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].
Conclusion
Early recognition and stabilization of the acute abdomen patient are essential for successful treatment. Critical patient assessment, in conjunction with cardiovascular, respiratory, and nervous system support in the form of aggressive shock treatment and oxygen therapy, is vital before surgical or other interventions.
4 Esophageal Foreign Bodies
Ivan Doran
Bristol Vet Specialists, Bristol, UK
Introduction
The caliber and distensibility of the canine esophagus means that it is well adapted to a diverse diet. Nonetheless, dogs with esophageal foreign bodies constitute a regular source of emergency cases. Ingested objects are principally bones [1, 2]; typically epiphyses and vertebrae of sheep or pigs. Raw hide chews and toys are also regularly encountered [2–4]. Terrier breeds, including the English Bull Terrier and the West Highland White Terrier, are well represented among the affected population [1, 4]. When presented with a non‐osseous foreign body, the clinician should include a search for esophageal dysmotility as an underlying cause. Cats are seldom seen with bulky esophageal foreign bodies by virtue of their more selective eating habits. Fishhooks and needles are periodically found in the esophagi of both species.
Anatomy
The esophagus begins at the level of the caudal border of the cricoid cartilage and ends at the cardia of the stomach. It is divided into cervical, thoracic, and abdominal portions. The cervical portion inclines from a dorsal position to the left of the trachea at its origin and remains on the left side of the trachea at the thoracic inlet. The thoracic portion extends from the thoracic inlet to the esophageal hiatus of the diaphragm. At the level of the tracheal bifurcation, the esophagus crosses the trachea to regain a dorsal position. The abdominal portion of the esophagus is the wedge‐shaped terminal part. The layers of the esophagus include the mucosa, submucosa, muscularis, and adventitial layer; the esophagus lacks a serosal covering. The lack of serosal covering may contribute to incisional dehiscence following surgery. Functional sphincters are located cranially and caudally at the pharyngoesophageal and gastroesophageal junction. The blood supply to the esophagus comes from multiple sources. The cranial and caudal thyroid arteries are the main arterial blood supply to the cervical esophagus (see Chapter 29, Figure 29.4). The cranial two‐thirds of the thoracic esophagus is supplied by the bronchoesophageal artery, and the remaining portion is supplied by branches of the dorsal intercostal arteries and the aorta (see Chapter 37, Figures 37.1 and 37.2). A branch of the left gastric artery supplies the terminal portion of the esophagus.
The esophagus is constrained at certain points (Figure 4.1). The aorta and trachea limit esophageal distension overlying the heart base. The esophageal hiatus of the diaphragm and cardiac sphincter similarly restrict esophageal dilatation. The incidence of foreign body lodgment is highest in the caudal thoracic esophagus (Figure 4.2) followed by the esophageal region adjacent to the heart base [1, 2, 4], although non‐referral cases may show a wider variety in foreign body location [5]. Fishhooks and needles appear to lodge with a more even distribution along the esophagus.
Pathophysiology of Esophageal Injury (Figure 4.3)
The presence of an esophageal foreign body provokes persistent waves of peristalsis. Over time, peristaltic activity weakens and there is a reduction in lower esophageal sphincter tone, which predisposes the animal to reflux esophagitis. This reflux further inflames the esophagus and a vicious circle is established. Repeated peristaltic waves crossing the foreign body itself create pressure necrosis of, respectively, mucosal, submucosal, and muscular layers. Esophageal inflammation is thought to further lower muscle tone at the cardia while mural swelling results in a yet tighter engagement of the esophageal wall around the luminal object. Certain cases undergo full‐thickness wall perforation. This can result from sharp protrusions of the foreign body or from pressure necrosis of the juxtaposed esophageal wall.