Bladder Scanning

A low-frequency 3.5- to 5-mHZ transducer should be placed suprapubically, and the bladder should be scanned in the longitudinal and transverse plane.

Anatomy

Within the bladder, the ureteral and urethral orifices demarcate the trigone and the uretheral orifice denotes the bladder neck. The neck and trigone remain constant in shape and position, but the remainder of the bladder wall changes shape and position depending on the volume of urine within it. The bladder wall is smooth with uniform thickness. While in the transverse plane (indicator to the patient’s right), sweep through from the superior dome to the base of the bladder (Fig. 10, 11).

Infection

Cystitis is commonly found in women when the urethra is colonized by rectal flora such as E. coli. It also occurs in men due to obstructive pathology or prostatitis. Patients are found to have irritable bladder and hematuria. Some noted findings in the bladder are mucosal edema and decreased bladder capacity.

On sonography, the most typical finding is diffuse bladder wall thickening (Fig. 12, 13). Occasional pseudopolyps may form if cystitis is focal.⁴

Other types of cystitis that have sonographic findings include emphysematous (air within the bladder wall) and chronic cystitis, which leads to Brunn’s nests and cyst formation and possibly eventual adenocarcinoma, all of which cause thickening of the bladder wall.

Other causes of thickened bladder wall on ultrasound are many, and it is difficult if not impossible to differentiate among them based solely on imaging.

Obstruction

Obstruction of the bladder most commonly occurs from bladder calculi,

either from migration of stones from the ureters or from urinary stasis (Fig. 14A, 14B). Urinary stasis is often linked to outlet obstruction, cystocele, neurogenic bladder, prostate enlargement, foreign body, or medications. Ureteral obstruction from a stone or other pathology can be noted by utilizing gray scale or color Doppler evaluation to identify ureteral jets (Fig. 15). On sonography, a mobile, echogenic focus with distal acoustic shadowing will be seen.⁴

Color Doppler Evaluation

Transabdominal evaluation of the ureteral orifices for jets is helpful to assess for obstruction. By using the color Doppler feature over the bladder, low-level echoes can be seen of urine entering the bladder from the ureteral orifice. The jet frequency may range from one per minute to continuous flow; the appearance of jet flow should be symmetrical in a healthy patient. This confirms renal function and ureteral patency. Patients with high-grade obstruction will have asymmetric jets. An accurate evaluation of jets requires a minimum of 10 minutes.⁵ In an emergency setting, the cost of this time must be taken into account.

Retention

Urinary retention has many causes. The use of bladder ultrasound in an emergency setting can assist in diagnosing urinary retention and aid in estimation of amount of urine in the bladder.

What Is the Bladder Volume?

In a study by Chan, bladder volume estimations were calculated using ultrasound with catheterized bladder volumes when urinary retention was suspected clinically; the correlation of the two measurements was highly significant, which supports using ultrasound in calculating bladder volume.⁶ Estimation of bladder volume can be obtained by using the automated volume calculations on your machine or by hand. A common formula to use is (0.75 × width × length × height) (Fig. 16A, 16B).

Conclusion

Bedside ultrasound of the bladder is useful in detecting possible infection, obstruction, and urinary retention. It can also be used in detecting ureteral jets for ureteral patency and estimating bladder volume.