| Chest radiograph | |
|---|---|
_chest_radiograph_(X-ray).jpg) A normal posteroanterior (PA) chest radiograph of someone without any signs of injury.Dx and Sin stand for "right" and "left" respectively. | |
| Specialty | Radiology |
| ICD-9-CM | 87.3-87.4 |
| MeSH | D013902 |
| MedlinePlus | 003804 |
Achest radiograph,chest X-ray (CXR), or chest film is aprojection radiograph of thechest used to diagnose conditions affecting the chest, its contents, and nearby structures. Chest radiographs are the most common film taken in medicine.
Like all methods ofradiography, chest radiography employsionizing radiation in the form ofX-rays to generate images of the chest. The meanradiation dose to an adult from a chest radiograph is around 0.02mSv (2mrem) for a front view (PA, or posteroanterior) and 0.08 mSv (8 mrem) for a side view (LL, or latero-lateral).[1] Together, this corresponds to abackground radiation equivalent time of about 10 days.[2]
Conditions commonly identified by chest radiography
Chest radiographs are used to diagnose many conditions involving the chest wall, including its bones, and also structures contained within thethoracic cavity including thelungs,heart, andgreat vessels.Pneumonia andcongestive heart failure are very commonly diagnosed by chest radiograph. Chest radiographs are also usedto screen for job-related lung disease in industries such as mining where workers are exposed to dust.[3]
For some conditions of the chest, radiography is good for screening but poor for diagnosis. When a condition is suspected based on chest radiography, additional imaging of the chest can be obtained to definitively diagnose the condition or to provide evidence in favor of the diagnosis suggested by initial chest radiography.Unless a fractured rib is suspected of being displaced, and therefore likely to cause damage to the lungs and other tissue structures, x-ray of the chest is not necessary as it will not alter patient management.
The main regions where a chest X-ray may identify problems may be summarized asABCDEF by their first letters:[4]
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Differentviews (also known asprojections) of the chest can be obtained by changing the relative orientation of the body and the direction of the x-ray beam. The most common views areposteroanterior,anteroposterior, andlateral. In a posteroanterior (PA) view, the x-ray source is positioned so that the x-ray beam enters through the posterior (back) aspect of the chest and exits out of the anterior (front) aspect, where the beam is detected. To obtain this view, the patient stands facing a flat surface behind which is an x-ray detector. A radiation source is positioned behind the patient at a standard distance (most often 6 feet, 1,8m), and the x-ray beam is fired toward the patient.
In anteroposterior (AP) views, the positions of the x-ray source and detector are reversed: the x-ray beam enters through the anterior aspect and exits through the posterior aspect of the chest. AP chest x-rays are harder to read than PA x-rays[citation needed] and are therefore generally reserved for situations where it is difficult for the patient to get an ordinary chest x-ray, such as when the patient is bedridden. In this situation, mobile X-ray equipment is used to obtain a lying down chest x-ray (known as a "supine film"). As a result, most supine films are also AP.
Lateral views of the chest are obtained in a similar fashion as the posteroanterior views, except in the lateral view, the patient stands with both arms raised and the left side of the chest pressed against a flat surface.
Required projections can vary by country and hospital, although an erect posteroanterior (PA) projection is typically the first preference. If this is not possible, then an anteroposterior view will be taken. Further imaging depends on local protocols which is dependent on the hospital protocols, the availability of other imaging modalities and the preference of the image interpreter. In the UK, the standard chest radiography protocol is to take an erect posteroanterior view only and a lateral one only on request by a radiologist.[5] In the US, chest radiography includes a PA and Lateral with the patient standing or sitting up. Special projections include an AP in cases where the image needs to be obtainedstat (immediately) and with a portable device, particularly when a patient cannot be safely positioned upright. Lateral decubitus may be used for visualization of air-fluid levels if an upright image cannot be obtained. Anteroposterior (AP) Axial Lordotic projects the clavicles above the lung fields, allowing better visualization of the apices (which is extremely useful when looking for evidence of primarytuberculosis).
