Polysplenia
Polysplenia is a rare congenital condition in which a person has multiple small spleens instead of a single normal-sized spleen. It is most often part of a broader pattern called left isomerism (a form of heterotaxy syndrome), in which several abdominal and chest organs develop with a more “left-sided” symmetry. Polysplenia is frequently associated with congenital heart disease, abnormal positioning of abdominal organs, biliary and vascular anomalies, and varying effects on splenic function. Imaging—particularly CT and MRI—is central to recognizing the condition and identifying associated anomalies.
What is it?
Polysplenia is a rare congenital condition in which an individual has multiple small spleens, often arranged in a cluster in the upper abdomen, instead of a single normal-sized spleen. The number of splenic nodules can vary widely, sometimes ranging from two to ten or more, with the combined splenic tissue varying in total volume. Polysplenia is generally not a disease of the spleen alone but is most often part of a broader developmental pattern called left isomerism—one form of heterotaxy syndrome—in which several internal organs develop in a more symmetric or “two-sided left” pattern.
During normal fetal development, the body is asymmetric: most people have one liver predominantly on the right, one spleen on the left, a particular arrangement of heart chambers and great vessels, and characteristic positioning of the intestines, lungs, and other organs. In heterotaxy syndromes, this normal asymmetry does not develop correctly. Right isomerism (sometimes called “asplenia syndrome”) typically involves absence of the spleen and a more “two-sided right” arrangement, while left isomerism typically involves multiple small spleens (polysplenia) and a more “two-sided left” arrangement. Some patients show overlapping features that do not fit neatly into either category.
Polysplenia is frequently associated with a constellation of anomalies that may include congenital heart disease (often involving the atria, atrioventricular connections, venous returns, and outflow tracts), abnormal arrangement of abdominal organs (such as a midline or right-sided stomach, malrotation of the intestines, and altered position of the liver), absence or interruption of the inferior vena cava with continuation through the azygos vein, abnormalities of the portal vein or other vessels, abnormalities of the gallbladder and biliary tree (such as biliary atresia, which can be a serious cause of liver disease in infancy), bilateral two-lobed (left-sided) lungs, and other features. Each individual with polysplenia has a unique combination of findings.
The severity of polysplenia varies widely depending on the associated anomalies. Severe forms—often diagnosed in infancy because of significant congenital heart disease or biliary atresia—can be life-limiting without specialized treatment. Milder forms with limited or no clinically important associated anomalies may be identified incidentally in adulthood on imaging done for other reasons and may produce few or no symptoms throughout life.
Splenic function in polysplenia is variable. Although total splenic tissue may be substantial, the immune function of multiple small spleens is often less effective than that of a single normal spleen. Some patients with polysplenia show evidence of partial or functional asplenia, with reduced ability to clear certain encapsulated bacteria from the bloodstream and an increased risk of serious infections. The peripheral blood smear may show Howell-Jolly bodies (small DNA remnants normally cleared by the spleen) in some patients, suggesting reduced splenic function. Other patients have largely normal splenic function despite the unusual anatomy.
Diagnosis combines clinical evaluation with imaging. In infants and children, congenital heart disease, jaundice from biliary atresia, or other early features often lead to comprehensive evaluation that reveals polysplenia and its associated findings. In adults, polysplenia is often identified incidentally on abdominal imaging done for unrelated reasons. Ultrasound, CT, and MRI of the abdomen can clearly show multiple splenic nodules, abnormal positioning of abdominal organs, and vascular and biliary anomalies. Echocardiography and additional cardiac imaging (such as cardiac MRI) characterize associated congenital heart disease. Peripheral blood smear can be helpful in assessing splenic function. Genetic counseling and evaluation may be appropriate in selected families, especially when there is a history of heterotaxy or related conditions, although most cases appear to be sporadic.
Important to Know
There is no specific treatment for polysplenia itself; management focuses on identifying and addressing the associated anomalies and—when relevant—reducing the increased risk of infections in patients with partial or functional asplenia. Care is best delivered by multidisciplinary teams that may include cardiologists (often with congenital heart disease expertise), pediatric or adult congenital heart disease surgeons, hepatologists, gastroenterologists, pediatric or general surgeons, hematologists, infectious disease specialists, geneticists, and primary care clinicians, with coordination tailored to each patient’s specific findings.
Congenital heart disease is often the most clinically important component of polysplenia and may require evaluation by congenital heart disease specialists, ongoing monitoring, medications, catheter-based procedures, or surgery depending on the specific anomalies. Lifelong follow-up by adult congenital heart disease specialists is typically recommended in adulthood. Care of arrhythmias, valve disease, and other long-term cardiovascular issues is integrated into the overall plan.
Biliary atresia, when present in infants, requires prompt evaluation and surgical treatment (typically the Kasai procedure) and, in some children, eventual liver transplantation. Long-term hepatology follow-up is important. Patients with vascular anomalies of the inferior vena cava or portal vein may require monitoring and, in selected cases, specific interventions, particularly if surgery in the abdomen is needed.
Abdominal organ malrotation may predispose to volvulus (twisting of the intestines), which can present with bowel obstruction. Patients and families benefit from awareness of warning signs and the importance of prompt evaluation of acute abdominal symptoms. Some patients are evaluated for prophylactic surgical procedures (such as a Ladd procedure) depending on the specific anatomy and risk.
Infection prevention is an important consideration in patients with reduced splenic function. While not all patients with polysplenia are functionally asplenic, those with evidence of impaired splenic function (such as Howell-Jolly bodies on blood smear) are generally treated as functionally asplenic. Recommended measures may include vaccinations against encapsulated bacteria (such as pneumococcal, meningococcal, and Haemophilus influenzae type b vaccines), influenza and COVID-19 vaccinations per current recommendations, antibiotic prophylaxis in selected patients (particularly children), education about prompt evaluation of fevers, and consideration of travel-related risks. Each patient’s needs are individualized based on age, splenic function assessment, and overall health.
In adulthood, patients with polysplenia identified incidentally and without significant associated anomalies may require limited specific intervention beyond awareness of their anatomy, monitoring of any cardiovascular or hepatobiliary findings, and—when warranted—infection prevention measures. Documentation of the diagnosis in the medical record helps ensure that imaging findings are not misinterpreted in the future and that any planned surgery or interventional procedure can take the variant anatomy into account.
Genetic counseling and evaluation may be appropriate in selected families. Most cases of polysplenia appear to be sporadic, but recognized inheritance patterns and gene associations are increasingly described, particularly when there is a family history of heterotaxy, congenital heart disease, or related conditions.
Patient and family education plays an important role. Understanding the diagnosis, the rationale for ongoing follow-up, warning signs of complications, and—when relevant—preventive measures contributes to better outcomes.
Red flag symptoms include sudden severe abdominal pain (especially when bowel obstruction or volvulus is a concern), high fever with chills (particularly in patients with reduced splenic function), severe shortness of breath, palpitations or fainting (which may suggest cardiac arrhythmias or complications), severe jaundice in infants (which may suggest biliary atresia), rapid clinical deterioration, or signs of shock. These warrant prompt or urgent medical evaluation.