Anatomy of the Abdomen

Peritoneal detail: Depends on the amount of serosal fat surrounding the organs. Fat is more radiopaque than non-adipose soft tissue, so it appears darker. Fat deposits are found in the omentum, the falciform ligament and in the retroperitoneal space.

The presence of gas within a viscus allows differentiation and identification of hollow organs.

Stomach: Its radiographic appearance varies with the position of the patient and the degree of gastric filling. Air will move upward, while fluid is dependent. The empty stomach is normally within the ribcage (doesnít project past the last rib).

The catís stomach is J-shaped. The catís pyloric antrum is to the left of the midline.

Descending duodenum: On the right side of the abdomen. It is larger than the remainder of the small intestine.

Small intestine: Individual loops should be recognisable. The serosal surface of the small intestine is smooth. The thickness of the bowel wall is 1/9 to 1/8 the width of the distended lumen. Mucosal detail can only be evaluated with contrast material or in air-filled segments.

Rule of thumb for intestinal size: = height of a lumbar vertebral body, or two rib widths. Small intestines wider than two ½-rib widths may be abnormal.

Large intestine: Usually contains more gas than the small intestine. Intraluminal food and gas make the intestine much easier to visualise.

Caecum: In the dog it appears as a corkscrew shape on the right side of the abdomen at the level of L3. It can be seen on survey films if it contains some intraluminal gas. In the cat the caecum is a small cone-shaped structure; it cannot be seen on survey films.

Ascending colon: Extends for a short distance from the caecum up the right side of the abdomen to be continued as the transverse colon.

Right colic or hepatic flexure: The point at which the ascending colon becomes the transverse colon.

Transverse colon: Crosses the abdomen from right to left and continues as the descending colon.

Left colic or splenic flexure: Where the transverse colon becomes the descending colon.

Descending colon: On the left side. Faecal material can usually be seen in it.

Rectum: Within the pelvic cavity.

The colon often provides clues to what is going on around it. The lumen contains radiopaque faecal material and/or gas, so it is usually visible. The colon is quite mobile because of its relatively long mesentery.

Medial iliac lymph nodes: Located at the termination of the abdominal aorta and not usually seen radiographically.

Liver: The largest organ in the abdomen, it is located in the cranial quadrants behind the diaphragm and in front of the stomach. Normally the edges are sharp. In adult dogs the liver does not extend past the last rib. It is relatively larger in the young animal. The liver is contrasted cranially by air filled lungs and caudally by gas in the stomach.

Gall bladder: A pear-shaped structure lying between the quadrate lobe and the right medial lobe. It is not normally visible unless it contains choleliths or gas.

Renal impression: Cups the cranial pole of the right kidney. A feature of the caudate process of the caudate lobe.

Clinically the axis of the stomach is used to evaluate the size of the liver. Assess stomach fullness; this can be misleading.
Try to three-dimensionally visualise the size of the liver from the lateral and the VD view, using the stomach axis.

Pancreas: A soft tissue structure normally not visible radiographically because of its small size and its similar radiopacity to surrounding structures.

Spleen: A parenchymatous organ loosely attached to the greater curvature of the stomach by the gastrosplenic ligament, in the left cranial abdomen. The tail of the spleen extends caudally, ventral and medial to the stomach. The head is normally tucked over in the left cranial quadrant of the abdomen with the kidney directly behind it in DV view. Splenic enlargement assessment is completely subjective, and depends on experience. The spleenís size is variable depending on the amount of engorgement with blood.

Mesenteric lymph nodes: Enlarged lymph nodes located in the root of the mesentery. Can give a radiographic enlargement in the middle of the abdomen. The root of the mesentery is at about the level of L2.

Kidneys: Located in the dorso-cranial part of the abdomen. Normally they are smooth and of equal size and shape. Visualisation of the renal borders is dependent on the amount of perirenal fat present. The kidneys of cats and overweight dogs are easier to see than those of young or emaciated dogs.
Compare the kidneys for size and check that there are two, especially if removing one.

Left kidney           Right kidney
Dog: L2 Ė L4              Dog: T13 Ė L3
Cat: L2 Ė L5               Cat: L1 Ė L4

Dog: 2.5 to 3.5 times the length of lumbar vertebra L2 on VD view
Cat: 2.5 to 3 times the length of L2