Two unusual variants of pancreatic neuroendocrine tumor and their potential pitfalls on fine-needle aspiration cytology

Challenges and Pitfalls in Pancreatobiliary Cytopathology

INTRODUCTION

The advances of minimally invasive endoscopy-guided procedures that usually yield limited diagnostic material changed pancreaticobiliary cytopathology into one of the most challenging areas of cytopathology given the abundance of differential diagnoses to be considered when dealing with limited specimens.

CASE PRESENTATION

We describe a few challenging examples of potential pitfalls in pancreatobiliary cytopathology evaluation collected from a busy academic hospital (tertiary) center. Case 1 illustrates the challenges in handling paucicellular specimens from pancreatic solid lesions in which differential diagnoses may include acinar cell carcinoma, neuroendocrine tumors, adenocarcinoma, or even benign pancreatic tissue, among others. Case 2 illustrates the pitfalls in evaluating limited specimens from patients with chronic pancreatitis, specially when distinguishing exuberant reactive atypia from dysplastic changes is mandatory. Case 3 illustrates pitfalls in distinguishing malignancy from reactive changes in biliary brushing specimens from patients with primary sclerosing cholangitis. Finally, cases 4 and 5 highlight the importance of including the possibility of pancreatic metastasis in the differential diagnoses of some pancreatic lesions.

CONCLUSION

Over time, there has been an increasing demand for pathologists to render diagnoses on limited specimens obtained through minimally invasive procedures which can be frequently challenging even for the most experienced professionals. In many difficult cases, salvaging additional material for a cell block can turn out to be extremely helpful given the possibility of utilizing additional ancillary tests for diagnostic confirmation.

Metastatic tumors to the pancreas, a 12-year single institution review

BACKGROUND

Tumors of the pancreas are often primary in nature, but are occasionally proven to be secondary. We report a 12-year review of all pancreatic tumors shown to be metastatic at the University of Colorado.

METHOD

The electronic pathology database was searched between 2008 and 2020, for all pancreatic fine-needle aspiration cases at the University of Colorado to identify and review metastatic tumors to the pancreas. Additional data points to include age, sex, radiographic features, and clinical management were analyzed.

RESULTS

Our data retrieval identified 39 metastatic tumors to the pancreas comprised of 12 (31%) renal cell carcinomas, 6 (15%) lung carcinomas, and 5 (13%) melanomas with the remainder of tumors originating from a variety of other sites. The most common location of these metastases within the pancreas was the pancreatic head (49%) followed by the body (20%). Eighty-five percentage of cases presented with a single radiographically identified mass.

CONCLUSION

While the majority of pancreatic tumors represent primary processes, metastatic tumors to the pancreas represent a possible pitfall. The most common tumors to metastasize to the pancreas in this series were renal cell carcinoma, lung carcinoma, and melanoma. General awareness of the most frequent tumors to metastasize to the pancreas is practical when faced with a pancreatic lesion that could represent a metastasis, or in the absence of clinical history.

Amyloid-Rich Pancreatic Neuroendocrine Tumors: a Potential Diagnostic Pitfall in Endoscopic Ultrasound-Guided Fine Needle Aspiration Cytology (EUS-FNAC)

Pancreatic neuroendocrine tumors (PanNETs) are rare neoplasms that include even rarer variants that may pose different diagnostic problems, especially in fine needle aspiration cytology (FNAC). We describe the diagnostic clues of the amyloid-rich variant of PanNETs in endoscopic ultrasound (EUS)-guided fine needle aspiration cytology (EUS-FNAC). Three cases of PanNETs with an amyloid-rich stromal component were retrieved and retrospectively reviewed. For every case, the pancreatic lesion was investigated by a EUS-FNAC procedure. The final diagnosis was supported by immunocytochemistry and Congo red staining. All cases had similar EUS-FNAC features: neoplastic cells were entrapped in an eosinophilic, homogeneous dense and amorphous matrix. The neuroendocrine nature was confirmed by immunoexpression of synaptophysin and chromogranin A, while the amorphous stroma was characterized as amyloid based on positive Congo red staining. Regarding the hormonal profile, no insulin or proinsulin reactivity was observed, but all cases were diffusely positive for amylin. The diagnosis of uncommon variants of PanNETs, such as the amyloid-rich, is challenging especially in EUS-FNAC procedures because of a unique and misleading morphology, potentially mimicking fibrotic conditions and amyloid deposition within systemic amyloidosis. In cytology specimens, the presence of amorphous material requires amyloid deposition to be considered in the differential diagnosis of pancreatic neoplasms with neuroendocrine phenotype.

Fibrous Extracellular Spheroids in an Endoscopic Ultrasound-Guided Pancreatic Fine Needle Aspiration Correlating to a Gyriform Pancreatic Endocrine Tumor with a Unique Cobblestone Pavement Growth Pattern

Pancreatic neuroendocrine neoplasms (PanNENs) are uncommon tumors. Fine needle aspiration (FNA) samples from PanNENs are typically of high cellularity and lack necrosis. In cytology slides from these tumors, dyscohesive cells are usually reported with variably round to oval to plasmacytoid forms exhibiting coarsely granular chromatin and showing immunoreactivity for synaptophysin. We present an unusual, and to our knowledge not previously described, example of an FNA of a PanNEN with large extracellular fibrous spheroids containing intrinsic fibroblasts and rimmed by small to intermediate sized neoplastic epithelial cells with high nuclear cytoplasmic ratios. The cytomorphology of the PanNEN in this case was in some ways reminiscent of that expected in adenoid cystic carcinomas of the salivary glands that most often contain large extracellular globules of basement membrane material and a somewhat biphasic population of lesional cells. The cytomorphology in this case was found to correlate well with the resection specimen histomorphology of an exaggerated gyriform pattern of growth resulting in a unique cobblestone-pavement like microscopic appearance. Knowledge of this potential cytomorphology will aid the cytology community through recognition and reporting of this previously undescribed pattern in an uncommon disease.