Abdominal imaging in emergency situations (Proceedings)

We experience veterinary emergencies on a weekly, if not daily, basis. Rapid and accurate patient assessment, diagnostic imaging interpretation and treatment can be the difference between patient survival and death. The goal of this talk is to provide a solid foundation for image interpretation in emergency situations. The emergency situations addressed in this talk are: ascites (hemoabdomen, uroabdomen, septic abdomen), free abdominal air, GDV, gallbladder mucocele, GI obstruction, intra-abdominal abscess and retroperitoneal fluid.

Ascites

Identification of ascites on radiographs can be subtle and knowing the radiographic findings can help distinguish free fluid from lack of intra-abdominal fat. One of the keys to identifying ascites is to evaluate the ventral abdominal margin. A patient with ascites may have a bulge associated with the ventral abdomen whereas a patient that has poor serosal detail due to a lack of fat will have a tucked appearance. It is also important to remember that juvenile patients normally have poor serosal detail due to a lack of fat and a small amount of ascites.

Hemoabdomen

Commonly dogs present due to intra-abdominal hemorrhage. The identification of hemorrhagic effusion can range from subtle to difficult depending on the quantity of fluid present. Frequently the animals present with a massive intra-abdominal hemorrhage making the initial diagnosis of hemoabdomen certain. However, the approach once a hemoabdomen is identified is more crucial. Evaluating a patient for a mass with intra-abdominal dissemination, right auricle involvement or pulmonary metastases is a critical step in helping the owners make an informed decision. Evaluating the entire radiograph for evidence of trauma is also important before jumping to the conclusion of a bleeding tumor. A coagulopathy should be ruled out and the ascites should be tapped and evaluated with the fluid PCV being compared to peripheral PCV. On the margin of the radiographs the caudal vena cava should be evaluated for evidence of hypovolemia.

Uroabdomen

Uroabdomen is a condition commonly associated with abdominal or pelvic trauma. Other etiologies of uroabdomen include urinary obstructive disorders such as urolithiasis and iatrogenic causes such as. urethral catheterization Uroabdomen results rapidly in life-threatening dehydration, metabolic acidosis, and electrolyte abnormalities. Although the presence of ascites on radiographs is not specific for uroabomen, a spastic appearance to the bowel and lack of a normal bladder silhouette can be useful in raising the suspicion of a uroabdomen. Abdominocentesis is performed with comparison to serum creatinine and potassium. Alternatively a cystourethrogram with iodinated contrast could be performed. Contrast dosage varies from 2-3 ml/kg for cats to 5 ml/kg for dogs. However the bladder should be palpated during filling to ensure that the cystogram does not result in an iatrogenic uroabdomen.

Septic abdomen

Septic peritonitis is a surgical emergency but direct visualization of intra-cellular bacteria can be difficult. Viscus rupture is the most common cause of septic peritonitis but localization of the affected bowel segment is frequently not possible. Rather identification of indirect clues for septic peritonitis is more useful. Radiographically there is ascites and flaccid small bowel. Ultrasonographically the fluid may contain echogenic material. Lateral to the spleen is the best location to identify fluid. Abdominocentesis should be performed and fluid analysis with cytology should be performed. Additionally the fluid glucose should be compared to the serum glucose and if the fluid glucose is 20 mg/dl or more lower than serum glucose then septic peritonitis is more likely.

Free abdominal air

Pneumoperitoneum is extremely important for a clinician to identify. The presence of even a small amount of air usually indicates a sinister process in the abdomen. A large amount of free air is usually associated with a gastric rupture or iatrogenic air introduction whereas a small amount of air can be due to a bowel perforation. On ultrasound free gas will be small hyperechoic areas which reside in the non-dependent region and can be easily overlooked. Horizontal beam radiographs can be used to confirm the presence of free abdominal air. Idiopathic pneumoperitoneum has been reported in the dog but is rare.

GDV

Gastric diliation and volvulus has a typical appearance which has been described as the "double bubble" or "popeye arm". Radiographic findings associated with GDV go further than just identifying the gastric location. Other important findings are splenic size and location, gas tracking in the gastric wall and caudal vena caval size. Also a chest radiograph should be obtained to evaluate for evidence of pneumonia.

Gallbladder mucocele

Gallbladder mucoceles are best diagnosed by abdominal ultrasonography. They are characterized by immobile, echogenic gallbladder contents with a cut kiwi or stellate pattern within the lumen of the gallbladder. Additional findings are possible distention of the intrahepatic or extrahepatic biliary system. Gallbladder rupture is the major concern. Findings suggestive of gallbladder rupture are loss of gallbladder wall continuity, fluid around the gallbladder, hyperechoic fat in the cranial abdomen and/or finely striated or stellate echogenic material adjacent to the gallbladder. The ultrasonographic appearance of a gallbladder rupture can be confused with pancreatitis or duodenal perforation since the ensuing peritonitis will be similar in all conditions. The presence of a gallbladder mucocele with rupture is considered a surgical emergency.

Intestinal obstruction

Mechanical ileus or foreign body intestinal obstruction, is a common occurrence in veterinary medicine. Causes include intussusception, neoplasia, and ingestion of foreign bodies. Survey radiographs can lend hints to the presence of a bowel obstruction. One of the most important radiographic findings is segmental bowel dilation. This occurs because the bowel orad to the obstruction is dilated while the bowel distal to the obstruction is empty. Upper GI studies and/or abdominal ultrasound can be performed to confirm the presence of a small bowel obstruction. If an upper GI study is to be performed prior to an ultrasound, iodinated contrast should be used because of the shadowing artifacts associated with barium.

Abscess

Intra-abdominal abscesses most commonly affect the liver and spleen but can also affect the pancreas or be associated with a foreign body. Liver abscesses are associated with underlying hepatic neoplasia. Gas producing bacteria within the abscess can have a characteristic stippled appearance on radiographs. Abscess formation is associated with ascites, peritonitis and functional ileus. Ultrasound is used to identify the location of the abscess and obtain free fluid samples. Percutaneous sampling of an abscess is no recommended since it could cause rupture of the abscess and spillage of the contents into the abdomen.

Retroperitoneal fluid

Retroperitoneal fluid may be secondary to renal, ureteral trauma, adrenal tumor with invasion or hemorrhage, abscess due to foxtail migration or hemorrhage. Occasionally mediastinal fluid can track to the retroperitoneal space. Retroperitoneal fluid has a different appearance and etiology than ascites. In cases of retroperitoneal fluid the retroperitoneal space is wispy or enlarged but abdominal detail is spared. There is loss of renal visualization and ventral displacement of the colon. The lumbar vertebra should be evaluated for evidence of spondylitis. Ultrasonographic evaluation with reveal fluid around the kidneys. The adrenal glands should be thoroughly evaluated for evidence of tumor with infiltration in cases with retroperitoneal hemorrhage.

Splenic torsion

Splenic torsion results from the spleen twisting along the axis of the blood supply. This torsion results in clamping off the veins but the thicker walled arteries remain patent. Due to continued arterial inflow and occluded venous drainage the spleen becomes severely enlarged from blood pooling. Eventually clots develop in the splenic vessels and splenic necrosis ensues. Splenic torsions are exceedingly painful and are associated with ascites. Radiographically a splenic torsion has splenomegaly with ascites. The ultrasonographic appearance of a splenic torsion is more characteristic and has been termed the "starry night appearance" due to the hypoechoic appearance with hyperechoic vascular speckling. Splenectomy is required.