So let's review the intrahepatic biliary system a little bit as well.
The intrahepatic bile duct should really be less than about 3 millimeters
or so in diameter. Most commonly this can be dilated
due to choledocholithiasis or obstruction of the common bile duct
with a stone or another abnormality such as sludge.
They can become dilated due to any kind mass lesion as well
which obscures the central biliary system.
Patients that have a central obstructing lesion
often present with jaundice and pruritis.
So those are the two most common findings of a patient
presenting with a central obstructing lesion.
So this is an example of intrahepatic biliary ductal dilatation.
We can see here two ultrasound images,
so here we have what look like dilated ducts.
You can see that on the Doppler you can tell
which one is the portal vein versus which one is a bile duct.
Although we had mentioned ways of telling the difference
where the portal vein has an echogenic rim around it and the bile duct doesn't,
sometimes it can be difficult especially when the bile ducts are dilated
so the other way of telling is to place Doppler and to see which one fills with color.
The one that fills with color is going to be the vessel
and the one that doesn't is going to be the duct.
So the duct isn't dilated here and if you look at the axial CT image,
you can see contrast within the portal venous system
and then surrounding the portal venous system we see linear areas
that are hypodense and these represent dilated bile ducts.
So what is an MRCP?
It stands for Magnetic Resonance Cholangiopancreatography.
It's a heavily T2 weighted sequence that's performed without contrast
and it's actually very helpful in determining the cause
and level of obstruction of the biliary system.
So this is an example of an MRCP.
You can see that there's mild intrahepatic
and extrahepatic biliary ductal dilatation
so these here represent intrahepatic bile ducts
and then as you come more centrally
you can see dilated extrahepatic bile ducts as well.
The extrahepatic ducts abruptly end right here at the level of an obstruction.
You can see here a similar MRCP image which shows contrast
and then an abrupt end where you see this dark round structure
and this represents a stone that's obstructing the distal common bile duct.
So an MRCP is a very good substitute to an ERCP
an ERCP is performed by a GI physician
and it's a lot more invasive than an MRCP is so often we start with an MRCP first
to take a look at the level of obstruction before we proceed to an ERCP
which can help resolve the obstruction as well.
So cholangiocarcinoma, this is a very important malignancy of the biliary system.
It can be located really at any level of the biliary tree
and the most common is the Klatskin tumor which is cholangiocarcinoma located
at the confluence of the right and left hepatic ducts.
So here is an example of a cholangiocarcinoma.
We can see two CT images.
We have an axial CT image, we have a coronal image,
and then we have again an MRCP image.
And you can see that there's a low density mass
at the confluence of the right and left hepatic ducts
and this results in an abrupt cut off of the biliary system
as you can see by this arrow here.
So we have multiple intrahepatic ducts that look dilated
and then we have an abrupt cut off
when we actually don't see the extrahepatic biliary system
because of this mass that's obstructing the biliary system
and this is an example of what a cholangiocarcinoma would look like.