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).
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.
- 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
- 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.
Urethral pressure profile
- 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- A specialized urethral catheter, mounted with microtransducers, is withdrawn at a slow and steady rate from the bladder until it exits the external urethral meatus.
Leak point pressure
- 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 ) and the absence of detrusor contraction
- May be performed during cystometry
Postvoid residual volume
- Outlet obstruction
- Weak detrusor
- 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)
The bladder should be full to visualize pelvic structures!
Renal scintigraphy (also known as renal radionuclide scan, radioisotope renography)
- IV administration of technetium (Tc-99m pertechnetate/gamma emitter) and measurement of its distribution in the body with a gamma camera
- Static renal scintigraphy
- Dynamic renal scintigraphy (MAG3 renal scan)
- Radiocontrast dye is injected into the bladder by means of a urinary catheter (retrograde contrast filling of the bladder)
- Serial x-rays are performed during voiding.
- Allows the ureter and urethra to be visualized
- During voiding pressure increases in the bladder and this may reveal previously hidden reflux
Intravenous urography (excretory urogram, IV urography)
- Indication: visualization of renal excretion and the course of the ureters
- Description: a CT with contrast dye injected inravenously to assess the anatomy and, to a certain degree, function of the urinary collecting system, renal calyces, ureters, and bladder.
- Indications: a first-line imaging test to assess for genitourinary abnormalities (e.g., malignancy, stricture)
- Indication: suspected anatomical and functional lesions of the urethra (e.g., urethral stricture, injuries)
Retrograde CT cystography
- Description: computed tomography to visualize the bladder after contrast dye is injected into the bladder via the urethra
- Indication: evaluation of the bladder for postoperative leakage or rupture following trauma