A dynamic ultrasound may be ordered to diagnose a hernia or to characterize the contents of a hernia and determine its reducibility. The ultrasound examination is dynamic because it can be performed as follows:
- In real time, showing motion live
- While the patient is lying on his/her back or standing upright
- When the patient is breathing quietly or straining vigorously
- While the hernia is being compressed with the ultrasound transducer
CT and MR scans, on the other hand, can only be done with the patient lying on his/her back and generally without straining. Because of the ability of ultrasound to show motion during dynamic maneuvers, ultrasound has several advantages over more expensive CT and MR scans in evaluating for groin and anterior abdominal wall hernias, including:
- CT and MR can show hernias, but cannot determine if they are reducible or non-reducible. This can only be demonstrated with direct pressure or certain positions, as with ultrasound. Only a minority of hernias are non-reducible. Most hernias are reducible and will fall back into the abdomen when the patient is quietly lying on his/her back on a table.
- Ultrasound, like CT and MR, can show larger non-reducible hernias, but can also smaller show reducible hernias that CT and MR cannot show. Because ultrasound images show real time motion, we can see reducible hernias moving in and out during dynamic maneuvers.
- During the ultrasound examination, any hernia that is found can be compressed with the ultrasound probe to determine if the hernia is reducible or tender. CT and MR, on the other hand cannot determine whether a hernia is tender. Tenderness is important, because hernias are so common that we often find "incidental" small hernias that are not the cause of the patient’s pain. If a hernia is tender when compressed by the ultrasound probe, it is far more likely that the hernia is really the cause of pain and not merely a common incidental finding.
- Ultrasound can identify hernias that are completely reducible when the patient is lying down, but become non-reducible and more tender when the patient is standing. CT and MRI cannot.