Pancreas ductal adenocarcinoma (PDAC) accounts for 85–90% of all pancreatic neoplasms and is one of the leading causes of death worldwide [1, 2]. Various other tumors and inflammatory lesions in the pancreas occasionally mimic PDAC. It is clinically important to differentiate PDAC from other pancreatic lesions because of different prognosis and treatment options [3, 4, 5]. PDAC commonly involves various major vessels around the pancreas and frequently accompanies distant metastases. As a result, less than 20% of patients with PDAC are eligible for resection at the time of diagnosis . On the other hand, patients with neuroendocrine tumors (NETs) or solid pseudopapillary tumors (SPTs) are usually good candidates for surgical resection and show better prognosis than those with PDAC [3, 7]. Moreover, most inflammatory lesions do not need surgical resection but rather conservative treatment [8, 9]. Therefore, the objective of this article is to assist in differential diagnosis by describing imaging features of PDAC and its mimics.
Computed tomography (CT) is a useful modality for detecting and staging PDACs . PDACs usually appear as low attenuating masses in the pancreatic and portal venous phases and typically accompany pancreatic duct dilatation with abrupt narrowing (Figures 1A, 1B, and 2A). Bile duct dilatation is occasionally combined with a dilated pancreatic duct in cases of pancreas head cancer; this is called the double duct sign (Figure 1B) . Vascular invasion is important for diagnosing PDAC and determining therapeutic options and is supposed when there is a vascular caliber change, irregular vessel wall, more than 180° of vessel is in contact with the tumor, or peritumoral fat infiltration is identified (Figures 1A, 2B, and 2C) [12, 13]. Liver metastases from PDAC usually show hypovascularity (Figure 2D).
Pancreatic NETs originate from the islet cells of Langerhans and are divided into low-, intermediate-, and high-grade according to the World Health Organization classification . High-grade NETs more frequently show vascular invasion, lymph node metastasis, and diffusion restriction compared with low-grade; therefore, high-grade NETs can mimic PDAC on images (Figure 3A) [7, 14, 15]. However, high-grade NETs usually do not show pancreatic duct dilatation. In addition, they occasionally accompany tumor thrombus, which can be helpful in the differential diagnosis of high-grade NETs from PDAC (Figure 3C) . Liver metastases from NETs frequently reveal findings of hypervascularity and intralesional hemorrhage, in contrast to those from PDAC, which reveal hypovascularity (Figure 3B and 3D) [17, 18].
SPTs are uncommon neoplasms with low malignancy potential, occurring predominantly in young women [3, 19]. Calcification, cystic change, and internal hemorrhage due to weak vascular channels are characteristic features of SPT [20, 21]. However, small (≤3 cm) SPTs show different imaging findings from larger ones, primarily a homogeneous nature. Small SPTs show a pure solid consistency, well-defined margin, and diffusion restriction on magnetic resonance (MR) imaging (Figure 4A–D) [22, 23]. After contrast infusion, small SPTs reveal an early heterogeneous nature, followed by a progressive enhancement pattern (Figure 4E and 4F) [22, 23].
A previous study  reported that up to 11% of patients with malignancy have pancreatic metastases at autopsy. In patients with another malignancy who have pancreatic mass, lack of pancreatic duct dilatation usually suggests that pancreatic metastases are more likely than PDAC (Figure 5) . However, pancreatic ductal involvement can unfortunately occur in some pancreatic metastases. In those cases, the absence of adjacent vascular invasion may be a clue for differentiation of metastases from PDAC [24, 26].
Autoimmune pancreatitis (AIP) is an uncommon form of chronic pancreatitis caused by an autoimmune mechanism . It is a challenge to distinguish focal AIP from PDAC because the two diseases show similar imaging features, but several reports [28, 29, 30, 31] have offered suggestions for discriminating between them. According to those studies, slightly lower or similar signal intensity compared with the spleen on unenhanced T1-weighted images, relatively homogeneous enhancement, signs of pancreatic duct penetration, smooth tapered narrowing of the pancreatic duct (icicle sign) or bile duct, multifocal stricture of the pancreatic duct, and a delayed enhancement pattern on dynamic enhanced images are features favoring AIP over PDAC (Figure 6). Another clue for diagnosis of AIP is involvement of an extra-pancreatic organ such as the biliary tree, retroperitoneum, salivary gland, or kidney (Figure 7) .
