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Accessory or ectopic spleen is present in at least 10% of the population and is most commonly (in 16% of cases) located near or in the tail of the pancreas.¹The size may range from a few millimeters to several centimeters and may enlarge after splenectomy.²In splenosis after trauma, the implantation of splenic tissue may occur anywhere in the abdomen, pelvis, or chest.³Most patients are asymptomatic, and the pancreatic tumor is usually discovered incidentally during an imaging workup for other reasons.⁴

The identification of an accessory spleen is important because it may mimic lymphadenopathy or a tumor in the pancreas, adrenal gland, or kidney.^2,5In addition, it can occasionally cause symptoms due to torsion, hemorrhage, spontaneous rupture, or cyst formation.^3,6Furthermore, for a surgeon intending to remove all of the functional splenic tissue, the presence of accessory or ectopic splenic tissue should be confirmed before the surgery to spare the patient an incomplete operation.⁷

The possibility of an ectopic spleen should be considered when a mass in the pancreatic tail has computed tomographic densities and MR imaging signal intensities equal or similar to those of the native spleen. An ectopic spleen may be confused clinically with an islet cell tumor, a pancreatic adenocarcinoma, or even metastases.⁸On computed tomographic and MR imaging, the presence of an accessory or ectopic spleen is suggested by its characteristic location and appearance similar to the spleen on nonenhanced and enhanced imaging.⁹The pancreatic tumor enhances identically to the adjacent spleen on dynamic-enhanced imaging after gadopentetate dimeglumine administration, including early and late arterial phases and early and late venous phases. This unique and typical enhancing pattern provides the clue for the diagnosis of an ectopic spleen.

Traditional confirmation of functioning ectopic splenic tissue can be obtained by means of scintigraphy using technetium Tc 99m sulfur colloid or technetium Tc 99m–labeled heat-damaged red blood cells, but its poor spatial resolution may lead to misdiagnosis.^8,10A recent study¹¹used T2-weighted MR imaging to detect the accessory spleen with a reticuloendothelial system–specific contrast medium (superparamagnetic iron oxides in this case). This technique is superior to scintigraphy because it offers better anatomical resolution and exposes the patient to no irradiation.¹¹With the increasing use of positron emission tomography, an accessory spleen could be misdiagnosed as a malignant tumor.¹²

In our case, the tentative diagnosis was islet cell tumor of the pancreatic tail; therefore, the distal pancreas and spleen were resected. The patient's symptoms resolved after surgery, suggesting that the symptoms may have been related to this lesion. However, the symptoms could have been unrelated because of the nonspecificity of the symptoms. The patient experienced an uneventful recovery and was discharged from the hospital on the eighth postoperative day.

Correspondence:Kao-Lang Liu, MD, Department of Medical Imaging, National Taiwan University Hospital, 7 Chung-Shan South Road, Taipei 100, Taiwan (lkl@ntu.edu.tw).

Accepted for Publication:November 8, 2006.

Author Contributions:Study concept and design: Chen and Liu. Acquisition of data: Chen, Tien, and Lin. Analysis and interpretation of data: Chen, Tien, Lin, and Liu. Drafting of the manuscript: Chen, Lin, and Liu. Critical revision of the manuscript for important intellectual content: Chen, Tien, Lin, and Liu. Administrative, technical, and material support: Chen, Tien, Lin, and Liu. Study supervision: Chen, Tien, and Liu.

Financial Disclosure:None reported.