Pancreatic Incidentaloma: Differentiating Nonfunctioning Pancreatic Neuroendocrine Tumors from Intrapancreatic Accessory Spleen

Abstract

To improve the preoperative assessment of pancreatic incidentalomas (PIs) by analysis of 1 index case and characterization of the published features of intrapancreatic accessory spleen (IPAS) compared to pancreatic neuroendocrine tumor (PNET). A search of the literature using the online database MEDLINE. In all, 46 cases of IPAS have been described to date: 17 were "presumed" as IPAS based on technetium-99m (Tc-99m) scanning, fine-needle aspiration (FNA) stain for CD8, or contrast-enhanced sonography; 29 were misdiagnosed as PNET and underwent surgery. The pancreatic lesions were 1) mostly solitary; 2) solid on imaging; 3) well defined; 4) located predominantly at the pancreatic tail; 5) not exceeding 3 cm in the largest diameter; 5) all detected in adults (22-81 years); 6) not related to sex. In subjects referred for surgery, standard imaging studies/imaging protocols did not differentiate between IPAS and PNET. FNA was performed in 5/46 cases, all of which were false-positive for PNET. Immunohistochemical staining for T-cells on FNA material and specific imaging features (characteristic arciform splenic enhancement pattern on dynamic computed tomography [CT]; nuclear scintigraphies with radioisotope specifically trapped by splenic tissue [Tc-99m]) or contrast-enhanced sonography offered valuable clues. Still, distal pancreatectomy and splenectomy was carried out in 72%, and the rest had distal pancreatectomies. IPAS should be considered before surgery in patients with PIs. A new practical algorithm is presented for better preoperative evaluation of such lesions; it combines the recognition of early indicators and sequential consideration of cytologic and imaging features to decrease the hazards of unnecessary major surgery. CT = computed tomography EUS = endoscopic ultrasound FNA = fine-needle aspiration HDRBC = heat-damaged red blood cells IPAS = intrapancreatic accessory spleen MRI = magnetic resonance tomography NF-PNET = nonfunctioning pancreatic neuroendocrine tumor PET = positron emission tomography PNET = pancreatic neuroendocrine tumor PI = pancreatic incidentalomas SPIO = superparamagnetic iron oxide Tc-99m = technetium-99m.