Veterinary Medicine - March 2008 - (Page 158)

Primary lung tumors PEER-REVIEWED 1. A lateral thoracic radiograph of a 10-year-old castrated male German shepherd presented for evaluation of an intermittent, nonproductive cough of six months’ duration. A soft tissue mass effect is identiﬁed in the left caudal lung ﬁeld. The histologic diagnosis was pulmonary adenocarcinoma. (Photograph courtesy of Dr. Laura Garrett.) 2. A lateral thoracic radiograph of an 8-year-old spayed female Labrador retriever presented for evaluation of a decreased appetite and lethargy of four weeks’ duration. Multiple soft tissue opacities affecting the pulmonary parenchyma are identiﬁed, which were cytologically consistent with bronchoalveolar carcinoma. (Photograph courtesy of Dr. Laura Garrett.) with two of the three patients presenting with hypertrophic osteopathy.21-23 Pulmonary lymphomatoid granulomatosis is an extremely rare, diffuse disease of the canine lung that has a yet undetermined cause and may be immunemediated or preneoplastic in origin.24-26 Fine-needle aspiration provides poor diagnostic yield with this disease process, and de nitive diagnosis must be based on histologic examination. However, because of the historically rapid response to chemotherapy, empirical treatment may be used to aid in diagnosis.24 Of the primary neoplastic diseases of the lungs, pulmonary lymphomatoid granulomatosis carries the best prognosis.24,25 The anatomical location and histologic subtype of primary pulmonary tumors in dogs tend to share similar distribution patterns observed in people. Adenocarcinomas usually present as peripheral, solitary, well-de ned masses (Figure 1), while bronchoalveolar carcinomas often manifest as peripheral multifocal densities (Figure 2).5,12,14,18 And primary lung squamous cell carcinomas tend to grow as solitary, hilar masses.10,12,14,18 In cats, adenocarcinomas tend to manifest either as a well-circumscribed, cavitated mass in the center or periphery of the lobe or as a localized (lobar) alveolar pulmonary in ltrate that is often calci ed (25% of cases). Bronchoalveolar carcinomas occur as pleomorphic, multifocal, or diffuse opacities located in the middle to peripheral portions of the affected lobes, with two-thirds of cases having pleural involvement on radiographs. Unlike in dogs or people, squamous cell carcinomas in cats show extreme variability in radiographic pattern but tend not to be hilar in origin.14 Despite certain growth and distribution patterns associated with primary lung tumors in companion animals, it remains impossible to de nitively classify such tumors based purely on topographic anatomy, mostly because, as mentioned earlier, canine and feline neoplasms are often too advanced at diagnosis to identify their anatomical site of origin.5,12 This limitation has been underscored in several veterinary studies in which no correlation was found between a tumor’s location and its histologic subtype. Thus, once a pulmonary mass has been identi ed on initial thoracic imaging, histologic or cytologic evaluation of the suspect lesion is absolutely necessary for de nitive diagnosis.8,16,19 involvement, the presence of metastatic disease, and the occurrence of paraneoplastic syndromes. Dogs The most common sign in dogs is a nonproductive cough, occurring in 52% to 58% of dogs with a primary lung tumor.2,4,8,12 Other respiratory signs may include tachypnea, wheezing, exercise intolerance, and hemoptysis. Nonspeci c signs in dogs are common and include lethargy, weight loss, and anorexia.2,4 Dyspnea may occur if a large portion of the lung is involved or if pneumothorax, pleural effusion, or concurrent disease (congestive heart failure or tracheal collapse) is present.1,8 Severe lameness and pain may also be a presenting complaint if hypertrophic osteopathy or bone metastasis has occurred.1,2,4,12 Despite many patients presenting with overt clinical signs associated with primary lung tumors, up to 30% of all dogs will have no signs of disease at the time of diagnosis.2,4,12 Cats Clinical signs seen in cats with primary pulmonary neoplasia are extremely variable, but dyspnea, weight loss, lethargy, anorexia, weakness, and vomiting are frequently reported.16,27 In one study of 35 cats with primary lung tumors, about CLINICAL SIGNS The clinical signs of primary lung tumors depend on many factors such as tumor invasiveness, the extent of lung tissue 158 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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