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Chest Imaging

Diaphragmatic paralysis

may be unilateral or bilateral. The most common cause of unilateral paralysis of the diaphragm is involvement of the phrenic nerve by a tumour. But there are many other causes. It occasionally occurs as a complication of various neurological diseases. Also injury to the phrenic nerve as a result of trauma to the thoracic cage or cervical spine and pressure upon the phrenic nerve from a substernal thyroid or aortic aneurysm can cause paralysis. Infectious processes involving the lung, pleura and/or mediastinum may result in temporary or permanent diaphragmatic paralysis. Finally diaphragmatic paralysis can be idiopathic. The radiological evaluation of diaphragmatic paralysis requires chest radiographs, adequate fluoroscopic tests and clinical information. In some cases chest ultrasonography can also be useful for studying and monitoring diaphragmatic movement. Four signs indicate diaphragmatic paralysis:

  • elevation of the diaphragm above the normal range;

  • diminished, absent or paradoxical movement on inspiration;

  • mediastinal shift on inspiration; and

  • paradoxical movement during sniffing (Fig.1).

    All these signs need not be present simultaneously but paradoxical movement during sniffing is generally considered as the sine qua non of diaphragmatic paralysis. However, these signs should be interpreted with care since false positive and false negative results occur and other diseases such as lung fibrosis, atelectasis, (hydro)pneumothorax, bronchial stenosis, pneumonia, emphysema and diaphragmatic injury can cause abnormal diaphragmatic position and motion. In addition, the sniff test can be normal in apparently normal patients. Though in these circumstances the paradoxal motion is small (< 2 cm) and predominantly seen in the anterior part of the diaphragm. The radiological diagnosis of bilateral diaphragmatic paralysis can be difficult and the fluoroscopic study of bilateral diaphragmatic paralysis requires simultaneous evaluation of diaphragmatic and chest wall movement.

    JV

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    Fig.1

    Paradoxical movement of the paralyzed hemidiaphragm in unilateral diaphragmatic paralysis is the result of increased abdominal pressure caused by downward displacement of the normal part of the diaphragm.
    Diaphragmatic paralysis, Fig.1