Thoracoabdominal sign

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Thoracoabdominal sign, a variation of the silhouette sign, is a frontal chest radiograph sign which helps to localize a thoracic lesion.

Since the posterior costophrenic sulcus is more caudal than the anterior lung, a thoracic lesion must be posterior if its caudal end is visible below the dome of diaphragm.

And also, convergence of the inferolateral border of the mass towards the spine suggests that the mass is probably entirely intrathoracic (negative thoracoabdominal sign), whereas lack of convergence or divergence indicates a segment silhouetted by the soft tissue density of the abdomen (positive thoracoabdominal sign).

History and etymology

Benjamin Felson (1913—1988) was an American radiologist who first described this sign.