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Gastrointestinal Imaging |
1 From the Department of Radiology, Thomas Jefferson University Hospital, 132 S 11th St, 7th Floor Main Bldg, Philadelphia, PA 19107. From the 1997 RSNA scientific assembly. Received May 21, 1998; revision requested July 14; revision received October 9; accepted December 16. Address reprint requests to P.T.J. (e-mail: johnson5@jeflin.tju.edu).
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Abstract |
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 TOP Abstract IntroductionMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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MATERIALS AND METHODS: A retrospective review of MR and pathology examination findings was performed for 24 patients with pancreatic ductal adenocarcinoma and seven with chronic pancreatitis who underwent dynamic gadolinium-enhanced breath-hold spoiled gradient-echo imaging. Arterial, portal, and delayed phase images were obtained after injection of gadopentatate dimeglumine. The MR images of 14 patients without clinical evidence of pancreatic disease were also reviewed as controls. Signal intensity (SI) was measured on the precontrast (pre) and gadolinium-enhanced (post) images of the area of the pancreas sampled at biopsy and of the nontumorous pancreas. Percentage enhancement was defined as SIpre/SIpost x 100.
RESULTS: Normal pancreas showed rapid enhancement that peaked in the arterial or portal phase. For both diseases, T1-weighted images showed hypointense masses with progressive enhancement (differences were significant [P < .05] on only delayed fat-saturated images). Differences in enhancement between either disease state and normal pancreas were significant for at least one phase. Nontumorous pancreas in patients with carcinoma showed gradual enhancement that was significantly different from that of normal pancreas.
CONCLUSION: Chronic pancreatitis and pancreatic carcinoma show abnormal pancreatic enhancement, but the two were not distinguished on the basis of degree and time of enhancement.
Index terms: Pancreas, MR, 77.121411, 77.121412, 77.121415, 77.12143 • Pancreas, neoplasms, 77.321 • Pancreatitis, 77.291
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Introduction |
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TOPAbstractIntroductionMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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A recent study compared images of the pancreas obtained with dynamic gadolinium-enhanced fast multiplanar spoiled gradient-echo (GRE), T1- and T2-weighted spin-echo (SE), and gadolinium-enhanced T1-weighted SE sequences. Dynamic gadolinium-enhanced multiplanar fast spoiled GRE images were found to result in more accurate and specific diagnoses of pathologic conditions in the pancreas (2). The purpose of this study was to determine if the contrast enhancement pattern on dynamic gadolinium-enhanced multiplanar fast spoiled GRE images of the pancreas could distinguish masses due to chronic pancreatitis from those due to pancreatic carcinoma.
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MATERIALS AND METHODS |
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The diagnosis of pancreatic carcinoma was confirmed at surgical excision of the mass by means of a Whipple procedure in seven of the 24 patients. Intraoperative biopsy was performed in 12 patients with unresectable tumors. The remaining five patients underwent US-guided fine-needle aspiration (n = 4) or core biopsy (n = 1); their tumors were deemed unresectable at preoperative imaging.
In the seven patients with the diagnosis of chronic pancreatitis, the pathologic correlation was obtained by means of US-guided fine-needle aspiration (n = 2), surgical resection of the mass (n = 1), or intraoperative biopsy (n = 4). Two of the patients who underwent intraoperative biopsy also underwent fine-needle aspiration or pancreatic duct brushing. Findings at follow-up (range, 3–17 months) MR imaging, CT, or endoscopic retrograde cholangiopancreatography confirmed no change in two patients. Two patients underwent follow-up MR imaging that depicted enlargement of the mass, but no further biopsies were performed. Three patients did not undergo follow-up imaging.
Fourteen patients who underwent dynamic imaging of the liver for indications unrelated to pancreatic disease served as control subjects. Their examinations were performed to evaluate hemangioma, fatty liver, or parenchymal liver disease.
