They may be almost any shape except lobar Most solitary shadows in patients with connective tissue disease or vasculitis represent pneumonia, organizing pneumonia or infarctionĪirspace opacities in these conditions are rarely solitary. The opacity is usually sublobar in size and nonspecific in shape. They need to be considered in patients with appropriate clinical features. These conditions are infrequent causes of solitary airspace shadowing. Hematomas resemble masses, may liquefy and cavitate, and take much longer to clear than contusions Pulmonary contusion may surround a pulmonary hematoma. Pneumatocele formation is a distinct feature. They are usually maximal in the general area of injury, although contrecoup damage may be seen at a distance. Septic infarcts cavitate frequently, whereas bland infarcts rarely cavitateĬontusions appear within hours of injury and clear within a few days. The rounded medial margin, known as Hampton hump (see Chapter 7), is a well known but infrequent sign suggestive, but not diagnostic, of the condition. The apex of the cone, which may be rounded, points towards the hilum. Their shape is similar to a truncated cone with the base on the pleura. Infarcts are usually segmental in size, rarely larger. Infarction or hemorrhage associated with pulmonary embolism Large areas of atelectasis that do not conform to either of these patterns may be indistinguishable from the other causes of airspace shadowing listed in this table Discoid atelectasis results in a characteristic bandlike shape coursing through the lung, often in a horizontal orientation. The appearances and causes are discussed in the section ‘Atelectasis/Collapse’ later in this chapter. The diagnosis of atelectasis is based on its characteristic shape. In adults an associated hilar mass suggests a centrally located neoplasm causing postobstructive pneumonia, whereas in children an associated hilar mass suggests primary tuberculosisĬan be responsible for a variety of radiographic patterns, including a focal or segmental-shaped area of consolidation Cavitation and accompanying pleural effusion are both distinct features. The opacity may be almost any shape from segmental/lobar to round or irregular. Pneumonia is the most common cause of solitary airspace filling. Table 3.1 Differential diagnosis of solitary airspace opacities on chest radiographs
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