splenunculi

Splenunculi, also known as accessory spleens, are small nodules of splenic tissue that are separate from the main spleen. They are congenital and occur in an estimated 10 to 30 percent of individuals, often discovered incidentally during imaging, surgery, or autopsy. Each splenunculus contains normal splenic tissue and a capsule, and they typically range from a few millimeters to several centimeters in size.

Embryology and anatomy: Splenunculi arise from persistence of splenic tissue that originates in the dorsal mesogastrium during early fetal development, usually between weeks 5 and 8. They are most commonly located near the splenic hilum but can be found along the greater omentum, in the splenorenal ligament, or near the tail of the pancreas. Each nodulus generally receives arterial supply from branches of the splenic artery, sometimes with a dedicated arterial twig.

Clinical significance: Most splenunculi are clinically silent. They may be mistaken for lymph nodes or other masses on imaging, leading to diagnostic confusion. They are particularly important in the context of splenectomy or plans for splenic irradiation, because residual accessory splenic tissue can sustain splenic function and may cause persistence or relapse of diseases treated by splenectomy, such as autoimmune cytopenias or hereditary spherocytosis.

Diagnosis and imaging: On ultrasound, accessory spleens appear as well-defined nodules with echotexture similar to the spleen. Computed tomography and magnetic resonance imaging typically show enhancement patterns identical to the spleen after contrast administration. Nuclear medicine studies using Tc-99m-labeled colloids or heat-damaged red blood cells can confirm splenic tissue by uptake, distinguishing splenunculi from other masses.

Management: Asymptomatic splenunculi require no treatment. Intervention is indicated if they cause symptoms or if complete removal of splenic tissue is needed during splenectomy to prevent disease persistence. Infarction or torsion of splenunculi is rare but reported.