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In: 50 Congresso Nazionale Multisala SCIVAC Radiography of Abdominal Masses Anne Bahr, DVM, MS, Diplomate, ACVR Assistant Professor Texas A&M University, College Station, Texas USA The key to successful evaluation of abdominal masses is recognition of displacement of adjacent normal structures. Th us, the ability to identify normal structures is critical to the evaluation. The appearance of masses is dependent upon the amount of enlargement. In addition, the effects of gravity can play a role in the appearance. If a mass is derived from an organ that is fixed in position, gravity will have minimal effect whereas if the mass is arising from an organ that is mobile, position and gravity will play a significant role in the appearance. There are three abdominal organs that may be enlarged in normal situations: stomach, bladder and uterus. It may be hard to determine if the enlargement of these organs is pathologic however evaluation of the history and clinical examination usually are helpful Case examples showing the different appearances of masses will be presented. Visceral Surface Detail Visualization of structures in the abdominal cavity is due to the differential radiopacity of the soft tissue structures which are primarily surrounded by fat. This is the key factor as there is very little free peritoneal fluid present in the normal dog or cat. Enhanced visualization of visceral surfaces in the abdomen can be due to pneumoperitoneum. Free air in the peritoneal space allows visualization of structures which are not normally seen: examples include the cranial pole of the right kidney, the visceral surface of the stomach and the diaphragm. Possible causes for pneumoperitoneum include iatrogenic causes (surgery, peritoneocentesis), penetrating wounds, ruptured viscus or gas forming bacteria. Diagnosis of pneumoperitoneum is dependent upon the amount of free air present. Sometimes routine radiography may be sufficient. However, the use of positional radiographs may be necessary to detect smaller amounts of air. This utilizes a horizontally directed x-ray beam. Often, left lateral recumbency will allow air to accumulate in the right cranial quadrant away from the fundus of the stomach. Loss of visceral detail can be due to a number of causes such as lack of abdominal fat in young or emaciated animals. This is usually not clinically significant. Other causes include accumulation of soft tissue opacity which silhouettes with the abdominal structures such as fluid or cellular infiltrates. Fluid such as transudates, modified transudates or exudates can cause loss of detail. Cellular infiltrates such as carcinomatosis can also cause loss of detail. Compression of abdominal contents can also cause a loss of visceral detail. This often is seen with large mass effects in the abdominal such as occurs with neoplasia or a large and distended urinary bladder. Often, ultrasound can be used to help determine the loss of visceral detail to differentiate fluid accumulation vs mass effect. It can also be used to obtain a sample of fluid, particularly if there is a small amount present. Normal Abdominal Structures Stomach The stomach is located just caudal to the liver with the visualization dependent upon the amount of surrounding fat as well as the contents of the stomach. Often, it is recognized because of the food within the lumen. If the stomach is empty of food, gas often helps to determine its location. In the dog, the fundus is located in the left cranial quadrant with the pylorus on the right.
On the VD view, the axis should be perpendicular to the spine. In the cat, the pylorus is located on midline and is C-shaped on the VD view. In both species, the axis of the stomach should be parallel to the ribs on the lateral view. In addition, if gas is present it can be manipulated using gravity to view the different portions of the stomach. It is necessary to realize that the fundus is slightly more dorsal than the body of the stomach as is the pylorus. Thus, if the animal is in left lateral recumbency, gas can be recognized in the pylorus. In right lateral recumbency gas rises to the fundus. On the VD view, gas will be in the body and on the DV view, gas will be in the pylorus and fundus. Normal Abdominal Structure Small Intestine The duodenum is fixed in position by its mesenteric attachments. It is normally the most lateral intestine on the right side and the descending duodenum is parallel to the body wall. The jejunum is relatively mobile. The serosal margins are visualized due to the surrounding fat. Mucosal margins can NOT be definitively visualized without positive contrast to outline the surface. In general, the overall diameter of the small intestine should not exceed 1-2 (sometimes up to 3) times the width of a rib (or 12 mm in the cat). Normal Abdominal Structure Liver The liver is located just caudal to the diaphragm. Normally in most breeds, it is located within the costal arch and has sharp margination. In cats, it is common to see a large falciform fat pad ventral to the liver giving it the appearance of floating. On the lateral view, the axis of the stomach should be essentially parallel to the ribs. Normal Abdominal Structure Spleen The head of the spleen is held in position by the gastrosplenic ligament. It can be seen on the lateral view just dorsal to the kidney in the cranial dorsal abdomen. On the VD view, it is seen just caudo-lateral to the stomach. The tail is mobile and can be found anywhere in the mid to caudal abdomen. The margination should be smooth and sharp. Normal Abdominal Structures Kidneys The kidneys are located in the retroperitoneal space. They are best seen on the VD view and are measured compared to the length of L2. In the dog, normal kidneys may be 2.5-3.5 times the length of L2 and in the cat 2.4-3 times the length of L2. The kidneys should be evaluated for disparity of size and margination as well as changes in opacity. The kidneys are normally at the level of T13-L4. The right kidney is usually more cranially located in the dog. In the cat, the kidney may be pendulous. Normal Abdominal Structures Ureters The ureters not normally seen radiographically. Anatomically, the proximal ureter is retroperitoneal while the most distal portion is peritoneal in location. The only way to evaluate the ureters is with contrast radiography Normal Abdominal Structure Urinary Bladder Survey radiographs are useful only for evaluating bladder position, opacity, shape and size. However, it may be necessary to perform a contrast study to complete the evaluation. The bladder is divided into 3 areas vertex, body, neck. The trigone is the dorsal aspect of the neck. Normal Abdominal Stucture Prostate and Uterus The prostate is located immediately caudal to the neck of the urinary bladder. The ability to visualize it radiographically is dependent upon the size and the amount that is located within the abdominal cavity. If enlarged, it may displace the bladder cranially. The prostate should not be more than two thirds the width of the pelvic inlet on the VD view.
The uterus is located between the urinary bladder and the colon. The ability to visualize it is dependent upon the reproductive status of the animal as well as the disease status (pyometra). If enlarged, the uterus may cause cranial displacement of the abdominal viscera (particularly the gastrointestinal tract). Possible origin of a mass as seen on the lateral projection -Craniodorsal Region -caudate and right lateral liver lobes -lead of spleen -adrenal glands -kidneys -right ovary -Cranioventral Region -right/left liver lobes -gall bladder/bile duct -Central Abdominal Region -body/tail spleen -right limb pancreas -mesenteric lymph nodes -intestinal tract -ovaries -cranial horns of uterus -Dorsocaudal Region -sublumbar lymph nodes -colon/rectum -distal ureters -Caudoventral Region -urinary bladder -uterus -prostate -pelvic masses Possible origing of a mass as seen on the ventrodorsal Projection -Right cranial region -pylorus -right liver lobes -gall bladder/bile duct -right kidney/adrenal gland -Left cranial region -left liver lobes -fundus/body stomach -spleen -left adrenal gland -Central Abdominal Region -spleen -left kidney -mesenteric lymph nodes -intestinal tract -ovaries -uterus
-Caudal Abdominal Region -urinary bladder -prostate/uterus -colon/rectum -sublumbar lymph nodes References: Thrall DE, ed. Textbook of Veterinary Diagnostic Radiology, 4 th ed. Philadelphia, WB Saunders, 2002. This manuscript is reproduced in the IVIS website with the permission of the Congress Organizing Committee