POLYSPLENIA

Polysplenia or bilateral left-sidedness, the right lung and bronchial tree morphologically mirror those of the left. It is also called left isomerism.

Spleen	Multiple spleens on both sides (probably impossible to recognize with certainty antenatally).
Liver	Usually midline and has symmetric lobes. Antenatally it may be suspected by demonstrating an abnormal course of portal circulation that does not have a clearly defined portal sinus bending to the right.
Hepatobiliary	Absent gallbladder, hypoplastic biliary structures.
Abdomen	Duodenal atresia, bowel malrotation, preduodenal portal vein.
Lung	Right lung and bronchial tree mirror those of the left. Bilateral bilobed lungs.
Major vessels	Intrahepatic interruption of the IVC with azygous continuation (75%). The IVC is interrupted and continues into the hemiazygous, which is ipsilateral and posterior to the aorta. Azygous vein may drain into either SVC. Hepatic vein does not join IVC but crosses over to the left and enters into the azygous continuation or into the nearest atrium (which is not always the RA). Bilateral SVC each entering its own atrium.
Heart	Partial anomalous pulmonary venous return (the pulmonary vein most commonly drains bilaterally into both atria. Atrial septal defects (smaller than those in asplenia). Obstructive lesions of the aortic valve. VSD or AV canal defects. Rarely transposition of the great vessels. Rarely double outlet right ventricle. Fetal heart block, absent SA node and bradycardia.