Description

• A radiological study that visualizes thoracic structures in a two-dimensional plane.
• Chest x-ray (CXR) is utilized in the preoperative period for examination of cardiopulmonary processes, detection of pacemakers, and confirmation of lines and tubes. In the intraoperative period, CXR is used for evaluation of acute pulmonary changes, confirmation of new line and tube placement, and possibly for evaluation of retained surgical instruments. In the postoperative period, CXR is used for confirmation of tube and line placement and evaluation of interval cardiopulmonary changes.
• Intensivists routinely utilize the CXR for monitoring interval pulmonary changes and checking line and tube placement in critically ill patients.

Physiology Principles

• Anatomic structures can be visualized by the differential penetration of ionizing radiation.
  • Inverse relationship between density of anatomic structures and penetration of ionizing radiation.
  • High-density structures such as bone and fatty tissue attenuate the x-ray beam, and appear white on film.
  • Low-density structures such as air appear black on CXR.
• The orientation of the ionizing radiation can affect the quality of the study.
  • Posterior to anterior (PA) orientation of radiation beams can produce a higher quality study but needs patient cooperation.
  • Anterior to posterior (AP) orientation of radiation beams distort anterior thoracic structures because these structures are further away from the x-ray plate that captures the image. The heart and pulmonary vessels appear larger on an AP view than its PA counterpart due to this difference. However, this study can be used more easily on patients who are otherwise immobile (patients in intensive care unit or operating room) or uncooperative.
  • Lateral films are typically performed in the upright position but can be performed supine. Lateral decubitus films can help the physician determine if there is layering of pleural fluid versus a loculated effusion.

Anatomy

• Technical considerations when ordering and examining CXR
  • Markings distinguishing between right and left are always placed by the technologist.
  • Incomplete inspiration may be misleading; decreased lung volumes give the illusion of other anatomic structures appearing larger.
  • Technique of film must be taken into account. The technologist uses various settings to determine energy and timing of radiation dose and this can affect the appearance of density/contrast on the CXR. It is possible to have two completely different appearing CXRs on the same patient by simply modifying the radiological technique.
• Cardiovascular
  • Relevant anatomy: Heart, superior vena cava (SVC), inferior vena cava, pulmonary arteries, pulmonary veins, ascending aorta, descending aorta.
  • Inspect the contour of the heart; it should have curves corresponding to the aorta, atrium, and ventricles. A heart devoid of these normal curves is suggestive of pericardial fluid.
  • The aorta should be visualized from the 12 o’clock to the 6 o’clock position as it goes from the left ventricle through the aortic arch and down to the descending aorta.
  • The SVC is a vague stripe along the left paratracheum that can be accentuated by the supine position.
  • The aortic knob and apex should be on the left. A right sided aortic knob is suggestive of situs inversus.
  • Heart size should take up 1/3^rd or less of the chest cavity.
• Pulmonary
  • Relevant anatomy: Trachea, mainstem bronchi, visceral pleura, diaphragm, costophrenic angle.
  • Trachea should be at the midline; assure that the right and left mainstem bronchi are symmetric (neither elevated nor depressed).
  • Lung markings should extend out to the periphery to rule out pneumothorax.
  • Pulmonary arteries should be symmetric. Large pulmonary arteries that rapidly taper are suggestive of pulmonary hypertension.
  • The density of both lungs should be the same. Air trapping, mucous plugging, and pneumothorax can cause hyperlucent lungs.
  • Costophrenic angles should be sharp. Pleural fluid, pleural thickening, or pleural-based mass can blunt these angles.
  • Diaphragm contours should be noted; flattening of the diaphragms can be suggestive of hyperinflation.
• Musculoskeletal
  • Relevant anatomy: Ribs, sternum, clavicle, scapula, shoulder girdle.
  • Sternum location should be assessed (pectus excavatum).
  • Clavicles should be symmetric.
  • Rib spacing should be symmetrical bilaterally at the respective levels.
  • Lytic or blastic lesions suggest bony destruction.
  • Lateral view: Vertebral body heights to exclude compression fractures.
• Gastrointestinal
  • Relevant anatomy: Esophagus, stomach.
  • An air-fluid level in the mediastinum can result from achalasia or distal esophageal obstruction from cancer.
  • Lateral view: Assess the posterior cardiac shadow for an air-fluid collection which can represent a hiatal hernia.
  • An enlarged esophagus can stretch its outer borders beyond the heart, mimicking a widened mediastinum.
  • Free air beneath the diaphragm. The stomach bubble is on the left and has a normal appearance of air. Gas in the liver can be suggestive of dead bowel (necrotizing enterocolitis).

