Diagnostic investigations and procedures in urology

Patients with urological symptoms are diagnosed using clinical evaluation and diagnostic studies. Urodynamic studies are used to evaluate functional and anatomical abnormalities of the lower urinary tract and commonly include cystometry, uroflowmetry, urethral pressure profile, and leak point pressure. Imaging studies (e.g., ultrasound, CT, MRI) may be used to evaluate for urinary tract abnormalities based on clinical suspicion. Cystoscopy provides direct visualization of the urethra, bladder, and urethral orifices. Urinary drainage procedures include transurethral catheterization, suprapubic catheterization, percutaneous nephrostomy, and ureteral stenting.

See also “Diagnostic evaluation of the kidney and urinary tract.”

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)
• Indications
  • To differentiate between detrusor overactivity and stress incontinence
  • To determine neurological abnormalities of the bladder (e.g., hypotonic bladder)
• Procedure
  • 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
  • The detrusor pressure is the difference in pressure between these two catheters

Uroflowmetry

• Description: : an objective, noninvasive test used in the evaluation of patients with suspected bladder outlet obstruction
• Indications
  • Outlet obstruction (e.g., benign prostatic hypertrophy, urethral overactivity, urethral stricture following surgery)
  • Weak detrusor (e.g., hypotonic bladder)
  • Increased Valsalva during voiding
• Procedure
  • Patient is asked to void into a funnel that measures the volume and rate of urine flow.
  • Measures the volume of urine voided over time
• Interpretation
  • Normal: a continuous, single bell-shaped curve with urine volume > 200 mL (over 15–30 seconds) and at a rate > 15 mL per second
  • Abnormal: an abnormal curve or urine volume at a rate < 15 mL per second
    • 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

Pressure-flow study ^[1]

• 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)
• Indications
  • Sphincter dysfunction (e.g., due to multiparity, low estrogen levels)
  • Urinary stress incontinence
• Procedure: 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

• 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 (PVR)

• Description: measures the volume of urine that remains in the bladder after voiding
• Indications
  • Bladder outlet obstruction
  • Weak detrusor
• Procedure: : may be performed using straight catheterization or ultrasound of the bladder
• Interpretation: PVR < 100 mL is usually considered normal. ^[2][3]

EMG

• Description: a procedure that studies the electrical potentials of depolarized muscle, specifically the neural pathways involved in micturition (by evaluating the segment of the sacral spinal cord involved)
• Indication: to determine neurological abnormalities of the bladder (e.g., hypotonic bladder)
• Procedure: Electrodes or a concentric needle are inserted into the urethral sphincter.

References:^[4][5][6][6]

Ultrasound

• Indications
  • Renal: visualization of renal tumors, renal cysts, nephrolithiasis, and hydronephrosis (see also “Renal POCUS”)
  • Bladder: to evaluate for bladder wall thickening, bladder calculi, tumors, urinary retention (see also “Bladder POCUS”)
  • Prostate; : to estimate prostate volume, shape, echogenicity, and evaluate for 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.

MRI

• 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

• Description: : a diagnostic procedure in which radioisotopes are used to assess the anatomy and function of the kidneys
• Indications
  • Assessment for renal scarring (usually caused by reflux) and significant urinary obstruction
  • Estimation of differential renal function
  • Screening for renal artery stenosis
  • Monitoring of renal transplants
• Procedure: IV administration of technetium (Tc-99m pertechnetate/gamma emitter) and measurement of its distribution in the body with a gamma camera
  • Static renal scintigraphy: a diagnostic test in which a radiotracer that is retained by the renal cortex is used to assess renal function as well as the degree of structural damage to the renal cortex
    • Injection of Tc-99m DMSA (Tc-99m dimercaptosuccinic acid; an injectable radioactive gamma-emitter dye that rapidly accumulates in the renal parenchyma and very small amounts are eliminated from the kidney)
    • Imaging is performed ∼ 3 hours after injection, when the dye has reached the kidneys for renal clearance.
  • Dynamic renal scintigraphy: a diagnostic test in which a radiotracer that is excreted by the kidney is used to assess renal perfusion as well as urine flow in the urinary tract
    • Injection of Tc-99m MAG3 (mercaptoacetyltriglycine; a form of injectable technetium that rapidly accumulates in the renal parenchyma and is cleared almost exclusively by tubular excretion)
    • Serial imaging from the time of injection until the end of the procedure (up to 30 minutes)

