Clinical diagnosis
Case 210
【Progress】
She underwent endoscopic ultrasound that showed low echoic lesion of 1 cm. Under endoscopic ultrasound, biopsy was conducted using fine aspiration needle which revealed a few small clusters of acinar cells without malignancy.
【Discussion】
Pancreas cancer is still one of the malignant tumors with the poorest survival. The reason is hard to find out the pancreas cancer in the early stage. The symptoms include abdominal pain, appetite loss, abdominal fulness, backache, emergence of diabetes mellitus, icterus and so on. When these symptoms appear, pancreas cancer is often found in an advanced stage. According to classification of pancreatic carcinoma by Japan pancreas society, surgical possible-resection rate is 20% and five-year survival is 10% (1, 2). T stage is as follows; T1, tumor localized within pancreas, T1a is 2cm or less, T1b is more than 2 cm; T2 tumor grows beyond pancreas without invasion to celiac axis or superior mesenteric artery (SMA) trunk, T2a without swollen local lymph-node, T2b with swollen lymph nodes irrespective of within or beyond pancreas; T3 tumor invades to celiac axis or SMA trunk: T4 tumor extends to distant organ. Possible surgical resection is limited to until T2. Then, it is imperative to find out the early stage-pancreas cancer with T1 or T2 for elevating the survival rate.
However, there is a situation of falling into a trap of finding pancreas cancer with T1 or T2. That is our case with mass-forming pancreatitis. Mass-forming pancreatitis arises from chronic pancreatitis or autoimmune pancreatitis. It appears in 30-40% of autoimmune pancreatitis (1, 2). The symptoms of mass-forming pancreas are emergence or deterioration of diabetes mellitus, mimicking pancreas cancer. Further, stenosis and/or dilatation of pancreatic duct occurs. Furthermore, imaging modality using contrast-enhanced CT, MRI&MRCP, abdominal echo irrespective of using endoscopy or not, shows a mass lesion in the pancreas, similar as the early pancreas cancer. Then, mass-forming pancreatitis is sometimes surgically resected under possible diagnosis of early pancreatic cancer. Especially, gastroenterologists with passion to attempt to find out early pancreas cancer are susceptible to falling into this pitfall. It indicates the disadvantage for patients with mass-forming pancreatitis.
In order to deter this situation, biopsy under endoscopically guided ultrasound is useful by gastroenterologist and MRI with diffusion weighted might be feasible to differentiate mass-forming pancreatitis by radiologist. ADC values are more lowered in pancreas carcinoma than mass-forming pancreatitis in many manuscripts (3-6) but others are not (7). ADC values can be elevated in the pancreas cancer with necrosis and fluid retention. Cut-off ADC values of 0.88 are reported to be useful to differentiate mass-forming pancreatitis from solid component of pancreas cancer (3). In our case, contrast-enhanced CT showed an area with low density on arterial phase in the pancreas body corresponded to the site of stenosis or occlusion of pancreatic duct. Ultrasound under endoscopy showed low echoic lesion of approximately 1 cm in diameter. Biopsy revealed small clusters of acinar cells without malignancy. Diffusion MRI showed no area with high signal intensity in the pancreas body and ADC values of the site of causing occlusion of pancreatic duct were 1.4, implying the lesion owing diffusion potency. Namely, there is no evidence of early pancreas cancer but mass-forming pancreatitis.
【Summary】
We present a fifty seven-year-old female with mass-forming pancreatitis mimicking early pancreas cancer. Contrast-enhanced dynamic CT showed a low density area on an arterial phase corresponded to the site where pancreatic duct began to dilate, mimicking early pancreas cancer of T1a. Diffusion weighted MRI depict almost the same signal intensity as pancreas itself and ADC values are 1.4. Endoscopically guided ultrasound showed low echoic area and biopsy showed clusters of acinar cells, indicating no malignancy. It is borne in mind that mass-forming pancreatitis arises from chronic pancreatitis or autoimmune pancreatitis. To differentiate mas-forming pancreatitis from early pancreas cancer, endoscopically guided biopsy and cut-off ADC values which are 0.88 to 0.94, are critical clues to solve the differentiation between mass-forming pancreatitis and pancreas cancer with solid component.
【References】
1.Classification of Pancreatic Carcinoma 2017. Japan Pancreas Society
2.Saka B et al.: Pancreatic ductal adenocarcinoma is spread to the peripancreatic soft tissue in the majority of resected cases, rendering the AJCC T-Stage protocol (7th Edition) inapplicable and insignificant : A size-based
3.Muhi A, et al. Mass‐forming autoimmune pancreatitis and pancreatic carcinoma: Differential diagnosis on the basis of computed tomography and magnetic resonance cholangiopancreatography, and diffusion‐weighted imaging findings. J. Magn. Reson. Imaging 2012;35:827–836.
4.Hur BY, et al. Magnetic resonance imaging findings of the mass-forming type of autoimmune pancreatitis: comparison with pancreatic adenocarcinoma. J Magn Reson Imaging 2012; 36:188–197 [Crossref]
5.Fattahi R, et al. Pancreatic diffusion-weighted imaging (DWI): comparison between mass-forming focal pancreatitis (FP), pancreatic cancer (PC), and normal pancreas. J Magn Reson Imaging 2009; 29:350–356
6.Kamisawa T, et al. Differentiation of autoimmune pancreatitis from pancreatic cancer by diffusion-weighted MRI. Am J Gastroenterol 2010; 105:1870–1875
7.Choi SY, et al. 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: 291-300
2020.10.28