Seashore sign | Radiology Signs

Answer:

The seashore sign is the normal M-mode appearance of the pleura and lung: the motionless chest wall above the pleural line produces horizontal parallel lines resembling waves, and the sliding lung below produces a homogeneous granular pattern resembling sand, so the two together look like a shoreline. Its absence, with horizontal lines continuing below the pleural line, is the barcode or stratosphere sign and indicates that pleural sliding has been lost, most importantly because of a pneumothorax. The interpretation must be disciplined, because absence of sliding is not synonymous with pneumothorax: it also occurs with main bronchus intubation, apnoea or breath holding, pleural adhesions and pleurodesis, dense consolidation, severe fibrosis and large bullae. The findings that resolve the question are the lung point, which is specific for pneumothorax, the presence of B-lines or a lung pulse, either of which excludes pneumothorax at that interspace because both require the two pleural layers to be in contact, and the clinical context. Scanning should be performed with a linear or phased array probe at the least dependent part of the chest in a supine patient, usually the third to fourth intercostal space in the midclavicular line, and both hemithoraces should be compared.

Why is it called so?

The banded chest wall above and the granular lung below resemble the sea meeting a sandy beach.

Pathophysiology

M-mode displays the echoes along a single ultrasound line over time. Structures that do not move, such as the skin, subcutaneous tissue, muscle and ribs of the chest wall, generate echoes at fixed depths and therefore trace continuous straight lines. Below the pleural line, the sliding of the visceral against the parietal pleura and the reverberation artefacts arising from the air-tissue interface change continuously with respiration, so the echoes are randomly distributed over time and appear as a uniform granular field. When air enters the pleural space, the beam is reflected entirely at the parietal pleura and no moving interface exists beyond it, so the artefacts become stationary and the granular pattern is replaced by the same horizontal lines seen above the pleura.

Alternative names: Sandy beach sign; seashore pattern

Other associated named signs: Barcode or stratosphere sign, the lung point sign, the lung pulse and B-lines

References

1. Beshara M, Bittner EA, Goffi A, Berra L, Chang MG. Nuts and bolts of lung ultrasound: utility, scanning techniques, protocols, and findings in common pathologies. Crit Care. 2024;28(1):328. PMID: 39375782.