Granular cell tumor of the pancreas mimicking pancreatic ductal adenocarcinoma: a case report

BACKGROUND: Granular cell tumor (GCT) is a benign Schwannian neoplasm that only exceptionally arises in the pancreas. Because of its infiltrative growth pattern, pancreatic GCT may radiologically mimic pancreatic ductal adenocarcinoma (PDAC). CASE PRESENTATION: A 38-year-old woman with Birt-Hogg-Dubé syndrome underwent magnetic resonance imaging as part of surveillance and was found to have an enhancing lesion causing ductal stricture at the junction of the pancreatic corpus and cauda. Computed tomography raised a strong suspicion of pancreatic ductal adenocarcinoma. The patient underwent distal pancreatectomy. Histologic examination revealed a 12-mm poorly circumscribed infiltrative tumor composed of sheets and nests of polygonal cells with abundant eosinophilic granular cytoplasm and small uniform nuclei. It extended along interlobular septa and encased small pancreatic ducts, providing a morphologic correlate for the ductal stricture seen on imaging. Periodic acid-Schiff with diastase (PAS-D) stain demonstrated diffuse intracytoplasmic diastase-resistant granules. Tumor cells showed diffuse expression of S100 protein, SOX10 and inhibin A, while neuroendocrine markers were negative. The findings were consistent with a granular cell tumor. CONCLUSION: Pancreatic granular cell tumor is a rare benign lesion that may present with imaging findings highly suspicious for PDAC. Its infiltrative growth pattern may closely mimic carcinoma on imaging and may lead to surgical resection for presumed malignancy. To our knowledge, pancreatic granular cell tumor has not previously been reported in association with Birt-Hogg-Dubé syndrome; whether this represents a coincidental finding remains uncertain.