Counter-intuitively, when insonating the lungs of healthy patients, we don’t “see” lung tissue. Instead we see and interpret artifacts arising from the pleural lines and the diaphragm. These artifacts change with pulmonary disease processes. In pneumonia, the airway spaces become inspissated with bacterial byproducts and consequently the sonographic appearance of lung tissue changes.
The transformation of lung tissue is termed hepatization: the lung tissue now appears similar to liver tissue.
This can be confusing in the lower lung fields, especially adjacent to the diaphragm because we use the mirror image artifact of the liver and spleen to indicate that lung tissue is normal. This mirrored, artifactual splenic or liver appearance could then be called pseudo-hepatization.
So, how do we differentiate hepatized lung versus pseudo-hepatized lung?
- Never use a single image for your diagnosis, scan through area and convince yourself (then save a representative image or clip for QA).
- Be systematic and scan down from the lung apices to the diaphragm.
- Hunt for the diaphragm and use it as a dividing line between the lung and the abdominal organs.
- Hepatized lung will often have a rim of fluid around it.