Q. Why is there splenomegaly in hemolytic anemias with intravascular hemolysis? For example, in hereditary spherocytosis, where there is intravascular hemolysis, why is the spleen big? Is it that both types of hemolysis, occur and it’s just that intravascular is increased a little bit more than extravascular?

A. The likelihood of a patient having splenomegaly depends on which particular hemolytic anemia the patient has.

In hereditary spherocytosis (HS), for example, there actually is a good deal of extravascular hemolysis (in addition to the intravascular component). The spleen is the main site of destruction for the abnormal red cells in HS. Spherocytes have a hard time passing through the cords of Bilroth, and they back up in the spleen, causing splenomegaly. Check out the image above of splenomegaly in a child with HS, from the Pediatric Surgery Department at Brown Medical School. Eventually, macrophages devour them and they disappear from circulation.

There is also some intravascular hemolysis in HS; spherocytes are more fragile than regular red cells, so they’re more likely to bust open in blood vessels. It’s not really the main thing that’s going on, though – it’s just a byproduct of the disease. So in HS, there is big-time splenomegaly, because that’s the site of most of the destruction.

In other types of hemolysis that have more of an intravascular component – like, say, acute hemolytic transfusion reactions (where the red cells die mostly in vessels) – the spleen doesn’t get as big (or may not get big at all).