Physiology/Pathophysiology

• Chronic obstructive pulmonary disease (COPD)
  • Findings: Hyperinflated "black" lungs, large pulmonary arteries that quickly taper, diminished heart size.
  • Lack of pulmonary vascularity in both lungs is due to pulmonary blebs. The relative hypovascularization creates the black appearance. Asymmetry of the mediastinal contour can be suggestive of cancer. The heart may appear to be smaller because of increased intrathoracic pressure.
• Partial pneumothorax
  • Findings: Absence of lung markings to the periphery, visceral pleural line demarcating lung tissue from air, commonly seen in apex.
  • In normal lungs, the visceral pleura approximates with the parietal pleura. In a partial pneumothorax, air comes between the visceral and parietal pleura, allowing the border of the parietal pleura to be visualized. An upright film is more sensitive than supine in detecting partial pneumothorax (collects at apex due to gravity).
  • The entire clinical picture must be taken into account. Generally, a stable patient with a small partial pneumothorax can be observed with serial CXR to confirm resolution.
• Tension pneumothorax
  • Findings: Complete lucency of the chest with shifting of the mediastinum away from the affected side, possible lucency in soft tissues of the neck and axilla.
  • One-way valve physiology allows air to enter the chest cavity but not escape. The increasing pressure pushes the trachea and mediastinal structures to the contralateral side.
  • Treatment requires emergent needle decompression at the second intercostal space, mid-axillary line. Do not wait for CXR in an unstable patient.
• Widened mediastinum
  • Findings: Mediastinum wider than 8 cm on a standard PA film. Note: a diseased mediastinum may appear <8 cm due to lung hyperinflation or radiological artifact. Alternatively, the supine position can produce an engorged SVC that may mimic a widened mediastinum (if possible, attain an upright CXR to minimize this artifact).
  • The differential diagnosis includes: Aortic aneurysm, lymphadenopathy, traumatic aortic dissection, mediastinal mass. Mediastinal masses can be further divided into superior (thyroid cancer, lymphoma, teratoma), anterior (thymoma, lymphoma), middle (carcinoma, lymphoma, esophageal rupture, mediastinal fluid, cardiac tamponade), and posterior (esophageal cancer, neurogenic tumors, vertebral trauma) locations.
• Lung carcinoma
  • Findings: Pulmonary nodule, spiculated mass, multiple masses.
  • Multiple masses in lungs suggest metastases or septic pulmonary emboli, especially in conjunction with cavitation.
  • Assess the mediastinum for contour and hilar enlargement.
• Heart failure
  • Findings: Pulmonary edema, enlarged pulmonary vasculature, cephalization of blood flow, increased interstitial markings, enlargement of cardiac silhouette, pulmonary vascular enlargement, loss of contour of cardiophrenic angle.
• Pulmonary edema
  • Findings: Kerley B lines (~2 cm lines perpendicular to the chest wall), interstitial edema, cardiomegaly, basilar involvement (gravity causes the lower regions of the lung to receive higher blood flow), distended SVC.
  • It is difficult to distinguish between cardiogenic (hydrostatic) and non-cardiogenic (permeability) pulmonary edema on CXR.
• Acute respiratory distress syndrome (ARDS)
  • Findings: Extensive bilateral opacities and air bronchograms.
  • Air bronchograms are pathological conditions that result from increased edema in the surrounding lung tissue making it appear "whiter" than normal. This causes the border between air and tissue to appear particularly sharp. Normally, there is a relatively small difference in contrast between the black appearing air in the conducting airways and the white appearing surrounding lung tissue.
  • Difficult to differentiate between pneumonia, edema, and ARDS; especially with diffuse lung involvement. Pneumonia is usually lobar and unilateral.
  • Therapeutic positive pressure ventilation can give the appearance of improvement on CXR in ARDS and inaccurately suggest that the patient is ready for weaning off the ventilator.
• Abdominal free air
  • Findings: Air beneath the right hemidiaphragm is often suggestive of abdominal free air. This is best observed on an upright CXR.
• Achalasia
  • Findings: Air–fluid level in mediastinum. Prominent esophageal stripe can mimic the appearance of a widened mediastinum.
• Lung calcifications
  • Findings: Almost always an indicator of a benign nodule.
  • Previously healed granulomatous disease (histoplasmosis, treated infection, or tumor).
• Aspiration pneumonitis
  • Findings: Initially, the CXR appears normal. Hours later a change in density, usually in the right lower lobe, appears.
• Negative pressure pulmonary edema
  • Findings: Extensive bilateral opacities suggesting alveolar fluid.
• foreign body
  • Trachea findings: If a ball valve mechanism is present, will see hyperinflation. If simple obstruction is present, will see alveolar collapse.
  • Esophageal findings: Difficult to see with PA or AP view. Lateral view may provide additional information.

Perioperative Relevance

• Preoperative CXR
  • The American Society of Anesthesiologists Task force recommendations state that chest radiograph abnormalities may be higher in smokers, patients with recent upper respiratory infection, COPD, and cardiac disease. However, they assert that extremes in age, smoking, stable COPD, stable cardiac disease, or resolved recent upper respiratory infection do not necessarily constitute an indication for CXR (4).
  • If a CXR finding is believed to change the management of the anesthetic, it may be considered.
  • Pacemaker or ICD type and presence can be assessed and confirmed. Also, confirm the absence of a pneumothorax, check the position of the leads to ensure that they are in the cardiac silhouette (right atrium, right ventricle), and look for fluid collection around the device.
  • Lines and tubes. Follow each line and tube in its entirety. It may be necessary to order additional radiological studies if the line or tube disappears from the borders of the CXR. Assess for pneumothorax and hemothorax.
• Intraoperative
  • Line and tube placement, acute pulmonary changes.
  • Retained surgical instruments: Order radiological study to cover areas of open or previously open cavities.
• Postoperative CXR
  • Line and tube placement, pulmonary status, endotracheal tube (2 cm above carina).
  • Atelectasis: Volume loss, with shifting of the mediastinum and bronchus towards the area of collapse. Changes are often subtle and difficult to appreciate.

Pregnancy Considerations

• Radiation Safety
• Acute Respiratory Distress Syndrome
• Pneumothorax
• Negative Pressure Pulmonary Edema
• Aspiration

Michael P. Hofkamp , MD

James M. Callas , MD