What is an accessory spleen?
An accessory spleen (also known as a splenule) is a discrete focus of normal splenic tissue that is separate from the spleen, usually 1 to 2 cm in size, and may be single or multiple. CT attenuation and MRI signal intensity properties of an accessory spleen are identical to those of the normal spleen.
This is encountered in ≈10% to 30% of patients, usually within the splenic hilum or near/within the pancreatic tail, and is important to recognize prior to planned splenectomy for treatment of patients with hematologic or autoimmune disorders.
6 Interesting Facts of Accessory spleen
- Accessory spleens are a common incidental finding on abdominal imaging
- Usually these are easily recognizable as small perisplenic masses with well-defined margins, but condition is less obvious when splenic tissue lies within adjacent pancreatic tail
- The 2 conditions can be confused because an accessory spleen can appear as a hypervascular mass, similar to neuroendocrine tumors
- Accessory spleens have a rounded shape and different enhancement pattern compared with pancreatic parenchyma
- To differentiate accessory spleen from a pancreatic neuroendocrine tumor, multiphasic CT or MRI can show the lesion following the enhancement pattern of the spleen over time
- Additionally, MRI can use diffusion-weighted sequences, which can detect restricted diffusion in normal lymphoid organs, such as spleen and lymph nodes