(Radiographics. 2002;22:e2.)
© RSNA, 2002
MR Imaging of the Pancreas: A Pictorial Tour1
Celso Matos, MD,
Olivier Cappeliez, MD,
Catherine Winant, MD,
Emmanuel Coppens, MD,
Jacques Devière, MD and
Thierry Metens, PhD
1 From the Department of Radiology, Hôpital Erasme, Université Libre de Bruxelles, 808 Route de Lennik, B-1070 Brussels, Belgium. Received March 14, 2001; revision requested September 12; revision received and accepted October 22. Address correspondence to C.M. (e-mail: cmatos@ulb.ac.be)
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Abstract
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Magnetic resonance (MR) imaging of the pancreas has undergone a major change because of its capability of providing noninvasive images of the pancreatic ducts, cross-sectional images of the parenchyma analogous to computed tomography (CT) images, and angiographic depiction of blood vessels. Recent technical issues include the use of half-Fourier T2-weighted pulse sequences and the administration of secretin for MR cholangiopancreatography (MRCP). Secretin improves pancreatic duct and side-branch delineation and the detection of anatomic variants such as pancreas divisum. It allows monitoring of pancreatic flow dynamics and evaluation of pancreatic exocrine function. Although contrast material—enhanced CT is still considered the standard of reference in severe acute pancreatitis and for the detection of calcifications in chronic pancreatitis, in patients referred for suspicion of pancreatic disease or with recurrent acute pancreatitis, MR imaging and secretin-enhanced MRCP are useful after unenhanced CT suggests the cause of disease. In advanced inflammatory disease, MR imaging and secretin-enhanced MRCP are useful for planning surgery or therapeutic endoscopy and for follow-up studies after therapy. MR imaging in combination with secretin-enhanced MRCP and MR angiography is useful in identifying pancreatic malignancies and in establishing resectability.
© RSNA, 2002
Index Terms: Bile ducts, MR, 76.12141, 76.12143 • Endoscopic retrograde cholangiopancreatography (ERCP), 770.1222 • Magnetic resonance (MR), comparative studies • Pancreas, function, 770.91, 774.91 • Pancreas, MR, 770.12141, 770.12143 • Pancreatic ducts, MR, 774.12141, 774.12143 • Pancreatitis, 770.291 • Secretin
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LEARNING OBJECTIVES
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After reading this article and taking the test, the reader will be able to:
- Describe the advantages and limitations of different MR sequences for imaging the pancreas.
- Recognize the current indications of secretin-enhanced MR cholangiopancreatography.
- Understand the current status of pancreatic MR imaging compared with CT and ERCP.
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Introduction
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The diagnosis of pancreatic diseases generally requires the combined use of different imaging modalities, allowing evaluation of the pancreatic ducts (endoscopic retrograde cholangiopancreatography [ERCP]) and the pancreatic parenchyma and adjacent soft tissues (ultrasound and helical computed tomography [CT]). Technical innovations in magnetic resonance (MR) imaging such as the use of phased-array coils that allow improved spatial resolution and faster T1- and T2- weighted sequences that permit imaging of the entire upper abdomen in a single breath hold make routine MR imaging of the pancreas feasible. Indeed, MR imaging has the unique capability of allowing noninvasive evaluation of the pancreatic ducts, pancreatic parenchyma, adjacent soft tissues, and vascular network in a single session. On the basis of our clinical experience with a series of more than 1000 patients, we describe and illustrate the advantages and limitations of the different MR imaging sequences used in the evaluation of pancreatic disease and discuss the rationale for MR imaging in pancreatic evaluation.
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Technique
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Comprehensive MR imaging of the pancreas should show pancreatic and biliary ductal anatomy, help detect and characterize parenchymal damage, delineate extrapancreatic extension of a mass or inflammatory process, and help evaluate vascular anatomy.
MR Cholangiopancreatography (MRCP)
Various pulse sequences and approaches have been described for imaging the pancreatic duct and biliary tract with MRCP (1–6). Imaging the pancreatic duct is dependent on heavily T2-weighted imaging that selectively displays static or slow-moving fluid-filled structures. Optimal sequence parameters differ with different imagers and depend on the availability of software and hardware applications.
Two different and complementary approaches are generally used for MRCP: a thick-slab, single-shot turbo spin-echo (TSE) T2-weighted sequence and a multisection thin-slab, single-shot TSE T2-weighted sequence. The detailed protocols used with our 1.5-T MR imager for both sequences are listed in Tables 1 and 2.
Thick-Slab, Single-Shot TSE (or Fast Spin-Echo) T2-weighted Sequence (Projective MRCP) (Table 1).
This technique uses a single, thick (20–50-mm) section that can be obtained in any plane with a single short breath hold (<3 seconds). This provides an excellent selective display of the whole extrahepatic biliary tract and pancreatic duct with no respiratory artifacts, few susceptibility effects, and a relatively good in-plane resolution (3–7). The final image resembles the conventional image obtained during ERCP (Fig 1).
