Page 1341 - Clinical Small Animal Internal Medicine

140 Cancer of the Airway and Lung 1279

results. The association in natural settings appears to be tumor. Metastasis occurs more commonly to the weight‐
VetBooks.ir weak, but the risk may be increased in brachycephalic dogs bearing digits. Multiple digits and multiple limbs are
commonly affected.
compared to dolichocephalic dogs. It is hypothesized that
dolichocephalic dogs possess greater surface area for fil­
tration of inhalant carcinogens. Diagnosis
There are no known epidemiologic factors influencing
the development of primary pulmonary tumors in cats. Many dogs with primary and metastatic lung tumors are
diagnosed via thoracic radiography. Most dogs will show
Signalment a solitary pulmonary mass that is well circumscribed and
located in the caudodorsal lung lobes. Diffuse and
The average age of dogs with primary lung tumors is alveolar infiltrative forms are also described. Radiographs
approximately 11 years (range 2–18 years). The risk of may also show regional lymphadenopathy or extension
developing lung cancer rises after the age of 13. Males of tumor into the surrounding pulmonary parenchyma.
and females are equally susceptible. Tumors occur more Computed tomography is being more frequently uti­
frequently in larger dogs, with 60% of cancers developing lized for the diagnosis of pulmonary neoplasia in dogs
in dogs weighing 20–30 kg. In cats, the average age at and cats and is ideal for surgical planning. Thoracic
diagnosis is 12–13 years (range 2–20 years) with most CT scan is superior to thoracic radiography for the
cats being >5 years of age. No breed or sex predisposition detection of tracheobronchial lymph node metastases
is consistently found in felines. and for detecting pulmonary metastases. The accuracy
rate for thoracic CT in detecting tracheobronchial
History and Clinical Signs lymph node metastases was 93%, compared to 57% for
radiographs. In another study, thoracic radiographs
Between 52–93% of dogs with primary lung tumors detected only 9% of CT‐detected pulmonary metastases.
present with a chronic nonproductive cough. Other Twenty one of 33 (64%) dogs had pulmonary nodules
signs include dyspnea, lethargy, weight loss, tachypnea, or masses detected on CT. Of the dogs that had positive
pyrexia, inappetence, and lameness. Many dogs are diag­ CT findings, 17 of 21 (81%) had pulmonary nodules or
nosed with primary lung tumors without any obvious masses detected on radiographs by at least one inter­
clinical signs during routine geriatric screening tests preter. In another study using CT as the gold standard
(e.g., thoracic radiographs). Pleural effusion may occur diagnostic tool, the sensitivity of radiography for
secondary to direct invasion of the tumor into the pleura detecting pulmonary metastases ranged from 71% to
or regional pulmonary lymphatics. This may occur with 95%, and specificity ranged from 67% to 92%. Radiography
primary or metastatic tumors within the lung tissue. had a positive predictive value of 83–94% and a nega­
Pneumothorax and hemoptysis may rarely occur. tive predictive value of 65–89%. This increased accu­
Signs related to the respiratory system are detected in racy of CT for detecting lesions is likely, in part, due to
one‐quarter to two‐thirds of cats with lung tumors. its higher resolution for identifying smaller lesions
Vomiting is reported in 20% of cats. Cats with lung (e.g., thoracic CT can detect lesions of 1 mm in size)
tumors are more likely to show nonspecific signs such as compared to radiographs (can detect lesions only when
lethargy, malaise, and inappetence compared with dogs. >7 mm in size). MRI of the thorax is not recommended
Hypertrophic osteopathy is a known paraneoplastic syn­ due to excessive motion artifact.
drome associated with primary and metastatic lung tumors Pleural effusion is more common in cats, and is identi­
in dogs and cats. Animals present with lameness of one or fied in approximately one‐third of patients. The diagnos­
more limbs. Radiographs will show periosteal proliferation tic utility of cytology of pleural effusion in providing a
occurring perpendicular to the shaft of the long bones. diagnosis of pulmonary neoplasia is variable, but if effu­
Hypertrophic osteopathy can resolve following removal sion is detected, it is recommended to submit a sample
of a primary lung tumor. Other known paraneoplastic for analysis as this is a relatively noninvasive technique
effects in dogs include hypercalcemia, polyneuropathy, that can provide significant information.
polymyopathy, fever, and ectopic adrenocorticotropic Bronchoalveolar lavage can be considered and has
hormone production leading to hyperadrenocorticism. been found to be superior to transtracheal wash for diag­
Metastasis to the digits is a well‐described clinical con­ nosing lung cancer in dogs.
sequence of primary pulmonary tumors in cats and some Fine needle aspiration of lung tumors is safe, but there
feline patients are initially diagnosed with bony lesions is a theoretical risk of seeding tumor cells within the tho­
within the phalanges prior to diagnosis of a pulmonary racic cavity during this procedure. Studies indicate fine