Magnetic Resonance CholangioPancreatography
By:Falguny Bhavan MS4
Oregon Health & Sciences University
Radiology Clerkship
Objectives
* Introduction
* Technique
* Advantages
* Limitations
* Clinical applications
Introduction
Anatomy of the Hepato-Biliary and Pancreatic system
Technique
* Basic principle: body fluids (bile and pancreatic secretions) have high signal intensity on heavily T2-weighted MR sequences therefore, appear white
o Background tissues generate little signal appear dark
* Stationary or slow-flowing fluid within the bile and pancreatic ducts appears bright relative to low signal intensity produced by adjacent solid tissues
* New MR advancements allow faster imaging in which imaging is performed during single breath-holding session to reduce motion artifact due to respiration
* New variants such as rapid acquisition with relaxation enhancement (RARE) and half-Fourier acquisition single-shot turbo spin-echo (HASTE) can be performed in a breath-hold period with a scan time of <20 seconds provide superior images
Advantages
* Does not require intravenous or oral contrast material to be administered into the ductal system
* Avoids complications of ERCP such as pancreatitis (3-5%), sepsis, perforation, hemorrhage, sedation
* Can be completed in 10 minutes, easily performed as outpatient examination
* Passive procedure; displays the ducts in the resting state and more accurately displays native caliber of the duct than ERCP.
o In ERCP, segments may be overdistended because of attempt to visualize the duct upstream from a stricture, or segments may be underdistended because of the operator's fear of inducing cholangitis or pancreatitis.
Limitations
* Purely diagnostic, does not provide access for therapeutic intervention (e.g. stone extraction, stent insertion, or biopsy)
* Image artifact due to other structures in abdomen with high fluid content
* Lack of patient compliance; claustrophobia, inability to breath-hold
* Dropout of signal can be caused by metallic clips, crossing defects induced by the right hepatic artery, or from severely narrowed ducts, such as occurs with primary sclerosing cholangitis
* Lower resolution than direct cholangiography
o Can miss small stones (<4 mm), small ampullary lesions, primary sclerosing cholangitis, and strictures of the ducts
Clinical applications: Diseases Diagnosed by MRCP
Biliary Disease
* Screening examination in patients with low or intermediate probability of choledocholithiasis
* Cholangiocarcinoma
* Anatomic variants (low or medial duct insertion, aberrant right hepatic duct)
* Failed or incomplete ERCP
* Post-operative anatomy or screening for biliary complications
* Primary sclerosing cholangitis
* Cystic disease of bile duct (choledochal cyst, choledochocele, Caroli’s disease)
Pancreatic Disease
* Anatomic variants (pancreas divisum)
* Chronic pancreatitis
* Pancreatic cancer
Clinical Applications: General guidelines for selection of MRCP or ERCP
Obstruction of the Common Bile Duct
* MRCP can visualize the normal or dilated common bile duct in 96 to 100 percent of patients.
* Strictures typically appear as focal areas of ductal narrowing or signal void with proximal dilatation.
* Cause of biliary strictures may be more difficult to determine on the basis of MRCP alone.
o lacks specificity
o differentiation between benign and malignant causes is based on a combination of clinical, radiographic, and pathological data
* Obstruction 2° to calculi, pancreatic adenocarcinoma, or pancreatitis is usually obvious with MRCP, and with aid of conventional MRI or CT
Obstruction
Combined Biliary-Duct Obstruction and Pancreatic-Duct Obstruction Due to a Small Mass in the Pancreatic Head.
The biliary-duct obstruction is indicated by the curved arrow, and the pancreatic-duct obstruction by the straight arrow. The mass was identified on axial, contrast-enhanced, T1-weighted images (not shown) obtained by routine MRI during the same examination. Arrowheads indicate the pancreatic duct.
* ERCP is more beneficial in pts with dilatation of the common bile duct who have obstruction at the ampulla, since it permits direct visualization of the ampulla, biopsy of lesions, manometry, or endoscopic sonography.
* MRCP Study of 79 cases of biliary obstruction found 14 due to malignant cause; 6 cases due to ampullary carcinoma.
o 2 of 6 cases were misdiagnosed as benign obstructions, and 2 cases of benign obstruction were thought to be ampullary cancers. (This study used an early form of the technique, and results may be more accurate with the currently available technology.)
* MRCP performed after pharmacologic stimulation with secretin has been shown to be helpful in evaluating ampullary obstruction
Secretin-enhanced MRCP
* Visualization of the pancreatic duct can be improved with imaging after administration of IV secretin
* Secretin frequently used when pancreatic duct is not apparent on MRCP
* Reduces the incidence of false positive findings of strictures
Secretin-enhanced MRCP
Dynamic MRCP with Intravenous Injection of Secretin in Patient with Abdominal Pain after a Whipple Procedure.
(ERCP was not attempted because the patient had a pancreaticoenteric anastomosis.)
