The spleen is an organ located in the upper left abdomen, playing an important role in filtering blood, removing old red blood cells, and supporting the immune system. Sometimes, a small, separate piece of tissue resembling the spleen can be found nearby, known as a splenule. This anatomical variation is often an incidental finding.
What is a Splenule
A splenule is an accessory or ectopic splenic tissue. This tissue is structurally identical to the primary spleen, containing the same cellular components such as red pulp for blood filtration and white pulp for immune responses. Splenules range in size from a few millimeters to a few centimeters in diameter, appearing as small, rounded masses.
Despite their small size, splenules are capable of performing functions similar to the main spleen, albeit on a reduced scale. These small splenic masses are most commonly found near the main spleen, often within the splenic hilum, which is the indentation where blood vessels enter and exit the spleen. However, they can also be located in other nearby areas such as the tail of the pancreas, within the omentum (a fatty tissue fold in the abdomen), or in the mesentery of the small bowel.
How Splenules Form
Splenules can originate through two primary mechanisms: congenitally or acquired later in life. Congenital splenules develop during embryonic growth when the splenic tissue undergoes formation. During this developmental process, small fragments of splenic tissue may separate or fail to fully fuse with the main developing spleen. These isolated fragments then mature into distinct, functional splenules.
Acquired splenules, often referred to as splenosis, form as a result of trauma to the main spleen or following splenic surgery, such as a splenectomy. When the spleen is injured or surgically removed, splenic cells can spill into the abdominal cavity. These cells have the unique ability to implant themselves onto the surfaces of other organs or tissues within the abdomen. Once implanted, these splenic cells can proliferate and differentiate, growing into new, functional splenules.
When Splenules Matter
Most splenules are asymptomatic. They are frequently discovered incidentally during medical imaging procedures, such as ultrasound, CT, or MRI scans, which are performed for unrelated reasons. In many cases, their presence is simply noted without requiring any specific intervention.
Occasionally, a splenule might be mistaken for a tumor or another type of abdominal mass during imaging, leading to further diagnostic investigation. To differentiate a splenule from other masses, specialized imaging techniques can be employed, such as a technetium-99m labeled heat-damaged red blood cell scan. This nuclear medicine scan specifically identifies splenic tissue based on its unique uptake of the damaged red blood cells, confirming if the mass is indeed a splenule.
Rarely, splenules can cause symptoms. These rare complications might include torsion, where the splenule twists on its blood supply, or spontaneous rupture and bleeding. If a splenule is confirmed to be asymptomatic, medical management involves reassurance and continued observation rather than active treatment.