Small Animal Radiology and Ultrasound: A Diagnostic Atlas and Text

180 Small Animal Radiolo g y and Ultrasono graphy
Fig. 2-162 A 4-year-old male cat
with a history of anemia and a heart
murmur. On the lateral thoracic
radiograph the cardiac silhouette is
mildly enlarged and irregularly
shaped. There is calcification of the
margins of the aorta (arrows). The
calcification extends into the ascending
and descending aorta.
Diagnosis: Aortic calcification. The
etiology was not determined. The
cat’s clinical signs were due to lymphocytic
leukemia.
density by comparing the right lung to the left. Similar densities and patterns should be
present in comparable areas. If available, previous radiographs should be compared
directly. If areas of abnormally increased or decreased density are observed, they should
be evaluated according to the portion (i.e., ventral, dorsal, peripheral, middle, hilar) or
number of lung lobes involved. The symmetry or asymmetry of the suspect lesion and
distribution of the abnormality should be noted. It should be determined if a lesion centers
on the pulmonary hilus and extends outward, seems more severe in the middle or
peripheral lung, or is uniformly dispersed throughout the lung. 502 Next, the pattern of
pulmonary density should be determined. The defined patterns include the alveolar,
interstitial, bronchial, or vascular pattern. 503 Many infiltrates will have features of more
than one type of pattern. The predominant pattern is used to develop the list of differential
diagnoses.
PULMONARY PATTERNS
A LV E O L A R PAT T E R N
Alveolar patterns result from flooding of pulmonary acini with fluid. An acinus consists of
that portion of lung that is distal to a terminal bronchiole (i.e., the respiratory bronchioles,
alveolar ducts, alveolar sacs, and alveoli). Each acinus has multiple communications with
the adjacent acini via multiple interalveolar pores, the pores of Cohn. An acinus, which represents
the basic unit of the end–air spaces, is the smallest pulmonary unit that is individually
visible on a radiograph.
An alveolar pattern is due to flooding of the acini with some type of fluid such as pus,
blood, edema or, rarely, cellular material. As individual acini become filled, the fluid then
spreads to adjacent acini through the interalveolar pores. This results in the typical radiographic
pattern of a poorly marginated (“fluffy”) density. The areas of density may spread
and their poorly defined borders will coalesce. This process may spread until all acini within
a lung lobe are filled. If this happens, there may be a sharply marginated border seen at the
edge of a lung lobe due to the dense connective tissue or pleura blocking further spread of
the fluid into the adjacent lung lobe. As the number of fluid-filled adjacent acini increases,