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The use of radiographs, ultrasound, and/or CT is indicated in all cases of acute abdomen to guide the diagnostic workup and decision to treat medically or surgically.

Three‐view abdominal radiography is readily available and useful in the rapid identification of gastrointestinal mechanical obstruction or the presence of abdominal masses, peritoneal fluid, and/or peritoneal gas. When the radiographic findings interpreted with clinical correlation, history, and other diagnostic findings do not yield a definitive answer, more advanced imaging techniques including ultrasound and abdominal CT may be useful.

Ultrasound examination may provide additional diagnostic information and better detail of soft‐tissue structures and is very useful to aid in the identification and sampling of abdominal effusions. Ultrasound gives practical information to support a diagnosis of pancreatitis (hypoechoic pancreatic parenchyma surrounded by bright mesentery and peri‐pancreatic anechoic fluid) and may aid in the identification of liver and gall bladder pathology, and intra‐abdominal lymph node abnormalities. Ultrasound gives a better picture of gastrointestinal wall layering or intestinal masses and can be extremely useful in confirming the diagnosis of intussusception.

Although its initial use and inception was for evaluation of trauma patients, an abdominal FAST scan is a useful bedside tool for identification of free abdominal fluid and making a general assessment of the major abdominal organs. This technique has been adapted for veterinary patients and has become widely available [11]. Scanning through the diaphragmatic–hepatic view in the cranial abdomen, the cystocolic view in the caudal abdomen, as well as the splenorenal and hepatorenal views along the lateral abdominal “gutters” will give a thorough overview of the abdomen. In cases where the patient is dehydrated, serial ultrasound exams during and after fluid resuscitation are recommended, as free fluid is not always evident on initial presentation.

CT is gaining tremendous popularity for use in the veterinary emergency service. Typically, abdominal radiographs are the imaging modality of choice for working up the dog with gastrointestinal obstruction. Traditionally, abdominal ultrasound is the next diagnostic test of choice. However, ultrasound (especially gastrointestinal ultrasound) is operator dependent. Those without extensive ultrasound training may not be as capable as a diplomate of the American College of Veterinary Radiology (ACVR) in making specific diagnoses. CT offers a fast, effective method for ruling gastrointestinal obstruction in or out. Because CT images the entire abdomen, there is no chance of “missed” segments of the bowel. CT may also aid in the diagnosis of other causes of vomiting/acute abdomen. In a study by Winter et al. comparing non‐contrast CT with abdominal ultrasound for the diagnosis of mechanical intestinal obstruction in dogs that all underwent exploratory laparotomy for definitive diagnosis, CT was comparable at worst and superior at best to abdominal ultrasound, and the study was much faster to acquire [12]. The study, however, had a small number of patients and interpretations of all studies were performed by diplomates of the ACVR rather than emergency medicine personnel. The use of intravenous iodinated contrast may further increase the diagnostic yield of such studies in their ability to diagnose concurrent pathology including but not limited to neoplasia, portal vein thrombosis, segments of bowel with impaired arterial flow or a myriad of other pathology in this patient population. CT has traditionally been challenging for the diagnosis of pancreatitis in dogs; however, triple phase (arterial, venous, portal‐venous) CT angiography has shown some promise toward improving our ability to definitively diagnose pancreatitis in this patient population [13].