Unilateral hypertranslucent hemithorax
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Unilateral hypertranslucent hemithorax has many potential causes. It may be the result of rotation away from an optimal position or because of pathology.
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. The rotated side has shorter tissue distance which increases the x-ray transmission that passes through it. When the patient is turned to the right, the right side will be hypertranslucent.
- poor patient positioning
Rarely, grid cutoff may also mimic a unilateral hypertranslucency.
Where rotation is not 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 SAFEPOEM.
Chest wall defects - muscle abnormalities
- Poland syndrome (absent pectoralis major muscle)
- surgical removal of pectoralis major muscle for flap surgery
- unilateral fatty atrophy to chest wall muscles
Pleura and pleural space
- airway obstruction
- Swyer-James syndrome
- pulmonary emphysema (asymmetric)
- congenital lobar overinflation (previously called congenital lobar emphysema)
- unilateral bullous/bullae
- compensatory hyperinflation
- unilateral lung transplant: 'abnormal' side may be ipsilateral or contralateral, depending on the reason for transplantation
- pulmonary embolism (if Westermark sign present)
- congenital heart disease
- congenital pulmonary artery hypoplasia/pulmonary artery stenosis
- shunt (e.g. Blalock-Taussig)
- unilateral absence of pulmonary artery
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