Diagnostic investigations in urology

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 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
  • To differentiate between detrusor overactivity and stress incontinence
  • To determine neurological abnormalities of the bladder (e.g., hypotonic bladder)

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)
• Indications
  • Outlet obstruction (e.g., benign prostatic hypertrophy, urethral overactivity, urethral stricture following surgery)
  • Weak detrusor (e.g., hypotonic bladder)
  • Increased valsalva during voiding

Pressure-flow study

• Description
  • To determine the underlying mechanism of an abnormal uroflowmetry assessment
  • Measures detrusor pressure while voiding
• Indications
  • Increased valsalva during voiding
  • Weak detrusor (e.g., hypotonic bladder)
  • Outlet obstruction (e.g., benign prostatic hypertrophy, urethral overactivity, urethral stricture following surgery)

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

Postvoid residual volume

• Description
  • Measures the volume of urine that remains in the bladder after voiding
  • May be performed using straight catheterization or ultrasound of the bladder
  • A postvoid residual volume < 50 ml is normal
• Indications
  • Outlet obstruction
  • Weak detrusor

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)

References:^{[1][2][3][4][5][6][6]}

Ultrasound

• Indications
  • Renal: visualization of renal tumors, renal cysts, nephrolithiasis, hydronephrosis
  • Bladder: bladder wall thickness, bladder calculi, tumors, urinary retention
  • Prostate; : to estimate prostate volume, shape, echogenicity, and prostatic abscesses or masses
  • Scrotal and penile: to evaluate for testicular torsion, cryptorchidism, trauma, testicular tumors, varicocele, and epididymitis.

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

• Indications
  • To differentiate between renal cysts and neoplasms
  • For accurate staging of bladder and prostate cancers
  • As an alternative to contrast CT in patients who are allergic to iodine-based radiocontrast

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

• Description
  • IV administration of technetium (Tc-99m pertechnetate/gamma emitter) and measurement of its distribution in the body with a gamma camera
  • Static renal scintigraphy
    • Procedure
      • Tc-99m DMSA is injected.
      • Imaging is performed ∼ 3 hours after injection, when the dye has reached the kidneys for renal clearance.
    • Helps visualize the renal morphology (position, form, size, anomalies)
  • Dynamic renal scintigraphy (MAG3 renal scan)
    • Assesses renal clearance (compared with glomerular filtration rate) and arterial perfusion rate
    • Procedure
      • Tc-99m MAG3 (mercaptoacetyltriglycine) is injected.
      • Serial imaging from the time of injection until the end of the procedure (up to 30 min)
• Indications
  • To detect bone metastases in prostate cancer, renal scarring (usually associated with reflux), significant urinary obstruction
  • Estimation of differential renal function
  • Screening for renal artery stenosis
  • Monitoring of renal transplants

Voiding cystourethrogram

• Description:
  • 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
• Indications
  • Diagnosis of vesicoureteral reflux and urethral stricture
  • Recurrent UTIs
  • Suspected obstruction (e.g. bilateral hydronephrosis)
  • Suspected bladder trauma or rupture

Intravenous urography (excretory urogram, IV urography)

• Description
  • Contrast dye is injected intravenously.
  • Serial pelvic x-rays (taken at specific time intervals) help assess the kidneys, ureters, bladder, and urethra.
• Indication: visualization of renal excretion and the course of the ureters
• Contraindications
  • Hyperthyroidism (iodine in contrast medium can cause a thyroid storm)
  • Renal insufficiency (contrast has a direct toxic effect on renal tubule cells and vasoconstrictive effects leading to impaired perfusion of the renal medulla)
  • Contrast medium allergy
  • Multiple myeloma

CT urography

• 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)

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)

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

References:^{[1][7][8][9][10][11]}

• Description
  • An endoscopic technique used to visualize the urethra, urinary bladder, and ureteral orifices
  • A flexible or rigid cystoscope is inserted into the urethra using an electrolyte-containing irrigation fluid or sterile water.
• Indications
  • Recurrent urinary tract infections
  • Hematuria
  • Urinary incontinence or overactive bladder
  • Suspected interstitial cystitis; , endometriosis, gynecological malignancies
  • Urinary tract injuries (traumatic or iatrogenic)
  • Urinary obstruction
  • Injection of therapeutic drugs (e.g., botulinum toxin for urinary incontinence)
• Complications
  • Postprocedural hematuria and/or dysuria
  • Urinary tract infection
  • Iatrogenic injury to the urethra or bladder

References:^[12]