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Bladder Ultrasound and Measurement of Postvoid Residual Volume

Ultrasonography of the bladder is a frequent examination in urological patients. Indications include (but are not limited to): abdominal pain, flank pain, hematuria, proteinuria, lower urinary tract symptoms, abdominal trauma, (recurrent or febrile) urinary tract infections, increased retention parameters, nephrolithiasis, in patients with kidney transplantation, planning and performing surgical procedures of the prostate or bladder, urinary incontinence, and dyspareunia.

Examination Technique

The transducer used for bladder ultrasound is a sector or curved array probe with 3.5–5 MHz. The examination requires a filled bladder. The bladder is systematically examined in the longitudinal (sagittal) and transverse planes. At the end of the investigation, the postvoid residual (PVR) urine volume is measured if the patient reports lower urinary tract symptoms.

Normal Findings

The urinary bladder is an echo-free filled hollow organ, but often ultrasound artifacts mimic echogenic structures in the urinary bladder (reverberations or side lobe artifacts). The filled bladder has an echogenic wall that is sharply defined without wrinkles or bulges. In the area of the trigonum, the ureteral orifices and the bladder neck can be recognized. Depending on the size of the prostate, the middle lobe protrudes into the urinary bladder and may be misinterpreted as a bladder tumor.

Bladder wall thickness:

The bladder wall should be measured with a filled bladder (greater than 50% of the capacity) on the anterior wall of the bladder. In adults, 7 mm is the upper limit for bladder wall thickness. In children, values above 2.5 mm are pathological and suspicious for subvesical obstruction.

Ultrasonography of the bladder: measurement of postvoid residual volume using the formula: Length × Width × Height × 0.5.

Measurement of Postvoid residual volume (PVR):

After micturition, the bladder's length, width, and height [in cm] are recorded in sagittal and horizontal planes [fig. postvoid residual volume]. The postvoid residual volume is calculated using the formula:

Postvoid residual volume (PVR) = length × width × height × 0.5

Various factors ranging from 0.5–0.7 are found in the literature. Depending on the bladder shape, considerable inaccuracy is possible. Usually, there is no residual urine. PVR volumes over 100–ml are considered significant in adults. In children, a PVR volume exceeding 10% of the urinary bladder capacity is pathological (Riedmiller et al., 2001). Please see the following table for the differential diagnosis of PVR.

Transabdominal Ultrasonography of the Prostate

Transabdominal imaging of prostate is possible through the filled bladder. After determining the length, width, and height in two planes, the prostate volume is calculated using the formula:

Prostate volume = Length × Width × Height × 0.5.

The transabdominal measurement method offers advantages in huge prostate glands due to the larger field of vision [fig. transabdominal prostate ultrasound]. In addition, transabdominal ultrasonography of the prostate quickly identifies enlarged median lobes or prostatic cysts.

Measurement of prostate size with transabdominal sonography: imaging of the prostate in the sagittal and transversal plane, measurement of length, width, and height. The prostate volume is calculated using the formula prostate volume = length × width × height × 0.5. In this case, the prostate volume was 229 ml.

References

Singer u.a. 2006 SINGER, Eric A. ; GOLIJANIN, Dragan J. ; DAVIS, Robert S. ; DOGRA, Vikram: What’s new in urologic ultrasound?
In: Urol Clin North Am
33 (2006), Aug, Nr. 3, S. 279–286

  Deutsche Version: Sonographie der Harnblase und Restharnmessung