Abdominal Radiography

Must be taken during the pause after expiration. Positioning and immobilisation of the patient are critical. Either the right or left recumbent lateral projections should be used consistently to eliminate this as a variable.  Standard views of the abdomen are the lateral and VD views. Standing lateral views use a horizontal beam direction through a standing animal and indicate fluid levels in the intestine or abdominal cavity. Special lateral recumbency views direct the beam horizontally through an animal in left lateral recumbency in the VD direction. These are used to detect small amounts of air in the abdomen. Oblique views are directed through the animal placed in VD or DV position and rotated 15 to 30°. These allow better visualisation of the oesophagus, stomach, colon, and urinary bladder by moving them away from the spinal column.

Air in the abdomen: Will go to the non-dependent site. Air first appears against the diaphragm. Usually only the lung side of the diaphragm is seen because the abdominal side is summated with the liver tissue. If both sides can be seen at once there is air in the abdomen. Horizontal views are used to detect a small amount of air in the abdomen. The animal is placed in left lateral recumbency (left side down).  A small amount of gas present will be detected between the right lobes of the liver and the diaphragm.
The right lateral recumbent view is preferred to the left lateral view, as the spleen is more consistently identified.

Positioning of film: Include the entire abdomen from the pelvic inlet to the diaphragm and centre the x-ray beam at the mid-abdomen.  Put the thickest end towards the cathode because of the heel effect.

Viewing abdominal films: Just as in the thorax, viewing needs to be systematic and consistent. The abdominal cavity is framed by the caudal thorax, diaphragm, spinal column, musculature of sublumbar soft tissue, the pelvis and the ventral body wall. It is essential to know anatomically where organs are located; if an organ not normally visualised is seen this indicates a problem. Mobile structures of the abdomen, such as the small and large intestines, can be displaced. A displaced organ may itself be normal but be displaced by an abnormal structure not seen.

Boundaries of abdomen
Cranial diaphragm
Dorsal spinal column
Caudal pelvic inlet
Lateral and ventral abdominal muscles
Ventral rectus abdominis muscle

Draw two imaginary lines on the VD abdominal view. The first line runs down the midline and the second is perpendicular to it, passing through the mid-abdomen. This divides the abdomen into four quadrants. Knowledge of the contents of each quadrant assists in interpretation of radiographs. The greatest number of individual structures are located in the cranial quadrants.

Lateral view of the abdomen
1. Liver: most cranial, contacts the diaphragm. The stomach is caudal to the liver.
2. Spleen: its distal part is seen as a triangle in the ventral abdominal wall just caudal to the liver.
3. Right kidney: appears in the craniodorsal abdominal cavity. Its cranial pole is embedded in the caudate process of the liver, and so is not seen.
4. Left kidney: ½ kidney length caudal to the right kidney and usually can be completely seen. It is also usually more ventral than the right kidney.
5. Transverse colon: crosses the abdomen caudal to the stomach and is seen in cross section when distended with gas.
6. Descending colon: usually sllightly ventral to the spine andextends caudally to the pelvis where it joins the rectum.
7. Urinary bladder: caudoventral abdomen.  Situated more cranially in the female than in the male.

A. Diaphragm
B. Liver: between stomach and diaphragm
C. Fundus of the stomach: located on the left side of the abdomen
D. Body of the stomach: crosses the midline
E. Pylorus: located on the right side of the abdomen in the dog, on the midline in the cat
F. Duodenum: passes down the right side of the abdomen
G. Small intestines: mostly on the right
H. Caecum: located on the right side of the abdomen caudal to the last rib.
I. Ascending colon: located on the right side
J. Transverse colon: crosses midline from right to left
K. Descending colon: travels down the left side
L. Spleen: located caudal to the stomach on the left side

Right lateral recumbency (left side up) air in the fundic region located in the dorsal abdomen.
Left lateral recumbency (right side up) air in the pyloric region located in the ventral aspect of the abdomen.
VD (ventral side up): gas will be in pyloric antrum and body, which are in the ventral part of the abdomen.

Stomach axis: Can be seen if there is gas in the stomach. Clinically the axis of the stomach is used to evaluate the size of the liver. In the lateral projection the normal position of the stomach axis falls between a line drawn vertical to the spine and a line parallel to the ribs. The pylorus is superimposed over the body or slightly cranial to it (10th-11th ribs). In the VD  view the axis of the stomach is perpendicular to the spine in the dog but lies completely to the left side of the spine in the cat.

Lateral projection of the spleen: appears as a soft tissue triangle in the middle of the ventral abdomen, just behind the liver in the dog.  It is only occasionally visible in the cat.
VD projection: the head of the spleen appears as a triangular shape lateral to and caudal to the stomach. Occasionally it may be seen superimposed over the caudal portion of the right kidney.

Positioning terms & techniques