Thoracic ultrasound is one of the hottest topics in emergency and critical care sononography. Assessment for pneumothorax is accurate and relatively easy to learn.
One important sign when assessing for pneumothorax is the lung point. This is the point where normal pleural interface contacts the boundary of the pneumothorax. It is the most specific sign for pneumothorax using ultrasound.
Using B-mode ultrasound, the lung point will appear as the boundary between normal lung sliding and still lung.
Lung point:
Using M-mode, the lung point will give the appearance of alternating normal lung and pneumothorax. The classic normal “waves on the beach” appearance will alternate with the pneumothorax pattern of waves and more waves (or stratosphere or barcode signs).
The utility of the lung point is added specificity in pneumothorax detection. In addition, some authors have argued one could map out the boundaries of a pneumothorax by marking where the lung point exists over the anterior chest wall. This technique may be limited due to respiratory variation in lung point position, and the fact that only the anterior projection of the pneumothorax can be detected. The volume of pneumothorax is a factor of depth as well as surface area, and only the latter may be assessed with the lung point.
There are two important mimics of the lung point which should be recognized. The lung interface with the heart in the left chest can be mistaken for a lung point, and so can the inferior edge of the lung at the diaphragm.
Left anterior chest wall- NOT lung point:
Right pleura and diaphragm, also NOT lung point:
In both cases, be sure to recognize the anatomy that the normal lung interfaces with. If normal lung touches pulsatile tissue in the left chest, it may be the heart. If solid organ is visible (liver or spleen) consider that the diaphragm and not a lung point is being insonated.
