MR imaging features of pancreatic schwannoma: a Chinese case series and a systematic review of 25 cases

Background There is a paucity of existing literature centering on the magnetic resonance (MR) imaging features of pancreatic schwannomas, due to the neoplasm’s nonspecific presentation and its rarity. We aimed to identify the characteristic imaging features of pancreatic schwannoma. Methods This retrospective search was conducted for histologically confirmed pancreatic schwannoma in multi-institutional database of pathology. Abdominal magnetic resonance imaging (MRI) was performed before histologic examination and their MR imaging studies were independently reviewed. The search yielded six adults (mean age, 46 years) with a definitive histologic postoperative diagnosis of single pancreatic schwannoma each. Additionally, a comprehensive English and Chinese literature review for pancreatic schwannoma and reported MR-imaging findings since 1961 was also conducted. MR imaging features of those cases in the literature were analyzed, summarized and compared with our case series. Results This rare entity appeared to be a well-circumscribed, exophytic, oval or round pancreatic mass with a mean greatest diameter of 3.7 cm. Five schwannomas were located in the pancreatic head-neck and one in the pancreatic tail. On MRI, all cases appeared hypointense on T1-weighted images, inhomogeneous hyperintense on T2-weighted images, and hyperintense on diffusion-weighted images. The mean apparent diffusion coefficient (ADC) values of pancreatic schwannoma were 1.11 ± 0.29 × 10− 3 mm2/s and significantly lower than the surrounding pancreas. The lesion-to-pancreas signal intensity ratio (SIR) at unenhanced T1-weighted images was 0.53 ± 0.07. On dynamic contrast-enhanced MRI, most of the lesions (67%, 4/6) showed homogeneously iso- or hypointense on arterial and portal venous phases, and hyperenhancement on delayed phase compared with the surrounding pancreas. In our analysis of the time intensity curves, all cases exhibited a gradual enhancement pattern. Conclusions A well-circumscribed mass displaying inhomogeneous hyperintensity on T2, marked hypointensity on T1, hyperintensity on DWI, and with early slight enhancement at arterial phase and progressive enhancement at portal venous and delayed phase, may suggest the diagnosis of pancreatic schwannoma.

CASE OF CYTOMORPHOLOGICAL DIAGNOSIS OF PANCREATIC SCHWANNOMA

Background: Schwannoma is an extremely rare non-epithelial tumor of the pancreas. Less than 50 cases of pancreatic schwannoma have been described in the literature over the past thirty years and only few cases report has described its findings on Fine-Needle Aspiration (FNA). Preoperative diagnosis of pancreatic schwannoma can be particularly challenging. Pancreatic schwannomas may mimic other, more common pancreatic lesions, such as cystic neoplasms, solid neoplasms, neuroendocrine tumors. Cytomorphological verification of the diagnosis is difficult due to the similarity of Schwannomas with other non-epithelial tumors from spindle cells. Therefore, pancreatic schwannomas have a very high rate of misdiagnosis. Objective: demonstration preoperative diagnosis and treatment of a rare pancreatic tumor. Materials and methods: Here we present a case of preoperative cytomorphological diagnosis of pancreatic schwannoma in a 58-year-old man. During magnetic resonance imaging, computed tomography and endosonography (EUS), the patient was diagnosed the tumor in the head of the pancreas with a diameter of up to 7 cm. For morphological verification of the process, a fine needle aspiration puncture of the formation was performed under EUS control. Diagnosis of pancreatic schwannoma was established by cytomorphological examination of cell block material using immunocytochemical method. Conclusion: the analysis of the result of cytomorphological diagnosis of pancreatic schwannoma is presented.