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Figure 1. For the main pancreatic duct, the resolution of MRCP approaches that of ERCP. This comparative MRCP (A) and ERCP (B) data obtained in an 80-year-old patient with senescent changes of the pancreatic duct clearly illustrates this assertion.
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Because of the short acquisition time and there being no need for postprocessing, interpretation is immediately available. In addition, the short acquisition time allows obtaining of sequential acquisitions, each during a single breath hold after stimulation with secretin (dynamic MRCP)(8,9) (Fig 2).
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Figure 2. Normal MRCP performed during secretin stimulation shows a slight and temporary increase in the caliber and signal intensity of the main pancreatic duct in A (arrow) and, concomitantly, progressive and complete duodenal filling (arrowheads in B). Complete filling of the Santorini duct (arrowhead in A) is also seen.
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However, there are some drawbacks associated with this single-section technique: (a) It requires good patient cooperation for breath holding. (b) Ductal visibility may be degraded by possible overlap with other fluid-containing organs (ie, the stomach and duodenum) and the presence of ascites or peripancreatic exudates in the field of view (Fig 3). To eliminate the signal from overlapping fluid-containing bowel, patients are asked to fast for at least 4 hours before the examination, and if residual fluid is still present, a T2-negative oral contrast agent may be administered (Fig 4). (c) Overlap between segments of the pancreatic duct or with cystic lesions may be a source of pitfalls that can be overcome by adapting the section thickness, orientation, and positioning of the thick slab to the patient's duct anatomy, which requires on-site tailoring by the radiologist during image acquisition. (d) Visualization of intraductal content such as stones, protein plugs, and hemorrhage may be suboptimal if they are not surrounded by fluid (Fig 5). (e) No signal from solid organs is displayed.
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Figure 3. Patient with acute necrotizing pancreatitis, a peripancreatic exudate, and ascites. Suboptimal visualization of the common bile duct and pancreatic duct (arrows) due to increased signal intensity of the background tissue is observed on this MRCP image. To avoid suboptimal visualization in such conditions, a 2D or 3D multisection acquisition with a targeted MIP can be used.
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Figure 4. MRCP before (A) and after (B) administration of a "negative" oral contrast agent. Better visualization of the pancreatic duct in the tail (arrowhead) and the peripancreatic collection (arrows) is seen after suppression of background fluid in the stomach (*) in B.
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Figure 5. Patient with obstructive chronic calcified pancreatitis. (A) Plain radiograph show a calcified stone (arrowhead) in the pancreatic area. (B) The MRCP shows dilatation of the main pancreatic duct and the side branches (arrowheads) and the level of obstruction. The obstructive intraductal stone may be suggested (arrow), but its visualization is suboptimal because it is only partially surrounded by fluid. (C) The location of the stone in the main pancreatic duct is clearly shown at ERCP (arrow).
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Multisection Single-Shot Thin-Slab TSE (or Fast Spin-Echo) T2-weighted Sequence (Table 2).
In this sequence, a series of contiguous thin sections (generally 4 mm thick) is acquired with a shorter echo time and echo train length than with the thick-slab acquisition technique. Therefore, it allows depiction of not only the ducts but the solid organs. Image quality is less dependent on patient cooperation and nearly unaffected by specific artifacts (chemical shift, magnetic susceptibility) or motion, the individual sections being acquired during a single shot lasting less than 1 second. However, in cooperative patients, it is preferable to acquire each section during a single breath hold to reduce misregistration artifacts (5–7).
With more recent software, it is also possible to acquire each section with respiratory triggering, the shot being performed during expiration without much penalty in acquisition time, which is convenient for more disabled patients. The sequence is ideally suited for imaging fluid-containing structures and lesions, and the analysis of the individual sections is mandatory for visualizing ductal-filling defects (visible as areas of decreased signal intensity) that may be missed with the thick-slab technique (Figs 6–8).
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Figure 6. Chronic calcified pancreatitis and pseudocysts demonstrated on MRCP (A), ERCP (B) and axial (C) and coronal (D) thin-section single-shot TSE T2-weighted images. In A, the damaged portion of the pancreatic duct (arrowheads) and the pseudocyst (arrow) are clearly depicted. However, ductal content and pseudocyst septation and content are better depicted in B, C, and D (arrows).
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Figure 7. Chronic calcified pancreatitis and multiple calculi in the main pancreatic duct demonstrated on MRCP (A) and coronal multisection thin-slab TSE T2-weighted images obtained with a shorter echo time (80 msec) (B, C, D). Filling defects corresponding to calculi in the pancreatic duct are better visualized in B, C, and D (arrowheads); however, the whole pancreatic duct anatomy is better displayed in A. The "filling defect" at the hilum of the liver (arrow) corresponds to a vascular impression.
