Smooth black lines in the soft tissue may represent normal fat – but irregular black areas may represent surgical emphysema
It is essential to assess the soft tissues on every chest X-ray you examine. You will often find important clues to help come to a diagnosis. Appearances of the soft tissues can be misleading and it is important to be aware of the pitfalls.
Breast tissue
Breast tissue varies greatly between men and women, and between individuals. Occasionally you may mistake breast tissue for increased density of the underlying lung, particularly if there has been a mastectomy on the other side.
Normal fat planes are often clearly defined in the soft tissues. These appear as smooth layers of low density (black), between layers of relatively dense (whiter) muscles. Irregular low density within the soft tissues may be due to tracking air as a result of injury to the airways or pleura. This is know as surgical emphysema and produces the distinctive clinical sign of palpable subcutaneous 'bubble-wrap.'
Occasionally subcutaneous gas may relate to infection, but this is usually more localised. As always, correlation with the clinical features is necessary.
Multiple irregular areas of low density within the chest wall soft tissues (arrowheads) due to surgical emphysema
Multiple rib fractures (#)
Clinical information
Road traffic crash
Chest pain, shortness of breath and marked clinical surgical emphysema
Diagnosis
Multiple rib fractures complicated by left hemidiaphragm injury, left pneumothorax (treated by drain) and widespread surgical emphysema (tracking subcutaneous air)