Page 472 - Atlas of Small Animal CT and MRI

462 Atlas of Small Animal CT and MRI

enhancement, and pulmonary metastatic disease was seen although those from malignant primary bone tumors,
in a few dogs in this report. Bronchial metastases from and occasionally other neoplasms, can be mineralized.
27
primary lung tumors can be extensive and occasionally Nodules mildly to intensely contrast enhance (Figures
involve lobes in the contralateral hemithorax, making 4.6.27, 4.6.28, 4.6.29, 4.6.30, 4.6.31, 4.6.32). A minority
them surgically unresectable. These tumors can be cavi- of lung metastases in people distribute through the pul-
tary and will occasionally mineralize. monary lymphatic vessels, producing a branching linear
CT has been shown to be more sensitive and accurate pattern rather than nodules, but this has not been
than survey radiography for diagnosis of tracheobronchial described in companion animals.
lymphadenopathy in dogs with primary lung tumors. CT
28
features included node enlargement and irregular mar- Degenerative disorders
gination with or without contrast enhancement.
Pulmonary osseous metaplasia
Tumors of mesenchymal origin Pulmonary osseous metaplasia manifests on CT images
Mesenchymal tumors include osteosarcoma, chondro- as multiple widely dispersed mineralized lung nodules
sarcoma, malignant histiocytosis, and lymphomatoid usually 3 mm or less in diameter. These have a tendency
granulomatosis. Of these, histiocytic sarcoma is most for subpleural and ventral lung field distribution
common, often affecting primarily Bernese Mountain (Figure 4.6.33). Although these nodules are usually
Dogs and Rottweilers, although the disorder has been inherently highly attenuating because of mineral con-
reported in other breeds as well. tent, partial volume averaging in widely collimated CT
Reported CT features of malignant histiocytic sar- images can yield apparent HU values lower than
coma in dogs include intrathoracic lymphadenopathy expected. Thinly collimated images through the nodule
(tracheobronchial and sternal lymphadenopathy pre- can yield more accurate HU measurements. We have
dominately) and the presence of pulmonary masses also seen patients with osseous metaplasia nodules with
preferentially located within the right middle lung lobe minimal mineralization that can reduce one’s confidence
(Figure 4.6.25). Masses are typically multiple, broncho- in diagnosis.
genic in origin, poorly margined, and mildly to moder-
ately contrast enhancing. Other CT features include Pulmonary fibrosis
pulmonary nodules, pleural effusion, and regional pul- Pulmonary fibrosis is often the sequela to a variety of dis-
monary patterns. 29 orders and represents the degenerative endpoint of such
insults as pneumonia, pulmonary toxins, radiation pneu-
Lymphoma monitis, and trauma. Depending on the initial cause,
Radiographic features of pulmonary lymphoma in dogs pulmonary fibrosis may be focal, regional, or diffuse. On
and cats have been reported, but as might be expected CT images, fibrosis can appear as a reticular interstitial
with this disorder, imaging characteristics are quite pattern or as a dense linear “scar” (Figures 4.6.34, 4.6.35,
variable and include bronchial, interstitial or alveolar 4.6.36). Lungs of older dogs without clinical signs of pul-
infiltrates, nodules or masses, pleural effusion, and lym- monary disease may also appear denser on radiographs
phadenopathy. CT features would be expected to parallel and CT images because of mild interstitial fibrosis, and
the radiographic findings (Figure 4.6.26). 30 anecdotally, this seems to occur primarily in dogs with
mitral insufficiency.
Pulmonary metastasis A specific entity, idiopathic pulmonary fibrosis, has
Computed tomography has been shown to be more sen- been described in West Highland White Terriers and has
sitive than radiography for pulmonary metastasis detec- similarities to usual and nonspecific interstitial pneumo-
tion. 31,32 In one study, only about 10% of nodules seen nias in people. These entities are part of a larger group
33
on CT studies were detected on radiographs, with nod- of pulmonary disorders that fall under the heading of
ules less than about 8 mm most frequently missed. interstitial lung disease, a related group of inflammatory
32
Metastases usually arise from tumor emboli from a disorders that lead to progressive and irreversible lung
distant neoplasm lodging in the pulmonary capillaries, scarring. Clinically, dogs with idiopathic pulmonary
leading to development of interstitial nodules and fibrosis suffer from restrictive lung disease and compro-
masses. On CT images, metastases run the spectrum mised gas exchange. Histologically, there is interstitial
from widespread and miliary to few and mass‐like and fibrosis, increased alveolar macrophages, and emphyse-
can be poorly to well demarcated. Associated hemor- matous change. CT features include linear and reticular
34
rhage or inflammation can cause nodules to be less opacities, nodules and nodular opacities, overall decreased
defined. Most metastases are soft‐tissue attenuating, lung opacity, and overall increased lung opacity.

462