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Figure 8. Acute necrotizing pancreatitis demonstrated on MRCP (A) and coronal thin-section single-shot TSE T2-weighted (B) images. In A, a distal common bile duct stricture (arrow), abnormal pancreatic duct side branches (solid arrowheads) and indirect signs of duodenal wall thickening (open arrowheads) are visualized. The peripancreatic fluid collections detected in B (arrows) are not detected in A, because of the shorter T2 relaxation time of the fluid in the peripancreatic collections. However, because of intrinsic limitations in signal-to-noise ratio and spatial resolution, this sequence is not useful for detection of solid lesions within the pancreas or the liver (Fig 9)
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Figure 9. Coronal thin-section single-shot TSE T2-weighted image obtained in a patient with a pancreatic tumor (*) and liver metatstases (arrows). Contrast between lesions and normal adjacent liver is suboptimal.
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In our current pancreatic duct imaging practice, we obtain thin sections as tomographic images only and the thick slab for projection images. MIP reconstructions are not routinely performed, because for the majority of patients, pancreatic duct anatomy is easy to assess with the single-thick-slab technique. Moreover, the latter allows interactive dynamic studies with secretin stimulation.
Secretin-enhanced Dynamic MRCP: Rationale.
The exogenous administration of secretin stimulates the secretion of fluid and bicarbonate by the exocrine pancreas (10). In endoscopic manometric studies, it has been shown that this effect is transient and associated in healthy subjects with an increase in pancreatic duct pressure after 1 minute, with an almost complete return to basal values after 5 minutes (11). This is explained by a secretin-stimulated increase in fluid secretion by the ductal cells in the ductal system and by simultaneous increased tonus of the sphincter of Oddi during the first 5 minutes, which inhibits the release of fluid through the papilla of Vater (12).
Consequently, the volume of stationary fluid in the pancreatic duct increases and its delineation may be improved at MRCP, secretin acting as an endogenous contrast medium for the duct. To detect such changes at MRCP, images must be acquired dynamically with good temporal resolution and show the full length of the pancreatic duct, extrahepatic biliary tract, and duodenum in one projection to evaluate duct flow dynamics and the release of pancreatic fluid into the duodenum. For this purpose, thick-slab MRCP is performed in the coronal plane, before and repeated every 15–30 seconds 10–15 minutes after intravenous (IV) administration of 1 mL of secretin per 10 kg of body weight (8). Secretin allows better delineation of the full length of the pancreatic duct and reduces the frequency of false-positive readings of duct strictures (Fig 10)
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Figure 10. (A, B) MRCP images obtained before (A) and after (B) secretin administration, (C) axial thin-section single-shot TSE T2-weighted image, and (D) axial TSE T1-weighted image obtained with a fat suppression spectral prepulse. Patient presented with a hemorrhagic pseudocyst (arrowheads) and suspicion of pancreatic duct rupture (arrow in A). In B, the full length of the pancreatic duct is delineated and a main duct rupture can be ruled out.
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Secretin administration allows better evaluation of the vaterian sphincter anatomy (Fig 11) and detection of anatomic variants such as pancreas divisum (13,14) (Fig 12) and depicts the progressive filling of duodenum with pancreatic fluid assessing indirectly the pancreatic exocrine reserve (8,9,15,16). The main limitation to its use remains the additional cost of the MRCP evaluation.
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Figure 11. Dynamic MRCP during secretin stimulation in a patient presenting with a pancreas divisum configuration. Fast repetition of data acquisition allows clear visualization of the intramural portion of the common bile duct and the pancreatic duct (arrowheads in B).
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Figure 12. MRCP images obtained before (A) and 10 minutes after (B) secretin administration in a patient with recurrent episodes of pancreatitis and pancreas divisum. In A, the ventral duct is not visible, while in B it is clearly delineated (arrowhead). The dorsal duct (arrows) shows a prolonged increase in caliber related to outflow impairment of pancreatic fluid.
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In healthy subjects, during the first 2–3 minutes after IV secretin administration, the pancreatic duct undergoes enlargement followed by a return to near baseline diameter as pancreatic juice fills the duodenum (Movie 1).
In a few cases, no enlargement of the pancreatic duct was detected but duodenal filling by pancreatic fluid was observed. With the exception of the head of the pancreas, delineation of side branches is rare. In the absence of obvious pancreatic duct involvement (obstruction, segmental narrowing, pseudocysts) before secretin administration, an impaired response of the duct to secretin includes (a) a prolonged dilatation (diameter >3 mm at 10 minutes) with delayed recovery of the baseline diameter that may be related to pancreatic outlet obstruction due to different causes (Fig 13); (b) visualization of side branches in the body and tail of the pancreas that could be related to mild changes due to chronic pancreatitis (Fig 14); (c) potential occurrence of a progressive enhancement of the pancreatic parenchyma mimicking acinar filling (17) (Fig 15), which has been observed in patients presenting with recurrent attacks of pancreatitis and disappears after endoscopic pancreatic sphincterotomy, suggesting an associated outlet obstruction (Fig 16); and (d) reduced filling of the duodenum that may suggest an impairment of the pancreatic exocrine reserve (16,18) (Fig 17).
