An accessory spleen is a small piece of splenic tissue found separate from the main spleen. Also known as a splenule or splenunculus, it is a congenital anomaly, present from birth, and typically does not cause health issues.
What is an Accessory Spleen?
An accessory spleen forms during early embryonic development, around the fifth week of fetal life, due to the incomplete fusion of mesenchymal buds that give rise to the spleen. This results in one or more small nodules of functional splenic tissue. While generally small, typically around 1 centimeter in diameter, their size can vary from a few millimeters up to several centimeters.
Accessory spleens are a common finding, occurring in an estimated 10% to 30% of the population. They can be located in various places within the abdomen, most frequently near the hilum of the main spleen (75-80% of cases) or adjacent to the tail of the pancreas (17-20% of cases). Other less common locations include areas along the splenic vessels, within ligaments, the omentum, or even in the walls of organs like the stomach or intestines.
Are Accessory Spleens Harmful?
In the vast majority of individuals, an accessory spleen is harmless and does not lead to symptoms or health problems. They are often discovered incidentally during medical imaging, such as an ultrasound, CT scan, or MRI, for an unrelated condition. These small splenic nodules are considered a normal anatomical variation and typically require no medical intervention or treatment.
Accessory spleens are functional, performing similar roles to the primary spleen, including filtering blood and participating in immune responses. Despite their functional capacity, their small size means they rarely contribute significantly to overall splenic function. Their presence does not warrant concern or further medical follow-up unless specific complications arise.
When an Accessory Spleen Causes Issues
While uncommon, an accessory spleen can become problematic and lead to symptoms. This occurs due to complications such as torsion (twisting of its vascular supply), rupture, hemorrhage, or cyst formation. Torsion is rare but can cause acute abdominal pain if the blood supply is cut off.
Symptoms that might indicate a problematic accessory spleen include acute or chronic abdominal pain, often localized to the left upper quadrant, along with nausea, vomiting, or fever. Diagnosis involves imaging techniques like ultrasound, CT scans, or MRI, which identify the accessory spleen’s presence and condition. A nuclear medicine scan, such as scintigraphy, may confirm splenic tissue. Occasionally, accessory spleens can be mistaken for enlarged lymph nodes or tumors on imaging, complicating diagnosis.
If an accessory spleen becomes symptomatic or causes complications, management depends on the specific issue. For acute pain due to torsion or rupture, surgical removal may be necessary. For individuals undergoing splenectomy for certain blood disorders, such as idiopathic thrombocytopenic purpura, removing any accessory spleens is important to prevent recurrence.
Living with an Accessory Spleen
For most people, living with an accessory spleen requires no special considerations or changes to their daily life. Since these extra splenic tissues are usually asymptomatic, they do not impact overall health or immune function. Regular check-ups with a healthcare provider are generally sufficient, with no specific monitoring of the accessory spleen typically needed. It is important to communicate with a doctor if new or unexplained abdominal pain develops, especially in the left upper abdomen. While many causes of abdominal pain exist, informing the healthcare provider about the presence of an accessory spleen can help in the diagnostic process.