Computed tomography
The correlation between tracheobronchial lymph node involvement and shorter remission times stresses the importance of computed
tomography (CT) in the diagnostic work-up of dogs with primary lung tumors.2,3,7 In a study of 14 dogs with primary lung tumors, researchers evaluated the accuracy of CT vs. thoracic radiography in determining
tracheobronchial lymph node involvement. CT had greater sensitivity and an increased predictive value for detecting tracheobronchial
lymph node metastasis. The overall accuracy of CT in detecting lymph node metastasis was 93% compared with 57% for thoracic
radiographs. False negative diagnoses made with thoracic radiographs may be attributable to the fact that the lymph nodes
were still small (< 15 mm) or may have been obscured by surrounding structures, including the primary tumor itself.7
5. A thoracic computed tomographic image from a 12-year-old castrated male domestic shorthaired cat presented for evaluation
of inappetence and weight loss. A cavitated mass (arrows) is identified in the periphery of the right caudal lung lobe. The
mass was removed with thoracoscopic lung lobectomy, and the histologic examination results revealed a well-differentiated
adenocarcinoma. (Photograph courtesy of Dr. Kristen O Dell-Anderson.)
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The sensitivity of CT is also superior in imaging metastatic pulmonary nodules when compared with thoracic radiography. CT
was found to detect not only smaller pulmonary nodules (1 mm, compared with the minimum nodule size of 7 to 9 mm detectable
on radiographs) but also a greater number of total nodules at more precise lobar locations (Figure 5). Radiographs failed to detect 90% of nodules detected on CT.39 These recent studies suggest that thoracic CT is rapidly becoming a mandatory diagnostic test performed before surgical
removal of any primary tumor with potential pulmonary metastasis.
METASTASIS AND STAGING
The presence of metastasis greatly affects prognosis, and appropriate clinical staging involves thoroughly investigating the
common sites of pulmonary tumor dissemination. Pulmonary carcinomas tend to invade locally and spread through the lymphatic
system to additional lung sites, hilar lymph nodes, and other thoracic tissues.2,3,5,12,15,16 Multiple tumor masses within the lung may indicate intrapulmonary metastasis or multicentric primary lung tumors.6 In addition to neighboring lung tissue, additional sites of metastasis include other lymph nodes, abdominal viscera, and
the kidneys.12 Less common sites include the uvea, brain, and adrenal gland.40
In dogs, the rate of metastasis correlates well with the histologic type of tumor. The reported rate of metastasis is 50%
for adenocarcinoma, with the most common sites of metastases being the tracheobronchial lymph nodes or other sites within
the thoracic cavity.2,3,12,15 The metastatic rate is 90% for the more aggressive squamous cell carcinomas and anaplastic carcinomas.12
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