1.       Introduction

Recent advances in diagnostic techniques including Ultrasonography (US), Endoscopic Ultrasonography (EUS), Computed Tomography (CT), and Magnetic Resonance Imaging (MRI), pancreatic ductal adenocarcinoma has been diagnosed easier [1]. However, the differential diagnosis between an early stage pancreatic ductal adenocarcinoma and a focal chronic pancreatitis is still difficult [1-3]. A recent report indicated that the false positive rate of pancreaticoduodenectomy for presumed malignancy to be as high as 5-11% [4]. We herein report a case with distal pancreatectomy for a focal chronic pancreatitis mimicking an early pancreatic ductal adenocarcinoma.

2.       Case Report

A 43-year-old man was admitted to our hospital for treatment of a pancreatic tumor detected by US on medical check-up. The patient had no past history of serious illnesses, including any pancreatic diseases, diabetes mellitus, operations, or any hospitalization. Enhanced CT revealed a low-density mass of 10 mm in diameter with no enhancement in the pancreatic body (Figures 1a-c). MRI demonstrated stenosis of the main pancreatic duct and dilatation of the distal pancreatic duct (Figure 2a), while, no tumor could be detected by Fat-suppressed T1-weighted Images (FST1WI) and Diffusion-weighted Images (DWI) (Figures 2b,c). US revealed a hypoechoic and avascular area with a diameter of 8 mm (Figures 3a,b). However, EUS did not detect the tumor of the pancreas. Endoscopic retrograde cholangio-pancreatography (ERCP) revealed stenosis of main the pancreatic duct and dilatation of the distal duct (Figure 3c). Laboratory investigations included serum pancreatic amylase of 61 IU/L, serum carcinoembryonic antigen of 5.5 ng/ml, serum carbohydrate antigen 19-9 of 12 U/ml, and serum DUPAN-2 of 25 U/ml. With a diagnosis of pancreatic ductal adenocarcinoma of the pancreatic body, the patient underwent distal pancreatectomy and splenectomy with regional lymph node dissection. Histological examination revealed chronic inflammation of the pancreas which formed a fibrotic nodule with a diameter of 11 mm×10 mm. The fibrotic nodule included granulation, fat necrosis, and chronic inflammatory change of the main pancreatic duct which caused the stenosis. Because postoperative pancreatic fistula was developed, the patient underwent US-guided percutaneous drainage. The patient made satisfactory recovered after drainage, discharged on the 39^th postoperative day, and remains well.

3.       Discussion

Focal pancreatitis is defined as a focal inflammatory process in the pancreas that may mimic pancreatic ductal adenocarcinoma [5,6]. The differential diagnosis between early pancreatic ductal adenocarcinoma and focal pancreatitis is one of the important points for better therapeutic outcome of pancreatic ductal adenocarcinoma. Enhanced CT indicates high sensitivity for the diagnosis of pancreatic carcinoma and is useful for differential diagnosis between early pancreatic carcinoma and focal chronic pancreatitis [1,7]. Because pancreatic carcinoma is characterized by abundant fibrous stroma and hypovascularity, typical features of pancreatic cancer by enhanced CT include poor enhancement of the tumor compared with surrounding normal pancreatic tissue in the early phase and gradual enhancement in delay phase [1]. In small lesion, delayed enhancement of pancreatic adenocarcinoma is predominantly observed [8]. In dynamic CT, pancreatic ductal adenocarcinoma shows increasing enhancement value, while chronic pancreatitis demonstrates delayed-washout pattern [9]. Recent reports indicate that apparent diffusion coefficient (ADC) of MRI quantification of the pancreatic ductal adenocarcinoma is significantly lower than that of pancreatitis [2,10]. In addition, DWI and FST1WI are useful for detecting small (£2cm in diameter) pancreatic ductal adenocarcinoma, which cannot be detected by dynamic CT [11,12]. In present case, focal pancreatitis lesion was detected by US and enhanced CT. However, EUS, MRI including FST1WI and DWI could not detect pancreatic tumor. These negative findings may be clue for correct diagnosis in our patient.

