CXR Flashcards
Define Inspiration in relation to CXRs
The patient should be examined in full inspiration. This greatly helps the radiologist to determine if there are intrapulmonary abnormalities. The diaphragm should be found at about the level of the 8th - 10th posterior rib or 5th - 6th anterior rib on good inspiration.
Define penetration in relation to CXRs
Adequate penetration of the patient by radiation is also required for a good film. On a good PA film, the thoracic spine disc spaces should be barely visible through the heart but bony details of the spine are not usually seen. On the other hand penetration is sufficient that bronchovascular structures can usually be seen through the heart.
Define Rotation in relation to CXRs
The technologists are usually very careful to x-ray the patient flat against the cassette. If there is rotation of the patient, the mediastinum may look very unusual. One can access patient rotation by observing the clavicular heads and determining whether they are equal distance from the spinous process of the thoracic vertebral bodies.
Lobes and Fissures of the Lung
On the PA chest x-ray, the minor fissure divides the right middle lobe from the right upper lobe and is sometimes not well seen. There is no minor fissure on the left. The major fissures are usually not well seen on the PA view because you are looking through them obliquely. If there is fluid in the fissure, it is occasionally manifested as a density at the lower lateral margin.
Bronchi
A physician should absolutely know the anatomy of the bronchi. The major bronchi are visible if you look carefully.
Pulmonary Vasculature
After the bronchi, remember that the left pulmonary artery arches over the left upper lobe bronchus and the right pulmonary artery passes posterior to the ascending aorta to divide into the truncus anterior and the descending RPA. Note that except in the right upper lobe, the pulmonary veins are generally anterior to the pulmonary arteries.
Technique for reading images
It is best to do a directed search of the chest film rather than simply gazing at the film. An abnormality will not likely hit you over the head. Remember that detail vision is only permitted at the fovea centralis of your retina. This area contains only cones and is the part that you use to read. The remainder of the retina helps you to put this detailed portion in context and helps to determine whether this is a saber tooth tiger sneaking up on you. Therefore, it is best to look for abnormalities and to have a planned search in mind. Your eye gaze should scan all portions of the film, follow lung/mediastinal interfaces and look again carefully in areas where you know that mistakes are easily made, such as over the spine on the lateral view and in the apex on the PA view.
The silhouette sign
One of the most useful signs in chest radiology is the silhouette sign. The silhouette sign is in essence elimination of the silhouette or loss of lung/soft tissue interface caused by a mass or fluid in the normally air filled lung. In other words, if an intrathoracic opacity is in anatomic contact with, for example, the heart border, then the opacity will obscure that border. The sign is commonly applied to the heart, aorta, chest wall, and diaphragm. The location of this abnormality can help to determine the location anatomically.
Air Bronchogram
An air bronchogram is a tubular outline of an airway made visible by filling of the surrounding alveoli by fluid or inflammatory exudates. Six causes of air bronchograms are; lung consolidation, pulmonary edema, nonobstructive pulmonary atelectasis, severe interstitial disease, neoplasm, and normal expiration.
Atelectasis
Atelectasis is collapse or incomplete expansion of the lung or part of the lung. This is one of the most common findings on a chest x-ray. It is most often caused by an endobronchial lesion, such as mucus plug or tumor. It can also be caused by extrinsic compression centrally by a mass such as lymph nodes or peripheral compression by pleural effusion. An unusual type of atelectasis is cicatricial and is secondary to scarring, TB, or status post radiation.
Atelectasis is almost always associated with a linear increased density on chest x-ray. The apex tends to be at the hilum. The density is associated with volume loss. Some indirect signs of volume loss include vascular crowding or fissural, tracheal, or mediastinal shift, towards the collapse. There may be compensatory hyperinflation of adjacent lobes, or hilar elevation (upper lobe collapse) or depression (lower lobe collapse). Segmental and subsegmental collapse may show linear, curvilinear, wedge shaped opacities. This is most often associated with post-op patients and those with massive hepatosplenomegaly or ascites .
Pulmonary Edema
There are two basic types of pulmonary edema. One is cardogenic edema caused by increased hydrostatic pulmonary capillary pressure. The other is termed noncardogenic pulmonary edema, and is caused by either altered capillary membrane permeability or decreased plasma oncotic pressure.
A helpful mnemonic for noncardiogenic pulmonary edema is NOT CARDIAC (near-drowning, oxygen therapy, transfusion or trauma, CNS disorder, ARDS, aspiration, or altitude sickness, renal disorder or resuscitation, drugs, inhaled toxins, allergic alveolitis, contrast or contusion.
