Unilateral Opacity of a Hemithorax

Figure 1: Supine chest radiograph shows a unilateral increased opacity in the left hemithorax, particularly at the mid to lower zones. There is no mediastinal shift. The left hemidiaphragm is in a normal position.

Differential Diagnosis

1. Lung: consolidation, mass, collapse
2. Pleura: effusion (layering or loculated), mass (metastasis, mesothelioma)
3. Chest wall: mass (breast, chest wall musculatures)
4. Extrathoracic: external structures

In this case, the opacity extends beyond the lung to the soft tissue of the chest wall, corresponding to the breast. It is unlikely to be a lung lesion because normal pulmonary vasculatures are visualized through it. Pleural lesion would not extend beyond the thoracic cage. Two main possibilities include a large breast mass or external structures (for example, nonradiopaque pads on the bed).

Comparison with the previous chest radiographs revealed that this is a new finding. Further query of patient's history confirmed the diagnosis of a large left breast mass. Chest CT scan (below) also shows the mass (invasive cancer).

Reference:

Chapman S and Nakielny R. Aids to radiological differential diagnosis. 4th edition, 2003.