(For the purpose of this examination, the right-sided twin is labeled "A" while the left-sided twin is labeled "B.")
Two cranial and cervical structures are demonstrated sharing a single trunk. There are two sets of spines converging to two sacra, which are fused medially. There is a pair of complete upper limbs, a single pelvis, and a pair of lower limbs. A third scapula and clavicle are seen at the midline of the upper thorax.
Each twin has a pair of lungs. The lung of twin A shows right-sided isomerism as evidenced by the symmetric eparterial bronchi. The lung of twin B shows situs solitus morphology (the right bronchus is eparterial while the left bronchus os hyparterial).
There is a single liver predominantly occupying the right upper abdomen. A spleen is seen on the left side. There are two stomachs, one in each side of the upper abdomen.
Two kidneys are seen, one on each side of the common abdominal aorta. A single urinary bladder is demonstrated.
There are two hearts fused at the midline sharing a common atrium. Common superior and inferior venae cavae, both of which drain into the common atrium, are seen at the midline.
Twin A shows the following cardiovascular findings:
- morphologic right atrium at the right side of the common atrium
- atrial septal defect
- tricuspid atresia
- morphologic right atrium and common atrium drain into a medially located prominent ventricle with left ventricular morphology
- rudimentary morphologic right ventricle located lateral to the prominent morphologic left ventricle
- ventricular septal defect
- transposed great arteries with the aorta arising from the rudimentary morphologic right ventricle and the main pulmonary trunk arising from the prominent morphologic left ventricle (ventriculoarterial discordance)
- right-sided arch and descending segment of the aorta
- innominate and right common carotid artery sharing a common origin fro the aortic arch
- right subclavian artery arising directly from the aortic arch
- the aorta of twin A descends into the abdomen and joins the aorta of twin B to form a common abdominal aorta
- patent ductus arteriosus
- supracardiac total anomalous pulmonary venous return
- right brachiocephalic and left internal jugular veins drain into the common superior vena cava
Twin B shows the following cardiovascular findings:
- morphologic left atrium at the left side of the common atrium
- common atrium draining into an anteriorly located morphologic right ventricle
- morphologic left atrium drains into a morphologic left ventricle, located at the left side
- no demonstrable interatrial or interventricular septal defect
- main pulmonary trunk arising from the morphologic right ventricle and aorta arising from the morphologic left ventricle (ventriculoarterial concordance)
- left-sided arch and descending segment of the aorta
- innominate and left common carotid artery sharing a common origin from the aortic arch
- left subclavian artery arises directly from the aortic arch
- aorta of twin B descends into the abdomen and merges with the aorta of twin A to form a common abdominal aorta
- all pulmonary veins drain into the morphologic left atrium
- right internal jugular vein drains into the common superior vena cava
- left internal jugular and left subclavian veins are small in calibers and drain into a persistent left-sided superior vena cava, which drains into the coronary sinus