Groove pancreatitis is an uncommon type of pancreatitis affecting the pancreaticoduodenal groove, defined as the potential space between the pancreatic head, common bile duct, and duodenum . This inflammatory lesion commonly develops in middle-aged men with a history of chronic alcoholism . On imaging, groove pancreatitis presents as an ill-defined lesion between the pancreatic head and the duodenum, sometimes with bile and pancreatic duct narrowing; therefore, it can mimic PDAC (Figure 8) [9, 25, 33]. However, groove pancreatitis reveals a sheet-like curvilinear appearance and delayed enhancement. In addition, it is accompanied by cystic dystrophy in the duodenal wall and smooth bile duct narrowing (Figure 8D) [9, 33].
Neoplastic lesions such as high-grade NETs, small SPTs, and metastases and inflammatory lesions including focal AIP and groove pancreatitis can mimic PDAC. Abrupt narrowing of a dilated pancreatic duct is a usual imaging finding of PDAC. Although some mimics occasionally accompany pancreatic duct dilatation, they have points of differential diagnosis: presence of tumor thrombus and hypervascular liver metastases, absence of adjacent vascular invasion, and delayed enhancement pattern. In addition to these imaging findings, the shape of the narrowed pancreatic duct is a key imaging feature for discrimination of PDAC from other disease entities. Familiarity with the imaging features of PDAC and its mimics is paramount for managing patients in daily practice.
|MRCP||Magnetic resonance cholangiopancreatography|
|PDAC||Pancreas ductal adenocarcinoma|
|SPT||Solid pseudopapillary tumor|
This research did not receive any specific grant from funding agencies in the public, commercial or not-for-profit sectors. This work was supported by the Soonchunhyang University Research Fund.
The authors have no competing interests to declare.
Jemal, A, Bray, F, Center, MM, Ferlay, J, Ward, E and Forman, D. Global cancer statistics. CA: a cancer journal for clinicians. 2011; 61(2): 69–90. DOI: https://doi.org/10.3322/caac.20107
Sener, SF, Fremgen, A, Menck, HR and Winchester, DP. Pancreatic cancer: a report of treatment and survival trends for 100,313 patients diagnosed from 1985–1995, using the National Cancer Database. Journal of the American College of Surgeons. 1999; 189(1): 1–7. DOI: https://doi.org/10.1016/S1072-7515(99)00075-7
Papavramidis, T and Papavramidis, S. Solid pseudopapillary tumors of the pancreas: review of 718 patients reported in English literature. Journal of the American College of Surgeons. 2005; 200(6): 965–72. DOI: https://doi.org/10.1016/j.jamcollsurg.2005.02.011
Rumancik, WM, Megibow, AJ, Bosniak, MA and Hilton, S. Metastatic disease to the pancreas: Evaluation by computed tomography. Journal of computer assisted tomography. 1984; 8(5): 829–34. DOI: https://doi.org/10.1097/00004728-198410000-00003
Klimstra, DS, Modlin, IR, Coppola, D, Lloyd, RV and Suster, S. The pathologic classification of neuroendocrine tumors: A review of nomenclature, grading, and staging systems. Pancreas. 2010; 39(6): 707–12. DOI: https://doi.org/10.1097/MPA.0b013e3181ec124e
Al-Hawary, MM, Francis, IR, Chari, ST, Fishman, EK, Hough, DM, Lu, DS, et al. Pancreatic ductal adenocarcinoma radiology reporting template: Consensus statement of the Society of Abdominal Radiology and the American Pancreatic Association. Radiology. 2014; 270(1): 248–60. DOI: https://doi.org/10.1148/radiol.13131184
