This article is from the the official alt.spleen FAQ, by Andrew Stellman with numerous contributions by others.
Andrew says: NOTE: PLEASE DO NOT SEND ANY MAIL TO ME REQUESTING MEDICAL ADVICE! I AM NOT A DOCTOR, AND WILL NOT GIVE YOU ANY USEFUL INFORMATION.
This is a very difficult question, and for the answer it was necessary to consult Nobel prizewinning surgeon Tom Whelan (firstname.lastname@example.org) for an educated medical opinion. Here's what he had to say:
"The human Spleen is capable of expanding greatly when under the influence of certain hemodynamic situations. In chronic portal hypertension (with poss. assc Rt heart failure), there may be portal fugue present, and the blood backs up to the the most compliant organ available, usually the Spleen. Since the spleen is compliant, it can engorge itself with blood and expand greatly. Some Splenamegaly reaches wheel-barrow proportions!, then, of course, the serum in the blood begins to leak into the peritoneal cavity (ascites), when the splenic volume is at its max. These poor souls with large spleens are usually found counting gum wrappers in the gutter, with a bottle of Mad-Dog in one hand. You may even find them tending a 7-11, or occupying a public office."