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Figure 13. Dynamic MRCP images (A obtained before secretin administration, B and C obtained 2 and 5 minutes, respectively, after secretin administration) in a patient with an ampullary tumor shows an increase in the caliber of the pancreatic duct (arrow) and an incomplete recovery of the baseline value 10 minutes (D) after the administration of secretin. Associated biliary tract dilatation is seen (arrowheads).
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Figure 14. Dynamic MRCP images obtained in a patient with mild changes of chronic pancreatitis before (A) and after (B) secretin administration. Improved visualization of side branches (arrowheads) is seen in B.
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Figure 15. (A—D) Dynamic MRCP images obtained in a patient with progressive enhancement of the pancreatic parenchyma (arrowheads) after secretin administration. A was acquired before the administration of secretin, and B was acquired 2 minutes after. (1—3) Corresponding ERCP images show a progressive increase in pancreatic duct caliber during retrograde injection of contrast material, which might be related to pancreatic tissue hypertension. Side-branch morphology (arrows) is compatible with early changes due to chronic pancreatitis.
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Figure 16. (A) MRCP image obtained in a patient with enhancement of pancreatic parenchyma (arrowheads) after secretin stimulation. B After endoscopic pancreatic sphincterotomy, parenchymal enhancement is no longer detected.
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Figure 17. (A) MRCP image obtained 10 minutes after secretin administration in a patient with normal duodenal filling. (B) MRCP image in another patient with chronic pancreatitis shows reduced duodenal filling (arrows).
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In patients with obvious pancreatic duct involvement by chronic pancreatitis, MRCP is less dependent on the administration of secretin because the affected segments of the duct are not dilated by secretin.
Imaging of Pancreatic Parenchyma
For imaging of the pancreatic parenchyma, various T2-weighted and T1-weighted sequences are used in transverse and coronal sections.
T2-weighted Sequences (Table 2).
Breath-hold or respiratory-triggered multisection, thin-section, HASTE T2-weighted sequences with short (40–80 msec) and long (325 msec) echo times are obtained in the axial and coronal planes. With these sequences, fluid-filled lesions in or around the pancreas are demonstrated and the common bile duct and the pancreatic duct are shown in cross sections and may be used to guide acquisition of MRCP series. Because it may decrease the conspicuity of pancreatic contours, fat suppression is not systematically applied unless peripancreatic exudates are suspected (19) (Fig 18).
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Figure 18. Patient with acute pancreatitis and peripancreatic exudate. Non-fat-suppressed (A, C) and fat-suppressed (B, D) axial and coronal HASTE T2-weighted images. Increased signal intensity of peripancreatic fat tissues (arrows) is better demonstrated in B and D.
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T1-weighted Sequences (Tables 3–5).
In our 1.5-T system, these images are obtained either with a fat-suppression TSE T1-weighted sequence using multiple breath-hold acquisitions (Table 3) or with a single-breath-hold gradient-echo (GRE) sequence with a water-stimulation prepulse (Table 4). Fat suppression or selective water stimulation (a) improves the delineation of pancreatic borders and the pancreas itself, which appears homogeneously bright compared with surrounding low-intensity fat (Fig 19); (b) is excellent for identifying pancreatic masses or focal pancreatitis (less intense than normal high-intensity pancreas) (Fig 20); and (c) is suitable for contrast-enhanced studies (21). However, breath holding requires patient cooperation, and these sequences are less accurate in demonstrating focal disease in the presence of diffuse chronic pancreatitis because of the homogeneous low signal intensity of the fibrotic pancreas (Fig 21).
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TABLE 5. Imaging Protocol for High-Resolution, Coronal, Dynamic Breath-hold Gadolinium-enhanced T1-weighted 3D GRE Sequence with SENSE
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Figure 19. Normal pancreas demonstrated on four contiguous sections obtained with a TSE T1-weighted sequence with a fat-suppression spectral prepulse. The pancreatic parenchyma has homogeneously high intensity, and delineation of pancreatic contours (arrowheads) is improved.
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Figure 20. Neuroendocrine tumor involving the tail of the pancreas shown on (A) MRCP, (B) axial respiratory-triggered TSE T2-weighted, and (C) fat-suppressed TSE T1-weighted images obtained at the level of the tumor. In A, a stricture with upstream dilatation of the pancreatic duct is displayed (arrow). In B, no difference in signal intensity is detected between the tumor (arrow) and the adjacent pancreas. In C, the tumor is clearly delineated (arrowhead).
