Magnetic Resonance Cholangiopancreaticography

Magnetic resonance cholangiopancreaticography (MRCP) (synonym: MR cholangiopancreaticography) is a noninvasive (not penetrating the body) imaging technique for visualizing the biliary and pancreatic ducts. In magnetic resonance imaging (MRI), examination protocols can be specially adapted so that the liver, bile ducts, and pancreas can be better visualized and consequently the examination is called MRCP. MRCP can be performed as an alternative or in combination with endoscopic retrograde cholangiopancreaticography (ERCP), which has been the gold standard for imaging the biliary and pancreatic duct systems. Various diseases such as anomalies (malformations), inflammations or tumors of the bile ducts can be detected non-invasively with the help of MRCP, so that patients can be spared ERCP as an invasive procedure. On the other hand, if interventions (here: invasive procedure) are necessary, ERCP cannot be dispensed with. Postinterventionally, MRCP may in turn be useful for recording complications that may have been caused by ERCP.

Indications (areas of application)

Biliary system:

  • Detection or exclusion of choledocholithiasis (bile duct stones) or cholecystolithiasis (gallbladder stones): gallstones are very common in the population (women about 15%, men about 7.5%) and consist of about 80% insoluble cholesterol and about 20% bilirubin (bile pigment resulting from blood breakdown). Neither type of stone shadows on conventional radiography, so other diagnostic methods must be resorted to. In MRCP, such concretions are visible as recesses in the bile duct or bladder, which is otherwise filled with bile.
  • Detection or exclusion of primary sclerosing cholangitis (PSC) – rare, chronic inflammation of the intra- and extrahepatic bile ducts.
  • Clarification of benign (benign) or malignant (malignant) bile duct stenosis:
    • Gallbladder polyps: 95% cholesterol deposits in the mucosa (mucosa) or adenomas (benign mucosal tumors), which must be removed if they progress in size (progression with increase in size) due to the risk of carcinomatous degeneration.
    • Gallbladder carcinoma: Can occur in the elderly usually as a result of cholelithiasis or chronic cholecystitis (gallbladder inflammation), usually show no early symptoms and therefore have a rather unfavorable prognosis due to late diagnosis.
    • Bile duct carcinoma (bile duct cancer): also called cholangiocellular carcinoma (CCC) with choledochal cysts, choledochal stones, primary sclerosing cholangitis (PSC, chronic bile duct inflammation) and parasitic diseases of the bile ducts as risk factors.
    • Klatskin tumor: special type of bile duct carcinoma with localization at the hepatic fork (bifurcation of the bile ducts formed by the union of the ductus hepaticus dexter and sinister to form the ductus hepaticus communis).
  • Detection or clarification of anatomical features: Bile duct malformations or postoperative changes such as biliodigestive anastomoses (artificially created connection between bile duct/bladder and gastrointestinal tract) can be detected and controlled in MRCP.
  • Detection of normovariant bile duct tracts, e.g., before partial liver resection (removal of parts of the liver) or liver transplantation (LTx).

Pancreas:

  • Imaging of pancreatic ducts to detect caliber irregularities or duct breaks due to, for example:
    • Pancreatitis (inflammation of the pancreas): unlike ERCP, MRCP can be performed in acute pancreatitis.
    • Pancreatic duct stones: usually as a result of chronic pancreatitis, visible as short-segment stenosis (narrowing) of the pancreatic ducts.
    • Pancreatic carcinoma: Usually originating from the pancreatic ducts and therefore detectable with one of the MRCP.
    • Papillary carcinoma: Rare malignant (malignant) tumor directly at the junction of the bile duct with the small intestine.
  • Detection of congenital pancreatic malformations (eg, pancreas divisum, pancreas anulare).

MRI is nowadays usually performed as a “one-stop-shop” MRI in a combination of MRI, MRCP, and MR angiography, resulting in the greatest sensitivity (percentage of diseased patients in whom the disease is detected by the use of the test, i.e., a positive test result occurs) and specificity (likelihood that actually healthy individuals who do not have the disease in question will be detected as healthy by the procedure). As a rapid, accurate, and especially noninvasive procedure, it should always be considered as an alternative to ERCP. Furthermore, MRCP may be indicated as a preliminary examination for planning and performing ERCP, e.g., to reduce the complication rate (pancreatitis, perforations, etc.) of ERCP. Advantages of MRCP over ERCP:

  • Lack of invasiveness (penetration into the body).
  • Low investigator dependence
  • Possibility of complete visualization of the ductal systems, i.e., before and after obstruction (transfer)
  • No sedation (drug sedation) of patients required.
  • No contrast agent application
  • Low complication rate

Advantages of ERCP over MRCP:

  • Combination of the diagnostic procedure with an intervention possible: e.g., stent placement or simultaneous biopsy sampling (removal of a tissue sample), so that benign or malignant stenoses can be differentiated immediately.
  • Low-grade stenoses with lack of poststenotic dilatation (widening) or stenoses of the peripheral bile ducts can be detected more accurately by ERCP, because the contrast medium is injected into the bile ducts with pressure and they are thus shown dilated. MRCP is still limited in its accuracy for very small stones.
  • Can also be performed if there is a contraindication to MRI.

Contraindications

The usual contraindications apply to MRCP as to any MRI examination:

  • Cardiac pacemakers (with exceptions).
  • Mechanical artificial heart valves (with exceptions).
  • ICD (implanted defibrillator)
  • Metallic foreign body in dangerous localization (e.g., in close proximity to vessels or eyeball)
  • Other implants such as: Cochlear/ocular implant, implanted infusion pumps, vascular clips, Swan-Ganz catheters, epicardial wires, neurostimulators, etc.

Contrast administration should be avoided in cases of severe renal insufficiency (renal impairment) and existing pregnancy.

Before the examination

Patients should fast for at least 4 hours before the examination. Fluid-filled sections of the small bowel may overlap the biliary and pancreatic ducts if necessary. It may be useful to administer negative contrast agents (e.g., Lumirem or blueberry juice) orally to patients prior to the examination to cancel the bowel signal. For improved visualization of pancreatic ducts, the pancreas can be stimulated by secretin administration, resulting in increased production of secretin and visualizing ducts that cannot be delineated natively. Secretin is rarely used today because of its high cost and because it is not yet approved in children.

The procedure

Examination protocols have been developed for MRCP that contain technically different sequences. Various T2-weighted sequences exist (e.g., T2 RARE, T2 HASTE, T2 3D), as well as complementary T1-weighted series natively and with KM administration when appropriate. Images should be acquired in both axial and coronal slice guidance. The principle of imaging the biliary and pancreatic ducts is based on very strong T2 weighting, which renders fluid-filled spaces with only a low flow velocity (e.g., biliary and pancreatic secretions) hyperintense (signal-rich). Surrounding soft tissue structures have a shorter T2 time and are thus lower in signal, resulting in clear contrast. Therefore, contrast agent administration is rarely necessary. However, if a contrast agent is used, it is a liver-specific one that has biliary excretion (excretion via the bile ducts) (e.g., Primovist). All examinations are performed using a breath trigger or breath-holding technique to avoid respiratory artifacts.

Possible complications

Ferromagnetic metal bodies (including metallic makeup or tattoos) can lead to local heat generation and possibly cause paresthesia-like sensations (tingling). Allergic reactions (up to life-threatening, but only very rare anaphylactic shock) may occur due to contrast medium administration. Administration of a contrast agent containing gadolinium may also cause nephrogenic systemic fibrosis in rare cases.