Page 471 - Atlas of Small Animal CT and MRI

Small Airways and Parenchyma 461

severity of pneumonia but often appear as a multifocal dogs. Infection results in an accumulation of P. carinii
consolidating pneumonia (Figure 4.6.16). Alveolar infil- cysts within alveolar exudates and an eosinophilic
trates are often not in the dependent regions of the lung, inflammatory response. CT features of P. carinii pneu-
25
and middle and caudal lobes are preferentially affected, monia include a nonuniform, diffuse increase in pulmo-
presumably because of the migratory path of the awns. nary parenchyma attenuation, which may represent
24
Foreign bodies often seed bacteria that can also lead to greater or lesser degrees of alveolar flooding in adjacent
more fulminant granulomatous pneumonia. secondary lobules (Figure 4.6.20).
Pulmonary abscess Parasitic pneumonia
Pulmonary abscesses are usually bacterial but are occa- A number of parasites can cause bronchitis and pneumo-
sionally sterile or fungal. Bacterial abscesses can occur as nia in dogs and cats and include migrating larval round-
a solitary lesion or in association with more widespread worms (Toxocara) and hookworms (Ancylostoma), feline
inflammatory disease. On unenhanced CT images, they lungworm (Aelurostrongylus), Filaroides species, and
appear as thick‐walled spheroid or ellipsoid cavitary lung flukes (Paragonimus). Pulmonary manifestations of
masses that contain fluid‐attenuating material and often these disorders in dogs and cats have not been widely
have a gas component that distributes to the nonde- reported and will vary depending on the specific parasite
pendent part of the cavity. Depending on size and loca- involved (Figure 4.6.21). Pulmonary CT features of these
tion, abscesses can cause bronchial obstruction and parasitic infestations would be expected to parallel the
lobar atelectasis (Figure 4.6.17). The abscess capsule radiographic features that have been described.
moderately to intensely contrast enhances, but attenua- Cardiovascular CT features of heartworm (Dirofilaria)
tion of abscess contents remains unchanged. infestation are described in Chapter 4.4. Embolic pneu-
monia can occur with heartworm disease, particularly
Infectious granulomatous pneumonia during therapy, when dead heartworms lodge in the
and related disorders peripheral pulmonary arteries. CT manifestations include
Although infectious granulomatous pneumonias are midzonal and peripheral interstitial to alveolar infiltrates
often mycotic, pyogranulomatous pneumonia can also with coalescence in more severely affected patients.
result from other microbial infections, such as feline coro- Pulmonary eosinophilic granulomatosis can also occur as
navirus and Nocardia and Actinomyces species. The latter an immune response to heartworm infestation.
two organisms often invade the chest cavity as a sequela to
plant awn migration (Figure 4.6.18). Fungal pneumonias Neoplasia
occur following inhalation exposure to causative agents,
the most common of which are Coccidioides immitis, The vast majority of primary lung tumors are malignant,
Blastomyces dermatitidis and Histoplasma capsulatum in and most are epithelial in origin, although primary mes-
North America. enchymal tumors occasionally occur. Older animals are
Pulmonary CT features of mycotic pneumonia range predisposed, and tumors most often arise in the caudal
from unstructured and nodular interstitial infiltrates to lung lobes. Other neoplasms involving the lungs include
complete lobar consolidation. Large nodules are typi- malignant histiocytosis, lymphoma, sarcomas, and
cally solid and soft‐tissue attenuating and are irregularly pulmonary metastasis. 26
margined reflecting the inflammatory nature of the dis-
ease. Tracheobronchial lymph nodes can be profoundly Pulmonary carcinoma
enlarged, causing depression of the terminus of the tra- Epithelial tumors are categorized by site of origin (bron-
chea and abaxial separation of the mainstem bronchi chogenic, bronchoalveolar, alveolar) and by cell character-
(Figure 4.6.19). Affected lungs and lymph nodes enhance istics (squamous cell, undifferentiated, adenocarcinoma). 26
following contrast medium administration, and a heter- To date, CT features of the various types of primary epi-
ogeneous pattern of enhancement may reveal lymph thelial lung tumors have not been found to be sufficiently
node abscessation. unique to distinguish one type from another (Figures 4.6.22,
Pneumocystis carinii, once classified as a protozoan 4.6.23, 4.6.24). However, a recent report on the CT charac-
but more recently reclassified as a yeast‐like fungus, is a teristics of 17 primary pulmonary carcinomas found
common cause of pneumonia in immunocompromised they are solitary, well circumscribed, and located either
people and can induce pneumonia in dogs as well. centrally or in the periphery of the lung. Tumors were
Miniature Dachshunds and Cavalier King Charles bronchocentric in origin and contained air bronchograms.
Spaniels seem to be predisposed, and there is some sug- Bronchial lumina are often narrowed and displaced. Most
gestion that immune incompetence also plays a role in tumors have mild to moderate heterogeneous contrast
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