Intrapancreatic accessory spleen (IPAS) is a rare benign lesion within the pancreas that frequently clinically and radiographically mimics a solid neoplasm. Distinguishing IPAS from pancreatic neoplasm/malignancy is extremely important from a treatment perspective. We report the case of a 77-year-old asymptomatic man with an incidentally detected 10 mm pancreatic tail mass. Dynamic computed tomography and contrast-enhanced harmonic endoscopic ultrasound revealed a round and well-circumscribed 10 mm hypervascular mass within the tail of the pancreas─the primary diagnostic consideration being a pancreatic neuroendocrine tumor. Superparamagnetic iron oxide-enhanced magnetic resonance imaging revealed an isointense mass relative to the spleen, consistent with IPAS. Subsequently, an endoscopic ultrasound-guided fine-needle aspiration biopsy was performed. Hematoxylin-eosin stained sections showed conspicuous thin-walled blood vessels in addition to inflammatory cells. Immunostaining for CD8 demonstrated strong positivity in endothelial cells of the thin-walled vessels. By correlating the pathological findings with the immunostaining result, we rendered the diagnosis of IPAS. Our experience in the present case supports the view that endoscopic ultrasound-guided fine-needle aspiration biopsy may enable a reliable preoperative diagnosis of IPAS and thus prevent unnecessary surgery.