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Figure 21. Normal pancreas (A, B) and chronic pancreatitis (C, D) demonstrated with an axial GRE T1-weighted sequence with a water-stimulation prepulse. As with fat-suppression sequences, spectral water stimulation suppresses the fat signal and normal pancreas has high intensity. In chronic pancreatitis, the signal is dramatically reduced (*) because of the diffuse fibrosis in the gland.
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When pancreatic cancer is suspected, a high-resolution, coronal, dynamic breath-hold gadolinium-enhanced T1-weighted 3D GRE sequence with SENSE (20) (Table 5) is used, allowing combined study of the pancreas with dual-phase MR angiography (after MIP reconstruction) to assess possible vascular involvement (Figs 22, 23)
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Figure 22. Normal pancreas demonstrated on coronal 3D GRE T1-weighted images obtained after an IV bolus injection of a gadolinium chelate in the (A) arterial, (B) early portal venous, and (C) delayed phases. Progressive and homogeneous pancreatic enhancement is seen (arrows). MIP images (D, E) calculated from data obtained in A and B, respectively, nicely demonstrate the arterial and venous networks.
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Figure 23. Adenocarcinoma of the head of the pancreas demonstrated on a coronal 3D GRE T1-weighted image obtained after an IV bolus of a gadolinium chelate in the portal venous phase (A) and the correponding MIP (B). The small tumor (arrow) is displayed in A, and no venous invasion is detected.
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This sequence requires not only patient cooperation for a perfect breath hold but also monitoring of the arrival of the gadolinium bolus to optimize pancreatic enhancement and dual-phase MR angiography.
Practical Setup for an MR Study of the Pancreas
- Locator: Fast GRE T1-weighted axial, coronal, and sagittal sections obtained during the same acquisition allow identification of correct positioning of the phase-array coil.
- Cross-sectional axial and coronal breath-hold or respiratory triggered HASTE T2-weighted scans with short and long echo times.
- Breath-hold TSE or GRE oblique (according to pancreatic angulation) T1-weighted sequence with fat suppression or water stimulation covering the entire pancreas.
- If residual fluid in the bowel might overlap with pancreatic duct delineation, a T2-negative oral contrast agent is administered before the MRCP series is performed. We use 200 mL of pineapple juice administered immediately before imaging.
- MRCP projections are then obtained according to pancreatic angulation in oblique coronal and axial views (Fig 24)
- If secretin injection is suitable, the appropriate projection (usually coronal) is repeated every 15–30 seconds for 10–15 minutes, starting immediately after IV administration of 1 clinical unit of secretin per kilogram of body weight.
- If a tumor is detected or suspected with the previous acquisitions, three coronal gadolinium-enhanced dynamic breath-hold GRE scans are acquired through the pancreas and liver.
- In acute pancreatitis, the water-stimulation GRE T1-weighted sequence is repeated after gadolinium chelate injection.
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Clinical Applications
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Table 6 shows the advantages and limitations of MR imaging relative to CT and ERCP in evaluation of the pancreas.
Acute Pancreatitis
Acute pancreatitis, an acute inflammatory process of the pancreas, can be triggered by several factors, of which alcoholism and choledocholithiasis are the most common (22,23). In the severe forms of the disease, imaging is performed to assess the perfusion of the pancreatic parenchyma, the extent of necrosis, and the presence and extent of fluid collections. Contrast medium—enhanced CT is currently considered the standard of reference for evaluating these parameters, which have been shown to correlate with the course of the disease (24). In addition, CT presents a more manageable environment for severely ill patients than does MR imaging. However, contrast-enhanced MR imaging and MRCP can also accomplish these goals (Fig 25) and have recently been suggested as an alternative to contrast-enhanced CT for the initial staging of acute pancreatitis (25). MR imaging that combines cross-sectional T2-weighted sequences and contrast-enhanced fat-suppressed T1-weighted sequences with MRCP may be used before therapeutic planning. Indeed, it has the advantage of demonstrating possible choledocholithiasis, the presence or absence of ductal distention, disruption or leakage of the pancreatic duct, and the size, location, and possible communication of a pseudocyst with the pancreatic duct (Figs 26–28). In addition, it better demonstrates local hemorrhage in or around the pancreas and helps assess the internal consistency and drainability of fluid collections (26) (Figs 29, 30), which may influence the choice of treatment. Therefore, MR imaging could serve as the diagnostic modality and limit ERCP to those patients in whom a therapeutic intervention is expected.
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Figure 25. Acute necrotizing pancreatitis is demonstrated with MRCP before (A) and after (B) secretin administration. In B, the "ductal defect" visualized in A is completely filled (arrows), allowing main pancreatic duct disruption to be ruled out. Fat-suppressed TSE T1-weighted images before (C) and after administration of IV gadolinium chelate (D) clearly demonstrate the extent of glandular damage (arrowheads). The extent of necrosis is better evaluated in D.
