Intrapancreatic accessory spleen

CLINICAL HISTORY AND FINDINGS

A 48-year-old man undergoing medical treatment for longstanding HIV presented with a month-long history of fever, night sweats, and weight loss. Physical examination and laboratory data were unremarkable and no abnormalities were found. Imaging was performed to gain further diagnostic information.

Axial abdominal CT in the venous phase after intravenous injection of iodinated contrast reveals diffuse enlargement of the pancreatic tail (Figure 1, arrow), such that the anteroposterior diameter is greater than 3 cm. This ill-defined lesion has slightly higher attenuation than adjacent pancreatic parenchyma, but no peripancreatic fat stranding is observed. A tumoral rather than inflammatory cause was suspected and MRI was recommended.

Axial, unenhanced T1-weighted fat-saturated gradient-echo MRI (Figure 2A) demonstrates a well-defined mass of low signal intensity (arrow), surrounded by the higher signal intensity pancreas. T2-weighted spin-echo sequence with fat suppression (Figure 2B) reveals a highly intense tumor (arrow) relative to the adjacent pancreatic tissue, mimicking an endocrine neoplasm. The tumor moderately and homogeneously enhances after IV injection of gadolinium (Figure 2C, arrow). No washout is seen on late images (not shown). The lesion shows very high intensity on diffusion-weighted imaging (b = 600) (Figure 2D, arrow), suggesting high cellularity. The lesion was of similar signal intensity to adjacent spleen on each MR image, suggesting intrapancreatic splenic parenchyma.

SPECT/CT was performed to confirm the diagnosis. Heatdamaged red blood cells labeled with technetium-99m were seen trapped within the intrapancreatic lesion and the spleen (Figure 3).

DIAGNOSIS AND DISCUSSION

Diagnosis: intrapancreatic accessory spleen.

Differential diagnoses include nonfunctioning islet cell tumors and metastasis. Pancreatic lymphoma and adenocarcinoma are less likely, owing to their hypoattenuat ing/hypointense behavior compared with adjacent pancreas and ductal obstruction typically associated with adenocarcinoma. A diagnosis of pseudopapillary tumor is also unlikely. These lesions, which are typically seen in young women, are often cystic, large, and very heterogeneous, due to hemorrhage and necrosis.

Accessory spleens are found in 10% of the general population, most often in the hilum or along the splenic artery.1 They can also be found in the gastrosplenic or splenorenal ligaments, in the mesentery, anywhere in the pelvis, or very rarely in the scrotum.² One-sixth of accessory spleens are found within the pancreatic tail.¹

An intrapancreatic accessory spleen will appear as a solid enhancing neoplasm on cross-sectional imaging, though it is rarely recognized radiologically. It can mimic intrapancreatic neoplasm, and may even be resected by mistake.³ On CT and MRI, a diagnosis of accessory spleen may be suggested from the characteristic location and appearance of the observed mass (exactly similar to the spleen on unenhanced and contrast-enhanced images).^4-6 Splenosis can be demonstrated with a variety of nuclear medicine agents, for example, Tc-99m sulfur colloid, indium- 111-labelled autologous platelets, and Tc-99m-labelled heat-damaged red blood cells. This latter agent is preferred owing to reduced uptake in the normal liver and bone marrow.^5,7,8

Symptoms of intrapancreatic accessory spleen are rare, but pain and nausea have been reported.^4,5 The clinical symptoms reported in our case were not explained by the diagnosis. In summary, radiologists need to be aware of the characteristic imaging findings of intrapancreatic accessory spleen. A multimodality approach helps obviate surgery and percutaneous biopsy, especially when malignancy is being considered.

Case submitted by Dr. Saad Alqahtani, Dr. Maria-Victoria Ocurto, Prof. Pierre Schnyder, Dr. Angelika Bischoff-Delaloye MD, and Dr. Sabine Schmidt, University Hospital of Lausanne, Switzerland.