X ray The Normal Chest: Methods Of I Nvestigation And Differential Diagnosis

Method of investigation

Plain films:

a PA, lateral

b AP, decubitus, supine, oblique

• Inspiratory-expiratory

d Lordotic, apical, penetrated

• Portable/mobile radiographs

• Tomography

• CT scanning

• Radionuclide studies

• Needle biopsy

• Ultrasound

• Fluoroscopy

• Bronchography

• Pulmonary angiography

• Bronchial arteriography

• MRI

• Digital radiography

• Lymphangiography

The plain postero-anterior (PA) chest film i s the most frequently requested radiological examination. Visualisation of the lungs is excellent because of the inherent contrast of the tissues of the thorax. Lateral films should not be undertaken routinely.

Comparison of the current film with old films is valuable and should always be undertaken if the old films are available. A current film is mandatory before proceeding to more complex

investigations.

Simple linear tomography remains a useful investigation when CT is unavailable. It is helpful for confirming that an abnormality suspected on a plain film is genuine and that it is intrapulmonary, although the high kilovoltage film has reduced the need for tomo graphy in these circumstances. In addition it is still used in some centres to assess a peripheral lung mass, the lung apices and the abnormal hilum.

However, conventional CT scanning i s far superior for staging malignancy, detecting pulmonary metastases, and assessing chest wall and pleural lesions, the lung mass, the hilum and mediastinum.

High-resolution CT scanning is of proven value in the diagnosis of diffuse lung disease, particularly in the early stages when the chest radiograph is normal, and for follow-up. In most centres highresolution scanning is used for the detection of bronchicctasis, and

surgery is undertaken without preoperative bronchography.

Pulmonary angiography remains the gold standard for the diagnosis of pulmonary embolism. It is usually undertaken in those patients with massive embolism when embolectomy or thrombol ysis is contemplated. However, spiral CT angiography is showing sensitivity and specificity rates approaching those of conventional angiography in the diagnosis of pulmonary embolism, and can reliably demonstrate vessels down to the subsegmental level.

Ultrasound i s of use for investigating chest wall and pleural lesions and lung lesions adjacent to the chest wall. It should be used for the localization of pleural fluid prior to a diagnostic tap or drainage to reduce the risk of a malpositioned catheter and pneumothorax.

However, the acoustic mismatch between the chest wall and air-containing lung results in reflection of the ultrasound beam at the lung-pleura interface, so that normal lung cannot be

demonstrated.

Biopsy of pulmonary lesions using a fine needle for aspiration has a high diagnostic yield for malignancy, excluding lymphoma. with a low incidence of complications. A cutting needle is associated with a higher complication rate but is more helpful in the diagnosis of lymphoma and benign lung conditions.

Turtle