Figures 1(a-c): Enhanced (a, b) and plane (c) computed tomography (CT) revealed a low-density area of 10 mm in diameter. No enhancement was seen in the early (a) or delayed (b) phase of enhanced CT.

Figures 2(a-c): Magnetic resonance imaging (MRI) (a) demonstrated stenosis of the main pancreatic duct (arrowhead) and dilatation of the distal duct. No tumor could be detected in the pancreas by fat-suppressed T1-weighted images (FST1WI) (b) and diffusion-weighted images (DWI) (c).

Figures 3(a-c): US (a) and endoscopic ultrasonography (b) demonstrated a hypoechoic and avascular area with a diameter of 8 mm (arrowheads). Endoscopic retrograde cholangio-pancreatography (ERCP) (c) revealed stenosis of the main pancreatic duct with distal dilatation (arrowhead).

1.       Miura F, Takada T, Amano H, Yoshida M, Furui S, et al. (2006) Diagnosis of pancreatic cancer. HPB 8: 337-342.

2.       Huang WC, Sheng J, Chen SY, Lu JP (2011) Differentiation between pancreatic carcinoma and mass-forming chronic pancreatitis: usefulness of high b value diffusion-weighted imaging. J Dig Dis 12: 401-408.

3.       van Gulik TM, Moojen TM, van Geenen R, Rauws EA, Obertop H, et al. (1999) Differential diagnosis of focal pancreatitis and pancreatic cancer. Ann Oncol 10(Suppl 4): 85-88.

4.       van Heerde MJ, Biermann K, Zondervan PE, Kazemier G, van Eijck CHJ, et al. (2012) Prevalence of autoimmune pancreatitis and other benign disorders in pancreatoduodenectomy for presumed malignancy of the pancreatic head. Dig Dis Sci 57: 2458-2465.

5.       Kim JK, Altun E, Elias J Jr, Pamuklar E, Rivero H, et al. (2007) Focal pancreatic mass: distinction of pancreatic cancer from chronic pancreatitis using gadolinium-enhanced 3D-gradient-echo MRI. J Magn Reson Imaging 26: 313-322.

6.       Neff CC, Simeone JF, Wittenberg J, Mueller PR, Ferrucci JT Jr (1984) Inflammatory pancreatic masses: problems in differentiating focal pancreatitis from carcinoma. Radiology 150: 35-38.

7.       Onda S, Kanehira M, Fujioka S, Okamoto T, Yanaga K (2011) Contrast-enhanced CT findings were useful for diagnosis of three cases of stage I pancreatic cancer. J Jpn Surg Assoc 72: 2919-2925.

8.       Furukawa H, Takayasu K, Murai K, Kanai Y, Inoue K, et al. (1996) Late contrast-enhanced CT for small pancreatic carcinoma: delayed enhanced area on CT with histopathological correlation. Hepatogastroenterology 43: 1230-1237.

9.       Yamada Y, Mori H, Matsumoto S, Kiyosue H, Hori Y, et al. (2010) Pancreatic adenocarcinoma versus chronic pancreatitis: differentiation with triple-phase helical CT. Abdom Imaging 35: 163-171.

10.    Fattahi R, Balci NC, Perman WH, Hsueh EC, Alkaade S, et al.  (2009) Pancreatic diffusion-weighted imaging (DWI): comparison between mass-forming focal fancreatitis (FP), pancreatic cancer (PC), and normal pancreas. J Magn Reson Imaging 29: 350-356.

11.    Irie H, Honda H, Kaneko T, Kuroda T, Yoshimitsu K, et al. (1997) Comparison of helical CT and MRI imaging in detecting and staging small pancreatic adenocarcinoma. Abdom Imaging 22: 429-433.

Shinya S, Sasaki T, Nagakawa Y, Guiquing Z, Yamamoto F, et al. (2008) Usefulness of diffusion-weighted imaging (DWI) for the detection of pancreatic cancer: 4 case reports. Hepatogastroenterology 55: 282-285.