Diseased dogs with non-specific clinical signs are a common challenge faced by the internal medicine specialist. Different tools are needed to obtain a correct diagnosis and provide treatment recommendations. Abdominal ultrasonography is extremely valuable in dogs, because it provides a large quantity of information in real-time, is non-invasive, and is cost-effective.
At the first presentation, the internal medicine specialist completes a history, a thorough clinical examination, blood work, and urinalysis. Further investigations, such as diagnostic imaging tests (i.e. radiographs and ultrasonography), are useful to clarify the clinical picture.
The internal medicine specialist must first communicate the clinical suspicion to the radiologist to optimize the subsequent investigation. Here, the abdominal organs are described to provide the most relevant information that helps complete the patient’s diagnostic workup from the perspective of the internal medicine specialist.
Ultrasonography of the gastrointestinal tract is often requested by the internal medicine specialist because among the most frequent presenting complaints of dogs are anorexia, vomiting, diarrhea, and weight loss. Major focuses of ultrasonography are the stomach’s lumen, the pylorus’s patency, the gastric and intestinal wall thickness, stratigraphy, and peristalsis. Unfortunately, due to intraluminal gas, the ultrasonographic examination can be suboptimal.
In a dog with vomiting, it is important to exclude the presence of gastric distension with liquid content that can result from gastric atony caused by, for instance, hypercalcemia or pancreatitis, or from an obstruction to the pyloric outflow. In addition, foreign bodies can cause obstructions to the transit of the ingesta at the pyloric level, neoplasia, and stenosis (Figure 1).
Another possible finding is a thickening of the gastric wall due to gastritis or neoplasia. The distribution, extent of thickening, and the involved layer might help differentiate these conditions. However, further diagnostic procedures are usually required to achieve a definitive diagnosis, such as ultrasound-guided biopsies or endoscopy.
In dogs with hematemesis, hematochezia, or melaena, it is important to look for gastric or intestinal ulcers or masses. Ultrasonography of the gastrointestinal tract is also useful for excluding small and large bowel obstructions and intussusceptions.
In dogs with chronic diarrhea and weight loss, ultrasonography can be useful to exclude diffuse or focal intestinal wall thickening attributable to inflammatory or neoplastic disorders.
The internal medicine specialist often needs the evaluation of the adrenal glands in dogs in which hypoadrenocorticism or hyperadrenocorticism is suspected. For these disorders, the diagnosis is initially based on a plethora of compatible clinical signs and laboratory findings, as well as endocrine tests (e.g. ACTH stimulation test).
Additionally, ultrasonography is very important to support the diagnostic suspicion; the size of the adrenal glands is assessed, obtaining different measurements, such as the transverse thickness or the presence of any masses.
Bilateral enlargement of the adrenal glands may suggest pituitary hyperadrenocorticism, while in the presence of mild and unilateral increase of thickness, it is difficult to differentiate the underlying condition. Adrenal tumors can appear as masses or cause an increase in the overall size of the gland; they are mainly represented by adenomas, carcinomas, pheochromocytomas, and metastatic tumors.
If the tumor is secreting excess cortisol, the contralateral adrenal gland may be atrophic. This finding is highly specific. In cases of hypoadrenocorticism, the bilateral reduction of the adrenal thickness is very common and, again, very specific.
Spleen liver and gallbladder
An ultrasonographic examination of the spleen is useful in dogs for evaluating its size, parenchyma, and vascularization. The presence of splenomegaly may indicate infiltrative disorders (e.g. lymphoma), inflammation (e.g. splenitis), hyperplasia (e.g. due to chronic ehrlichiosis), or venous congestion.
Heterogeneous parenchyma and the presence of focal lesions can suggest either a tumor or non-tumoral processes. Given, in most cases, the findings are non-specific, an ultrasound-guided biopsy of the organ is essential to differentiate the disorders. The splenic veins are also evaluated during ultrasonography to exclude the presence of thrombosis (e.g. due to torsion, protein-losing nephropathy) (Figure 2).
An ultrasonographic examination of the liver is of particular importance to clarify some clinical signs, such as anorexia, vomiting or diarrhea, abdominal pain, jaundice, or any increase in circulating liver enzymes in dogs. With ultrasonography, it is possible to evaluate its size, echogenicity, vascularization, and any alterations in the parenchyma.
The parenchyma evaluation helps identify inflammatory processes, hyperplastic nodules, cysts, hematomas, abscesses (which are rare), and tumors. Due to the limited specificity of most features, it is often advisable to perform ultrasound-guided biopsies of the organ to better characterize the lesions.