All examinations were performed on a 1.5-T system (GE Medical Systems, Milwaukee, Wis). The following parameters were used in the multiplanar fast spoiled GRE sequence: repetition time msec/echo time msec, 100–170/1.3–2.9; flip angle, 90°; matrix, 256 x 128 to 256 x 192; one signal acquired; section thickness, 7–9 mm; gap, 1–2 mm; field of view, 24–38 cm. Gadopentatate dimeglumine (Magnevist; Berlex Laboratories, Wayne, NJ) was administered (0.1 mmol/L per kilogram of body weight) intravenously at approximately 2 mL/sec by means of hand injection followed by a 20-mL saline solution flush. Imaging was initiated after 10 mL of the flush had been infused.
Imaging was performed with four breath-hold gadolinium-enhanced sequences in most patients. These sequences correlated approximately with arterial dominant (n = 45), portal venous (n = 45), parenchymal (n = 38), and delayed (n = 42) phases of contrast enhancement. Eight patients with pancreatic cancer underwent imaging with only three gadolinium-enhanced sequences (only one delayed sequence was performed). Five of the eight patients did not undergo imaging with the third gadolinium-enhanced sequence, and three did not undergo imaging with the final delayed fat-saturated sequence. All seven of the patients with chronic pancreatitis underwent imaging with all four sequences.
During review of each case, an adequate bolus was confirmed on the basis of the presence of a moiré pattern in the spleen, absence of hepatic vein contrast enhancement, and corticomedullary differentiation of the kidneys. On the basis of these criteria, two patients were excluded because of an inadequate bolus. The final delayed fat-saturated sequence usually required two breath holds.
The original MR imaging data were loaded onto a workstation (Cannon; Sun Microsystems, Palo Alto, Calif) by means of software (RATIONAL IMAGING; Intuitive Software, West Hills, Calif). Each study was reviewed with the pathology report and US-guided biopsy report or intraoperative note to confirm the location of the mass sampled at biopsy. In the patients with pancreatic carcinoma or chronic pancreatitis, the largest possible region of interest was drawn when the signal intensity of the mass or the nontumorous pancreas was measured proximal to tumor. In the control subjects, region-of-interest measurements were obtained from the pancreatic head and body or tail. The signal intensity was measured on the precontrast and gadolinium-enhanced multiplanar fast spoiled GRE images (n = 31). All regions of interest were placed by one author (P.T.J.).
Percentage enhancement values for the pancreatic mass, nontumorous pancreas, and normal pancreas were calculated by dividing the gadolinium-enhanced signal intensity by the precontrast signal intensity and multiplying by 100. A Student two-tailed t test was performed to compare the percentage enhancement of carcinoma, nontumorous pancreas proximal to tumor, chronic pancreatitis, and normal pancreas.
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RESULTS |
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In the setting of a pancreatic head carcinoma, the nontumorous pancreatic body or tail (n = 19) showed gradual progressive enhancement after administration of gadopentatate dimeglumine that peaked on the delayed fat-saturated images (Fig 4). The percentage enhancement of the body or tail was significantly different from that of the normal pancreatic body on the portal venous phase (P = .003), parenchymal (P = .005), and delayed fat-saturated (P < .001) gadolinium-enhanced images. The nontumorous body and tail demonstrated a decreased precontrast signal intensity (Fig 5), which accounted in part for the differences in percentage enhancement.
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DISCUSSION |
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TOPAbstractIntroductionMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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In many studies, CT has been used in an attempt to distinguish chronic pancreatitis from pancreatic carcinoma. Karawasa et al (10) evaluated the pancreatic duct caliber and contour and found that smooth or beaded dilatations of the duct are more common with an obstructing neoplasm. Chronic pancreatitis more frequently results in an irregularly dilated duct, often with intraductal calcification. Additionally, they found a statistically significant difference in the ratio of duct caliber to pancreatic gland width, which is higher in patients with cancer (10). Megibow et al (11) originally described thickening of the celiac artery or superior mesenteric artery as specific for carcinoma. However, more recent work by Baker (8) and Shulte et al (12) demonstrates that acute and chronic inflammatory processes can result in infiltration of the fat around the superior mesenteric artery and encasement of the vessel by a mass or periarterial adenopathy. Recognizing that periarterial findings are nonspecific, Elmas et al (13) measured the diameter of the superior mesenteric artery and vein in patients with chronic pancreatitis or pancreatic carcinoma. They found that the artery enlarges in the setting of cancer, and carcinoma should be suspected if the artery-to-vein ratio is greater than 1.0.
