Page 517 - Feline diagnostic imaging

529

30

Peritoneal Cavity
Merrilee Holland

Department of Clinical Sciences, College of Veterinary Medicine, Auburn, AL, USA

30.1 Normal Anatomy 30.3 Normal Ultrasonographic
Appearance
The peritoneal sac lines the abdominal and pelvic cavities.
The peritoneum can be divided into parietal (covers inner In young normal patients, a small volume of free fluid can
walls), visceral (covering organs), and connecting (folds be seen on abdominal ultrasound scans. A small accumula-
suspending the jejunum and ileum). Retroperitoneal struc- tion of fluid between the intestinal loops or adjacent to the
tures refer to organs that are suspended in the abdominal urinary bladder are the most common locations for fluid
or pelvic cavities and are covered by only one layer of peri- accumulation.
toneum [1].
30.3.1 Fluid/Free Air Accumulation on Ultrasound
30.2 Normal Radiographic Appearance Accumulation of more than a small amount of fluid within
the abdominal cavity is abnormal. The echogenicity of the
Adult cats in normal body condition have adequate sero- fluid may assist in determination of the fluid source.
sal detail present on abdominal radiographic images However, collection of fluid for analysis is the only way to
(Figures 30.1 and 30.2) due to fat accumulation between the definitively determine the underlying etiology. Anechoic
viscera. Serosal detail is particularly noticeable in obese cats fluid is associated with lower cellularity and more consist-
(Figure 30.3). In kittens, the abdominal detail is decreased ent with a transudate. The more echogenic foci found
due to the presence of brown fat, which has a higher water within the fluid, the more concern for an exudative process
content (Figure 30.4). or hemorrhage (Figure 30.7). Free air in the peritoneal cav-
ity can be found with the patient in lateral recumbency on
the independent side just beneath the body wall because
30.2.1 Abnormal Radiographic Appearance air will rise to the highest point. Free air will appear as
with Fluid
hyperechoic foci with varying degrees of reverberation arti-
Fluid accumulation in the abdominal cavity causes decreased fact (Figure 30.8).
abdominal detail. This decrease can be focal (Figure 30.5) or
diffuse (Figure 30.6). The amount of fluid in the abdomen
causes a variable decrease in abdominal detail. The type of 30.4 Alternate Modalities
fluid cannot be delineated on radiographs as all fluid results
in a soft tissue opacity. Sampling of the fluid is necessary to Computed tomography (CT), magnetic resonance imag-
determine the underlying etiology. With small amounts of ing (MRI), and positron emission tomography (PET) have
fluid, there may be a streaking or wispy appearance overly- been used in human medicine for staging of neoplasia
ing the abdominal contents. In cases with peritoneal metas- which may metastasize to the peritoneum, omentum, and
tasis, called carcinomatosis, there can be a general loss of mesentery. Abdominal ultrasound in human medicine is
detail and focal areas of more organized soft tissue. used more for biopsy sampling of pathology and not as

Feline Diagnostic Imaging, First Edition. Edited by Merrilee Holland and Judith Hudson.
© 2020 John Wiley & Sons, Inc. Published 2020 by John Wiley & Sons, Inc.