1355 Accessory Spleen: An Unusual Pancreatic Mass Posing a Diagnostic Dilemma

Abstract

INTRODUCTION: There are two main causes of accessory spleen; failure of fusion of the splenic anlage during the fifth week of fetal life and following autotransplantation after a splenectomy. They are structurally identical to the spleen and are most commonly found in the splenic hilum or pancreatic tail. Although rarely noted on radiograph due to low spatial resolution, their detection is increasing with more advanced modalities. This can result in the finding of a pancreatic mass that poses a diagnostic dilemma. CASE DESCRIPTION/METHODS: The patient is a 62-year-old man with a history of hepatitis B infection. On routine surveillance he had ultrasound findings of a liver calcification with inability to determine the presence of cirrhosis and a mildly elevated alpha-fetoprotein level. He was sent for an MRI, which revealed a 2.3 × 1.9 cm mass in the pancreatic tail showing mild hyperintense T2 signal and hypointense T1 signal. A CT from 2011 showed a slight contour bulge to the pancreatic tail in the same region, without appreciation of a discrete lesion. He underwent EGD with endoscopic ultrasound (EUS). A 21.4 × 13.7 mm well-circumscribed, homogeneous lesion was found in the pancreatic tail and biopsied. The pathology shows an immunohistochemical-staining pattern consistent with splenic tissue, confirming the diagnosis of an intrapancreatic accessory spleen (IPAS). No further intervention was needed and the patient was sent home. DISCUSSION: Pancreatic cancer has a 5-year survival rate of 9%, therefore it is imperative that all pancreatic masses are investigated thoroughly and promptly. In cases of an IPAS, its differentiation from a pancreatic mass is difficult as splenic tissue can mimic pancreatic tumors, especially on MRI. It is essential to differentiate between the two as IPAS are only clinical relevant when there is torsion, rupture, hemorrhage, or the patient carries a diagnosis of idiopathic thrombocytopenic purpura requiring the removal of all splenic tissue. Imaging modalities such as ultrasound, CT, MRI, and scintigraphy can aid in the diagnosis of IPAS. However, these have limitations and have not shown to provide a definitive diagnosis. EUS with fine needle aspiration is being increasingly used to characterize pancreatic lesions. In this case, it enabled adequate tissue sampling while avoiding unnecessary procedures. This case illustrates another use for EUS in an otherwise difficult diagnostic scenario.