A solitary pulmonary nodule is defined as a well-circumscribed round or oval lesion measuring less than 3 cm in diameter. There are only two specific and reliable signs of benignancy on chest radiographs: (1) identification of a benign pattern of calcification or (2) demonstration of absolute absence of growth over a 2-year period. For cases that do not meet one of these criteria, thin-section CT is generally recommended for further evaluation. In comparison with radiography, CT allows a more accurate assessment of the margins of a nodule; moreover, CT is more sensitive for identifying the presence and distribution of calcium and fat within a nodule.
The nodule in this case has spiculated margins, a finding that is highly suspicious for malignancy. Depending on local practice patterns and clinical circumstances, a preoperative biopsy may be requested. The peripheral location of this nodule makes it best suited for a transthoracic needle biopsy.
The most common cell type of lung cancer is adenocarcinoma. It most often presents as a solitary, peripheral nodule with spiculated margins. Based on size criteria outlined in recent revisions to the TNM staging system for lung cancer, this 4.0-cm mass is a T2a lesion. The revisions establish the following size cut-off points for T designations: T1a: tumor ≤2 cm in greatest dimension; T1b: tumor >2 cm but ≤3 cm in greatest dimension; T2a: tumor >3 cm but ≤5 cm in greatest dimension; T2b: tumor >5 cm but ≤7 cm in greatest dimension; T3: tumor >7 cm (see Thoracic Radiology: THE REQUISITES, Table 11-1).
Pneumothorax is defined as the presence of air or gas within the pleural space. Although there are a wide variety of causes, spontaneous pneumothorax is the most common etiology. Affected patients are usually in the third or fourth decade of life.
Spontaneous pneumothoraces are almost always secondary to rupture of an apical bleb, which represents a gas pocket within the elastic fibers of the visceral pleura. Note the presence of a small bleb along the visceral pleural margin in this patient, best demonstrated on the coned-down image of the left upper lobe (arrow, second figure). Such blebs have been reported to be detectable on chest radiographs in approximately 15% of cases of spontaneous pneumothorax. However, blebs are rarely evident on chest radiographs following resolution of the pneumothorax. CT is much more sensitive than radiography for detecting blebs and has been shown to detect blebs in approximately 80% of patients following resolution of spontaneous pneumothoraces. The size and number of apical blebs detected on CT have been shown to correlate with the risk of recurrent pneumothoraces and the need for surgical intervention.
Tension pneumothorax is a life-threatening condition. Affected patients present with clinical signs of tachypnea, tachycardia, cyanosis, sweating, and hypotension. Radiographic findings may include contralateral mediastinal shift, diaphragmatic depression, rib cage expansion, and flattening of the contours of the right heart border and/or venae cavae.
Inadvertent insertion of a catheter into the azygos vein is a relatively uncommon complication of central venous catheter placement, with an estimated frequency of approximately 1%. Detection of a malpositioned catheter at this site is important, because there is a relatively high frequency of associated venous perforation.
Note the abnormal curve of the catheter at the level of the azygos arch on the posteroanterior (PA) chest radiograph. The precise location is confirmed on the lateral chest radiograph (second figure), which demonstrates the posterior course of the catheter within the azygos arch.
Interestingly, azygos vein cannulation occurs most commonly following left-sided catheter insertion. This association is thought to occur secondary to anterocaudal arching of the left brachiocephalic vein, which may preferentially promote entry of a catheter into the azygos vein rather than the superior vena cava. In contrast, catheters placed from the right side of the thorax have a more direct course to the superior vena cava via the right brachiocephalic vein.
The chest radiograph demonstrates numerous partially calcified lesions bilaterally, several of which are plateau-like in configuration and parallel the inner margin of the lateral thoracic wall and the right hemidiaphragm. CT confirms the pleural location of these lesions and demonstrates the calcification more precisely. The findings are typical of pleural plaques related to prior asbestos exposure.
