1. CT of the Hepatobiliary System and Pancreas
Kelly Pollak, MS3

2. Module Outline Part I: Liver Parenchyma Part II: Biliary Tract
Part III: Gallbladder
Part IV: Pancreas

3. Part I:
Liver Parenchyma

4. Normal Anatomy (as seen on un-enhanced CT):
CT of the Liver
Normal Anatomy (as seen on un-enhanced CT):
Hepatic parenchyma high density (liver > spleen > muscle)
Homogenous appearance of parenchyma
Hepatic veins and portal veins branch through parenchyma as lower density structures

5. Hepatic Anatomy – Segments
The liver is composed of right and left lobes (separated anatomically by a vertical plane through the IVC, gallbladder fossa, and middle hepatic vein), and a total of 8 segments, which are divided by main hepatic veins and portal veins (inferiorly)
Each segment has its own vascular supply and biliary drainage
The segments are numbered clockwise when the liver is viewed ventrally
It is useful to learn the individual segment locations on CT in order to localize masses

6. Hepatic Segments as seen on CT
Superior liver: Left, middle, and right hepatic veins (arrows) can be used to demark segments II, IV, VII, and VIII, and the IVC can be used to locate I (which lies next to it) :
Inferior liver: Fissure for falciform ligament appears (block arrow) and the left, middle, and right hepatic veins (black arrows) now can be used to demark segments III, IV, V, VI:

7. Role of intravenous contrast in liver CT
Increases the density of normal liver parenchyma
Emphasizes difference between parenchyma and poorly enhancing lesions
Scans at different time intervals after contrast administration allow visualization of different phases of opacification, enabling distinction of lesions such as hemangiomas and neoplasms

8. IV Contrast Distribution Over Time
Three phases of hepatic enhancement post-contrast injection:
Vascular: Rapid rise in aortic enhancement and gradual hepatic enhancement
Redistribution: Contrast diffuses from central blood compartment to extravascular liver compartment (increase in hepatic enhancement and decrease in aortic)
Equilibrium: Aortic and hepatic enhancement gradually decline as contrast diffuses back into central vascular compartment and to muscle and fat compartments

9. Normal liver, unenhanced CT Note the areas of hypodensity (arrows), which are normal hepatic and portal veins coursing through the liver.
Photo, Armstrong et al, 2004

10. Normal liver CT, enhanced Note the increased density of the hepatic and portal veins. Also note the adjacent stomach, which is filled with contrast.
Photo, Armstrong et al. 2004

11. Systematic Approach to Examining Liver Parenchyma
Observe for:
Overall shape
Should have smooth edges
cirrhosis
Homogeneity of parenchyma
Parenchyma should be homogenous. This helps in determining:
Liver metastases
Primary tumors
Abscesses
Cysts
Trauma

12. Shape Normal liver edges should be smooth:
In Cirrhosis, liver edges have a nodular contour:
Photo Lee et al, 1998
L=liver, C=caudate lobe

13. Homogeneity: Primary Benign Liver Masses
Contrast enhancement helps determine presence of hemangiomas:
In early vascular phase, hemangiomas are lower density than surrounding parenchyma
During later phases, hemangiomas appear higher density than surrounding parenchyma

14. CT Detection of Hemangioma
Early arterial phase
Later (redistribution) phase
Photos, Armstrong et al, 2004

15. Homogeneity – Hepatic Neoplasms
Contrast enhancement also helps identify hepatic neoplasms:
Neoplasms, both metastases and primary neoplasms, can be hyper- or hypovascular. Hypervascular enhance brightly during early arterial phase, whereas hypovascular are hypodense in the early arterial phase (but enhance during the redistribution phase).

16. Homogeneity – Hepatic Neoplasms
Knowing which lesions are hypervascular and which are hypovascular can help identify the type of neoplasm, but the key thing is that they are of a different density than the surrounding liver parenchyma.
Hypervascular examples: carcinoid tumor mets, hepatocellular carcinoma
Hypovascular examples: colon cancer mets, cholangiocarcinoma
Most mets, as opposed to primary tumors, are rounded and well demarcated from surrounding parenchyma on enhanced scans.

17. Appearance of various liver neoplasms during early arterial phase
Hypovascular metastasis due to colon cancer
Hypovascular primary cholangiocarcinoma
Carcinoid tumor metastasis is hypervascular
Primary hepatocellular carcinoma is hypervascular (hypodense area is necrosis)

18. Homogeneity – Cysts and Abscesses
Contrast also helps identify cysts and abscesses, which contain collections of fluid
Cysts: Have well-defined margins and are low density (attenuation similar to water), unenhancing lesions
Note: cysts below ~ 1cm in size cannot be reliably distinguished from neoplasms
Abscesses: appear similar to cysts, but usually their walls are thicker (due to surrounding edema) and more irregular
May not be able to distinguish from a necrotic tumor

19. Hepatic Cyst vs. Abscess
Photo, Novelline et al, 2004
Photo Lee et al, 1998
Left, hepatic cyst; right, hepatic abscess. Note the thickened wall of the abscess.

