CT of the Hepatobiliary System and PancreasKelly Pollak, MS3

Module Outline

Part I: Liver Parenchyma

Part II: Biliary Tract

Part III: Gallbladder

Part IV: Pancreas

Part I:Liver Parenchyma

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

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

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:

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

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

Normal liver, unenhanced CTNote the areas of hypodensity (arrows), which are normal hepatic and portal veins coursing through the liver.

Photo, Armstrong et al, 2004

Normal liver CT, enhancedNote the increased density of the hepatic and portal veins. Also note the adjacent stomach, which is filled with contrast.

Photo, Armstrong et al. 2004

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

Shape

Normal liver edges should be smooth:

In Cirrhosis, liver edges have a nodular contour:

L=liver, C=caudate lobe

Photo Lee et al, 1998

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

CT Detection of Hemangioma

Photos, Armstrong et al, 2004

Early arterial phase Later (redistribution) phase

Homogeneity – Hepatic NeoplasmsContrast 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).

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.

Appearance of various liver neoplasms during early arterial phase

Carcinoid tumor metastasis is hypervascular

Primary hepatocellular carcinoma is hypervascular (hypodense area is necrosis)

Hypovascular metastasis due to colon cancer

Hypovascular primary cholangiocarcinoma

Homogeneity – Cysts and AbscessesContrast 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

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.

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

Hepatic Laceration

Photo, www.e-radiography.net

Quiz time

Identify and localize the following liver abnormalities on CT

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

AnswerThere 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.

What is the abnormality?

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

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

Image, www.learningradiology.com

Answer

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

Part II:Biliary Tract CT

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

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).

Appearance on CT, cont’d.

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.

CHD

Portal vein

Hepatic artery

Portal vein forming

Common hepatic duct forming

Appearance on CT, cont’d.

Most inferior: Gallbladder appears, left lobe of liver starts to disappear

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

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

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

Photo Armstrong et al, 2004

Note the greatly enlarged intrahepatic bile ducts. As expected, they are hypodense compared to the liver parenchyma.

Part IIIGallbladder

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

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

Systematic Approach to Observing Gallbladder on CTObserve 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

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

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)

Photo Novelline RA, 2004

Notice the rim of enhancement around the gallbladder, indicating calcification.

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

Part IVPancreas

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

Portal vein

Sup mesenteric vein

Sup mesenteric artery

Pancreas

Spleen

Duodenum

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

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.

Locating the Body of the Pancreas

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.

Pancreatic duct

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

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

Left click on the image to play

Coronal views of the body illustrating the various parts of the pancreas

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).

duodenum

Systematic Approach to Viewing the PancreasThings 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

Abnormalities – Acute Pancreatitis

Typical Presentation: Size/shape: swollen,

diffuse enlargement Density: may not

enhance w/contrast (signals necrosis)

Margins: ill-defined Surroundings:

inflammation The pancreas is diffusely enlarged and there is inflammation in the surrounding area, notably around the kidneys

Photo Lee et al, 1998

inflammation

Abnormalities - Acute Pancreatitis - PseudocystsPresentation: 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.

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

Abnormalities – Pancreatic CarcinomaMost 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.

Quiz Time

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

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

Can you tell what the abnormality is?

Answer

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

Inflammation

Can you identify the abnormality?

Photo, Lee et al, 1998

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

References

Armstrong, P, et al. Diagnostic Imaging, 5th Ed. Blackwell Publishing, Malden. 2004.

Brant WE and Helms CA. Fundamentals of Diagnostic Radiology, 2nd Ed. Williams and Wilkins, Baltimore. 1999.

Lee, JKT, et al. Computed Body Tomography with MRI Correlation, 3rd Ed. Lippincott-Raven, Philadelphia. 1998.

Netter FH, Atlas of Human Anatomy, 3rd Ed. Icon Learning Systems, Teterboro. 2003.

Novelline RA. Squire’s Fundamentals of Radiology, 6th Ed. Harvard University Press, Cambridge. 2004.

www.learningradiology.comwww.e-radiography.net