Lung point sign | Radiology Signs

Answer:

The lung point is the location on the chest wall where, in real time, an area with absent pleural sliding gives way to an area with normal sliding during the respiratory cycle, and on M-mode where the barcode pattern alternates with the seashore pattern at the same point. It marks the boundary of a pneumothorax, where the partially collapsed lung intermittently reapposes to the parietal pleura on inspiration, and it is regarded as essentially 100 per cent specific for pneumothorax, although its sensitivity is limited and it is absent in a complete pneumothorax where the lung never touches the chest wall. The diagnostic sequence taught in point-of-care protocols is systematic: absence of lung sliding raises the possibility, absence of B-lines and of a lung pulse supports it, and demonstration of a lung point confirms it. Each preceding step alone has important false positives, since sliding is also absent in main bronchus intubation, apnoea, pleural adhesions or pleurodesis, severe consolidation, acute respiratory distress syndrome and bullous disease. The position of the lung point along the chest wall gives a rough estimate of the size of the pneumothorax and can guide the decision between observation and drainage. Ultrasound outperforms the supine chest radiograph for pneumothorax detection in trauma and critical care and is far faster than CT.

Why is it called so?

The sign is named for the point at which lung reappears against the chest wall during the breath.

Pathophysiology

Normally the visceral and parietal pleura are in contact and slide against each other with respiration, which ultrasound displays as shimmering movement at the pleural line and as the granular seashore pattern below the pleural line on M-mode. Air in the pleural space separates the two layers and reflects the ultrasound beam completely, so no movement and no lung artefacts are seen and M-mode shows only horizontal lines, the barcode or stratosphere pattern. At the margin of the pneumothorax the collapsed lung expands sufficiently during inspiration to touch the parietal pleura and then falls away again during expiration, so a single point on the chest wall alternates between the two patterns, which is what generates the sign and why it can only exist where lung and air meet.

Alternative names: Lung point; transition point

Other associated named signs: Seashore sign and barcode (stratosphere) sign on M-mode, the lung pulse and the bat sign

References

1. Lichtenstein DA. BLUE-protocol and FALLS-protocol: two applications of lung ultrasound in the critically ill. Chest. 2015;147(6):1659-1670. PMID: 26033127.