Abstract: Objective:To summarize the computed tomography (CT) and magnetic resonance imaging (MRI) features of acinar cell carcinoma of the pancreas (ACCP).
Methods:The retrospective and descriptive study was conducted. The clinicopathological data of 21 patients with ACCP who were admitted to the Affiliated Hospital of Inner Mongolia Medical University from January 2015 to December 2019 were collected. There were 5 males and 16 females, aged (57±9)years, with a range from 41 to 74 years. Patients underwent CT and MRI examinations. Observation indicators: (1) imaging examination; (2) imaging features on CT; (3) imaging features on MRI; (4) pathological examination and immunohistochemistry staining; (5) treatment and follow-up. Follow-up using outpatient examination and telephone interview was conducted at 1, 3, 6 months after discharge and once every 6 months thereafter to detect survival of patients up to December 2019. Measurement data with normal distribution were represented as Mean±SD. Count data were described as absolute numbers.
Results:(1) Imaging examination. Of the 21 patients, 7 underwent single CT examination, 11 underwent MRI examination, and 3 underwent both CT and MRI examinations. ① Tumor shape: all the 21 patients had single tumor, including 17 showing round or quasi-round shape, and 4 showing irregular clumps. ② Tumor location: of the 21 patients, 6 had tumor located at pancreatic head, 2 had tumor located at pancreatic head and body, 2 had tumor located at pancreatic body, 4 had tumor located at pancreatic body and tail, 4 had tumor located at pancreatic tail, and 3 had had tumor located at ampulla. ③ The maximum tumor diameter was (43±29)mm, with a range from 11 to 129 mm. ④ Adjacent organ invasion: 10 of the 21 patients had invasion of adjacent organ, including 2 with invasion of stomach, spleen and left adrenal gland invasion, 4 with invasion of duodenum,3 with invasion of duodenum and common bile duct, 1 with invasion of spleen. ⑤ Vascular invasion: 12 patients had invasion of splenic artery or splenic vein, including 1 combined with invasion of both common hepatic artery and superior mesenteric vein, 1 combined with invasion of celiac root. ⑥ Pancreatic and bile duct invasion: 8 patients had pancreatic and bile duct dilation, including 4 with bile duct and upper pancreatic duct dilation, and 4 with pancreatic duct dilation. ⑦ Lymph node metastasis:2 patients had perineoplastic lymph node enlargement. ⑧ Other conditions: 7 patients had tumor center with cystic necrosis. Four patients had atrophy pancreatic parenchyma. Two patients had splenic vein tumor thrombosis. Two patients had cysts. One patient had multiple liver metastases. (2) Imaging features on CT. ① The solid part was dominant in the main body of the 10 patients undergoing CT examination, demostrating equal density, of which 3 cases had clear boundaries, 2 cases had pseudocapsule around the lesion, and 5 cases had low-density necrotic area in the center of lesion. ② In arterial phase of CT examination, the solid part of tumor had a lower enhancement compared with the normal pancreatic tissues in 7 patients, while the solid part of tumor had a high enhancement compared with the normal pancreatic tissues in 3 patients. ③ In delayed phase of CT examination, the tumor density was slightly lower than or equal to density of normal pancreatic parenchyma in 7 patients, showing slightly progressive enhancement, while the tumor density was slightly higher than or equal to density of normal pancreatic parenchyma in 3 patients. (3) Imaging features on MRI. ① MRI plain scan of 14 patients showed that 8 patients demostrated slightly longer T2 and slightly longer T1 signals in lesions, while 6 patients demostrated mixed signals dominated by long T2 and equal T1 signals. The area of cystic necrosis was observed in lesions of 4 patients and was not observed in 10 patients. No antiphase signal reduction was observed in the 14 patients. ② MRI dynamic enhanced scan of 12 patients showed that 11 patients presented mild progressive enhancement in lesions and 1 patient presented obvious confounding enhancement and clearance in the delayed phase. Compared with adjacent normal pancreatic parenchyma, diffused weighted imaging showed high signals in 6 cases, slightly high signals in 6 cases, and high signal halo in 2 cases. The apparent diffusion coefficient in 14 lesions was (1.22±0.14)×10^-3mm²/s. (4) Pathological examination and immunohistochemistry staining. Results of pathological examination in the 21 patients: acinic cell carcinoma, mixed ductal-acinic cell carcinoma, acinar-endocrine carcinoma, and atypical hyperplasia inacinus were detected in 14, 5, 1, and 1 patients, respectively. Of the 21 patients, 10 had invasion of adjacent organ, 3 had invasion of bile duct, 2 had invasion of lymph node. Results of immunohistochemistry staining in 17 patients: 17 patients had proliferation index of Ki-67 as 1%-80%; 10 out of 16 patients were positive for synaptophysin; 6 out of 16 patients were positive for CD56 protein; 2 out of 14 patients were positive for Chromogranin A; 12 out of 13 patients were positive for α-antitrypsin; 9 out of 11 patients were positive for cytokeratin; 8 patients were positive for β-catenin; 2 patients were positive for B lymphoma-10 protein. (5) Treatment and follow-up. Of the 21 patients, 10 cases underwent pancreatico-duodenectomy, 6 cases underwent pancreatic body and tail pancreatectomy combined with splenectomy, 2 cases underwent pancreatic body and tail pancreatectomy, 1 case underwent pancreatic tail tumor enucleation, 1 case underwent liver metastasis resection, and 1 case underwent ultrasound-guided pancreatic lesion puncture biopsy. All the 21 patients were followed up for (30±16)years, with a range from 2 to 52 months. There were 13 patient surviving and 8 cases of death. They had survived for (19±13)months, with a range from 2 to 35 months.
Conclusions:The CT and MRI enhanced scan of ACCP showed slightly progressive enhancement, with cystic necrosis seen in the center and high signals in diffused weighted imaging. Dilation of bile duct and pancreatic duct is common in patients with pancreatic head tumors, and invasion of splenic artery and vein is common in pancreatic body and tail tumors. Calcification and cyst are rare and lesions of pancreatic head and body cause atrophy in pancreatic tail.