20. Homogeneity – Liver Trauma
Trauma can cause hepatic parenchymal lacerations, subcapsular and intrahepatic hematomas
All are low-density areas relative to contrast-enhanced parenchyma
Leakage of contrast = active bleeding

21. Hepatic Laceration
Photo,

22. Identify and localize the following liver abnormalities on CT
Quiz time
Identify and localize the following liver abnormalities on CT

23. What is the abnormality, and what segment is it located in?

24. Answer
There is hepatocellular carcinoma in the second segment of the liver. Notice how it enhances here during an early arterial phase scan (hypervascular) and is less well defined than metastases would appear.

25. What is the abnormality?

26. Answer
This represents cirrhosis of the liver. Note the nodular appearance of the liver, instead of the usual smooth edges characteristic of a normal, healthy liver.

27. What is the abnormality, and in what segment is it located?
Image,

28. Answer
There is a laceration from a traumatic injury to the liver, located in segment VII.

29. Part II:
Biliary Tract CT

30. Normal Anatomy
Bile (green tract in image) flows thru biliary tree from periphery of liver to duodenum
Biliary tree: intrahepatic ducts, common hepatic duct (CHD), and common bile duct (CBD)
Intrahepatic ducts course from periphery centrally to hepatic hilum
Join to form centrally located main left and right hepatic ducts
Portal triad: intrahepatic ducts are located adjacent to portal veins and hepatic arteries
Left and right hepatic ducts join to form common hepatic duct near liver margin
Porta Hepatis – CHD runs with portal vein and hepatic artery
CHD joins cystic duct to form CBD inferior to the liver

31. Appearance on CT
Superior slices: With contrast, intrahepatic ducts appear as hypodense areas in the periphery of the parenchyma (look very closely to see); they appear near portal veins and hepatic arteries, which enhance.
More inferior slices: As move inferiorly, right and left hepatic ducts appear centrally (hypodensities, arrows), adjacent to the right and left portal veins (brightly enhancing, block arrows).

32. Appearance on CT, cont’d.
Common hepatic duct forming
Further inferiorly: The left and right main hepatic ducts fuse to form the common hepatic duct, and the left and right portal veins fuse to form the portal vein.
Even more inferior: Common hepatic duct (and porta hepatis) appears.
Portal vein forming
CHD
Hepatic artery
Portal vein

33. Appearance on CT, cont’d.
Most inferior: Gallbladder appears, left lobe of liver starts to disappear

34. Click through the following slides to familiarize yourself with the progression of the biliary system superior-to-inferior within the liver

45. Systematic Approach to Examining Biliary Tract on CT
Things to look at:
Bile duct size
Peripheral ducts: mean diameter=1.8mm
Central ducts: mean diameter=2mm
Common hepatic duct: mean diameter=2.8mm
Bile duct wall
Wall enhances to varying degrees with IV contrast (insensitive indicator of pathology)
Thickness important; normal 1-1.5mm
Density
Normal is near water density

46. Abnormalities – Biliary Dilatation
Dilated biliary ducts are a feature of biliary obstruction, common causes of which include:
Impacted stone in CBD
Carcinoma in head of pancreas
Carcinoma in ampulla of Vater
Note the greatly enlarged intrahepatic bile ducts. As expected, they are hypodense compared to the liver parenchyma.
Photo Armstrong et al, 2004

47. Part III
Gallbladder

48. Gallbladder Anatomy Gallbladder is a storage organ
It is located within the gallbladder fossa of the liver, which separates the right and left lobes of the liver
Its wall is normally thin, and it is usually filled with bile

49. Gallbladder Appearance on CT
Sits in fossa between right and left lobes of liver
Density: fluid density, free of particulate debris
Usually distended with bile

50. Systematic Approach to Observing Gallbladder on CT
Observe for three things: size, density, and surroundings:
Size:
Overall size: Diameter 2-5cm
Wall size: 3mm thickness
Density: Homogenous, fluid density
Surroundings: No surrounding edema should be present

51. Abnormalities – Acute Cholecystitis
Size: distended gallbladder, possibly thickened wall, subserosal edema. CHD or CBD may be dilated if they are occluded.
Density: gallstones may be visible (usually hyperintense spots); high density bile
Surroundings: pericholecystic stranding and fluid (indicating inflammation)
Notice the thickened gallbladder wall (arrowheads) and dilated CHD.
Photo Lee et al, 1998

52. Abnormalities – Chronic Cholecystitis
Size:
Small, irregularly shaped overall
Wall: dystrophic calcification (aka, Porcelain Gallbladder)
CHD or CBD may be dilated if they are occluded
Density:
Bile w/particulate matter and high concentration of calcium cmpds appears radio-opaque (aka, Milk of Calcium Bile)
Notice the rim of enhancement around the gallbladder, indicating calcification.
Photo Novelline RA, 2004

53. Abnormalities – Gallbladder Carcinoma
Major manifestations:
Focal/diffuse wall thickening (hard to distinguish from chronic cholecystitis)
Discrete intraluminal mass
Shape: well-differentiated, papillary
Density: hypointense
Mass replacing the gallbladder (most common)
Shape: irregular
density: heterogeneous enhancement 2° to tumor necrosis)
All may demonstrate dilated bile ducts 2° to obstruction and/or tumor extension to adjacent structures
Notice here the distinct mass within the gallbladder wall.
Here the neoplasm appears to be replacing the normal gallbladder (the gallbladder wall also appears thickened).
Photos Lee et al, 1998

