Intrapancreatic accessory spleen: CT appearance and differential diagnosis

Although autopsy studies report that the second most common site of the accessory spleen is in the tail of the pancreas, intrapancreatic accessory spleens (IPASs) are rarely recognized radiologically. With recent improvements in imaging techniques, IPASs are more commonly detected on imaging studies. IPAS can be mistaken for other type of mass-forming lesions in the tail of the pancreas, particularly an asymptomatic small neuroendocrine neoplasm. Rarely, an epidermoid cyst originating from IPAS may simulate other cystic pancreatic lesion. Accurate preoperative diagnosis would obviate unnecessary surgery. IPAS should be considered when a hypervascular mass is seen in the tail of the pancreas on CT. Typical location, similar attenuation of the lesion to the spleen on noncontrast, and postcontrast CT at different phases are helpful to make diagnosis of IPAS. In particular, characteristic heterogeneous contrast enhancement of IPAS on the arterial phase may be helpful for correct diagnosis. However, when it remains difficult to exclude the other diagnosis, ^99mTc labeled heat-damaged red blood cell scintigraphy or superparamagnetic iron oxide-enhanced MRI can be used to confirm the diagnosis of IPAS.