A few examples of challenging abdominal imaging cases are reviewed and discussed.

Biliary Tract

Cholecystocentesis is considered a relatively safe technique and it is routinely performed in many veterinary hospitals.¹ Therapeutic cholecystocentesis has been proposed as a way of relieving the pressure from the biliary system in patients suffering from extrahepatic biliary obstruction secondary to pancreatitis.² However bile leakage and subsequent peritonitis are potential complications of percutaneous cholecystocentesis. Currently there is limited published information regarding the success rate of this procedure in the veterinary field.

Pancreatitis

Early diagnosis of acute pancreatitis is essential as it carries a high mortality rate in dogs. In order to reach a diagnosis of acute pancreatitis the clinician takes into consideration clinical history, physical examination, serum biochemistry (including the Spec cPL assay for canine pancreatic lipase), and abdominal ultrasound results. The reported sensitivities and specificities of these tests are variable; thus, these tests are sometimes insufficient to reach a final diagnosis.

A recent study comparing ultrasound and computed tomographic angiography (CTA) in the diagnosis and evaluation of acute pancreatitis in dogs showed that, in comparison to US, CTA better identified dogs with more severe acute pancreatitis and those with portal vein thrombosis, factors that may predict longer hospitalization and increased risk of relapse.³

It is important to notice that a 3-phase CTA protocol was used for this study. The authors used a 16-slides CT, a bolus trace protocol and a power injector.

Normal Renal Pelvis, Ureteral Calculi, and Pyelonephritis

Urinary tract obstruction secondary to ureteral calculi has become increasingly common in feline veterinary medicine. Young patients are often affected and present with non-specific signs of renal failure. Diagnostic imaging is essential to identify the calculi and differentiate urinary obstruction from other causes of renal failure. Ultrasound is an effective imaging modality to identify dilatation of the renal pelvis and urinary calculi, including ureteral calculi.

An attempt by d’Anjou et al. was made to determine whether it is possible to predict the underlying cause of renal pelvis dilatation on the basis of the size of the renal pelvis dilatation measured on ultrasound.⁴ Dogs and cats with hydronephrosis were divided in 6 groups: clinically normal renal function, normal renal function with diuresis, pyelonephritis, acute or chronic renal insufficiency, obstructive disorders, and a miscellaneous group. Minimal to mild dilatation of the renal pelvis (RP) was observed in patients with clinically normal renal function. Mild to moderate dilatation of the renal pelvis has been associated with increased diuresis (e.g., secondary to intravenous fluid administration, diuretics administration), pyelonephritis, outflow obstruction, and chronic parenchymal renal disease.

Dilatation of the renal pelvis is variable in dogs and cats with pyelonephritis (dogs = 5.6 +/- 3.7 mm; cats = 4.6 +/- 3.6 mm). The RP can be up to 12 mm but also minimally dilated (below 2 mm). Minor dilatation of the renal pelvis may be related to the short duration of the infection. In conclusion only when the pelvic width was more than 13 mm it was possible to reliably associate it with obstruction. Renal pelvis width in ten cats with clinically normal renal function was between 0.8 and 3.2 mm. In case of renal pelvis width of less than 13 mm, it was not possible to differentiate between the groups on the basis of imaging alone.

Ultrasound-Guided Antegrade Pyelogram

Intravenous urography is often not particularly useful to diagnose ureteral obstruction because of the ureter is not clearly visualised due to lack of contrast excretion secondary to renal failure. The same problem can occur when performing computed tomography after intravenous administration of contrast.

In the presence of hydronephrosis, when the cause of obstruction is not readily identified, an ultrasound-guided antegrade pyelogram is indicated. Antegrade pyelography helps determining whether there is partial or complete obstruction. The study should be performed with the patient anaesthetized. The area over the kidney is clipped and aseptically prepared. The renal pelvis dilatation is measured and the safest path for insertion of the needle is selected with ultrasound. Under ultrasound guidance a hypodermic needle (23-gauge needle - 1 inch) connected to a small extension set and 3 way-taps is inserted into the renal pelvis. If possible, urine is collected from the dilated renal pelvis before injection of contrast. The contrast injected is equal to 75%–100% of the urine volume removed. Lateral and ventrodorsal abdominal radiographs (or fluoroscopic images) should be obtained immediately, at 5 minutes and possibly at 15 minutes post-injection.⁵ This technique is also useful to detect possible ureteral tears.

Abdominal Active Bleeding

In humans CT is used to demonstrate the presence of small sources of active bleeding in the peritoneal cavity. Identification of the “sentinel clot sign” defined as the highest attenuation haematoma adjacent to a bleeding organ in humans with haemoabdomen has been suggested as a potentially useful indicator of source of bleeding in dogs with haemoabdomen.⁶

References

1.  Sciborra F, McConnell JF, Maddox TW. Percutaneous ultrasound-guided cholecystocentesis: complications and association of ultrasonographic findings with bile culture results. J Small Anim Pract. 2017;58(7):389–339.

2.  Herman BA, Brawer RS, Murtaugh RJ, et al. Therapeutic percutaneous ultrasound-guided cholecystocentesis in three dogs with extrahepatic biliary obstruction and pancreatitis. J Am Vet Med Assoc. 2005;227(11):1728–1753.

3.  French JM, Twedt DC, Rao S, et al. Computed tomographic angiography and ultrasonography in the diagnosis and evaluation of acute pancreatitis in dogs. J Vet Intern Med. 2019;33(1):79–88.

4.  D’Anjou MA, Bedard A, Dunn ME. Clinical significance of renal pelvis dilatation on ultrasound in dogs and cats. Vet Radiol Ultrasound. 2011;52(1):88–94.

5.  Kulendra NJ, Syme H, Benigni L, et al. Feline double pigtail ureteric stents for management of ureteric obstruction: short- and long-term follow-up of 26 cats. J Feline Med Surg. 2014;16(12):985–991.

6.  Specchi S, Auriemma E, Morabito S, et al. Evaluation of the computed tomographic “sentinel clot sign” to identify bleeding abdominal organs in dogs with haemoabdomen. Vet Radiol Ultrasound. 2017;58(1):18–22.