Diagnosis

Intrapancreatic accessory spleen

Findings

Images consist of an axial contrast-enhanced CT, axial T2-weighted, axial gradient echo, axial T1 precontrast, axial T1 with fat saturation during arterial phase of contrast administration, and an axial T1 with fat saturation after a 15-minute delay.

An ovoid-enhancing lesion is present within the pancreatic tail. Relative to pancreatic parenchyma, the lesion is hyperintense on T2-weighted images, hypointense on T1-weighted images, hypointense on gradient echo images, and enhances on arterial phase and delayed images. The lesion follows splenic attenuation on CT and splenic signal intensity on all MRI sequences.

Discussion

Accessory spleens are found in at least 10% of the population with approximately 15% of these occurring within or near the pancreatic tail. These lesions are incidental findings with no clinical significance. However, these lesions have been mistaken for enhancing neuroendocrine tumors with resultant unnecessary surgery.

Intrapancreatic accessory spleens are most commonly discovered incidentally during CT examinations for other causes. On CT, the lesion will be round or ovoid, enhanced, and follows the attenuation of splenic parenchyma on all phases of contrast material administration. A definitive diagnosis cannot be made by CT, but should be mentioned as a diagnostic consideration if the morphology and attenuation are appropriate. The diagnosis is ultimately made by MRI or nuclear scintigraphy using technetium-99m-labeled sulfur colloid or ^99m Tc-labeled heat-damaged RBCs. While nuclear scintigraphy may make the diagnosis, it lacks the anatomic resolution of MRI and could result in a misdiagnosis. On MRI, accessory spleens will follow the signal intensity of splenic parenchyma on all imaging sequences including all phases of contrast material administration. It is important to compare the signal intensity of pancreatic lesions to spleen as the signal intensity of the lesion relative to pancreatic parenchyma is worrisome for a neuroendocrine tumor — hyperintense on T2WI, hypointense on T1WI, hypointense on gradient echo sequences, and enhancing on arterial phase images.

Familiarity with the diagnosis of an intrapancreatic accessory spleen is crucial to avoiding unnecessary invasive procedures and the associated morbidities.

1. Kim SH, Lee JM, Choi BH, et al. Intrapancreatic accessory spleen: Findings on MR imaging, CT, US, and scintigraphy, and the pathologic analysis. Korean J Radiol. 2008;9:162-174.
2. Harris GN, Kase DJ, Bradnock H, Mckinley MJ. Accessory spleen causing a mass in the tail of the pancreas: MR imaging findings. AJR Am J Roentgenol. 1994;163:1120–1121.
3. Boraschi P, Donati F, Volpi A, Campori G. Intrapancreatic accessory spleen: Diagnosis with RES-Specific contrast-enhanced MRI. AJR Am J Roentgenol. 2005;184:1712-1713.