54. Part IV
Pancreas

55. Pancreas Anatomy Pancreas runs obliquely Retroperitoneal
Tail: next to spleen
Body:
Ant to left kidney
Ant to sup mesenteric a.
Head:
Med to 2nd part of duodenum
Spleen
Portal vein
Pancreas
Sup mesenteric vein
Sup mesenteric artery
Duodenum

56. Pancreas on CT
Need several slices to identify all parts of pancreas (due to its oblique orientation)
Important to know and make use of surrounding anatomy to locate the pancreas

57. Locating the Tail of the Pancreas
The tail lies next to the spleen and ventral to the splenic vein (SV). It is the first part to come into view when advancing through slices superior-to-inferior.

58. Locating the Body of the Pancreas
Pancreatic duct
The body next comes into view. One can recognize it by its tongue-like shape, and by the hypodense pancreatic duct that runs horizontally through it.

59. Locating the Head of the Pancreas on CT
The head lies next to the second part of the duodenum and actually wraps around and lies dorsal to the SMV and SMA:
CBD=common bile duct; SMV=superior mesenteric vein; SMA=superior mesenteric artery; D=duodenum; P=pancreas head

60. Use the following video of successive abdominal CT cross-sectional slices to familiarize yourself with locating the various parts of the pancreas

61. Left click on the image to play

62. Coronal views of the body illustrating the various parts of the pancreas
duodenum
spleen
tail
head
Can you also see the lesions in the liver? These are hypovascular metastases (this is the same patient from the prior movie).

63. Systematic Approach to Viewing the Pancreas
Things to observe:
Size and shape:
Tongue-shaped,12-15cm long
Diameters:
Head: max 3cm
Body: max 2.5cm
Tail: max 2.0cm
Duct: 3-4mm, tapering at tail
Density: similar to liver parenchyma
Margins: normally appear fluffy

64. Abnormalities – Acute Pancreatitis
Typical Presentation:
Size/shape: swollen, diffuse enlargement
Density: may not enhance w/contrast (signals necrosis)
Margins: ill-defined
Surroundings: inflammation
Photo Lee et al, 1998
The pancreas is diffusely enlarged and there is inflammation in the surrounding area, notably around the kidneys
inflammation

65. Abnormalities - Acute Pancreatitis - Pseudocysts
Presentation:
Size: enlarged to varying degrees (cyst can be up to several cm in diameter)
Shape: cyst is usually rounded and well-circumscribed
Density: cyst is hypodense, thick walled area within pancreas
Surroundings: peripancreatic fluid collections/inflammation may be present
Note the large pseudocyst in the head of the pancreas.

66. Abnormalities - Chronic Pancreatitis
Size and shape:
Pancreas: may enlarge generally or focally, or may appear atrophied
Duct: may be enlarged and irregular
Density: areas of fibrosis and calcification appear hyperintense w/contrast
Surroundings: surrounding fluid collections may not be present
Chronic pancreatitis, demonstrating numerous areas of calcification

67. Abnormalities – Pancreatic Carcinoma
Most neoplasms are adenocarcinomas occurring in the head (2/3)
Size and shape:
tumor size can be variable; focal mass deforms the outline of the gland
Pancreatic duct may be dilated 2° to obstruction by tumor
Density:
tumor of lower density than pancreatic tissue on enhanced CT
Surroundings:
tumor spread to lymph nodes, liver, surrounding vessels common
A tumor in the body of the pancreas has greatly deformed the shape of the pancreas.

68. Quiz Time

69. Can you find the pancreas? What part is located here?

70. Answer
The pancreatic body and tail are seen on this slice. Notice the tail lying next to the spleen. Also note the pancreatic duct running through the body.
Pancreatic duct
tail
spleen

71. Can you tell what the abnormality is?

72. Answer
This is acute pancreatitis. Note the diffusely enlarged pancreas and considerable inflammation surrounding it (especially apparent around the kidneys)
Inflammation

73. Can you identify the abnormality?
Photo, Lee et al, 1998

74. Answer
There is a pancreatic pseudocyst in the head of the pancreas. There is not a lot of peripancreatic inflammation present, largely because this represents a pseudocyst that has been resolving over time.
Pseudocyst

75. References
Armstrong, P, et al. Diagnostic Imaging, 5th Ed. Blackwell Publishing, Malden
Brant WE and Helms CA. Fundamentals of Diagnostic Radiology, 2nd Ed. Williams and Wilkins, Baltimore
Lee, JKT, et al. Computed Body Tomography with MRI Correlation, 3rd Ed. Lippincott-Raven, Philadelphia
Netter FH, Atlas of Human Anatomy, 3rd Ed. Icon Learning Systems, Teterboro
Novelline RA. Squire’s Fundamentals of Radiology, 6th Ed. Harvard University Press, Cambridge