Biliary ducts

14.3.1. Normal anatomy, variations Intrahepatic and extrahepatic biliary ducts

In the left and right lobes collecting biliary ducts form the right and the left hepatic ducts at first, then the main biliary duct (ductus choleductus) develops from their confluences.

In a normal case the intrahepatic biliary ducts cannot be imaged and the diameter of the main biliary duct cannot exceed the 7 mm.

Diverticulum can be also observed on the main biliary duct, which can result symptoms and biliary duct passage distrubance depending on its localisation.

In a case of a postcholecystectomic status the diameter of the main biliary duct can be also 8-10 mm, this is not a pathologic aberration itself.

The significance of biliary MRI:

Investigation of the extrahepatic biliary ducts is an old tradition in radiology, but the intrahepatic biliary ducts can be investigated by ultrasound only approximately.

The invasive procedure of ERC (endoscopic retrograde cholangiography) is well known, however, it is slowly forced back to the right place where it fits: to the interventional

radiology. Helical CT cholangiography is a more effective way of CT imaging instead of the previously applied cholangiography using iodinated contrast agents. The disadventage is that the CT cholangiography can be performed only in case of good liver function: in case of icterus there is no excretion and therefore no biliary duct imaging can be performed. In addition, no pancreatic duct(s) can be imaged. However, because of the dependence on the hepatocyte function it is (would be) precisely very beneficial to image the functioning liver areas map-likely. Unfortunatelly, the production of the contrast agent was discontinued (it was toxic, prudence was required).

MR cholangiopancreatography (MRCP) is only the liquid content of the bile inside the biliary ducts, its imaging is possible because of its no flow. However, the biliary duct is gracile – so in many cases the imaging of the normally dilated biliary ducts is doubtful, but even the slightly dilated intrahepatic (and extrahepatic) biliary ducts and the pancreatic duct(s) can be also exquisitely visualized. The fluid-filled gallbladder is also always

visualized. The empty stomach and duodenum is helpful in technical point of view, because the extrapolation of especially the duodenum can be difficult from the imaging of the biliary duct by the rotation of the three-dimensional image. Extent ascites may thwart the

examination. Less ascites behaves itself as a "curtain", and you can look behind it only by applying „tricks‖. Other fluid-filled cavities do not cause confusion, but the liquor content of the vertebral canal can be deceiving at first glance.

Based on the above mentioned facts, MRCP can be applied in case of biliary duct tumors (malignancy in the liver hilum, Klatskin tumor), intrahepatic or extrahepatic biliary duct strictures or dilatations, investigation of intrahepatic or extrahepatic outflow disorders of unclear origin by other imaging methods, localisation of pancreas head and papilla area

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Above all, important to note and apply: MRCP, which is much less threatening to the patient, must be always the first choise before (in most cases pancreatic enzyme failure causing) ERCP (not a foregone intervention)!

14.3.2. Cholangitis

It does not accompany with a really specific US sign, but the biliary ducts‖ wall can be a bit more hyperechoic on the inflammatoric intrahepatic sections in case of a long-term clinical existence.

14.3.3. Choledocholithiasis

As mentioned above, the existing smaller stones can migrate down to the main biliary duct and choledocholithiasis can be developed if they stick in there (Figure 36).

Figure 36: Choledocholithiasis, US

The direct US imaging of the main biliary duct stone may need more experience, the proper rotation of the patient and the competent diversion of the duodenal bowel gas can help in the US imaging of the distal segment of the main biliary duct.

In order to solve the choledocholithiasis, endoscopically acute ERCP following by a stone extraction by dormia basket can be performed. If the stone obstructed high in the main biliary duct and it cannot be extracted endoscopically, a percutaneous intervention can be tried. It is important to note, that ERCP is an insecure procedure, very serious pancreatitis can develop as complication, so the indication of the certain procedure must be taken very circumspectly.

14.3.4. Malignant tumor of the biliary duct, cholangiocellular carcinoma (CCC) Intrahepatic, extrahepatic (perihilar) and distal extrahepatic forms can be distinguished.

The perihilar form of the malignant tumor originating from the biliary ducts is called Klatskin tumor.