Canellas, R, Burk, KS, Parakh, A and Sahani, DV. Prediction of pancreatic neuroendocrine tumor grade based on CT features and texture analysis. American Journal of Roentgenology. 2018; 210(2): 341–6. DOI: https://doi.org/10.2214/AJR.17.18417
Vlachou, PA, Khalili, K, Jang, H-J, Fischer, S, Hirschfield, GM and Kim, TK. IgG4-related sclerosing disease: Autoimmune pancreatitis and extrapancreatic manifestations. Radiographics. 2011; 31(5): 1379–402. DOI: https://doi.org/10.1148/rg.315105735
El-Nekidy, AE-AM, Ibrahim, ME, Abdelgawad, MS, Abouyoussef, RA, Abdelkader, AA and Elfaiomy, TA. Groove pancreatitis: Imaging features and management. The Egyptian Journal of Radiology and Nuclear Medicine. 2016; 47(4): 1175–84. DOI: https://doi.org/10.1016/j.ejrnm.2016.09.016
Tamm, EP, Balachandran, A, Bhosale, PR, Katz, MH, Fleming, JB, Lee, JH, et al. Imaging of pancreatic adenocarcinoma: Update on staging/resectability. Radiologic Clinics of North America. 2012; 50(3): 407–28. DOI: https://doi.org/10.1016/j.rcl.2012.03.008
Gangi, S, Fletcher, JG, Nathan, MA, Christensen, JA, Harmsen, WS, Crownhart, BS, et al. Time interval between abnormalities seen on CT and the clinical diagnosis of pancreatic cancer: Retrospective review of CT scans obtained before diagnosis. American Journal of Roentgenology. 2004; 182(4): 897–903. DOI: https://doi.org/10.2214/ajr.182.4.1820897
Horton, KM and Fishman, EK. Multidetector CT angiography of pancreatic carcinoma: Part I, evaluation of arterial involvement. American journal of roentgenology. 2002; 178(4): 827–31. DOI: https://doi.org/10.2214/ajr.178.4.1780827
Lu, D, Reber, HA, KraSny, RM, Kadell, BM and Sayre, J. Local staging of pancreatic cancer: Criteria for unresectability of major vessels as revealed by pancreatic-phase, thin-section helical CT. AJR American journal of roentgenology. 1997; 168(6): 1439–43. DOI: https://doi.org/10.2214/ajr.168.6.9168704
Gallotti, A, Johnston, RP, Bonaffini, PA, Ingkakul, T, Deshpande, V, Castillo, CF-d, et al. Incidental neuroendocrine tumors of the pancreas: MDCT findings and features of malignancy. American Journal of Roentgenology. 2013; 200(2): 355–62. DOI: https://doi.org/10.2214/AJR.11.8037
Wang, Y, Chen, ZE, Yaghmai, V, Nikolaidis, P, McCarthy, RJ, Merrick, L, et al. Diffusion-weighted MR imaging in pancreatic endocrine tumors correlated with histopathologic characteristics. Journal of Magnetic Resonance Imaging. 2011; 33(5): 1071–9. DOI: https://doi.org/10.1002/jmri.22541
Rockall, AG and Reznek, RH. Imaging of neuroendocrine tumours (CT/MR/US). Best practice & research Clinical endocrinology & metabolism. 2007; 21(1): 43–68. DOI: https://doi.org/10.1016/j.beem.2007.01.003
Rha, SE, Jung, SE, Lee, KH, Ku, YM, Byun, JY and Lee, JM. CT and MR imaging findings of endocrine tumor of the pancreas according to WHO classification. European journal of radiology. 2007; 62(3): 371–7. DOI: https://doi.org/10.1016/j.ejrad.2007.02.036
Debray, M, Geoffroy, O, Laissy, J, Lebtahi, R, Silbermann-Hoffman, O, Henry-Feugeas, M, et al. Imaging appearances of metastases from neuroendocrine tumours of the pancreas. The British journal of radiology. 2001; 74(887): 1065–70. DOI: https://doi.org/10.1259/bjr.74.887.741065
Buetow, PC, Buck, JL, Pantongrag-Brown, L, Beck, KG, Ros, PR and Adair, CF. Solid and papillary epithelial neoplasm of the pancreas: Imaging-pathologic correlation on 56 cases. Radiology. 1996; 199(3): 707–11. DOI: https://doi.org/10.1148/radiology.199.3.8637992