On a CXR, cardiogenic pulmonary edema can show; cephalization of the pulmonary vessels, Kerley B lines or septal lines, peribronchial cuffing, “bat wing” pattern, patchy shadowing with air bronchograms, and increased cardiac size. Unilateral, miliary and lobar or lower zone edema are considered atypical patterns of cardiac pulmonary edema. A unilateral pattern may be caused by lying preferentially on one side. Unusual patterns of edema may be found in patients with COPD who have predominant upper lobe emphysema.
Differences between atelectasis and pneumonia on a CXR:
Atelectasis: Volume Loss Associated Ipsilateral Shift Linear, Wedge-Shaped Apex at Hilum
Pneumonia: Normal or Increased Volume No Shift, or if Present Then Contralateral Consolidation, Air Space Process Not Centered at Hilum
Air bronchograms can occur in both.
Pleural Effusion
Common causes for a pleural effusion are CHF, infection (parapneumonic), trauma, PE, tumor, autoimmune disease, and renal failure.
On an upright film, an effusion will cause blunting on the lateral and if large enough, the posterior costophrenic sulci. Sometimes a depression of the involved diaphragm will occur. A large effusion can lead to a mediastinal shift away from the effusion and opacify the hemothorax. Approximately 200 ml of fluid are needed to detect an effusion in the frontal film vs. approximately 75ml for the lateral. Larger effusions, especially if unilateral, are more likely to be caused by malignancy than smaller ones.
In the supine film, an effusion will appear as a graded haze that is denser at the base. The vascular shadows can usually be seen through the effusion. An effusion in the supine view can veil the lung tissue, thicken fissure lines, and if large, cause a fluid cap over the apex. There may be no apparent blunting of the lateral costophrenic sulci.
A lateral decubitis film is helpful in confirming an effusion in a bedridden patient as the fluid will layer out on the affected side (unless the fluid is loculated). Today, ultrasound is also a key component in the diagnosis. Ultrasound is also used to guide diagnostic aspiration of small effusions.
Pneumothorax
A pneumothorax is defined as air inside the thoracic cavity but outside the lung. A spontaneous pneumothorax (PTX) is one that occurs without an obvious inciting incident. Some causes of spontaneous PTX are; idiopathic, asthma, COPD, pulmonary infection, neoplasm, Marfan’s syndrome, and smoking cocaine. However, most pneumothoraces are iatrogenic and caused by a physician during surgery or central line placement. Trauma, such as a motor vehicle accident is another important cause. A tension PTX is a type of PTX in which air enters the pleural cavity and is trapped during expiration usually by some type of ball valve-like mechanism. This leads to a buildup of air increasing intrathoracic pressure. Eventually the pressure buildup is large enough to collapse the lung and shift the mediastinum away from the tension PTX. If it continues, it can compromise venous filling of the heart and even death.
On CXR, a PTX appears as air without lung markings in the least dependant part of the chest. Generally, the air is found peripheral to the white line of the pleura. In an upright film this is most likely seen in the apices. A PTX is best demonstrated by an expiration film. It can be difficult to see when the patient is in a supine position. In this position, air rises to the medial aspect of the lung and may be seen as a lucency along the mediastinum. It may also collect in the inferior sulci causing a deep sulcus sign.
A hydropneumothorax is both air and fluid in the pleural space. It is characterized by an air-fluid level on an upright or decubitus film in a patient with a pneumothorax. Some causes of a hydropneumothorax are trauma, thoracentesis, surgery, ruptured esophagus, and empyema.
Emphysema
Emphysema is loss of elastic recoil of the lung with destruction of pulmonary capillary bed and alveolar septa. It is caused most often by cigarette smoking and less commonly by alpha-1 antitrypsin deficiency. Functional hallmarks are decreased airflow (decreased FEV1) and diffusing capacity (decreased DLCO2).
Emphysema is commonly seen on CXR as diffuse hyperinflation with flattening of diaphragms, increased retrosternal space, bullae (lucent, air-containing spaces that have no vessels that are not perfused) and enlargement of PA/RV (secondary to chronic hypoxia) an entity also known as cor pulmonale. Hyperinflation and bullae are the best radiographic predictors of emphysema. However, the radiographic findings correlate poorly with the patientâs pulmonary function tests. CT and HRCT (high resolution CT) has emerged as a technique to evaluate different types, panlobular, intralobular, paraseptal and for guidance prior to volume reduction surgery.
Occasionally the trachea is very narrow in the mediolateral plane in emphysema. “Saber sheath” tracheal deformity is when the coronal diameter is less than 2/3 that of the sagittal.
In smokers with known emphysema the upper lung zones are commonly more involved than the lower lobes. This situation is reversed in patients with alpha-1 anti-trypsin deficiency, where the lower lobes are affected.
Chronic bronchitis commonly occurs in patients with emphysema and is associated with bronchial wall thickening.
