Situs solitus refers to the normal position of the thoracic and abdominal organs.
On plain radiograph, careful attention should be directed at the location of the aortic arch, gastric fundus, cardiac apex, pulmonary fissures and the branching pattern of the bronchi, in order the ensure that the situs is solitus.
The aortic arch, gastric fundus, cardiac apex and splenic shadow should all be left-sided. The bronchi branching pattern should not be symmetrical; the right main bronchus should be shorter and more vertically oriented than the left main bronchus. The minor fissure should be only visible on the right side. The liver shadow should be right-sided.
Ultrasound, CT and MRI
The above findings also apply to these modalities, albeit seen with more precision than on plain radiograph.