Accessory Spleen
An accessory spleen is a small, extra spleen that develops during fetal development and persists as a separate piece of splenic tissue. These congenital variations are common, occurring in approximately 10-30% of the population, and are typically discovered incidentally during imaging studies performed for other reasons.
What is it?
An accessory spleen, also known as a splenunculus or supernumerary spleen, is a small mass of functioning splenic tissue that exists separately from the main spleen. These develop during embryonic life when the spleen forms from multiple tissue buds that normally fuse together. When one or more buds fail to fuse with the main spleen, they persist as accessory spleens.
Accessory spleens are found in 10-30% of the general population and are considered a normal anatomical variant rather than a pathological condition. They are typically small, ranging from a few millimeters to 2-3 centimeters in diameter, and most commonly located near the splenic hilum (the area where blood vessels enter the main spleen). However, they can occasionally be found elsewhere in the abdomen or pelvis.
Important to Know
Accessory spleens are almost always benign and require no treatment. However, they become clinically significant in certain situations: after splenectomy (surgical removal of the main spleen), an accessory spleen may grow larger and take over splenic function; in patients with blood disorders requiring splenectomy, undetected accessory spleens may lead to recurrence of symptoms; and rarely, they may be mistaken for lymph nodes, tumors, or other masses on imaging studies. It’s important for radiologists to recognize accessory spleens to avoid unnecessary procedures or anxiety.