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Figure 26. Pancreatic duct disruption and pseudocyst complicating acute pancreatitis demonstrated with MRCP before (A) and after (B, C) secretin administration and a coronal HASTE T2-weighted sequence (D). In C, a more targeted projection clearly demonstrates the communication (arrow) of the pseudocyst with a pancreatic fistula originating in the tail (arrowhead). Note that the pancreatic duct appears normal (arrow in B) downstream to the rupture. In B, the pseudocyst (*) increased in volume compared to that seen in A, suggesting a communication with the pancreatic duct. In D, the topography of the fistula (arrow) is better demonstrated.
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Figure 27. Acute pancreatitis and pancreatic duct disruption with peripancreatic fluid collection. (A) Axial HASTE T2-weighted image demonstrates the anteriorly located fluid collection (*). (B) MRCP after secretin administration depicts a bright spot (arrow) in the pancreatic duct overlapping the fluid collection (*) and corresponding to the site of disruption (Movie 2). Morphologic changes involving the side branches in the tail are also depicted (arrowhead).
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Figure 28. Acute pancreatitis, pancreatic duct disruption, and pseudocyst demonstrated with MRCP after administration of secretin (A) and with coronal (B) and axial (C, D) HASTE T2-weighted sequences with fat suppression. In A, a pancreatic duct defect (arrow) not filled by secretin is seen in conjunction with a heterogeneous pseudocyst (*) and an upstream dilatation of the pancreatic duct (arrowhead). The pseudocyst wall, internal septation (arrowhead in D), and topography are better depicted in B—D.
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Figure 29. Chronic pancreatitis with a pancreatic duct rupture and a pseudocyst with necrotic debris in the tail of the pancreas demonstrated with MRCP (A) and corresponding axial (B) and coronal (C, D) HASTE T2-weighted sequences. The pseudocyst "wall", the necrotic debris, and the relationship with the wall of the stomach (*) are better visualized in B, C, and D (black arrows). The morphologic changes in the pancreatic duct (arrowheads) and a small fistula tract (white arrow) are better depicted in A.
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Figure 30. Acute pancreatitis with local hemorrhage around the head of the pancreas. (A) MRCP shows a normal pancreatic duct and a cystic lesion (arrow) in the tail. (B) Axial HASTE T2-weighted image also shows the cystic lesion (arrow). (C) On an axial HASTE T2-weighted image, the head of the pancreas (*) seems enlarged. (D) Fat-suppressed TSE T1-weighted image shows a focal area of hyperintensity (arrow) corresponding to hemorrhage.
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In patients presenting with recurrent attacks of pancreatic pain of unknown cause, the accuracy of MR imaging as a viable means of screening for pancreatic diseases still needs to be demonstrated; however, it is of major interest, since these patients have the highest risk for post-ERCP pancreatitis (27–30). When performed with secretin stimulation, MRCP has the potential to discriminate between healthy subjects and those with an obstructive pancreatic disease that may be related to the presence of major or minor ampullar obstruction (ie, pancreas divisum) (13,14) (Movie 3) (Figs 31, 32).
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Figure 31. Pancreas divisum and acute pancreatitis. (A, B) Unenhanced CT scans obtained at the level of the body (A) and head (B) of the pancreas clearly demonstrate glandular enlargement (*) with diffuse hypoattenuating areas related to inflammatory changes. (C, D) Corresponding MRCP images obtained before (C) and after (D) secretin administration. Improved delineation of the pancreatic duct and minor ampulla dilatation (arrow) are seen in D.
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Figure 32. Pancreas divisum and pancreatitis. (A) Contrast-enhanced helical CT shows an enlarged dorsal duct (arrowhead) anterior to the common bile duct (arrow). (B, C) Corresponding unenhanced (B) and secretin-enhanced (C) MRCP images demonstrate dorsal duct enlargement (arrow), abnormal side branches (arrowheads), and reduced duodenal filling.
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In this setting, ERCP includes the opportunity for visual inspection of the ampulla and the potential to diagnose small tumors not detectable at MR imaging. In the presence of diffuse or segmental distention of the pancreatic duct or a side branch without an associated stricture or chronic pancreatitis stigmata, the diagnosis of an intraductal mucin-producing tumor may be suggested (31–34). These lesions were previously diagnosed with ERCP, which allows fluid sampling for cytologic examination and intraductal biopsy. With the use of MRCP, a more accurate diagnosis without the risk of post-ERCP acute pancreatitis can now be achieved for those lesions involving a side branch (Figs 33–35).
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Figure 33. Intraductal papillary mucinous tumor in patient presenting with recurrent pancreatitis. (A) Unenhanced CT at the level of the head of the pancreas shows a well-delineated hypoattenuating lesion (arrow) not extending to the peripancreatic fat. (B) Corresponding MRCP image shows a pancreas divisum with a minute communication (arrow) in conjunction with a homogeneous, hyperintense lobulated lesion (*) in the ventral pancreas. (C) Coronal fat-suppressed HASTE T2-weighted image more clearly demonstrates communication of the lesion with the duct (arrow).