Reasons to investigate the gallbladder are represented by jaundice or increased liver enzymes. Through ultrasonography, biliary tract obstruction due to mucocele and, less often, stones, tumors can be identified.
Thickening of the bile gallbladder may suggest cholecystitis. In the latter case, the internal medicine specialist can ask to collect a bile sample through ultrasound-guided fine-needle aspiration for bacteriology and cytology; the procedure, performed under sedation, is safe in most cases.
The liver vasculature is also important from an internal medicine perspective. For example, portosystemic shunts are relatively frequent in dogs, whereas arteriovenous fistulas are rare. In the former case, the internal medicine specialist can suspect the vascular abnormality based on, among the others, decreased liver function parameters (e.g. albumin, cholesterol) and abnormal liver function tests (e.g. increased post-prandial bile acids).
Pancreas kidney and urinary tract
Diseases of the exocrine pancreas can cause non-specific clinical signs in dogs, such as vomiting, diarrhea, and a painful abdomen. The ultrasonographic abnormalities can be focal (e.g. nodular hyperplasia, cysts, abscesses) or diffuse (i.e. pancreatitis); however, neoplasia is uncommon and is usually focal (e.g. adenocarcinoma) rather than diffuse.
Acute pancreatitis, the most frequently diagnosed disorder, can be suspected if the organ has reduced echogenicity, heterogeneous parenchyma, mild peritoneal effusion, or peri-pancreatic steatitis (Figure 3). Frequently, a normal ultrasonographic appearance of the pancreas does not rule out acute pancreatitis. Laboratory analyses, including canine-specific pancreatic lipase assay, are normal in some cases; hence, confirming acute pancreatitis in dogs can be a real challenge.
Diseases of the kidney or urinary tract are suspected in dogs with pollakiuria, stranguria, anuria, incontinence, polyuria, polydipsia, or hematuria. Additionally, the biochemical profile and urinalysis may unveil, among the others, increased circulating creatinine and urea, diluted urine, or proteinuria.
In puppies and young dogs with polyuria and polydipsia, congenital disorders can be identified, such as ectopic ureters, and, rarely, renal dysplasia. In the former, the dilated ureters are easily identified with ultrasonography; in the latter, abnormally shaped kidneys with loss of cortico-medullary definition can be observed.
Ultrasonography enables easy detection of any renal parenchymatous masses, even if their appearance generally does not allow the definitive diagnosis. The neoformations can be fluid-filled (e.g. renal cysts) or solid (e.g. hematomas, granulomas, abscesses, primary, or metastatic neoplasia). Acute kidney injury is diagnosed based on clinical and laboratory findings, and kidney ultrasonography may be normal in several of those cases; one exception is ethylene glycol intoxication, during which there is an increase in the echogenicity of the renal cortex.
Chronic kidney disease can be associated with few ultrasonographic abnormalities (e.g. slightly increased echogenicity of the cortex) or important ones (e.g. smaller kidneys with irregular margins and loss of cortico-medullary definition). Dilation of the pelvis caused by pyelonephritis or stones can be easily documented through ultrasonography and can be mono or bilateral. Tumors, blood clots, polyps, and stenosis of the ureters are rare.
Ultrasonography allows the examination of the bladder in dogs if distended by urine easily. It is possible to evaluate its wall, sometimes ventrally thickened due to cystitis or the presence of stones, blood clots, and diverticula.
Transitional cell carcinomas can be identified in the trigone, bladder neck, and proximal urethra. As above for prostatic tumors, fine-needle aspiration of suspected transitional cell carcinoma of the bladder can also cause seeding.
Ultrasonographic evaluation of the prostate is requested by internal medicine specialists in intact and older dogs with haematuria, dysuria, fecal tenesmus, or stiff gait (without orthopedic diseases). Rectal examination of the prostate may unveil pain, enlargement of the organ, or the presence of cystic lesions. As palpation does not allow the characterization of prostatic diseases, ultrasonography is recommended.
The diagnostic toolbox
The synergy between the internal medicine and the diagnostic imaging specialists allows veterinarians to complete the diagnostic workup in most dogs and, in turn, provide treatment recommendations and monitor disease progression. Hence, ultrasound is an important instrument that should be present in the toolbox of all veterinarians.
Dr. Eric Zini achieved the Diploma of the European College of Veterinary Internal Medicine (Dipl. ECVIM-CA, Internal Medicine) in 2005 and a PhD in Small Animal Nephrology 2006. Throughout his career, he has authored more than 150 articles in international scientific journals and textbooks. Dr. Zini currently serves as AniCura practice manager and AIS associate editor.