The chest radiograph in this case demonstrates multifocal areas of consolidation in both lungs, with a striking peripheral predominance in the upper lobes (best demonstrated on the coned-down image in the second figure). The distribution is typical of chronic eosinophilic pneumonia.
Affected patients typically present with symptoms of dyspnea, fever, chills, night sweats, and weight loss. Symptoms are usually present for an average of nearly 8 months prior to diagnosis. Women are affected more frequently than men, and there is a history of asthma in about one half of cases. Eosinophilia is present in the majority of patients and is usually mild to moderate.
The typical radiographic appearance is a peripheral pattern of consolidation, often with an apical or axillary distribution. The lung bases are less frequently involved. Also note the presence of right basilar consolidation in the first figure. In some patients, the opacities resolve and recur in the same location. When peripheral consolidation surrounds the lungs, the pattern is referred to as a photographic negative of pulmonary edema. Pleural effusions (which are present in this case) are infrequently encountered (less than 10% of cases).
Buterbaugh JE, Erly WK: Paratracheal air cysts: a common finding on routine CT examinations of the cervical spine and neck that may mimic pneumomediastinum in patients with traumatic injuries. AJNR Am J Neuroradiol 29:1218-1221, 2008.
The conventional tomogram in the first figure demonstrates a well-marginated, septated cystic structure in the right paratracheal region adjacent to the right lung apex. The differential diagnosis includes a right paratracheal air cyst, apical bullae, and an apical lung hernia. The CT image in the second figure demonstrates that the cystic structure is mediastinal in location, directly communicates with the right posterolateral wall of the trachea, and does not demonstrate lung architectural features. The imaging characteristics are typical of a large right paratracheal air cyst, an abnormality of the trachea that is thought to represent a tracheal diverticulum.
Such diverticula occur most commonly at the right posterolateral wall of the trachea at the level of the thoracic inlet and vary in size from a few millimeters to several centimeters. Although once considered relatively rare, small diverticula are recognized with increased frequency with modern multidetector CT (MDCT) scanners and have been reported in about 4% of neck CT scans of children and adults that included the thoracic inlet region. In the setting of trauma, a small diverticulum may potentially mimic pneumomediastinum, but its characteristic location and appearance should allow for an accurate diagnosis.
It has been proposed that acquired tracheal diverticula may occur in response to raised intratracheal pressures related to repeated bouts of coughing in patients with chronic respiratory disorders such as emphysema. However, many diverticula are considered to be congenital in etiology and are incidentally detected in both children and adults. Although usually asymptomatic, patients with diverticula may rarely present with clinical symptoms of prolonged productive cough, hemoptysis, and chest pain. Symptomatic lesions are treated surgically, but asymptomatic diverticula require no intervention.
Following median sternotomy, the sternal wires are typically maintained in a vertical row along the midline of the sternum. The coned-down chest radiograph shows a scrambled arrangement of the sternal wires, with the first and fourth wires displaced to the right of the midline (arrows). Displacement of sternal wires is a highly sensitive and specific sign for sternal dehiscence, an uncommon but serious complication following median sternotomy.
Although sternal dehiscence is often evident on the basis of physical examination findings, it may be clinically occult in some cases. Sternal wire abnormalities, most notably displacement, are seen in the majority of patients with this condition; importantly, such abnormalities may precede the clinical diagnosis in some cases. Thus, when reviewing postoperative radiographs of a patient who is status post median sternotomy, you should carefully assess the sternal wires. Interval displacement or rotation of one or more wires (in comparison with their appearance on the first postoperative radiograph) should prompt careful clinical assessment for signs of dehiscence.
The high frequency of sternal wire displacement in patients with sternal dehiscence fits well with the proposed mechanism of this complication. It has been proposed that sternal separation is the result of sternal sutures pulling or cutting through the sternum rather than breaking. As the sternum separates, some sutures will travel with the right side of the sternum and others will migrate to the left side. The term wandering wires has been used to describe the characteristic alterations in sternal wires on radiographs of patients with sternal dehiscence.
Mediastinitis is a relatively uncommon but serious complication following median sternotomy. Mediastinitis refers to inflammation and infection of the mediastinum and is a more serious complication than superficial infection localized to the peristernal soft tissue structures of the chest wall.
The CT diagnosis of mediastinitis is based primarily on the presence of mediastinal air and fluid collections. It is important to be aware that such findings can be seen normally in the early postoperative period in patients without mediastinitis.
In a study of patients with postoperative mediastinitis by Jolles and colleagues, it was reported that the CT findings of localized mediastinal fluid and pneumomediastinum (arrow) are highly sensitive (100%) for mediastinitis. The specificity of these findings is quite low (33%) within the first 14 days following surgery but increases significantly (100%) after postoperative day 14. Thus, when evaluating the CT scan of a postoperative patient with suspected mediastinitis, you must correlate CT findings with the time interval since surgery.
Although these data suggest that CT is most helpful in the late postoperative period, there is a role for CT imaging in the early postoperative period as well. For example, a negative CT scan of the mediastinum can be useful for directing attention to other sites of possible infection. Moreover, the identification of localized retrosternal fluid collections may be helpful for guiding aspiration procedures in patients in whom there is a strong clinical suspicion for mediastinitis.