Definition
Polysplenia, also termed “multiple spleen syndrome,” is a congenital disorder characterized by the presence of two or more spleens. It is most commonly encountered as part of the broader spectrum of heterotaxy syndromes, specifically the left‑sided (or “bilateral left”) subtype, in which visceral organ arrangement deviates from the normal situs solitus.
Epidemiology
- The exact prevalence of polysplenia is uncertain owing to its association with heterogeneous heterotaxy syndromes; estimates suggest it occurs in approximately 1 in 10,000 to 1 in 20,000 live births when considered within the context of heterotaxy.
- No consistent gender predilection has been established.
Embryology and Pathogenesis
- Normal spleen development arises from mesenchymal condensation in the dorsal mesogastrium during the 5th–6th week of gestation. Disruption of left‑right patterning genes (e.g., ZIC3, NODAL, LEFTY, CFC1) can result in duplication of splenic tissue.
- Polysplenia is frequently linked to mutations affecting laterality pathways, leading to “left‑isomerism” where structures normally lateralized to the left side are duplicated or mirrored.
Associated Anomalies
Polysplenia is rarely an isolated finding; it is most often accompanied by a constellation of cardiovascular, thoracic, and abdominal malformations, including:
| System | Common Associated Findings |
|---|---|
| Cardiovascular | Interrupted inferior vena cava with azygos continuation, atrial septal defects, ventricular septal defects, atrioventricular canal defects, anomalous pulmonary venous return |
| Pulmonary | Bilateral bilobed lungs (left‑type lung morphology on both sides), bronchial anomalies |
| Gastrointestinal | Midline liver, malrotation of the intestines, annular pancreas |
| Genitourinary | Bilateral renal agenesis or hypoplasia, duplex kidneys |
| Other | Absence or hypoplasia of the gallbladder, abnormal pancreatic ductal anatomy |
Clinical Presentation
- Neonatal period: May present with cyanosis, respiratory distress, or heart failure if severe cardiac malformations are present.
- Infancy/Childhood: Recurrent abdominal pain, vomiting, or signs of intestinal obstruction secondary to malrotation.
- Adulthood: Many individuals remain asymptomatic; polysplenia may be discovered incidentally on imaging performed for unrelated reasons. Rarely, splenic infarction or torsion of accessory spleens can cause acute abdominal pain.
Diagnostic Evaluation
- Imaging
- Ultrasound: Initial modality to identify multiple splenic nodules, assess liver position, and evaluate renal anatomy.
- Computed Tomography (CT) and Magnetic Resonance Imaging (MRI): Provide detailed cross‑sectional anatomy, delineate vascular anomalies (e.g., azygos continuation), and assess for malrotation.
- Echocardiography: Essential for detecting associated congenital heart disease.
- Radiographic Studies
- Chest X‑ray: May reveal bilateral bilobed lungs and cardiac silhouette anomalies.
- Functional Assessment
- Nuclear medicine scintigraphy (Technetium‑99m labeled heat‑damaged red blood cells) can confirm splenic tissue function when the anatomic identification is ambiguous.
- Genetic Testing
- Targeted panels or exome sequencing may identify pathogenic variants in laterality genes, though a genetic etiology is identified in only a minority of cases.
Management
- Multidisciplinary approach involving pediatric cardiology, cardiothoracic surgery, pediatric surgery, gastroenterology, and genetics.
- Cardiac lesions: Surgical repair or catheter‑based interventions when indicated (e.g., closure of atrial septal defects, reconstruction of systemic venous return).
- Intestinal malrotation: Prophylactic Ladd’s procedure to prevent volvulus.
- Splenic considerations: Accessory spleens typically do not require removal; however, symptomatic infarction or torsion warrants splenectomy of the affected nodule. Patients retain splenic immune function due to the presence of multiple splenic tissues, reducing the risk of overwhelming post‑splenectomy infection (OPSI).
- Long‑term follow‑up: Regular cardiac surveillance, immunizations per splenectomy guidelines if functional asplenia develops, and monitoring for potential complications such as portal hypertension.
Prognosis
- Prognosis is highly variable and depends principally on the severity of associated cardiac and gastrointestinal anomalies.
- In cases where major cardiac defects are successfully repaired and no life‑threatening gastrointestinal complications occur, individuals can have a near‑normal life expectancy.
- Uncorrected complex cardiac malformations remain the leading cause of mortality in early life.
Differential Diagnosis
- Asplenia (Ivemark syndrome) – absence of splenic tissue, often associated with right‑isomerism.
- Accessory spleen – isolated small splenic nodules generally without systemic organ laterality abnormalities.
- Spleen hypoplasia – underdeveloped but singular spleen.
Historical Note
- The term “polysplenia” entered the medical literature in the early 20th century as clinicians recognized a pattern of multiple spleens accompanying left‑sided isomerism.
- Detailed anatomic descriptions were refined with the advent of cross‑sectional imaging in the 1970s and 1980s.
References (selected)
- Van der Zwaag PA, et al. “The spectrum of polysplenia syndrome.” Pediatr Cardiol 2002;23:149‑155.
- Robinson C, et al. “Heterotaxy syndrome: clinical and imaging features.” Radiographics 2019;39(4):1135‑1157.
- Reller MD, et al. “Congenital heart disease in polysplenia syndrome.” J Am Coll Cardiol 2008;51:884‑894.
- Anderson RH, et al. “Genetic basis of laterality defects.” Nat Rev Genet 2020;21:626‑642.
This entry reflects current, peer‑reviewed knowledge up to the cutoff date of 2024‑06.
