Page 402 - WSAVA2018
P. 402

 25-28 September, 2018 | Singapore
G. Seiler1
1North Carolina State University,
Molecular Biomedical Sciences, Raleigh, USA
Gabriela S. Seiler DECVDI, DACVR
College of Veterinary Medicine, North Carolina State University, 1052 William Moore Drive, Raleigh, NC 27607, USA.
The urinary bladder is often thought to be one of the easier organs to evaluate with ultrasound. However, there are many pitfalls for bladder ultrasound interpretation because of artifacts which are more common and more apparent in the urinary bladder, and because of mobility of intraluminal structures as well as the potentially intrapelvic location of the caudal aspect of the urinary bladder and urethra. Knowledge of ultrasound artifacts, how they can be avoided or interpreted, and good scanning technique are very important when interpreting ultrasound examinations of the urinary bladder.
Scanning technique
As with any other ultrasound examination it is important to prepare the skin properly by clipping the haircoat and applying alcohol and ultrasound gel. The urinary bladder, depending on body composition and degree of filling typically has a very superficial location along the abdominal wall. High frequency linear transducers are ideal to evaluate the wall thickness and wall layering in most animals. Curvilinear, microcurved or sector probes may be necessary to evaluate the urethra and prostate due to deeper location and better access
to the pelvic inlet with a smaller footprint probe. It is important to adjust the focal zone during evaluation of the urinary bladder. For the superficially located ventral or ventrolateral (depending on patient position) bladder wall the focal zone should be moved into a superficial position whereas it should be moved further down when evaluating the far bladder wall. Since the urine in the bladder lumen is poorly sound attenuating there is fair amount of distal acoustic enhancement which can be corrected by adjusting the time gain compensation to a curvilinear shape, decreasing the amount of intensification of the deeper echoes. The bladder
can be examined with the patient in lateral or dorsal position, keeping in mind that bladder position relative
to midline can vary with degree of filling and presence
of gastrointestinal contents. The bladder should be examined in long axis and in transverse image planes, and care should be taken to follow the urethra as far as possible into the pelvic canal to determine if there are mural or intraluminal lesions. For a complete evaluation of the urinary bladder the regional lymph nodes,
ureters and kidneys should be examined as well. The ureterovesicular junctions are located in the caudodorsal bladder wall at the level of the trigone and are variable
in their visibility and appearance. If visible, they present as focal tissue thickening or protrusion into the urinary bladder lumen. The ureters are typically poorly visible unless dilated or thickened. Examination of the kidneys is important to determine presence of obstructive lesions, infection, nodules or masses and other lesions that
could result from or manifest in urinary bladder disease. The sublumbar lymph center including the medial and internal iliac lymph nodes is the closest draining lymph center and is closely associated with the bifurcation of the aorta and caudal vena cava.
Common artifacts
As mentioned above, distal acoustic enhancement is
a common artifact associated with the urinary bladder and can easily be corrected by adjusting time gain compensation. Also common is the occurrence of “pseudosludge”. This is characterized by increased echogenicity in the far field over the urinary bladder with a curvilinear surface and could be confused with real urinary sediment. The underlying cause is a combination of slice thickness artifact where a portion of the curved echogenic urinary bladder wall is averaged with the hypoechoic bladder lumen resulting in an intermediate echogenicity along the bladder wall. The second component is called side lobe artifact. This artifact is caused by sound beams originating from the transducer that travel in a slightly different direction from the main beam. If reflected back to the transducer by a highly reflective surface such as the descending colon, some of these sound waves may return to the transducer
and result in creation of an image along the main axis of the beam again mimicking urinary bladder sediment. This artifact is not unique to the urinary bladder but
can happen anywhere in the abdomen, the difference is that these stray or side lobe echoes are visible in
the otherwise anechoic urinary bladder whereas they blend in with the abdominal contents elsewhere. Near field artifacts are unavoidable and are encountered throughout the abdomen as well. They are particularly disrupting in the urinary bladder though since the thin bladder wall is in a very superficial position and is difficult to evaluate when obscured by these artifacts. Linear transducers help with improving the near field, and as mentioned above adjustment of the focal zone, use of harmonic imaging or image compounding can help as well. A very useful artifact in the urinary bladder

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