This type of malignant tumor is detected in the background of an ictreus of unknown origin unfortunatelly even more frequently. In certain cases ERCP is useful in the cytologic sampling, but sometimes an imaging method guided biopsy is needed for the histological verification. According to the localisation, the following types are known (Bismuth-classification):

Type 1 – localised to the main biliary duct (cystic duct can be also affected),

197 Type 2 – localised to the upper portion of the main biliary duct and the distal portion of the two hepatic ducts with itself,

Type 3./a – type 2 + localised to the right sided segmental branches, Type 3./b – type 2 + localised to the left sided segmental branches,

Type 4 – forms 3./a + /b together, furthermore the distal portion of the main biliary duct can be also affected segmentally with itself.

In case of an inoperable tumor or a high hilar localisated Klatskin tumor (Figure 37), the bridging of the certain stenosis can be tryed by percutaneous intervention from the direction of both lobes (left and right sided double hepatic duct drainage and stent implant).

Figure 37: Klatskin tumor, PTC, punction from left biliary duct of the liver Additional relevant details can be found in the nonvascular intervention chapter.

14.4. Pancreas

14.4.1. Normal anatomy, variations

The pancreas is a retroperitoneally located, endocrine and exocrine gland.

In the anatomical respect, head, body and tail regions can be distinguished.

Important evolutionary variations:

Pancreas divisum (abscense of the fusion of the anterior and posterior pancreatic ducts). – This is a very important variation, since it exists in almost 25% of the patients suffering from recurrent, idiopathic pancreatitis.

Accessoric pancreatic duct (Santorini).

Annular pancreas.

Agenesis.

Hypoplasia.

Ectopic pancreas.

Almost twenty-sort of enzyme is producted in the course of the exocrine gland function, which are drained by the pancreatic (Wirsungianus) duct and flow into the duodenum with the bile coming from the main biliary duct. Normally it measures 3 mm in diameter by young adults (measured at the body), whileas 5 mm in the elderly population.

The endocrine gland function consists of the so-called Langerhans islands, which product multifarious hormons and they play a very important role in the glucose metabolism by producing insulin.

Radiograph imaging:

The pancreas can be only observed on the traditional radiograph if multiple bigger

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calcifications are located in the gland parenchyma (in case of chronic calcific pancreatitis) or a big space occupying lesion in the pancreas head (tumor or pseudocyst) shifts away the bowel gas-containing duodenal horseshoe.

Arising from its location, it is not an ideal organ for an US examination. Its visualisation can be influenced by the gas content of the stomach and the bowels remarkably (Figure 38).

Figure 38: US of the pancreas, disturbing intestinal gas in the body-tail region Its US examination needs a bigger experience and attention as the average, moreover an effective physical requisition as well (the epigastrically located, disturbing bowel gases can be eliminated only by a compression involving an adequate effort in many cases)!

Because of all these CT and MRI have a primary role as additional imaging methods in the pancreas imaging.

Due to the adaptation of multidetector CT scanners, the adjudication of the pancreas became increasingly more accurate. The sensitivity and specificity has been improved with the three-phase (arterial, venous, late venous) scans.

Favorably, the signal-free MR vessels create better orientation conditions compared to CT scan.

The posterior contour of the pancreas is provided by the splenic vein draining to the portal vein. Anterior to the pancreas, two vessels run in the small bay created by the uncinate process and the body: medially the superior mesenteric vein (in the longitudinal axis of the body), to the left of the superior mesenteric vein the superior mesenteric artery can be identified with smaller caliber. (The artery is always separated by a small fat rim from the parenchyma which is not present by the vein. It is good to know in case of the adjudication of the tumorous infiltration.)

The juvenile pancreas has a glandular solid structure. By aging, the organ becomes adipous because of the fat deposition among the lobules.

The variatious shape of the pancreas can be often identified: pancreas divisum (developmental variation) and the shape and size of uncinate porcess can be also very altering. It is important to notice it in order to distinguish from the space occupying processes.

The excretory ducts of the pancreatic gland (Wirsung duct, Santorini duct) are frequently variatious. If its size (1-3 mm) is appropriate, the excretory ducts can not be visualized, but 3D technique is able to image them in order to replace ERCP.

MR imaging of pancreatic diseases:

The most frequent aim of the examination is to clarify the resecability before surgery: the relationship of pancreatic carcinoma (usually previously clarified by imaging methods) and vascular structures. T1-weighted images are suitable for this purpose.

The T2-weighted images detect the intratumorous necrosis mainly, in addition the relationship