Page 501 - Atlas of Small Animal CT and MRI

5.1

Body wall, retroperitoneum,

and peritoneal cavity

Multislice CT can be used to rapidly acquire images with Effusion
high contrast and high spatial resolution in anesthetized,
sedated, or awake animals and is well suited for exami- Perirenal fluid can accumulate in animals with acute
nation of the body wall, retroperitoneum, and peritoneal renal failure due to infectious inflammatory disease, renal
cavity. MR is used less often in imaging these regions toxicity, or renal obstruction (Figure 5.1.3). Although this
1
because of respiratory motion artifact during image has not been described with CT or MR imaging, veteri-
acquisition. nary ultrasonographic studies have shown the association
The retroperitoneal space, which is often difficult to between unilateral or bilateral perirenal fluid accumula-
evaluate with other imaging modalities, is well visual- tion and acute renal failure. 3
ized on cross‐sectional and reformatted CT images. The Increased vascular pressure or permeability can lead
abdominal aorta and caudal vena cava course through the to peritoneal effusion. This appears as dependent
fat contained in the retroperitoneal space. The major retro- pockets of fluid attenuation conforming to the regional
peritoneal organs include the kidneys and adrenal glands. anatomy (Figures 5.1.4, 5.1.5).
Paraaortic lymph nodes are inconsistently seen unless
enlarged. The larger medial iliac lymph nodes are located Inflammatory disorders
lateral to the iliac branches of the aorta, and the hypogastric Infectious inflammatory disease may be localized in
lymph nodes can be detected between the iliac arteries.
The body wall consists of thin muscle layers inter- the retroperitoneal space or body wall. Abscesses in
spersed with fat, which are readily evaluated on CT certain geographic regions may be caused by penetra-
images. The peritoneal space is filled with fat that tion of migrating grass awns through the body wall,
which may connect with external draining tracts or
surrounds the serosal surface of the abdominal organs.
cause body wall masses. Alternatively, the foreign body
Trauma may enter the retroperitoneal space via the pleural
space secondary to inhalation. Pleural foreign bodies
Trauma to the spine can cause hemorrhage to extend often migrate through the diaphragm into the lumbar
into the spinal musculature and retroperitoneal space. musculature, causing cellulitis or abscess and clinical
On CT images, hemorrhage may be slightly hyperatten- signs of acute abdominal or back pain. CT features
uating or isoattenuating and has ill‐defined margins as it of foreign bodies migrating from the pleural space
dissects through the retroperitoneal space (Figure 5.1.1). include a round‐ or oval‐walled tract with central fluid‐
On MR images, edema and hemorrhage appear as T2 attenuating material and gas, which extends from
hyperintensity in the spinal musculature and retroperi- the diaphragm to the sublumbar musculature. On
toneal space. Hemorrhage may also be seen in the contrast‐enhanced images, the wall of the tract is
2
pelvic retroperitoneal space (Figure 5.1.2). moderately contrast enhancing. The inflammation may

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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