Ultrasound bladder scanner presents falsely elevated postvoid residual volumes

Discussion

Portable ultrasound bladder scanning is frequently done in elderly patients; ultrasound bladder scans assess urinary retention and are part of the workup in the assessment of urinary incontinence. In all hospitals, and in some clinics, bladder scanning is routinely used to assess urinary retention and incontinence because it is noninvasive and there is no risk of injury or discomfort to the patient. Bladder emptying is assessed by determining the presence of residual urine in the bladder immediately after voiding.

There are 2 methods for estimating PVR urine volume: urethral catheterization and bladder ultrasound. In-and-out catheterization can be done after asking the patient to void. A PVR volume of less than 50 mL is considered adequate bladder emptying; in the elderly, between 50 and 100 mL is considered normal.1 In general, a PVR volume greater than 200 mL is considered abnormal and could be due to incomplete bladder emptying or bladder outlet obstruction. A PVR volume greater than 400 mL is considered to be high.

In the clinical setting, when the patient has a high PVR volume, the nurse will attempt to provide relief by inserting an in-and-out catheter. A high PVR volume recording by bladder scan should correlate with the in-and-out catheterization done in clinical practice. In the case of our 83-year-old patient, the high PVR volume seen on bladder scan was owing to the presence of pelvic and kidney cysts and not to urinary retention. There are few case reports that have discussed cystic and pelvic pathology presenting as falsely elevated PVR urine when measured by portable bladder scanner.2–4

Understanding the results of a bladder ultrasound requires special skills on the part of the performing technologist. A patient’s characteristics are also a factor to successful interpretation of the ultrasound. Sonographic images are limited somewhat by the patient’s body habitus, as the modality requires sound waves to travel through the body in order to create an image. Obese patients generally produce lower-quality images. Simple cysts are predominantly echo free and the echogenicity looks similar to water. The advantage of the bladder ultrasound scanner is that it is both the least expensive of all cross-section imaging modalities and portable, as it can be used at the bedside; its disadvantage, however, is that it is operator dependent.