A convoluted list of terms is used to refer to polysplenia; heterotaxy, situs ambiguous or left isomerism are often used as synonyms. Conditions more commonly found in
pediatric patients with polysplenia are bilateral two-lobed lungs with hyparterial
bronchi, abdominal heterotaxia with bowel malrotation, and interruption of the inferior vena cava with
azygos continuation. Frequent variations in the great
veins are observed as well. The
superior vena cava can be bilateral, meaning both right and left superior vena cava are present instead of the normal disappearance of the left superior vena cava during development, may terminate in the coronary sinus, or, less commonly, can connect directly to the left
atrium instead of the right. The
coronary sinus itself may be absent, a finding often associated with the persistence of a left-sided superior vena cava. The
inferior vena cava is frequently interrupted, with venous return continuing through the azygos system instead of continuing to the heart as usual.
Atrial septal defects, particularly of the endocardial cushion type, can also occur in some cases. The organ developmental stages related to polyspenia, such as spleen formation, separation of aorta and pulmonary artery into two separate outflow track (septation of the conotruncus), formation of the three lobes of the lungs (lobulation of the lung) and gut rotation, all occur by the 36th day of
gestation. Hence, it is thought that these heterotaxy syndromes are all different forms of the same embryonic developmental abnormality caused by a teratogenic insult during the 31st to 36th days of gestation.
Potential relevant genes The molecular genetics of polysplenia syndrome are not well understood. Many genes that encode proteins of the TGF-β,
transforming growth factor beta, pathway are considered candidates for left-sided or right-sided isomerism. Two secreted ligands of the TFG-β superfamily amplify the expression of
PITX2 transcription factor, a key determinant of left identity.
Inheritance A specific inheritance pattern for polysplenia has not been established. Some studies state that it is possibly inherited with an autosomal recessive pattern while other studies had data that could not confirm such inheritance. and another on two first cousins suggested autosomal dominant inheritance with incomplete penetrance.
Diagnosis Asplenia and polysplenia are difficult to diagnose using
ultrasound since the structure of the spleen itself is hard to visualize due to its anatomical location. The wide-ranging clinical presentation of polysplenia poses additional diagnostic challenges. In another adult case, a 60 year old male patient came in for an acute left renal colic and CT-scan performed found multiple spleen and other abnormalities associated with polysplenia like azygous continuity of inferior vena cava, partial development of dorsal pancreas, and hepatic veins from the liver sending blood directly into the right atrium instead of draining into the inferior vena cava which takes the blood to the right atrium in normal conditions. These abnormalities caused no perturbation in his life. The patient was diagnosed with left ureteral calculi, which means that a kidney stone was present in the left ureter, causing the initial pain. Treatment for the left ureteral calculi was provided, and no treatment for the polysplenia was required; the patient was only made aware of its existence. ==See also==