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Figure 34. Intraductal papillary mucinous tumor in patient presenting with recurrent pancreatitis. (A) MRCP after secretin administration demonstrates a pancreas divisum with minute communication and an irregular fluid-filled lesion (arrow) communicating with the ventral portion of the duct. (B, C) Corresponding ERCP images obtained after selective retrograde iodine contrast material injection fails to demonstrate the cystic tumor. In C, selective catheterization of the ventral portion of the pancreatic duct is shown.
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Figure 35. Intraductal papillary mucinous tumor in patient presenting with recurrent pancreatitis. (A, B) Contrast-enhanced CT scan (A) and corresponding axial HASTE T2-weighted iamge (B) clearly demonstrate a ventral pancreatic duct enlargement (arrows) and no tumor. (C, D) MRCP (C) and corresponding ERCP (D) better demonstrate the extent of the intraductal lesion, its irregular margins, and filling defects (arrows), corresponding to mucus production and papillary hyperplasia.
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Chronic Pancreatitis
The role of imaging in the evaluation of chronic pancreatitis is to establish the diagnosis, to monitor possible complications (biliary involvement, pseudocysts, fistulas), and to plan therapy. The diagnosis is based on evaluation of the functional integrity of the gland and on morphologic changes in the glandular tissue, pancreatic duct, and side branches. Ductal involvement includes dilatation, narrowing or stricture formation, irregular contour, pseudocysts, and filling defects representing calculi, mucinous plugs, or debris, as defined in the 1983 Cambridge symposium (35,36).
Patients with advanced disease, presenting with these hallmarks of chronic pancreatitis, are easily recognized at CT.
MRCP with secretin administration demonstrates the ductal anatomy, the degree and level of pancreatic duct obstruction, associated pseudocysts, common bile duct stricture, and possible exocrine function impairment, all of which may be helpful before planning therapy (Figs 36, 37).
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Figure 36. Chronic calcified pancreatitis. (A) Plain radiograph of the pancreatic area shows multiple calcified stones. (B) ERCP with the catheter placed in the ventral pancreatic duct shows that stones are partially broken (arrowhead) after extracorporeal shockwave lithotripsy. Stones are located in the Santorini duct. (C, D) MRCP in the axial (C) and coronal (D) planes clearly demonstrates the exact location of the filling defects (arrows) in the Santorini duct and the marked ductal alterations of chronic pancreatitis (enlargement of the main duct, irregularities, and side branch dilatation). This case illustrates the potential of MRCP as a guide for endoscopic therapy and for follow-up studies.
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Figure 37. Obstructive chronic calcified pancreatitis. (A) MRCP shows characteristic alterations with marked ductal dilatation, filling defects, and a smooth common bile duct stricture (arrowhead). (B, C) Corresponding cross-sectional MR images demonstrate glandular enlargement and decreased signal intensity on the water-stimulated GRE T1-weighted image (arrowheads in C). Extrinsic gastric wall compression (arrows) due to glandular enhancement is also displayed on both MRCP (A) and coronal HASTE T2-weighted (B) images.
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One disadvantage of MR imaging may be its poor sensitivity in detecting scattered calcifications throughout the pancreas or in the distal portion of the pancreatic duct (Fig 38) and in detecting and helping determine the cause of noncalcified filling defects (Fig 39).
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Figure 38. Chronic calcified pancreatitis. (A) Unenhanced CT scan shows the calcified stones (arrow) in the head of the pancreas. (B) Axial HASTE T2-weighted image does not show the stones. (C) MRCP shows the extent of ductal damage and side-branch involvement (arrowheads) but does not clearly demonstrate the stones and their distribution, nor the exact morphology of the ducts in the head of the pancreas.
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Figure 39. Intraductal mucus-producing lesions mimicking chronic pancreatitis. (A) MRCP shows a mild dilatation of the pancreatic duct and side branches (arrowheads) and no filling defects. (B) Fat-suppressed TSE T1-weighted image through the pancreas shows a subtle decrease in signal intensity in the tail (arrow). (C, D) ERCP at the level of the head and body (C) and tail (D) of the pancreas shows that the duct was partially filled with mucus (arrows).
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Therefore, at our institution, we combine unenhanced CT and MR imaging with MRCP to evaluate advanced disease before therapy. Because it is completely noninvasive, MR imaging is potentially suitable for follow-up in patients with chronic pancreatitis after relief of ductal obstruction is obtained with endoscopic therapy (Figs 40, 41) or surgical bypass (37,38). The detection of mild forms of chronic pancreatitis and differentiation from pancreatic carcinoma remain major challenges for noninvasive imaging methods. At present, ERCP is the most sensitive imaging procedure for detecting the characteristic side-branch involvement of early stages of chronic pancreatitis. The accuracy of MR imaging for the detection of these early changes is not known. The administration of secretin improves side-branch visualization at MRCP and is suitable for patients with inconclusive CT or cross-sectional MR imaging findings (Figs 42-44).
