Meet the spleen, the strange little organ that can multiply

On a crisp New England fall day, college freshman Jordan Taylor was playing Ultimate Frisbee when he collided with another player. Taylor was rushed to the hospital, where doctors realized he'd been hit hard enough to tear the delicate covering of his spleen, and he was bleeding internally. A quick surgery fixed the spleen, but doctors saw something strange while they were operating.

"As the doctor was speaking to me post-surgery, he mentioned he'd noticed I had a bunch of extra spleens," Taylor says. We asked if the additional organs gave him spleeny superpowers.

No, alas. But "now I have a pretty good fun fact for when I meet new people," he says. "Never fails to get a follow-up question."

Beyond that, Taylor says, he goes about his days the same ways he always has. He tries not to think about his extra spleens too much. They sort of gross him out.

Spleens are strange organs, located on the upper-left side of the abdomen behind the stomach. They're about the size and shape of an orange wedge, if the orange was squishy and full of blood. They're relatively fragile, and because they contain so much blood, injuries can become serious.

A very informal poll of NPR employees, friends and random Uber drivers reveals that most people don't have any idea what spleens are for. If they did know anything about spleens, it was this: You don't need one to live.

The deep red, squishy spleen has been relegated to the organ bargain-basement, something to be cut out and discarded along with the appendix and wisdom teeth. But the spleen is seriously underrated, and we would like to give it a chance to redeem itself.

In ancient Greek and medieval humoral medicine, few body parts were more crucial than the spleen. People believed that the spleen was responsible for making "black bile," one of the four humors that needed to be kept in balance to stay healthy. If a spleen made too much black bile, it would make someone sad or depressed. But the spleen also cleansed the bile, so it was associated with happiness and laughter.

Because the spleen was so important, it squirmed its way into modern language, says Alisha Rankin, an associate professor and medical historian at Tufts University. Poems were written about the organ, and 19th-century women with depression were said to be plagued by spleen.

"It's funny — in English, the spleen has a dual function. If you have dark and angry thoughts, you can be splenetic or vent spleen. But you can also bust a spleen laughing," says Rankin.

So when Shakespeare's King Richard III tried to rally his troops by shouting, "Fair St. George, inspire us with the spleen of fiery dragons!" we can only assume that his army was motivated and won the battle (spoiler alert: it didn't).

The spleen reigned supreme for several centuries. But eventually, says Rankin, Louis Pasteur discovered bacteria and Alexander Fleming found penicillin. Doctors realized that black bile and imbalanced humors didn't make you sick — germs did. No longer responsible for our joy or sorrow, the spleen fell into obscurity.

And for over a century, that's where it stayed.

"Up until the 1950s, nobody knew what the spleen was for. We thought it didn't matter," says Dr. David Shatz, a surgical critical care specialist at the University of California, Davis, whose research focuses on spleen trauma.

We know that while you're still a fetus, the spleen makes red blood cells. And as an adult, the spleen acts as a garbage can, filtering out damaged blood cells and platelets. But you can live with some old broken blood cells, so if you injured your spleen in the 1950s, doctors wouldn't waste time trying to stitch it up. They'd cut it out in a splenectomy and send you on your way.

But modern imaging technology has left us with a different picture of the spleen, realizing that it has a role in the immune system. Blood slows down as it passes through the spleen, which gives the immune system time to recognize and make antibodies for certain types of bacteria.

"It processes encapsulated bacteria — ones that cause meningitis and ones that cause pneumonia," says Shatz. Without the spleen to keep these bacteria in check, about 0.5 percent of people who have their spleens removed develop sepsis, a potentially deadly blood infection.

"It's not very common, but it's common enough to be a problem," says Shatz. Generally, doctors try to reduce the risk of sepsis with vaccination for pneumococcus, H. influenzae type B (Hib), and meningococcus, so patients' immune systems can recognize these bacteria without a spleen's assistance.

But not everyone gets those vaccinations, so some doctors have tried other tactics. Because it turns out that spleens can do something no other organ can: They can make more of themselves.

Remember Taylor and his extra spleens? When a spleen is injured, cells from the organ scatter throughout the abdomen. If the cells are lucky enough to land somewhere with a lot of blood vessels, they start to grow into tiny extra spleens called splenunculi. The whole process is called splenosis, and it seems to be pretty common: about 1 in 5 people have accessory spleens. It's likely Taylor had had a minor spleen injury earlier on in his life — not enough to need a doctor, but enough to release spleen cells.

"As far as we know, the spleen is the only organ that can do this," says Shatz. Even livers, with their impressive regenerative powers, can't replicate like a spleen.

To reduce the rates of post-splenectomy sepsis, some doctors have tried to deliberately make accessory spleens. Instead of removing a spleen entirely, they've cut spleens up into tiny pieces and left the bits inside patients to grow. Studies have also been done in animals, and according to Shatz, the procedure was fairly side-effect-free. Unfortunately, it's hard to tell whether these accessory spleens have any real benefit. Although the spleen-bits attached and grew, only a handful of cases were looked at, so it's hard to tell whether the new spleens did their jobs as well as their full-sized counterparts — or better than no spleen at all.

Shatz hopes to one day do a large clinical trial. "We'll assign a random number; some spleens will get cut up, and some spleens will go in a bucket." But it hasn't been a research priority, says Shatz. Spleens are cool, but they're not critical.

In the meantime, cheers to the spleen, an underappreciated but impressive organ, filtering away whether you need it to or not. Count your blessings (or count your spleens), and if you aren't in the 18.8 percent with spare splenunculi, don't whine about it. Or, as my dad would say, "don't get spleeny."

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