Large pancreatic myoepithelial hamartoma associated with familial insulin dependent diabetes mellitus

Abstract

Presenter: Jeffrey Ord BS | Duke University Medical Center Background: Pancreatic myoepithelial hamartoma (PMEH) is a rare, benign solid and cystic lesion of the pancreas which can appear as a solid mass or solid-cystic lesion. Patients with pancreatic hamartomas may present with vague abdominal pain, pancreatitis, biliary obstruction or may be entirely asymptomatic. Histologic features of PMEH include small to medium-sized ductal structures lined by columnar epithelium and disarranged acini surrounded by smooth muscles and varying amounts of fibrous stroma. While several reports of pancreatic hamartomas exist, there are only 3 confirmed cases of PMEH in the literature, all of which presented as discrete pancreatic head masses. Two of these cases were associated with a single family, all originated in Eastern Asia. Methods: The first case of an adult with a giant myoepithelial hamartoma extending throughout the pancreatic gland associated with familial diabetes is described. Results: A 46-year-old male was referred to Duke University Hospital with recurrent acute pancreatitis. CT showed a 10.3x9.3x6.7cm heterogeneous calcified pancreatic head solid-cystic mass (figure 1). Pertinent medical history includes insulin dependent diabetes mellitus (IDDM) diagnosed at age 30 and family history of endocrine and exocrine pancreatic disease in paternal lineage. Paternal grandmother similarly had early adult onset IDDM and chronic pancreatitis which required a pancreaticoduodenectomy, revealing a 3x4x2cm necrotic pancreatic pseudocyst with hamartomatous characteristics. Endoscopic ultrasound (EUS) showed a large heterogenous, calcified, mixed solid and cystic mass extending from the pancreatic head through the pancreatic body. Fine-needle aspiration (FNA) returned benign pancreatic acinar tissue and smooth muscle without evidence of malignancy. Surgery was performed due to recurrent bouts of pancreatitis requiring multiple hospitalizations. Total pancreatectomy was performed due to the diffuse nature of the cystic disease and preexisting IDDM. On gross examination, the pancreas was diffusely enlarged, particularly in the head with replacement of normal parenchyma by pale tan to white whorled solid tissue with multiple cystic spaces up to 1.3x1cm filled with viscous fluid and calculi (figure 2). Microscopic hematoxylin-eosin staining showed disorganized bundles of smooth muscle with numerous embedded small ducts and cysts, with scattered pancreatic exocrine lobules exhibiting chronic inflammation and pancreatic calculi (figure 3). Immunohistochemical stain for desmin and caldesmon was strongly positive in smooth muscle cells. The histopathologic diagnosis was consistent with myoepithelial hamartoma. Conclusion: There are three published cases of PMEH, all originating from Eastern Asia. This is the first case of PMEH reported in the western literature and the first case of diffuse PMEH with near total replacement of the entire pancreatic parenchyma. This case draws several similarities to one case series of PMEH in mother, son and daughter—including possible familial inheritance, recurrent episodes of acute pancreatitis, honeycombed/microcystic appearance on MRI. However, uniquely, this case includes a strong family history of heritable IDDM. Improved identification and management of rare conditions including PMEH will heavily depend on increasing awareness, reporting and genetic study of future cases.