Pleural plaques are the most common manifestation of asbestos exposure and typically occur after a latency period of approximately 15 to 20 years. They do not cause symptoms and are usually discovered incidentally. Pathologically, pleural plaques are composed of dense bands of avascular collagen and are not considered premalignant lesions.
The radiographic appearance of pleural plaques is dependent on whether the plaques are calcified, and whether they are seen in profile or en face. When observed in profile, a plaque appears as a dense band of soft tissue opacity paralleling the inner margin of the lateral thoracic wall or an adjacent hemidiaphragm. When observed en face, a plaque appears as a veil-like opacity with irregular edges, often described as a “holly leaf” configuration. Plaques are usually bilateral and often symmetric. The lower half of the thorax is most often affected, usually between the sixth and the ninth ribs.
Thoracic spine fracture is an infrequent but serious complication of blunt trauma. Unfortunately, the portable trauma chest radiograph is not very reliable in detecting spinal fractures. Moreover, thoracolumbar spine radiographs have been shown to have a sensitivity of only 32% for detecting acute spinal fractures.
Radiographic findings associated with spinal fracture include findings related to mediastinal hemorrhage (such as widening of the paraspinal lines, mediastinal widening, and left apical pleural cap) and vertebral abnormalities. The latter are more specific for spinal injury and include loss of height of the vertebral body and obscuration of the pedicle(s). When you identify a mediastinal hematoma that is confined to the posterior mediastinum, you should diligently search for evidence of a vertebral body fracture. If a spinal fracture is not evident on chest radiography, you should proceed to CT. Multidetector CT (MDCT) has been shown to have a much higher sensitivity than radiographs for detecting fractures and its sensitivity can be further enhanced by coronal and sagittal reformations.
Radiographic abnormalities in patients with emphysema are related to overinflation of the lungs and lung destruction. The latter is characterized by reduced vascularity or the presence of bullae. Overinflation of the lungs may be characterized by a number of findings, most notably flattening of the hemidiaphragms and an increase in the retrosternal airspace diameter.
Chest radiographic abnormalities are usually evident in moderate to severe cases of emphysema, but radiographs are frequently normal in patients with early emphysema. HRCT is superior to chest radiographs in detecting and characterizing emphysema and has a high sensitivity and specificity for establishing the diagnosis.
A miliary pattern refers to the presence of numerous small (approximately 1- to 2-mm-diameter) lung nodules. Such nodules are difficult to detect radiographically because of their small size. It has been suggested that these tiny nodules become visible radiographically because of the effect of summation.
The classic entity associated with this pattern is miliary TB, which refers to the diffuse hematogenous dissemination of TB. This pattern typically occurs in patients with altered host resistance to the primary infection. Affected patients usually present with fever, chills, and night sweats.
Because of the small size of miliary nodules, it is not surprising that CT (particularly HRCT) is more sensitive than radiography for detection. In fact, it has been estimated that it may take up to 6 weeks for miliary nodules to become apparent on chest radiographs! On HRCT, the nodules are shown to be diffuse and random in distribution.
When visible on chest radiographs, cutaneous chest wall lesions such as neurofibromas, moles, and nipples demonstrate a characteristic incomplete, sharp border. The sharp border is produced by the interface of the lesion with adjacent air, and it becomes incomplete where the lesion is continuous with the soft tissues of the chest wall. The identification of such a border is helpful for differentiating chest wall lesions from intrapulmonary lesions.
In this particular case, the cutaneous location of the nodules is easily confirmed on the lateral projection. When in doubt about a possible cutaneous location of a focal nodular opacity, one should perform a repeat radiograph with small lead markers for confirmation.
Atelectasis is defined as a decrease in volume (i.e., reduced inflation) of all or a portion of the lung. The most common type of atelectasis occurs secondary to obstruction of a central bronchus. It is referred to as resorption atelectasis and usually involves an entire lobe.
