Chest Imaging And Bronchoscopy - pediagenosis
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Thursday, December 6, 2018

Chest Imaging And Bronchoscopy

Chest Imaging And Bronchoscopy
Standard (two-dimensional) chest X-rays to detect, diagnose or follow morphological abnormalities in the chest are the mainstay of thoracic radiographical imaging and account for more than 50% of procedures. Recent innovations include digital, three-dimensional computed tomography (CT) scans and physiological (positron emission tomography, ventilation-perfusion scans) imaging. Specifi radiographical abnormalities are discussed in individual chapters.

Posteroanterior (PA) and lateral chest radiographs (CXRs) allow two-dimensional visualization of the lungs, great vessels, heart, diaphragm and mediastinum. PA film should be performed upright in full inspiration. Routine lateral film are not required for screening purposes. Figure 21a and 21b illustrates CXR features and interpretation. Portable anterior-posterior film (AP) in patients unable to stand magnify the heart and mediastinum and do not allow detailed visualization of lung parenchyma.
A standard PA and lateral CXR should allow visualization of both lungs, including the diaphragmatic position, as well as the normal trachea, main carina, main stem bronchi, major and minor fissures aorta, main pulmonary arteries and heart. Understanding of the normal anatomy of a CXR is essential to allow recognition of abnormal lung parenchymal infiltrates enlarged lymph nodes adjacent to the trachea or in the hila, enlarged pulmonary arteries, volume loss of a lobe or segment or cardiac enlargement. In the case of a suspected pleural effusion, lateral decubitus films allow visualization of as little as 50 mL of free-flowing fluid Digital CXRs are being developed that allow more detailed views of the denser portions of the thorax and show finer detail of the lung parenchyma.
Chest Imaging And Bronchoscopy

Computed tomography: a limitation of standard CXR imaging is that the two-dimensional image obscures details and averages densities in the third dimension (anterior-posterior on the PA film). CT allows thin slice axial images and fine-detailed examination of intrathoracic structures. It is more sensitive at detecting small lesions and in determining their relationship to other intrathoracic structures. Gross features are shown in Fig. 21c. Indications for CT are:
Bronchial carcinoma: to detect and assess operability and prognosis of tumours (Chapter 40) by determining location, size and the presence of abnormal lymph nodes (e.g. mediastinal and axillary).
Lung parenchymal disease: to detect and localize interstitial lung infiltrates  bronchiectasis, cavities, bulla, fluid collections and airway abnormalities.
Mediastinal masses: to determine extent, relationship to other structures.
Pleural disease: to detect asbestos-related plaques, mesothelioma and to determine the cause of pleural effusions.
Pulmonary emboli (PE): administration of intravenous contrast allows imaging of the pulmonary blood vessels and detection of emboli. Examples of CT scans are shown in several chapters. Newer technology allows complete axial scanning of the thorax with a single breath-hold.

Ventilation–perfusion (V/Q) scans are mostly performed in the evaluation of pulmonary embolism (Chapter 28). Gamma cameras can visualize radiopharmaceuticals either injected into the venous blood (perfusion) or inhaled (ventilation). Thromboembolism classically causes a V/Q mismatch, with absence of perfusion in the presence of ventilation. Unfortunately, the value of V/Q scans is limited by the observation that many PEs result in indeterminate V/Q scans that show small mismatches or matched V/Q deficits In these cases, other studies must be utilized to demonstrate thromboemboli. Contrast CT scans are increasingly used to detect PE (see above) and are being investigated as possible replacements for V/Q scanning. Quantitative V/Q scans may be used in preparation for lung resection surgery, to assess regional lung function and estimate the amount of residual lung function.

Pulmonary angiography visualizes the vasculature following injection of contrast medium (Chapter 28). It may be required in patients with suspected pulmonary emboli but equivocal V/Q scans, pulmonary hypertension and pulmonary vascular disease, including vasculitis and arteriovenous malformations. These studies are often preceded by echocardiography to visualize right ventricular function and estimate pulmonary artery pressure using Doppler imaging.

Positron emission tomography (PET) utilizes a f uorinated analogue of glucose (FDG) to give images of the lung that highlight areas of increased glucose metabolism. Malignant cells have increased glucose uptake and appear as increased densities on PET images. Recent studies have demonstrated that PET is useful in distinguishing between benign and malignant solitary pulmonary nodules and in detecting small nodal metastases that are not detected on CT scanning. For these indications, PET has a sensitivity and specificit of 80-97% with false-positive scans seen in cases of infection or granulomatous inflammation Whole body PET was recently used to detect clinically inapparent distant metastases.

Bronchoscopy enables direct visualization down to the fourth and fifth divisions of the endobronchial tree. Chest physicians perform most bronchoscopies as day cases under local anaesthetic in the sedated but awake patient, using a flexible fibreopti instrument. It has the advantages of visualization of the upper lobes and is a safe technique with a low complication rate. Saturation and heart rhythm should be monitored and supplemental oxygen should be administered during the procedure. Facilities for resuscitation should always be immediately available. Thoracic surgeons may use a rigid bronchoscope in the fully anaesthetized patient. This instrument allows larger biopsies and better suctioning, and is the method of choice when removing inhaled foreign bodies. Bronchoscopy is most frequently performed to investigate if a shadow on a chest radiograph is due to a lung cancer (Chapter 40). If an endobronchial tumour is seen, biopsies for histological analysis and washings and brush samples for cytological analysis can be taken. In addition, information regarding the operability of the tumour can be obtained. Bronchoscopy can also be used to diagnose parenchymal lung disease using the technique of transbronchial biopsy, which obtains parenchymal and bronchial tissue for histological examination. Collection of bronchoalveolar fluid (bronchoalveolar lavage, BAL) is useful in diagnosing alveolitis (raised lymphocyte count in sarcoidosis), infection in the immunocompromised patient (e.g. Pneumocystis carinii pneumonia) and tuberculosis. Bronchoscopy also aids investigation of collapsed segments or lobes. Therapeutically, bronchoscopy is used to remove inhaled foreign bodies, to aspirate sputum plugs and secretions, to relieve stenosis by placement of stents and during treatment of endobronchial tumours with laser or endobronchial radiotherapy. Haemorrhage, pneumothorax and cardiac arrhythmia, although uncommon, are the main complications of fibreoptinchoscopy.

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