Censorship

Either way I don't think it's "censoring" as @ELRavenous is assuming. It could be that only ~10K images of a spleen in Adobe Stock is not enough to generate results. And even with that number most of them are illustrations not anatomically accurate or photos.

Capital "S"?

When I use your prompt, Kevin, I get this error directly linked to the word "spleen":

I also get it when I go to your image link and generate.

    droopy

Not sure what specific prompt you were using but "Medical illustration of a Spleen organ" worked just fine without issues.

https://firefly.adobe.com/public/t2i?id=urn%3Aaaid%3Asc%3AUS%3A13ae34b1-c263-4f5a-9fdd-ce5250a25e1d&ff_channel=shared_link&ff_source=Text2Image