20% of Humans Have an Extra Spleen—Here's Why

TL;DR

Extra spleens arise in two ways: accessory spleens form when embryonic tissue buds do not fully join, while splenosis develops when an injury scatters splenic tissue elsewhere in the body. An estimated 10–30% of people are born with an accessory spleen, and both forms are usually benign. Read on to compare their origins, anatomy, function, and possible complications.

Transcript

This SciShow video is supported by LMNT. Head to D-R-I-N-K-L-M-N-T dot com/scishow for a free sample pack of electrolyte drinks with any order. [♪ INTRO] We generally know that there are organs in the human body that we can quite literally live without. Your appendix, your gallbladder, your spleen… these organs are kind of optional. But there’s a ... Read More

Key Insights

• 🖐️ The spleen, although not vital, plays a role in the immune system and filtering blood.
• ❓ Extra spleens, such as accessory spleens and splenosis, are relatively common and usually benign.
• ❓ Accessory spleens can provide some residual function after spleen removal.
• 💗 The ability of the spleen to regenerate and grow additional spleens is still not fully understood.
• ❓ Understanding spleen regeneration may have implications for regenerating other organs.
• ❤️‍🩹 Extra spleens are typically harmless, but complications can arise if they end up in the wrong locations.
• 🚚 The liver, another organ involved in blood filtration, also has the ability to regenerate.

Questions & Answers

Q: Why do some people have an extra spleen?

Some people are born with an accessory spleen because several embryonic tissue buds fail to link up completely while the spleen is forming. Others develop splenosis after an injury separates pieces of splenic tissue and allows them to settle elsewhere in the body.

Q: How common is an accessory spleen?

Medical literature estimates that 10–30% of people are born with an accessory spleen, or roughly one in five people. An estimated 26% of people with accessory spleens have more than one.

Q: What is the difference between an accessory spleen and splenosis?

An accessory spleen is present from birth, contains smooth muscle, and receives blood from the splenic artery. Splenosis develops after a spleen injury; its tissue lacks smooth muscle and draws blood from nearby vessels instead.

Q: What does the spleen do?

The spleen is part of the immune system and serves as a gathering point for infection-fighting white blood cells. It also filters old or damaged red blood cells from the blood.

Q: Can a person live without a spleen?

Doctors can safely remove a damaged spleen, and a person can generally continue living without it. However, the absence of a spleen increases susceptibility to illness and infection, so doctors may recommend certain vaccinations and long-term antibiotic therapy, potentially for life.

Q: Can an accessory spleen function after the main spleen is removed?

An accessory spleen can provide some residual function after a splenectomy and may grow larger as it takes on more work. It is still less effective than a full-sized spleen.

Q: Are extra spleens dangerous?

Accessory spleens and splenosis are benign and rarely cause problems. Complications can occur when splenic tissue settles in the wrong location, and doctors may need to distinguish an unexpected lump on a scan from cancer.

Q: Why can spleen tissue regenerate?

Scientists do not yet have a complete explanation for the spleen’s regenerative ability. In 2017, researchers in Japan and Australia identified a stromal cell described as a “spleen organizer” that is thought to help control tissue regeneration.

Summary & Key Takeaways

• The spleen is a non-vital organ that plays a role in the immune system and blood filtration.

• It can be safely removed if damaged, but without a spleen, individuals are more susceptible to infections and illnesses.

• Some people are born with extra spleens (accessory spleens), and others can develop additional spleens (splenosis) following injuries to the primary spleen.