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Figure 40. Chronic pancreatitis with obstructive stones. (A) Contrast-enhanced CT section at the level of the head of the pancreas shows the stones and pancreatic duct dilatation (arrowheads). (B) MRCP performed before endoscopic stone extraction reveals the filling defect (arrow) and the marked pancreatic duct dilatation; no anatomic variant is seen, and the common bile duct is slightly enlarged. (C) After stone removal, MRCP shows a substantial decrease in pancreatic duct and common bile duct caliber.
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Figure 41. Chronic pancreatitis with pseudocyst in the head of the pancreas. (A, B) Coronal (A) and axial (B) HASTE T2-weighted images show the pseudocyst in the head of the pancreas and its relationship with the ventral pancreatic duct (arrow). (C, D) MRCP images obtained before (C) and after (D) endoscopic stent insertion clearly demonstrate the distention of the pancreatic duct and side branches (arrowheads in C), as well as the pseudocyst (arrow in C) and the dramatic reduction in the caliber of the pancreatic duct and disappearance of the pseudocyst after stent insertion (arrow in D).
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Figure 42. Mild chronic pancreatitis. Comparative study with unenhanced CT, MR imaging, and secretin-enhanced MRCP. At unenhanced CT (A), no calcifications, pancreatic duct enlargement, or glandular atrophy are depicted. Cross-sectional T2-weighted image (B) and MRCP (C) demonstrate main pancreatic duct and side-branch enlargement (arrowheads) compatible with mild chronic pancreatitis changes.
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Figure 43. Chronic pancreatitis with an increase in pancreatic lipase and amylase in a symptom-free patient. (A, B) Contrast-enhanced CT scans in the delayed phase shows a homogeneous pancreas without calcifications and a subtle enlargement of the pancreatic duct in the head (arrow). (C, D) Secretin-enhanced MRCP images obtained 2 (C) and 8 (D) minutes after secretin administration show pancreatic duct dilatation, irregularities of the borders, and side-branch dilatation (arrowheads) compatible with chronic pancreatitis changes.
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Figure 44. Chronic pancreatitis. Unenhanced (A) and secretin-enhanced (B) MRCP, ERCP (C), and axial HASTE T2-weighted image (D). Ductal changes are clearly depicted in A—C (arrowheads), while they are less conspicuous on the cross-sectional MR study (D). This case illustrates the need for MRCP studies even in the absence of ductal dilatation at cross-sectional MR imaging.
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In a recent study, MR imaging allowed the diagnosis of mild forms of chronic pancreatitis in 19 of 28 patients with suspected pancreatic disease who underwent ERCP (15). Follow-up of morphologic changes and functional assessment with secretin may help determine the accuracy of MR imaging for the detection of the early stages of chronic pancreatitis. The differential diagnosis of focal chronic pancreatitis and pancreatic carcinoma remains difficult. Both have low signal intensity on T1-weighted images, are associated with ductal obstruction, and show abnormal pancreatic enhancement (39). In this setting, in patients with a preserved pancreatic exocrine function, MRCP with secretin administration may help demonstrate the associated pancreatic duct stricture, its filling dynamics, and the location of the side branches at the level of the stricture (Figs 45–48).
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Figure 45. Chronic pancreatitis and main pancreatic duct stricture in the body of the pancreas. (A, B) Secretin-enhanced MRCP demonstrates that at the level of the stricture, side branches are located close to the stricture (arrowhead). Duodenal filling is normal. (C, D) Axial HASTE T2-weighted (C) and axial fat suppressed TSE T1-weighted (D) images confirm the absence of a space-occupying lesion (arrows). Moreover, in D, the hyperintense normal pancreas is clearly differentiated from the hypointense fibrotic parenchyma (arrowheads).
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Figure 46. Complication of acute pancreatitis. Unenhanced (A) and secretin-enhanced (B) MRCP images. In A, a single distal pancreatic duct stricture and proximal dilatation are visualized (arrowheads). In B, complete filling of the stricture (arrowheads) was obtained after IV secretin administration.
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Figure 47. Groove pancreatitis. (A) MRCP demonstrates a "double duct" stricture with proximal dilatation of the common bile duct and pancreatic duct (arrow). A cystic lesion (arrrowhead) is seen between the common bile duct and the duodenal wall. (B) Axial fat-suppressed TSE T1-weighted image at the level of the head of the pancreas shows the normal hyperintense pancreas (arrow) and no tumor. However, the pancreas is medially shifted because of the presence of a hypointense lesion (*) located between the head of the pancreas and the gallbladder. (C, D) Axial unenhanced (C) and delayed gadolinium-enhanced (D) GRE T1-weighted images, demonstrate diffuse enhancement (arrow) of the sheetlike mass, which corresponded to fibrotic tissue (40).
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Abstract
LEARNING OBJECTIVES
