Page 408 - Atlas of Small Animal CT and MRI

4.2

Pleural space

Normal pleural space re‐expand the lungs, which can improve imaging detec-
tion of underlying lesions of pulmonary origin.
Because normal pleura measure less than 1–2 mm in A prominent CT feature of uncomplicated pneumo-
thickness, and because except for the small volume of thorax is collection of free gas in nondependent regions
normal lubricating pleural fluid, the pleural cavity is of the pleural space (Figure 4.2.1). Lung lobe volume will
anatomically a potential space, characteristic imaging be variably reduced depending on the severity of the
features of the normal pleural space are conspicuously pneumothorax, resulting in an increase in pulmonary
absent. Fine lines corresponding to pleural margins can attenuation. This may be relatively uniform, although
be identified on CT images of the normal thorax, but dependent lung is usually more affected and may be
they are typically subtle and generally not confused with overtly atelectatic. Lateral shift of the heart and medi-
pleural pathology. astinum may also be seen as a result of passive displace-
ment, with unilateral or asymmetrical effusions. In
Pneumothorax patients with concurrent pleural disease, the pleural
membrane may be thickened and can be readily recog-
Pneumothorax most often results from penetrating nized by evaluating the lung margins at their interface
injury of the chest wall or from disruption of the vis- with the free pleural air. 1,2
ceral pleura. Pulmonary causes of pneumothorax
include rupture of peripheral pulmonary bulla or Pleural effusion
subpleural blebs, shear injuries of the lung paren-
chyma, penetrating and migrating foreign bodies, Pleural effusions result from a variety of disorders
and necrotizing inflammatory and neoplastic lung and are classified as transudative, modified transuda-
lesions. Occasionally, injury to the trachea or esopha- tive (e.g. chylous), exudative, or hemorrhagic. The
gus with concurrent involvement of adjacent medias- volume of effusion is variable and may be diffusely
tinal parietal pleura can result in pneumothorax and distributed, unilateral, or regionally compartmental-
pneumomediastinum. ized (Figure 4.2.2).
Although thoracic radiography is recognized as an
excellent screening tool for detecting and quantifying Transudative effusion
pneumothorax, small volumes of free pleural air can be Transudative pleural effusions are most commonly
missed. In general, CT is performed after a diagnosis of caused by right‐sided heart failure or marked hypopro-
pneumothorax has been made and the patient appropri- teinemia. Because the macromolecular concentration
ately stabilized. In many patients, thoracostomy cathe- and cellularity of transudates are low, the attenuation of
ters have been placed to evacuate free pleural gas and the fluid approaches that of water, and these effusions

Atlas of Small Animal CT and MRI, First Edition. Erik R. Wisner and Allison L. Zwingenberger.
© 2015 John Wiley & Sons, Inc. Published 2015 by John Wiley & Sons, Inc.
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