Voiding cystourethrography ^[7][8]

• Description: a diagnostic procedure used to determine the presence and severity of vesicoureteral reflux and detect anatomical abnormalities
• Indications ^[9]
  • Abnormal ultrasound findings, e.g.:
    • Vesicoureteral reflux
    • Urinary tract obstruction (e.g., hydronephrosis, hydroureter)
  • Recurrent UTIs
  • Suspected urethral stricture
  • Trauma
• Contraindications
  • UTI
  • Contrast allergy
• Procedure
  • Radiocontrast dye is injected into the bladder using a urinary catheter (retrograde filling of the bladder with contrast).
  • Fluoroscopy is performed during voiding.
  • Increased bladder pressure during voiding may reveal previously undetected reflux. ^[10]
• Complication: UTI

Intravenous urography ^[11]

• Description: a diagnostic procedure that involves intravenous contrast agent and x-rays to provide images of the genitourinary tract
• Indication: visualization of renal excretion and the course of the ureters
• Procedure
  • Contrast dye is injected intravenously.
  • Serial pelvic x-rays (taken at specific time intervals) help assess the kidneys, ureters, bladder, and urethra.
• Contraindications
  • Hyperthyroidism
  • Renal insufficiency
  • Contrast medium allergy
  • Multiple myeloma

CT urography

• Description: an imaging study that uses CT with intravenous contrast 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)
• Procedure: CT with contrast dye injected intravenously

Retrograde urethrography ^[12]

• Description: : a diagnostic test in which contrast agent is injected into the urethra to evaluate for urethral injuries and disorders via x-ray
• Indications: suspected anatomical and/or functional urethral lesions, e.g.:
  • Urethral strictures
  • Urethral injuries
  • Urethral fistulas
• Contraindications
  • UTI
  • Contrast allergy
• Procedure
  1. Insert a small catheter (e.g., 8 Fr Foley catheter) into the urethra.
  2. Slowly inflate the balloon to enable a snug fit.
  3. Slowly inject contrast material into the urethra.
  4. Obtain x-rays.
• Findings
  • Intact urethra: no urethral extravasation with contrast in bladder
  • Partial urethral disruption: urethral extravasation with contrast in bladder
  • Complete urethral disruption: urethral extravasation and no contrast in bladder
• Complications: UTI

Retrograde cystography ^[12][13]

• Description: an imaging modality in which contrast is injected into the bladder via a catheter to inspect bladder anatomy and assess for abnormalities via x-ray
• Indications: suspected bladder injury, e.g., traumatic or iatrogenic injury
• Contraindications: suspected urethral injury
• Procedure
  • A transurethral catheter is inserted.
  • Contrast is injected into the bladder.
  • A series of x-rays, including postvoid images, are obtained.
• Findings: contrast extravasation in bladder injuries

CT retrograde cystography

• Description: imaging modality using computed tomography to visualize the bladder after retrograde filling with contrast agent
• Indication: evaluation of the bladder for postoperative leakage or rupture following trauma
• Procedure: CT after contrast dye is injected into the bladder via the urethra

Retrograde pyelography

• Description: a diagnostic procedure in which x-rays are taken as a water-soluble contrast agent is injected into the ureter via cystoscopy
• Indication
  • Contraindications to IV/CT urography
  • Secondary study to confirm or further characterize findings
• Procedure
  • Contrast medium is injected into the ureter using a catheter.
  • Serial x-rays of areas of interest are taken.