Choi, J-Y, Kim, M-J, Kim, JH, Kim, SH, Lim, JS, Oh, YT, et al. Solid pseudopapillary tumor of the pancreas: Typical and atypical manifestations. American Journal of Roentgenology. 2006; 187(2): W178–W86. DOI: https://doi.org/10.2214/AJR.05.0569
Al-Qahtani, S, Gudinchet, F, Laswed, T, Schnyder, P, Schmidt, S, Osterheld, M-C, et al. Solid pseudopapillary tumor of the pancreas in children: Typical radiological findings and pathological correlation. Clinical imaging. 2010; 34(2): 152–6. DOI: https://doi.org/10.1016/j.clinimag.2009.06.024
Yu, MH, Lee, JY, Kim, MA, Kim, SH, Lee, JM, Han, JK, et al. MR imaging features of small solid pseudopapillary tumors: Retrospective differentiation from other small solid pancreatic tumors. American journal of roentgenology. 2010; 195(6): 1324–32. DOI: https://doi.org/10.2214/AJR.10.4452
Baek, JH, Lee, JM, Kim, SH, Kim, SJ, Kim, SH, Lee, JY, et al. Small (≤3 cm) Solid Pseudopapillary Tumors of the Pancreas at Multiphasic Multidetector CT 1. Radiology. 2010; 257(1): 97–106. DOI: https://doi.org/10.1148/radiol.10092089
Ahmed, S, Johnson, PT, Hruban, R and Fishman, EK. Metastatic disease to the pancreas: Pathologic spectrum and CT patterns. Abdominal imaging. 2013; 38(1): 144–53. DOI: https://doi.org/10.1007/s00261-012-9856-8
Coakley, FV, Hanley-Knutson, K, Mongan, J, Barajas, R, Bucknor, M and Qayyum, A. Pancreatic imaging mimics: Part 1, imaging mimics of pancreatic adenocarcinoma. American Journal of Roentgenology. 2012; 199(2): 301–8. DOI: https://doi.org/10.2214/AJR.11.7907
Klein, KA, Stephens, DH and Welch, TJ. CT characteristics of metastatic disease of the pancreas. Radiographics. 1998; 18(2): 369–78. DOI: https://doi.org/10.1148/radiographics.18.2.9536484
Cheuk, W and Chan, JK. IgG4-related sclerosing disease: A critical appraisal of an evolving clinicopathologic entity. Advances in anatomic pathology. 2010; 17(5): 303–32. DOI: https://doi.org/10.1097/PAP.0b013e3181ee63ce
Kim, HJ, Kim, YK, Jeong, WK, Lee, WJ and Choi, D. Pancreatic duct “Icicle sign” on MRI for distinguishing autoimmune pancreatitis from pancreatic ductal adenocarcinoma in the proximal pancreas. European radiology. 2015; 25(6): 1551–60. DOI: https://doi.org/10.1007/s00330-014-3548-4
Choi, S-Y, Kim, SH, Kang, TW, Song, KD, Park, HJ and Choi, Y-H. Differentiating Mass-Forming Autoimmune Pancreatitis From Pancreatic Ductal Adenocarcinoma on the Basis of Contrast-Enhanced MRI and DWI Findings. American Journal of Roentgenology. 2016; 206(2): 291–300. DOI: https://doi.org/10.2214/AJR.15.14974
Hur, BY, Lee, JM, Lee, JE, Park, JY, Kim, SJ, Joo, I, et al. Magnetic resonance imaging findings of the mass-forming type of autoimmune pancreatitis: Comparison with pancreatic adenocarcinoma. Journal of Magnetic Resonance Imaging. 2012; 36(1): 188–97. DOI: https://doi.org/10.1002/jmri.23609
Sun, G-F, Zuo, C-J, Shao, C-W, Wang, J-H and Zhang, J. Focal autoimmune pancreatitis: Radiological characteristics help to distinguish from pancreatic cancer. World J Gastroenterol. 2013; 19(23): 3634–41. DOI: https://doi.org/10.3748/wjg.v19.i23.3634
Itoh, S, Yamakawa, K, Shimamoto, K, Endo, T and Ishigaki, T. CT findings in groove pancreatitis: Correlation with histopathological findings. Journal of computer assisted tomography. 1994; 18(6): 911–5. DOI: https://doi.org/10.1097/00004728-199411000-00011
Raman, SP, Salaria, SN, Hruban, RH and Fishman, EK. Groove pancreatitis: Spectrum of imaging findings and radiology-pathology correlation. American Journal of Roentgenology. 2013; 201(1): W29–W39. DOI: https://doi.org/10.2214/AJR.12.9956