Veterinary Medicine - March 2008 - (Page 162)

Primary lung tumors PEER-REVIEWED 3. A photomicrograph of a cytologic sample revealing primary lung adenocarcinoma in a geriatric dog. A cohesive cell population is identiﬁed with cytologic criteria of malignancy including anisocytosis, anisokaryosis, multiple nucleoli, nuclear molding, and foamy cytoplasm (Wright’s stain, 1,000X). (Photograph courtesy of Dr. Laura Garrett.) sample retrieval using 18-, 22-, or 25-ga needles.34 These studies suggest that 22-ga needles should be suf cient to offer good diagnostic yield with a low complication rate. In addition to needle size, the technique used for sampling is important, as fenestration (sampling without the use of negative pressure) has proved to be more effective than aspiration (using a syringe to create negative pressure). Although sample volume is decreased with fenestration, cellularity is improved because of less hemodilution.35 The limitations of ne-needle aspiration cytology include poor cell recovery, poor exfoliation of certain cell types (i.e. mesenchymal cells), failure to obtain a representative sample, and the inability to provide architectural information (i.e. vascular lesions or brosis).30 Other methods of obtaining cytology samples such as transtracheal wash and bronchoalveolar lavage offer poor diagnostic yield with primary pulmonary tumors when compared with ne-needle aspiration.4,16,30,36-38 4. A thoracic ultrasonogram in a dog with a peripherally located primary lung tumor demonstrates a hypoechoic lesion immediately adjacent to the thoracic wall (arrows). Ultrasound-guided ﬁneneedle aspiration improves the chances of a diagnostic sample. (Photograph courtesy of Dr. Laura Garrett.) 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 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 Primary pulmonary adenocarcinomas in cats appear to have a higher rate of metastasis than those in their canine counterparts and may be partially explained by a higher incidence of poorly differentiated adenocarcinomas in cats.5,10,16 In a study of 162 March 2008 VETERINARY MEDICINE

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Veterinary Medicine - March 2008 Contents Toxicology Brief Idea Exchange A Challenging Case An Update on Diagnosing and Treating Primary Lung Tumors CE Form Product Preview Advertiser Index Marketplace/Classifieds Mind Over Miller

Veterinary Medicine - March 2008

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