• Description: an endoscopic procedure in which a thin tube with a light and a camera is inserted through the urethra into the bladder, allowing for visualization of the urethra, bladder, and ureteral orifice
• Indications
  • Hematuria
  • Suspected interstitial cystitis, gynecological malignancies, endometriosis
  • Recurrent urinary tract infections
  • Urinary incontinence or overactive bladder
  • Urinary tract injuries (traumatic or iatrogenic)
  • Urinary obstruction
  • Injection of therapeutic drugs (e.g., botulinum toxin for urinary incontinence)
• Procedure: A flexible or rigid cystoscope is inserted into the urethra using an electrolyte-containing irrigation fluid or sterile water.
• Complications
  • Postprocedural hematuria and/or dysuria
  • Urinary tract infection
  • Iatrogenic injury to the urethra or bladder

Bladder catheterization ^[12]

• Description: placement of a catheter into the bladder via the urethra or percutaneously through the suprapubic abdominal wall
• Indications
  • Sterile urine sample collection
  • Measurement of urinary output and/or PVR
  • Bladder drainage, e.g., for urinary retention; , urinary obstruction, patients with impaired mobility
  • Access for intravesical therapy, e.g., bladder irrigation, chemotherapy
  • Urological studies, e.g., cystography
• Types of bladder catheterization
  • Transurethral catheterization (e.g., with a Foley catheter)
  • Suprapubic catheterization

Urethral injury (known or suspected) and acute bacterial prostatitis are relative contraindications for transurethral catheterization.

Suprapubic catheterization ^[12]

• Description: : a surgical procedure in which a catheter is inserted into the bladder through an incision in the abdominal wall above the pubic symphysis
• Techniques
  • Open cystostomy
  • Percutaneous cystostomy
• Indications
  • Unsuccessful transurethral catheterization, e.g., secondary to urethral strictures, benign prostate hyperplasia (BPH)
  • Contraindications for transurethral catheterization, e.g., suspected urethral injury, recent urethral surgery, acute bacterial prostatitis
  • Need for long-term indwelling bladder catheter
• Contraindications vary by technique and may include:
  • Empty or abnormally positioned bladder
  • History of bladder irradiation or surgery
  • Bladder cancer
  • Overlying cellulitis
  • Coagulopathy
• Advantages
  • More comfortable for the patient and easier to replace than transurethral catheters
  • Minimizes risk of urethral trauma and stricture formation
  • Reduces incidence of catheter-associated bacteriuria
• Complications
  • Intraprocedural: injury to nearby structures, e.g., bowel perforation, vascular injury
  • Postprocedural
    • Infection, e.g., UTI, wound infection
    • Catheter dislodgement resulting in loss of cystostomy tract

Ureteral stenting ^[14][15][16]

• Description: a urological procedure that involves insertion of a thin, hollow tube into the ureter to enable drainage of fluid from the renal pelvis into the bladder
• Indications ^[16]
  • Upper urinary tract obstruction (e.g., nephrolithiasis, tumors, pregnancy)
  • Ureteral injuries or fistulas with urinary leakage
  • Prevention of ureteral obstruction from passing stone fragments after lithotripsy
• Contraindications ^[16]
  • Urinary bladder outlet obstruction (e.g., due to BPH) or urinary tract infection
  • Uncorrectable coagulopathy
• Procedure
  • Insertion of a double-J stent into the ureter
  • Cystoscopy-guided transurethral (retrograde) placement or via percutaneous puncture of the renal pelvis under fluoroscopic guidance (antegrade)
  • Stent should be exchanged every 3–6 months
• Complications
  • Ureteral injury
  • UTI
  • Stent encrustation or displacement

Percutaneous nephrostomy ^[17][18]

• Description: a urological procedure that involves the insertion of a pigtail catheter (nephrostomy tube) into the dilated renal pelvis
• Indications ^[18]
  • Upper urinary tract obstruction (if ureteral stent cannot be placed)
  • Ureteral injuries or fistulas
  • Access for urological procedures (e.g., percutaneous nephrolithotomy, delivery of chemotherapeutic agents)
  • Antegrade pyelography
• Contraindications: uncorrectable coagulopathy ^[18]
• Procedure
  • Insertion of a catheter into the renal pelvis under ultrasound guidance using the Seldinger technique
  • Consider preoperative antibiotic prophylaxis.
  • Catheter should be exchanged every 3 months.
• Complications
  • Damage of adjacent organs
    • Vascular injury and hemorrhage
    • Bowel perforation
    • Pleural complications (e.g., pneumothorax, hemothorax)
  • Urosepsis (especially in patients with pyonephrosis)
  • Catheter encrustation or displacement