Comparison of Thoracic Radiographs and Single Breath-Hold Helical CT for Detection of Pulmonary Nodules in Dogs with Metastatic Neoplasia

Abstract

Imaging studies in people indicate that x-ray computed tomography (CT) is a more sensitive technique than thoracic radiography for the detection of pulmonary metastasic neoplasia. Systematic studies comparing CT and thoracic radiographic techniques in veterinary patients have not been performed. The present retrospective study was designed to directly compare the efficacy of these 2 techniques in detecting pulmonary nodules in dogs. Eighteen dogs with histologically confirmed pulmonary metastatic neoplasia had contemporaneous thoracic radiographs and pulmonary CT scans compared. Quantitative analyses included estimation of pulmonary nodule size, number, and lobar distribution on thoracic radiographs and CT images. Only 9% of CT-detected pulmonary nodules were identified on thoracic radiographs (P , .003). The lower size threshold was approximately 1 mm to detect pulmonary nodules on CT images and 7-9 mm to reliably detect nodules on radiographs (P , .0001). Additionally, pulmonary nodules were detected in a significantly greater number of lung lobes using CT as compared with thoracic radiographs (P , .0001). These data indicate that CT is significantly more sensitive than thoracic radiography for detecting soft-tissue nodules in dogs. As such, thoracic CT should be considered in any patient with neoplasia that has potential for pulmonary metastasis to more reliably stage the disease, particularly when accurate characterization of the extent and distribution of pulmonary metastatic disease affects therapeutic planning. T horacic radiography is currently the most commonly employed test to screen for pulmonary metas-tases in veterinary cancer patients. However, computed tomography (CT) has been used as a standard screening test in human medicine for many years and has been found to be more accurate than thoracic radiography for detecting pulmonary nodules. 1-7 The improved sensitivity of CT compared with thoracic radiography for detecting pulmonary metastases is due primarily to the superior contrast resolution of CT and the lack of anatomic superimposition on pulmonary parenchyma due to thin-section collimation of CT images. However, the specificity of CT for detecting pulmonary metastatic nodules can be lower than that of thoracic radiography because more small, nonneoplastic, and clinically insignificant nodules are likely to be identified. 8-11 Systematic studies comparing thoracic radiographic and CT techniques in veterinary patients with suspected pulmonary metastatic disease have, to our knowledge, not been reported. A study that directly compared the 2 techniques in a canine model of human disease found that CT was more sensitive than thoracic radiography for detecting pulmonary infarcts. 12 Further, in a case series report that investigated 3 dogs with metastatic carcinoma for which thoracic radiographic studies revealed only an interstitial pattern, high-resolution CT was found to be helpful in defining additional pulmonary pathology; however, overt nodules were found in only a single patient. 13 In anoth...

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