In Panel A, the pancreatic duct (arrowheads) is incompletely visualized on MRCP before the administration of secretin.
In Panel B, an MRCP obtained 15 minutes after the administration of secretin shows prominent and prolonged dilatation of the pancreatic duct upstream of a stricture (arrow) at the pancreaticoenteric anastomosis.
Common duct stones
* Displayed by MRCP as a signal void within bright signal arising from bile
* MRCP is a useful means of determining presence or absence of CBD stones, as well as number, size, and location
* MRCP is as accurate as ERCP for detecting choledocholithiasis
o Sensitivity = 95-100%
o Specificity = 85-100%
* Increased sensitivity in pts with suspected gallstone pancreatitis, and pts with non-specific abdominal pain and normal LFTs
* Stones larger than 4 mm are readily seen but difficult to differentiate from filling defects such as blood clots, tumor, sludge, or parasites
o Other mimickers include flow artifacts, biliary air, and a pseudostone at the ampulla
* In the presence of a dilated CBD, MRCP has a 90 to 95 percent concordance with ERCP in diagnosing CBD stones over 4 mm in diameter
* ERCP is preferred in pts with cholangitis because it allows therapeutic drainage
Cholangiocarcinoma
* Role of MRCP in the diagnosis and management of bile duct malignancy is not yet defined
* Useful noninvasive adjunct
* Capability to evaluate the bile ducts both above and below a stricture while also identifying any intrahepatic mass lesions
* Study of 126 patients with suspected bile duct obstruction showed that MRCP alone has limited specificity in the diagnosis of malignant strictures
o Malignant obstruction dx by MRCP in 12 out of 14 pts
o Positive predictive value = 86%
o Negative predictive value = 98%
Pancreatitis
* Acute pancreatitis
o MRCP is useful for evaluating bile ducts and cystic duct remnants for stones, for evaluating the pancreatic ducts, and for documenting the presence of cysts in or around the pancreas.
o ERCP is often preferred in patients with gallstone pancreatitis since endoscopic papillotomy can be performed in pts with obstructive jaundice or biliary sepsis.
* Chronic pancreatitis
o MRCP is useful in demonstrating complications such as, ductal dilatation, strictures, intraductal calculi, fistulas, and pseudocysts
o Defines ductal anatomy and extent of ductal disease prior to surgical drainage
* MRCP is as accurate as ERCP for distinguishing pancreatic cancer from chronic pancreatitis.
o In study of 124 patients who were suspected of having pancreatic cancer, pts underwent a number of diagnostic studies, including ERCP and MRCP. The correct diagnosis was confirmed histologically and clinically. 37 patients (30 percent) dx with pancreatic cancer; others had chronic pancreatitis (46 percent) or other causes.
o MRCP sensitivity (84%) and specificity (97%) for diagnosis of pancreatic cancer
o ERCP sensitivity (70%) and specificity (94%)
* Secretin-enhanced MRCP is being increasingly studied for evaluation of pancreatic exocrine function and in the early diagnosis of chronic pancreatitis
Variant ductal anatomy
* MRCP is also useful in demonstrating variant anatomy and congenital anomalies of the biliary tract and pancreatic duct
o Pancreas divisum
o Choledochal cyst
o Annular pancreas
o Abnormal pancreaticobiliary junctions
o Aberrant bile ducts
* And in evaluation of pts prior to laparoscopic cholecystectomy
Normal Extrahepatic Bile Duct and Incidental Pancreas Divisum.
Magnetic resonance cholangio-pancreatography is an accurate method of diagnosing pancreas divisum because it shows the dominant dorsal pancreatic duct (arrowheads) continuously from the tail to the head of the pancreas, crossing the common bile duct (curved arrows) and draining at the minor papilla (straight arrow) superiorly and separately from the common bile duct.
GB denotes gallbladder.
Failed or incomplete ERCP
* ERCP is technically challenging
o Associated with 10-20% failed cannulation rate
o Anatomic variants can contribute to failed ERCP attempts
* MRCP is useful in demonstrating variant anatomy
o MRCP may have advantages compared to ERCP in specific settings such as pts who have gastric outlet or duodenal stenosis or who have had surgical rearrangement (eg, Billroth II) or ductal disruption, resulting in ducts that can’t be assessed by ERCP
* MRCP also allows evaluation of ducts in pts with contraindications for ERCP:
o Cervical spine fractures, head and neck tumors, sleep apnea, other diseases/ injuries that preclude placement of endoscope or positioning
Post-surgical anatomy
Normal Results of Magnetic Resonance Cholangiopancreatograpy in a Patient after Cholecystectomy.
Imaging was performed in two seconds with the thick, single-slice technique. The normal common bile duct (arrow) and pancreatic duct (arrowheads) are clearly visible.
Du denotes duodenal bulb.
References
Magnetic Resonance CholangioPancreatography.ppt
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