Unilateral hypertranslucent hemithorax

A unilateral hypertranslucent hemithorax has many potential causes. It may be the result of rotation away from an optimal position or because of pathology.

Rotation

A unilateral hypertranslucent hemithorax may be caused by the positioning of the patient. Rotation away from the radiation beam alters the attenuation of the beam differently on either side of the thorax. When the patient is turned to the right, the right side will be hypertranslucent.  

• poor patient positioning
• scoliosis

Pathology

Where rotation isn't thought to be the cause of the differential transradiancy, it may be useful to consider the potential causes by the structures they involve, in the order in which the radiation beam hit them. The age of the patient is also a factor that should be considered.

A helpful mnemonic is SAFE POEM

Chest wall defect

• mastectomy
• Poland syndrome (absent pectoralis muscle)

Pleura and pleural space

• pneumothorax
• pleural effusion (contralateral)

Mediastinal

• mediastinal fibrosis

Pulmonary (Ventilation)

• airway obstruction
  • bronchial compression (hilar mass, cardiomegaly)
  • endobronchial obstruction with air trapping (foreign body, tumour, mucous plug)
  • obliterative bronchiolitis
• Swyer-James syndrome
• pulmonary emphysema (asymmetric)
• congenital lobar emphysema
• unilateral bullus / bullae
• compensatory hyperinflation
• pneumonectomy

Vascular (Perfusion)

• pulmonary embolism
• congenital heart disease
• congenital pulmonary artery hypoplasia / pulmonary artery stenosis
• shunt (e.g. Blalock Taussig)
• unilateral absence pulmonary artery (UAPA)