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19

Diaphragm
Martha M. Larson

Department of Small Animal Clinical Sciences, Virginia-Maryland College of Veterinary Medicine, Virginia Tech, Blacksburg, VA, USA

19.1 Normal Appearance cranial to the diaphragm. The most frequently herniated
organ in the cat is the liver, followed by small intestines,
The diaphragm separates the thoracic and abdominal cavi- stomach, omentum, spleen, pancreas, and large intestines
ties, and is composed of three peripheral muscular seg- [2]. On thoracic radiographs, a diaphragmatic hernia is
ments and a central tendinous component. The pars diagnosed easily when gas‐containing organs (stomach,
lumbalis forms the right and left crura, and attaches to the intestines) are seen cranial to the diaphragm (Figures 19.1
ventral aspect of the third and fourth lumbar vertebrae. and 19.2). Herniation of the liver or spleen (soft tissue
The pars sternalis attaches to the xiphoid cartilage, while organs) may be more difficult to differentiate from pleural
the pars costalis attaches to ribs/costal cartilages of ribs effusion or pulmonary consolidation. Border effacement of
8–13. The central tendinous portion encloses the foramen the herniated organs with the diaphragm results in a loss of
of the caudal vena cava [1]. Spaces between the caudal por- visualization. Herniated organs may cause cranial and
tion of the diaphragm and thoracic wall (phrenicocostalis either medial or lateral displacement of the heart (medi-
recess), and between the diaphragm and spine (phreni- astinum) or lungs. On abdominal radiographs, cranial dis-
columbalis recess) are formed due to cranial extension of placement of nonherniated abdominal viscera may be
the diaphragm into the thoracic cavity. noted. Herniation of only omental/falciform fat is very dif-
Typically, the dependent dorsal half of the diaphragm is ficult to diagnose (Figures 19.3 and 19.4). Occasionally, the
displaced cranially, allowing differentiation of left and herniated viscera has a focal soft tissue appearance, mim-
right lateral positioning. However, this difference is mini- icking a pulmonary mass (Figure 19.5) [3,4]. Pleural effu-
mized in the cat, with little visible difference in the appear- sion often accompanies diaphragmatic hernias, especially
ance of the diaphragm between lateral views. The same is those that are more chronic.
true of the appearance of the diaphragm in ventrodorsal Not all diaphragmatic hernias are recognized immedi-
(VD) versus dorsoventral (DV) views. While distinct ately, likely due to minimal clinical signs, poorly defined
changes may be identified in the dog, it is difficult to dif- radiographic changes, or lack of awareness of a traumatic
ferentiate DV versus VD on feline images. The thoracic sur- incident [5]. Oral administration of barium sulfate will aid
face of the diaphragm can be visualized radiographically in determining the location and possible displacement of
due to contrast with air‐filled lungs. The abdominal side the stomach and proximal small intestines. Positive con-
can be visualized only if contrasted by large amounts of trast peritoneography, using iodinated contrast agent, has
falciform fat, or if free abdominal gas accumulates between been used to check for communication between the perito-
the diaphragm and the cranial aspect of the liver. neal and thoracic cavities, but is rarely performed today.
Ultrasonographic evaluation of the thorax and abdomen
can identify displaced abdominal organs, as well as evalu-
19.2 Traumatic Diaphragmatic Hernia ate the diaphragm for disruption in most cases. Ultrasound
is especially helpful when pleural fluid obscures radio-
Traumatic rupture of the diaphragm in the cat, often graphic identification of a hernia. Computed tomography
secondary to vehicular trauma or falls, typically results in can also be used to identify abdominal viscera cranial to the
displacement of varying amounts of abdominal viscera diaphragm in these patients.

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