In the average person, the diaphragm should be intersected by the 5th to 7th anterior ribs at the mid-clavicular line, and 9 to 10 posterior ribs should be viewable on a normal PA inspiratory film. An increase in the number of viewable ribs implies hyperinflation, as can occur, for example, withobstructive lung disease or foreign body aspiration. A decrease implies hypoventilation, as can occur withrestrictive lung disease,pleural effusions oratelectasis. Underexpansion can also causeinterstitial markings due to parenchymal crowding, which can mimic the appearance ofinterstitial lung disease. Enlargement of the right descending pulmonary artery can indirectly reflect changes ofpulmonary hypertension, with a size greater than 16 mm abnormal in men and 15 mm in women.[6]
Appropriatepenetration of the film can be assessed by faint visualization of the thoracic spines and lung markings behind the heart. The right diaphragm is usually higher than the left, with the liver being situated beneath it in the abdomen. Theminor fissure can sometimes be seen on the right as a thin horizontal line at the level of the fifth or sixth rib. Splaying of thecarina can also suggest a tumor or process in the middlemediastinum or enlargement of theleft atrium, with a normal angle of approximately 60 degrees. The right paratracheal stripe is also important to assess, as it can reflect a process in theposterior mediastinum, in particular the spine or paraspinal soft tissues; normally it should measure 3 mm or less. The left paratracheal stripe is more variable and only seen in 25% of normal patients on posteroanterior views.[7]
Localization of lesions or inflammatory and infectious processes can be difficult to discern on chest radiograph, but can be inferred bysilhouetting and thehilum overlay sign with adjacent structures. If eitherhemidiaphragm is blurred, for example, this suggests the lesion to be from the corresponding lower lobe. If the right heart border is blurred, than the pathology is likely in the right middle lobe, though acavum deformity can also blur the right heard border due to indentation of the adjacent sternum. If the left heart border is blurred, this implies a process at thelingula.[8]
Alung nodule is a discrete opacity in the lung which may be caused by:
There are a number of features that are helpful in suggesting the diagnosis:
If the nodules are multiple, the differential is then smaller:
A cavity is a walled hollow structure within the lungs. Diagnosis is aided by noting:
The causes include:
Fluid in space between the lung and the chest wall is termed apleural effusion. There needs to be at least 75 mL of pleural fluid in order to blunt thecostophrenic angle on the lateral chest radiograph and 200 mL of pleural fluid in order to blunt thecostophrenic angle on the posteroanterior chest radiograph. On a lateral decubitus, amounts as small as 50ml of fluid are possible. Pleural effusions typically have ameniscus visible on an erect chest radiograph, but loculated effusions (as occur with anempyema) may have alenticular shape (the fluid making anobtuse angle with the chest wall).
Pleural thickening may cause blunting of the costophrenic angle, but is distinguished from pleural fluid by the fact that it occurs as a linear shadow ascending vertically and clinging to the ribs.
The differential for diffuse shadowing is very broad and can defeat even the most experienced radiologist. It is seldom possible to reach a diagnosis on the basis of the chest radiograph alone: high-resolutionCT of the chest is usually required and sometimes a lungbiopsy. The following features are usually noted:
Pleural effusions may occur with cancer, sarcoid, connective tissue diseases andlymphangioleiomyomatosis. The presence of a pleural effusion argues against pneumocystis pneumonia.
Disease mimics arevisual artifacts, normal anatomic structures or harmless variants that may simulate diseases and abnormalities.
![A prominent thymus, which can give the impression of a widened mediastinum.[10]](/mt/?noimg=&dark=on&url=http%3a%2f%2fen.wikipedia.org%2fwiki%2fFile%3aX-ray_of_an_infant_with_a_prominent_thymus.jpg)
While chest radiographs are a relatively cheap and safe method of investigating diseases of the chest, there are a number of serious chest conditions that may be associated with a normal chest radiograph and other means of assessment may be necessary to make the diagnosis. For example, a patient with an acute myocardial infarction may have a completely normal chest radiograph.
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