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Accessory Spleen
KEY FACTS
Terminology
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Benign ectopic splenic tissue of congenital origin
Imaging
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Most splenules located in or near splenic hilum or ligaments
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20% are near or within pancreatic tail and can mimic pancreatic neuroendocrine tumor
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May also be in diaphragmatic, pararenal, and gastric sites
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CT: Same enhancement and attenuation as normal spleen
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Isodense to main spleen on noncontrast images
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Serpiginous enhancement on arterial phase
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Homogeneous enhancement on venous/delayed images
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MR: T1WI hypointense and T2WI hyperintense
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Follows appearance of spleen on all sequences
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DWI: Isointense to spleen with similar ADC values
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Nuclear medicine: Technetium (Tc-99m) sulfur colloid or Tc-99m heat-damaged red blood cell (RBC) scan
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Functional uptake in splenic tissue differentiates splenule from other masses
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Top Differential Diagnoses
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Splenosis
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Polysplenia
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Peritoneal metastases and lymphoma
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Visceral mass (especially pancreatic neuroendocrine tumor)
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Splenic artery aneurysm or pseudoaneurysm
Pathology
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Congenital: Failure of some embryonic splenic buds to unite within dorsal mesogastrium
Clinical Issues
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Asymptomatic (vast majority of cases)
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May be mistaken for pancreatic or other abdominal mass
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Following splenectomy for lymphoma or ITP, disease may recur if accessory spleen was not removed
Axial CECT shows a small spherical accessory spleen
near the splenic hilum. Note the foci of calcification from histoplasmosis in the main and accessory spleen. This appearance is so characteristic as to require no additional evaluation.
near the splenic hilum. Note the foci of calcification from histoplasmosis in the main and accessory spleen. This appearance is so characteristic as to require no additional evaluation.
Axial CECT demonstrates a large mass
abutting the pancreatic tail and the splenic hilum. The mass was thought to be a neuroendocrine tumor and was resected. Note that the mass is isodense to the spleen. The mass was found to be a splenule at surgery.
abutting the pancreatic tail and the splenic hilum. The mass was thought to be a neuroendocrine tumor and was resected. Note that the mass is isodense to the spleen. The mass was found to be a splenule at surgery.
Axial CECT shows an enlarged spleen due to portal hypertension in this patient with cirrhosis. Note the prominent accessory spleen
as well as the varices
. An accessory spleen may enlarge in parallel with the main spleen.
as well as the varices . An accessory spleen may enlarge in parallel with the main spleen.
Axial CECT shows a hypervascular mass
within the pancreatic tail that mimics an islet cell tumor. A heat-damaged red blood cell scan (not shown) proved this to be an accessory spleen. Masses in the splenic hilum may arise from or involve the tail of the pancreas or spleen.
within the pancreatic tail that mimics an islet cell tumor. A heat-damaged red blood cell scan (not shown) proved this to be an accessory spleen. Masses in the splenic hilum may arise from or involve the tail of the pancreas or spleen.
TERMINOLOGY
Synonyms
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Splenule, splenunculus
Definitions
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Benign ectopic splenic tissue of congenital origin
IMAGING
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