Accessory spleen

Last updated: 8 July 2026
Reviewed by: Specialist doctors from the Elfcare quality team

Has a recent abdominal scan turned up a small rounded mass near your spleen? Maybe it was picked up by chance, with no symptoms at all. If so, you're probably looking at an accessory spleen (also called a splenunculus): a small nodule of normal spleen tissue that ended up in the wrong place during foetal development. It is one of the most reassuring incidental findings an abdominal MRI can produce.

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What is an accessory spleen?

An accessory spleen is a harmless, tiny, extra nodule of normal spleen tissue that forms near your main spleen during a baby's early development. Found in up to 30% of healthy people, it functions exactly like the main spleen, and doesn't put your health at risk.

While they are completely silent, they are most often found in predictable spots:

  • The splenic hilum: right next to the main spleen's blood vessels (accounting for 75% of cases).

  • The tail of the pancreas: tucked near the pancreas, where it can easily be mistaken for a pancreatic tumor on lower-quality scans.

  • The abdominal fat: floating loose in the abdominal fat.

Because an accessory spleen is made of the same tissue as your main spleen, it shares the identical visual signature on an Elfcare MRI. That matching signal is what lets doctors tell it apart from an abnormal lymph node or tumour, so you're not sent for unnecessary follow-up testing.

Symptoms of an accessory spleen

An accessory spleen almost never causes symptoms and is discovered incidentally on imaging. However, there are a couple of exceptions are worth knowing about:

  • If a mobile accessory spleen twists on its blood supply (torsion), it can cause sudden, sharp pain on the left side of the abdomen that needs urgent attention.

  • After a splenectomy, an accessory spleen can grow larger and take over some of the main spleen's job. That's helpful in conditions like hereditary spherocytosis, but a problem in cases like immune thrombocytopenia, where the goal of removing the spleen was to stop it destroying platelets.

What causes an accessory spleen?

An accessory spleen isn’t a disease, but a variant of how some people’s anatomy develops. Contributing factors include:

  • Embryological separation during foetal development, small portions of splenic tissue in the dorsal mesogastrium fail to fuse with the main splenic mass and develop as independent nodules of splenic tissue.

  • Normal developmental variation accessory spleens are considered a normal anatomical variant, present in 10 to 30% of individuals, with no pathological significance in the vast majority of cases.

  • Splenosis is a related but separate condition where splenic tissue seeds itself around the abdomen after trauma or surgery to the spleen. Unlike an accessory spleen, splenosis is acquired rather than something you're born with, though it can look similar on imaging.

How is an accessory spleen detected?

An accessory spleen is detected through abdominal imaging. Blood tests don't play a role in finding one, though they can matter afterwards in certain situations, mainly after a splenectomy.

Abdominal MRI Elfcare’s full body MRI covers the upper abdomen as standard, which is where accessory spleens show up. Because the scan can match the nodule's signal to that of the main spleen, it can usually tell you right away that what you're looking at is a harmless variant rather than a lymph node or tumour. This includes the trickier case where it's sitting in the tail of the pancreas and could otherwise be mistaken for something more serious.

Blood tests are not routinely needed just to assess an accessory spleen, but a few markers become relevant in specific situations. Relevant markers in Elfcare's panel include:

  • Full blood count including platelet count relevant after a splenectomy if the accessory spleen may be taking over splenic function, since this shows up as changes in platelet count and red cell shape.

  • CRP relevant when torsion of an accessory spleen is suspected, with elevated CRP reflecting the resulting inflammatory response.

  • Hemoglobin and red cell indices relevant in the post-splenectomy context when accessory spleen function is being assessed.

Why early detection matters

For most people, the main benefit of catching this early is peace of mind. An unexplained mass on a scan can be unsettling, but once it's identified as an accessory spleen, with a signal that matches the main spleen, there's usually nothing more to do.

For the smaller proportion of cases where clinical relevance exists, knowing about the accessory spleen before any planned splenectomy allows the surgical team to identify and address it appropriately, preventing the recurrence of conditions such as immune thrombocytopenia or haematological disease that would otherwise recur from the residual splenic tissue.

How Elfcare can help

Elfcare's full body MRI images the spleen and surrounding abdominal structures directly as part of the standard abdominal sequence, identifying accessory spleens and providing the characteristic MRI signal that confirms the diagnosis confidently in the vast majority of cases. For a finding that can cause significant anxiety when described as an abdominal mass on imaging, a confident MRI diagnosis of an accessory spleen provides immediate and definitive reassurance.

Our blood panel covers full blood count and inflammatory markers that are relevant in the specific clinical contexts where accessory splenic tissue has functional implications.

If the MRI turns up something that needs a closer look, we'll arrange further testing or refer you to the right specialist.

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Summary

An accessory spleen is a small nodule of normal splenic tissue developing outside the main spleen as a congenital developmental variant, present in approximately 10 to 30% of the population and almost always entirely benign and asymptomatic. Elfcare's full body MRI images the spleen and surrounding structures directly, identifying accessory spleens and confirming their diagnosis through their characteristic MRI signal that perfectly matches the main spleen, distinguishing them from lymph nodes, pancreatic masses, and other abdominal lesions. Early identification provides definitive reassurance, eliminates unnecessary further investigation, and ensures the finding is documented for any future surgical planning where its presence is clinically relevant.

Last updated: 8 July 2026
Reviewed by: Specialist doctors from the quality team at Elfcare

FAQ

  • An accessory spleen, or splenunculus, is a small nodule of entirely normal splenic tissue that developed outside the main spleen during foetal development. It is a common congenital anatomical variant, present in approximately 10 to 30% of the population, and is almost always entirely benign and asymptomatic. It is most commonly found at the splenic hilum but can also occur in the pancreatic tail, where it can mimic a pancreatic tumour on imaging.

  • An accessory spleen almost never causes symptoms and is discovered entirely incidentally on abdominal imaging. In the rare event of torsion of a mobile accessory spleen, sudden acute abdominal pain may occur. Following splenectomy, an accessory spleen may hypertrophy and assume splenic function, which can be beneficial or problematic depending on the indication for the original splenectomy.

  • A congenital separation of a small portion of developing splenic tissue from the main splenic mass during embryological development, resulting in an ectopic nodule of normal splenic tissue. It is a normal developmental variant with no pathological significance in the vast majority of cases. Splenosis, a distinct acquired condition from splenic trauma or surgery, produces a similar appearance but is not congenital.

  • Abdominal MRI is the primary detection and diagnostic tool, identifying the characteristic signal that is isointense to the main spleen on all sequences, distinguishing it from lymph nodes, pancreatic tumours, adrenal masses, and other abdominal lesions. This MRI appearance is essentially diagnostic in the vast majority of cases without requiring biopsy.

  • Yes. Elfcare's full body MRI images the spleen and surrounding abdominal structures directly as part of the standard abdominal sequence, identifying accessory spleens and confirming their diagnosis through their characteristic MRI signal. If an accessory spleen or a lesion requiring further characterisation is identified, we take care of further diagnostics or refer you to the appropriate specialist.

  • An accessory spleen in isolation requires no treatment. In the context of haematological conditions where splenectomy is being considered, identification of an accessory spleen before surgery allows it to be removed simultaneously, preventing recurrence of the underlying condition from residual splenic tissue. In immune thrombocytopenia in particular, failure to identify and remove an accessory spleen at the time of splenectomy is a recognised cause of treatment failure. No intervention is required for an incidentally discovered accessory spleen in an otherwise healthy individual.