The chest radiograph and CT image reveal the classic features of complete left lower lobe atelectasis. On chest radiographs, complete left lower lobe atelectasis appears as a triangular opacity behind the heart. The displaced major fissure is seen as an interface between the opacified atelectatic lobe and the hyperexpanded left upper lobe. Note the presence of several secondary signs of atelectasis in this case, including inferomedial displacement of the left hilum, slight leftward shift of the mediastinum, and compensatory hyperinflation of the left upper lobe.
In an outpatient setting, the presence of lobar collapse is usually indicative of an obstructing central mass. In an adult patient, primary lung cancer and carcinoid are important diagnostic considerations. In a child, an aspirated foreign body is the most likely diagnosis. CT is helpful in identifying the centrally obstructing lesion and for guiding bronchoscopic procedures.
PAH is defined as a condition of sustained elevation of pulmonary artery pressure. PAH may occur secondary to one of three basic mechanisms: (1) increased pulmonary blood flow (e.g., left-to-right shunt), (2) decreased cross-sectional area of the pulmonary vasculature (e.g., chronic pulmonary embolism), and (3) increased resistance to pulmonary venous drainage (e.g., mitral valve disease). Another framework for categorizing causes of PAH is to broadly divide them as either precapillary (changes limited to the arterial pulmonary circulation) or postcapillary (primary abnormalities within the pulmonary venous circulation).
The majority of cases of PAH occur secondary to a known cause. These cases are collectively referred to as secondary PAH. In a minority of cases, the etiology of PAH remains unknown. These cases are referred to as primary PAH. This condition tends to affect women younger than 40 years of age.
Regardless of the type of PAH, the characteristic findings on chest radiographs are similar. There is usually marked enlargement of the main and hilar pulmonary arteries, which rapidly taper as they course distally. The degree of pulmonary artery enlargement varies considerably, and significant PAH can be present in the setting of a normal chest radiograph. CT is more accurate than chest radiography for detecting pulmonary artery enlargement.
Published rates of complications of central venous catheter placement vary considerably and are dependent upon both operator experience and anatomic site. The most common complication of central venous catheter placement is malposition, which occurs in up to 40% of cases. Pneumothorax is the second most common complication, occurring in up to 5% of cases. Less common complications include hemothorax, extrapleural hematoma, cardiac arrhythmias, vascular or cardiac perforation, peripheral venous thrombosis, catheter fragmentation, septic emboli, and mycotic aneurysms.
Because of its high flow rate and large volume, the superior vena cava is the ideal location for a central venous catheter. The distal portion of the catheter should lie parallel to the direction of blood flow, and it should not abut the vessel wall.
Catheter malposition is usually evident on a frontal chest radiograph. In some cases, however, a lateral view is necessary to determine the precise location of the catheter tip. In a small minority of cases, a contrast study is necessary to verify catheter location.
Sarcoidosis is a systemic disorder of unknown etiology that is characterized pathologically by widespread noncaseating granulomas. Because this pathologic finding may also be seen in a variety of other conditions, a diagnosis of sarcoidosis requires consistent radiologic, clinical, laboratory, and pathologic findings, as well as exclusion of other entities (especially granulomatous infections).
The chest radiograph is abnormal in approximately 90% of patients with sarcoidosis. Bilateral, symmetric hilar lymph node enlargement is the most common radiographic abnormality and is frequently accompanied by mediastinal lymph node enlargement. Lung parenchymal disease is usually nodular or reticulonodular in appearance, with a predilection for the upper and mid-lung zones.
On CT examination (particularly HRCT), sarcoid granulomas typically appear as small (1- to 2-mm-diameter) nodules, with a characteristic perilymphatic distribution. This distribution includes the peribronchovascular lymphatics, the interlobular septa, and the subpleural lymphatics (peripherally and along the fissures). Approximately 20% of patients with radiographic evidence of interstitial lung disease develop interstitial fibrosis.