patients with suspected pancreatic carcinoma. Cancer. 2003;99(5):285-292.

Rizk M.K., Gerke H. Utility of endoscopic ultrasound in pancreatitis: a review. World J. Gastroenterol.. 2007;13(47):6321-6326.

Computed Tomography of the Liver and Biliary Tree

Contraindications

Contraindication to iodinated intravenous (i.v.) contrast medium (contrast-enhanced computed tomography (CECT)) – see Chapter 2.

Technique

Single-phase (portal phase) contrast-enhanced CT

This is the technique for the majority of routine liver CT imaging. The liver is imaged during the peak of parenchymal enhancement, i.e. when contrast-medium-laden portal venous blood is perfusing the liver. This begins about 60–70 s after the start of a bolus injection. Oral contrast may be given but is not necessary if only the liver is being investigated. Slice thickness will depend upon the CT scanner specification but should be 5 mm or less.

Multi-phasic contrast-enhanced CT

The fast imaging times of helical/multi-slice CT enable the liver to be scanned multiple times after a single bolus injection of contrast medium. Most liver tumours receive their blood supply from the hepatic artery, unlike the hepatic parenchyma, which receives 80% of its blood supply from the portal vein. Thus liver tumours (particularly hypervascular tumours) will be strongly enhanced during the arterial phase (beginning 20–25 s after the start of a bolus injection) but of similar density to enhanced normal parenchyma during the portal venous phase. Some tumours are most conspicuous during early-phase arterial scanning (25 s after the start of a bolus injection), others later, during the late arterial phase 35 s after the start of a bolus injection. Thus a patient who is likely to have hypervascular primary or secondary liver tumours should have an arterial phase scan as well as a portal venous phase CT scan (see above). Early and late arterial phase with portal venous phase is appropriate for patients with suspected hepatocellular cancer (triple phase). In general, late arterial and portal venous scans are appropriate to investigate suspected hypervascular metastases, although an alternative strategy would be to perform an unenhanced scan followed by a portal venous phase scan.

Haemangiomas often show a characteristic peripheral nodular enhancement and progressive centripetal ‘fill-in’. After the initial dual- or triple-phase protocol, delayed images at 5 and 10 min are obtained through the lesion.

COMPUTED TOMOGRAPHIC CHOLANGIOGRAPHY

Magnetic resonance (MR) cholangiography is non-invasive but sometimes fails to display the normal intra-hepatic ducts. Multidetector CT cholangiography can be useful in this instance. With this technique the biliary tree is opacified using an i.v. cholangiographic agent. Isotropic data from 0.625 mm section thickness can be reconstructed to provide high-resolution three-dimensional images.

Contraindications

Allergy to iodinated contrast agents.

Indications

1. Screening for cholelithiasis

2. Pre-operative screening of anatomy

3. Supected traumatic bile-duct injury

4. Other biliary abnormalities, e.g. cholesterol polyps, adenomyomatosis and congenital abnormalities.

Technique

1. Patient fasted for at least 6 h

2. 100 ml i.v. cholangiographic agent, e.g. meglumine iotroxate, infused for 50 min as a biliary contrast ¹ or iodipamide meglumine 52%- 20 ml diluted with 80 ml of normal saline infused over 30 min.²

3. CT scans should be obtained at least 35 min after infusion of contrast agent.²

1 Hashimoto M., Itoh K., Takeda K., et al. Evaluation of biliary abnormalities with 64-channel multidetector CT. Radiographics. 2008;28(1):119-134.

2 Schindera S.T., Nelson R.C., Paulson E.K., et al. Assessment of the optimal temporal window for intravenous CT cholangiography. Eur. Radiol.. 2007;17(10):2531-2537.

Further reading

Francis I.R., Cohan R.H., McNulty N.J., et al. Multidetector CT of the liver and hepatic neoplasms: effect of multiphasic imaging on tumor conspicuity and vascular enhancement. Am. J. Roentgenol.. 2003;180(5):1217-1224.

Erratum in. Am. J. Roentgenol.. 2003;181(1):283.

Oto A., Tamm E.P., Szklaruk J. Multidetector row CT of the liver. Radiol. Clin. North Am.. 2005;43(5):827-848.

Computed Tomography of the Pancreas

Indications

1. Epigastric pain

2. Obstructive jaundice

3. Suspected pancreatic malignancy

4. Acute pancreatitis and its complications

5. Chronic pancreatitis and its complications.

Contraindications

2. Contraindication to iodinated intravenous contrast medium – see Chapter 2.

Technique

1. Negative (e.g. water) or positive (e.g. iodinated) oral contrast may be given. A positive oral contrast agent is contraindicated if CT angiography is to be performed. Volume and timing of oral contrast agent will depend upon whether it is necessary to opacify distal bowel loops.

2. Venous access is obtained.

3. The patient is supine on the CT scanner.

4. A scout view is obtained.

5. A non-contrast enhanced examination can be performed initially if detection of subtle calcification is required.

6. The volume of i.v. contrast used will depend upon the type of scanner. Faster acquisition will necessitate a smaller volume of contrast, generally 100 ml or less. The timing of the scan in relation to i.v. contrast will depend upon the clinical question. Pancreatic phase enhancement (40 s after commencement of bolus injection) is necessary for optimum contrast differences between pancreatic adenocarcinoma and normal pancreatic tissue, with portal venous phase scans included in the protocol to investigate hepatic metastatic disease. Islet cell tumours and their metastases may show avid enhancement on arterial phase scans and become isodense with normal pancreatic tissue on portal phase scans. A portal phase scan is generally necessary to investigate flow and the relationship of the tumour to the portal vein.

7. The volume and strength of the i.v. contrast will depend upon the speed of the scanner.

8. Slice thickness should be 3 mm or less.

Further reading

Fletcher J.G., Wiersema M.J., Farrell M.A., et al. Pancreatic malignancy: value of arterial, pancreatic, and hepatic phase imaging with multi-detector row CT. Radiology. 2003;229(1):81-90.

Goshima S., Kanematsu M., Kondo H., et al. Pancreas: optimal scan delay for contrast-enhanced multi-detector row CT. Radiology. 2006;241(1):167-174.

Magnetic Resonance Imaging of the Liver

Indications

1. Lesion detection particularly prior to hepatic resection for hepatic metastatic disease.

2. Lesion characterization following detection by CT or US.

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