As MR imaging techniques improve, findings in comparative studies reveal potentially higher diagnostic accuracy compared to that with other modalities in the evaluation of pancreatic disease (3,5). The study by Semelka et al (3) compared MR imaging with CT and revealed significantly diminished delayed contrast enhancement at MR imaging in chronic pancreatitis compared to nonnecrotic acute pancreatitis or normal pancreas. The more recent work by Gohde et al (2) compared a dynamic gadolinium-enhanced multiplanar fast spoiled GRE sequence to T1- and T2-weighted SE sequences and a gadolinium-enhanced T1-weighted SE sequence with fat saturation. The multiplanar fast spoiled GRE sequence has higher sensitivity, specificity, and accuracy for detection of pancreatic disease and yields images of higher quality with better delineation of pancreatic anatomy.
In several studies, MR imaging was used in an attempt to distinguish pancreatic diseases. Jenkins et al (14) found that there is no statistically significant difference in T1 and T2 between chronic pancreatitis and pancreatic carcinoma, although the relaxation times for cancer differed from normal findings in control subjects. More recently, Sittek et al (15) used fast multiplanar MR imaging to demonstrate that chronic pancreatitis and cancer enhance differently from normal pancreas or unaffected pancreatic parenchyma in patients with a mass. Semelka et al (3) compared calcific versus noncalcific chronic pancreatitis imaged with fast GRE and fat-suppressed SE sequences. Percentage contrast enhancement is significantly different between the two groups (16).
The promising work in CT and MR imaging combined with the higher diagnostic accuracy of the dynamic multiplanar fast spoiled GRE sequence prompted us to compare the dynamic multiplanar MR characteristics of chronic pancreatitis with those of pancreatic carcinoma. Both pathologic entities resulted in gradual progressive enhancement of the involved pancreatic parenchyma that would be difficult to distinguish subjectively. Although there was a significant difference in percentage enhancement between the two diseases with the delayed fat-saturated sequence, the amount of overlap would preclude distinguishing the two subjectively on this basis.
Evaluation of the histology of chronic pancreatitis and carcinoma reveals abundant fibrosis in both pathologic conditions (Figs 2, 3), which likely accounts for their similar imaging appearance. Additionally, the pancreas proximal to an obstructing mass may undergo atrophy and fibrosis that lead to an altered pattern of enhancement when compared to that of normal pancreatic parenchyma. Interestingly, this pattern of gradual enhancement in the nontumorous body of a pancreas with a pancreatic head mass was more similar to the enhancement of the cancer itself than to that of chronic pancreatitis. This may be due to the lack of inflammation that accompanies typical chronic pancreatitis.
In conclusion, masses due to pancreatic carcinoma and chronic pancreatitis show a pattern of contrast enhancement after dynamic infusion of gadopentatate dimeglumine that is altered compared to that of normal pancreas. The similar gradual pattern of enhancement and overlap in peak enhancement preclude distinction of the two entities on the basis of gadolinium-enhanced MR findings. Further work must address other dynamic MR imaging features that may help distinguish the two pathologic entities.
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Footnotes |
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Author contributions: Guarantor of integrity of entire study, P.T.J.; study concepts and design, P.T.J., E.K.O.; definition of intellectual content, P.T.J., E.K.O.; literature research, P.T.J.; clinical studies, P.T.J., E.K.O.; data acquisition and analysis, P.T.J., E.K.O.; statistical analysis, P.T.J., E.K.O.; manuscript preparation, P.T.J.; manuscript editing, P.T.J., E.K.O.
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TOPAbstractIntroductionMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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= P < .005) and peaks on the delayed fat-saturated image (Post #4). Error bars represent mean plus or minus SD.
