• Clinical science

Diagnostic investigations in urology

Abstract

Patients with urological symptoms are diagnosed based on clinical features and routine diagnostics. Urodynamic tests help to evaluate functional and anatomical abnormalities of the lower urinary tract. The most common tests are cystometry, uroflowmetry, urethral pressure profile, and leak point pressure. Imaging may be used in combination to diagnose underlying pathologies and is often used to assess for anatomical obstructions or abnormalities (e.g., urinary obstructions caused by kidney stones, renal masses).

For more on renal function tests, urinalysis, urine dipstick, and renal biopsy, see diagnostic evaluation of the kidney and urinary tract.
For more on urine culture, see “Laboratory tests” under diagnostics in urinary tract infections.

Urodynamic studies

Urodynamic studies use the characteristics of urinary flow (pressure and flow rate at various points during micturition and at rest) to evaluate the functional and anatomical abnormalities of the lower urinary tract.

Cystometry

  • Description
    • Assesses bladder pressure during filling
    • Determines detrusor and bladder function (activity, sensation, capacity, and compliance)
    • The bladder is filled with water through a urethral catheter at a steady rate → the vesical pressure is measured through this urethral catheter, while the intraabdominal pressure is measured via a vaginal or rectal pressure catheter → detrusor pressure = the difference in pressure between these two catheters
  • Indications

Uroflowmetry

  • Description
    • Measures the volume of urine voided over time
    • The patient is asked to void into a funnel that measures the volume and rate of urine flow.
      • Normal: a continuous, single bell-shaped curve with urine volume > 200 mL (over 15–30 seconds) and at a rate > 15 mL/sec
      • Abnormal: an abnormal curve or urine volume at a rate < 15 mL/sec (a urine volume < 150 mL increases the risk of an inaccurate assessment)
        • Bell-shaped with a flattened curve → indicates obstruction (most likely due to benign prostatic hypertrophy)
        • Rapid rise followed by a plateau → indicates obstruction (most likely due to urethral stricture)
        • Irregular, undulating, wavy → indicates bladder sphincter dyssynergia
  • Indications

Pressure-flow study

  • Description
    • To determine the underlying mechanism of an abnormal uroflowmetry assessment
    • Measures detrusor pressure while voiding
  • Indications

Urethral pressure profile

  • Description
    • Assesses intrinsic sphincter function
    • Measures the intraluminal urethral integrity at different pressures (filling and voiding pressures are measured under different types of provocation, e.g., Valsalva maneuver, coughing, etc.)
    • A specialized urethral catheter, mounted with microtransducers, is withdrawn at a slow and steady rate from the bladder until it exits the external urethral meatus.
  • Indications
    • Sphincter dysfunction (e.g., due to multiparity, low estrogen levels)
    • Urinary stress incontinence

Leak point pressure

  • Description
    • Assesses intrinsic sphincter function (but during dynamic testing, unlike urethral pressure profile testing)
    • Determines the intravesical pressure required to produce urine leakage in the presence of increased abdominal pressure (i.e., during valsalva maneuver) and the absence of detrusor contraction
    • May be performed during cystometry
  • Indications
    • Sphincter dysfunction (e.g., due to multiparity, low estrogen levels)
    • Urinary stress incontinence

Post-void residual volume

Electromyelogram (EMG)

  • May be performed during cystometry
  • Studies the electrical potentials of depolarized muscle, specifically the neural pathways involved in micturition (by evaluating the segment of the sacral spinal cord involved)
  • Electrodes or a concentric needle are inserted into the urethral sphincter.
  • Indication: to determine neurological abnormalities of the bladder (e.g., hypotonic bladder)

Nerve conduction studies

  • Assess nerve conduction rates after stimulation of specific nerves involved with micturition
  • Indication: to determine neurological abnormalities of the bladder (e.g., hypotonic bladder)

References:[1][2][3][4]

Imaging techniques

Ultrasound

The bladder should be full to visualize pelvic structures!

CT

  • Indications
    • Investigation of choice to detect urinary calculi and renal masses
    • Visualization of the urothelium in suspected malignancies and cases of obstruction
    • CT angiography helps evaluate acute pelvic trauma and tumor blood supply, as well as diagnose renal vascular malformations.

MRI

  • Indications

Renal scintigraphy (also known as renal radionuclide scan, radioisotope renography)

Voiding cystourethrogram

Intravenous urography (excretory urogram, IV urography)

Retrograde urethrogram

  • Description
    • Contrast dye is injected into the bladder via the urethra.
    • Serial x-rays are performed to visualize the integrity of the urethra up to the bladder.
  • Indication: suspected anatomical and functional lesions of the urethra (e.g., urethral stricture, injuries)

References:[1][2][3]

Cystoscopy

References:[1][2][3]

  • 1. Hanson KA. Diagnostic Tests and Tools in the Evaluation of Urologic Disease: Part II. Urol Nurs. 2003; 23(6). url: http://www.medscape.com/viewarticle/467796_1.
  • 2. Whitfield HN. Urological evaluation. BMJ. 2006; 333(7565): pp. 432–435. doi: 10.1136/bmj.333.7565.432.
  • 3. Warrell DA, Cox TM, Firth JD. Oxford Textbook of Medicine. Oxford University Press; 2015.
  • 4. DeRidder PA, Dauben RD. Electromyelography, a useful test for evaluation of the sacral spinal cord. J Urol. 1981; 125(6): pp. 835–838. pmid: 7195434.
  • Manski D, et al. Urologie Online Lehrbuch. http://www.urologielehrbuch.de.
  • Hacking C, Shetty A. Voiding cystourethrography. https://radiopaedia.org/articles/voiding-cystourethrography-1. Updated January 16, 2017. Accessed January 16, 2017.
  • Chernecky CC, Berger BJ. Laboratory Tests and Diagnostic Procedures. Elsevier Health Sciences; 2012.
  • Nitti VW. Pressure flow urodynamic studies: The gold standard for diagnosing bladder outlet obstruction. Rev Urol. 2005; 7(Suppl 6): pp. S14–S21. url: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1477621/.
  • Chapple CR, MacDiarmid SA, Patel A. Urodynamics Made Easy. Elsevier Health Sciences; 2012.
  • Adam A, Dixon AK, Gillard JH, Schaefer-Prokop C, Grainger RG, Allison DJ. Grainger & Allison's Diagnostic Radiology E-Book. Elsevier Health Sciences; 2014.
  • Weerakkody Y, Shetty A et al. Intravenous Urography. https://radiopaedia.org/articles/intravenous-urography. Updated January 1, 2017. Accessed November 19, 2017.
  • Morgan MA, Shetty A et al. Urethrography. https://radiopaedia.org/articles/urethrography. Updated January 1, 2017. Accessed November 19, 2017.
  • Reynard J, Brewster S, Biers S. Oxford Handbook of Urology. OUP Oxford; 2013.
last updated 11/08/2018
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