Radiographic Changes

A CT image at the lung base shows a large, right lower lobe nodule, and a smaller, subpleural nodule at the lateral, posterior thorax.

CT, especially helical or spiral CT, is more sensitive than plain chest radiography for identifying pulmonary nodules [1]. Whereas lung nodules less than 1 cm in diameter are frequently missed by chest radiography, they are easily seen by CT. Nodules obscured by the apical structures, the heart and mediastinum, and the diaphragm (as in this case) can be easily missed on chest radiography, but are clearly seen with CT. Although the sensitivity for metastatic lung disease is higher with CT compared to plain chest radiography, the specificity is somewhat less. For example, 6% of nodules seen at CT in patients with seminoma proved to be benign in one series [2], and in another series of patients with extrathoracic malignancy and normal chest radiographs, most of the nodules detected by CT were benign [3]. In patients over 35 years of age with an extrathoracic squamous carcinoma and a smoking history, a lung nodule is often a separate lung primary carcinoma [4]. Small subpleural lesions (as in this case) are frequently due to normal lymph nodes, but can be due to primary or metastatic malignancy.

This CT scan (soft tissue window) shows subcarinal adenopathy with central low attenuation (arrow), a finding often associated with central necrosis.

References

1. Remy-Jardin M, Remy J, Giraud F, et al. Pulmonary nodules: detection with thick-section spiral CT versus conventional CT. Radiology 1993; 187:513-520.

2. Williams M, Husband J, Heron C. Intrathoracic manifestations of metastatic testicular seminoma: a comparison of chest radiographic and CT findings. AJR 1987; 149:473-475.

3. Chalmers N, Best J. Significance of pulmonary nodules detected by CT but not by chest radiography in tumour staging. Clin Radiol 1991; 44:410-412.

4. Cahan W, Castro E, Hajdu S. The significance of a solitary lung shadow in patients with colon carcinoma. Cancer 1974; 33:414-421.

Clinical summary Image 4

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