Bladder and reproductive ultrasonography: the good the bad and the really ugly (Proceedings)
Clipping the hair and applying alcohol and ultrasound gel is important for maximizing image quality. Ultrasound of the bladder should be performed with the bladder distended; therefore, the patient should not urinate prior to the exam. If the bladder is small and disease is suspected waiting until it fills or filling the bladder with isotonic saline is recommended. The bladder in dogs and cats is easily identified in the caudal abdomen with the animal in dorsal recumbency (lateral recumbency can also be used). The standing position can also be used to try to determine whether a structure in the bladder is gravity dependent. Occasionally a small, intrapelvic bladder can be difficult to locate. A transducer with a small footprint may be necessary for intrapelvic imaging, while a linear or curvilinear can be used for most animals. Generally a 5-10 MHz transducer is adequate for most dogs. Higher frequency may be used for cats and small dogs for the best image resolution. Scanning the bladder completely in the longitudinal and transverse plane is important so lesions are not missed.
Ultrasound of the normal bladderThe size of the bladder is highly variable. The bladder wall thickness will be highly variable depending on degree of distention. In dogs the thickness of the bladder wall increases with body weight. In a cat the wall thickness is around 1.5 mm. The ureters are not seen unless abnormal, but occasionally the ureteral papilla is seen as a focal thickening of the wall in the trigone region. At the trigone occasionally ureteral jets can be seen as an intermittent burst of hyperechoic speckles. This only occurs if there is a difference between the specific gravity of the urine within the bladder and the ureter. Urine is anechoic, but may have variable amounts of echoes even in the normal animal. The proximal urethra may be visible dependent on the positioning within the pelvic canal. In the male dog the penile urethra can be seen via a perineal and preputial window.
Ultrasound of bladder abnormalities
Calculi are variable in size and shape, but should be hyperechoic with distal acoustic shadowing. Calculi are gravity dependent; therefore, should move around with positioning of the animal (which is sometimes helpful in distinguishing calculi from wall mineralization). Urethral calculi can be seen depending on their location (if US is accessible to the area). Dilation of the urethra is consistent with obstruction (calculi, neoplasia, stricture, inflammation, etc.).
Crystals can be seen as hyperechoic echoes within the lumen that swirl when the bladder is agitated and often settle to the gravity dependent portion.
Transitional cell carcinoma is the most common bladder and urethral neoplasia. Neoplasia results in a thickening of the wall, most commonly in the trigone region, but it can occur anywhere. Neoplasia generally has a broad-based attachment to the wall with a very irregular mucosal margin. Echogenicity of a mass is highly variable. Mineralization, hyperechoic with distal acoustic shadowing, can occur within the mass. Color Doppler will show blood flow within the mass. If the mass is at the ureteral papilla then obstruction resulting in hydroureter and hydronephrosis can be seen. Masses can also extend into the urethra. The medial iliac lymph nodes should always be evaluated to look for extension of disease. Abdominal radiographs are also indicated to assess for changes in the caudal lumbar vertebrae.
Cystitis causes irregular thickening of the bladder wall that is commonly most severe at the cranioventral aspect. Polypoid cystitis, which is much less common, is seen as hyperechoic, pedunculated masses that project into the lumen.
Emphysematous cystitis is defined as gas within the bladder wall. The gas will be variable amounts of hyperechoic interfaces with distal reverberation. When trying to decide if gas is within the bladder wall or free within the lumen repositioning the animal is helpful. Luminal gas should redistribute to the non-dependent portion of the bladder when repositioned.
Intraluminal blood clots are sometimes seen and are most often hyperechoic, mobile structures. If adhered to the bladder wall these can sometimes be mistaken for neoplasia. Color Doppler can help in the evaluation, as blood clots will not have blood flow. Mural bleeding can also cause thickening of the wall.
Congenital anomalies such as ectopic ureters, urachal diverticuli, and ureteroceles are sometimes seen. Ectopic ureters are most easily visualized if they are dilated and can be followed beyond the trigone region. Ureteroceles are cystic dilations of the ureter within the bladder. Urachal diverticuli result in a triangular, convex, out-pouching of the bladder at the apex.
Tears in the bladder wall secondary to trauma are difficult to visualize with ultrasound. Most commonly a diagnosis of rupture is made either by sampling abdominal effusion or by positive contrast cystography.
The colon can sometimes indent the dorsal bladder wall and be mistaken for a calculus. Changing the transducer orientation from the transverse to the longitudinal scan plane should clarify this artifact.