Smiths General Urology, Seventeenth Edition (LANGE Clinical Medicine)

Authors: Macfarlane, Michael T.

Title: Urology, 4th Edition

Copyright 2006 Lippincott Williams & Wilkins

> Table of Contents > Part Two - Selected Topics > Chapter 36 - Diagnostic Techniques

Chapter 36

Diagnostic Techniques

History and Physical Examination

The history is the foundation of all diagnosis and should be performed in a systematic and orderly fashion to avoid errors of omission. This cannot be overemphasized. History taking should be tailored to the patient's chief complaint and should include a review of major signs and symptoms of genitourinary disease, as well as a general review of systems.

Historical Data

• Voiding problems:

  • Storage (irritative) symptoms (frequency, urgency, nocturia)

  • Voiding (obstructive) symptoms (hesitancy; straining; dysuria; slow, weak, or intermittent stream; terminal dribbling; retention); incontinence (get details)

• Urethral discharge (onset, color, consistency, last sexual contact)

• Hematuria (when started, how much, how often, color)

• Bloody ejaculation

• Fever, chills, flank pain

• Pyuria, pneumaturia

• Sex-related problems

• History of genitourinary problems kidney, bladder, prostate, infections, stones, or difficulty urinating

• General medical history with review of systems (cardiorespiratory, hypertension, diabetes, neurologic, gastrointestinal, and careful review of medications and allergies)

Physical Examination

• Abdomen pain or tenderness, palpable masses, auscultation for bruits, palpate for bladder

• Penis discharge, foreskin, palpable plaques, meatus

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• Testes size, tenderness, palpable masses, hydrocele, spermatocele, varicocele, transillumination, beading of vas

• Vaginal examination discharges, cystocele, rectocele, enterocele, prolapse, bimanual palpation

• Rectal examination sphincter tone, prostate (size, consistency, nodules, mobility, tenderness)

• Skin lesions morphology and distribution

Urinalysis

Urinalysis is the single most important screening test available to the urologist.

Urine Collection

Proper urine collection is necessary for accurate interpretation of urinalysis or culture. All tests must be performed on a freshly voided specimen. Urine that has been left standing becomes alkaline, with lysis of red blood cells, disintegration of casts, formation of crystals, and proliferation of bacteria.

Male Patients

A voided, midstream clean-catch urine sample is routine; however, split voided specimens are sometimes helpful in localizing the source of infection or hematuria (see Technique for Urine Specimen Localization, later).

Female Patients

A voided specimen in female patients must be obtained in the lithotomy position after proper cleansing with the assistance of a nurse. Often urethral catheterization is necessary to obtain a clean specimen.

Infants

Suprapubic needle aspiration is usually the only effective method for obtaining a noncontaminated specimen for culture.

Gross Inspection

Color and appearance should be noted. A cloudy or milky appearance can be due to the precipitation of phosphates (phosphaturia) in alkaline urine, pyuria, or, rarely, chyluria.

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Specific Gravity

Specific gravity, measured by hydrometer or refractometer, can give a good estimate of the patient's hydration, barring significant renal impairment. The normal range is 1.003 to 1.030. Glucose, protein, or intravenous contrast agents in the urine can cause a falsely elevated value.

Chemical Dipstick

The urine dipstick permits simultaneous performance of a battery of useful chemical tests in less than 2 minutes. These are screening tests, and positive results generally need confirmation by other more precise tests.

pH

pH is normally slightly acidic, except after a meal. A highly alkaline pH (>8) suggests infection with a urea-splitting organism such as Proteus.

Protein

Protein estimation by the dipstick can be a tip-off to significant disease such as glomerulopathy or cancer. Some other causes of positive protein readings include white cells, vaginal secretions, prolonged fever, and readings after excessive exercise. Persistently positive results must be confirmed by quantitative tests. Normal is less than 200 mg protein per 24-hour urine collection.

Glucose

Glucose determination by dipstick is both sensitive and specific, with most positive readings occurring in diabetics. False positives can result from large doses of aspirin, ascorbic acid (vitamin C), or cephalosporins.

Hemoglobin

Hemoglobin by dipstick is not specific for red cells; however, it is a good screening test. Positive results must be confirmed by microscopic analysis. Free hemoglobin and myoglobin will cause false-positive results. Ascorbic acid in the urine can cause false negatives. Dipsticks that have been left exposed to air will be inaccurate.

Microscopic Examination

Microscopy of the centrifuged urinary sediment is essential for every urinalysis.

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Procedure

Ten milliliters fresh urine is centrifuged at 2,000 rpm for 3 to 5 minutes. Nearly all supernatant is removed by turning the tube upside down. After returning to the upright position, the centrifuge tube is vigorously tapped to resuspend the sediment. This suspension is then tapped onto the glass slide and covered with a coverslip.

Microscopy

Microscopy is first performed at low power [100 magnification (i.e., 10 objective)], looking specifically for cells, casts, trichomonads, or crystals. Once any of these elements is observed, then high power [400 magnification (i.e., 40 objective)] should be used for specific identification. The approximate volume of urine under a coverslip at high-power magnification is 1/20,000 to 1/50,000 of a milliliter.

Red Blood Cells

Red blood cells in the urine can be differentiated into two morphologic types: epithelial and glomerular.

• Epithelial red blood cells are regular with smooth, rounded, or crenellated membranes and an even hemoglobin distribution. As few as one per high-power field (hpf) suggests urologic disease.

• Glomerular red blood cells are dysmorphic with irregular shapes and cell membranes and minimal or uneven hemoglobin distribution. More than 1,000,000 are normally excreted in the urine over a 24-hour period. The upper limit of normal is 1,000/mL urine or one for every two hpf. Two or more per hpf suggest glomerulonephritis.

White Blood Cells

Generally more than five to eight white blood cells (WBCs)/hpf is considered abnormal (pyuria) in a properly collected specimen. This finding would justify empiric therapy in a patient with symptoms of infection. Clumping suggests a more severe inflammatory response. Causes of pyuria include urinary tract infection (pyelonephritis, cystitis, prostatitis, urethritis, etc.), renal tuberculosis (sterile pyuria), and urolithiasis.

Casts

Casts are formed in the distal tubules and collecting ducts from a mucoprotein matrix of the Tamm Horsfall protein and cellular elements. They generally signify intrinsic renal disease.

• Red blood cell casts are diagnostic of glomerular bleeding (i.e., glomerulonephritis).

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• White blood cell casts are rarely seen but suggest pyelonephritis. Peroxidase staining is necessary to confirm that they are indeed polymorphonuclear leukocytes.

• Granular casts (coarse, fine, and waxy) represent sloughed renal tubular epithelial cells and indicate intrinsic renal tubular disease.

Squamous Epithelial Cells

Squamous epithelial cells in the sediment suggest contamination of the specimen (common in female patients).

Bacteria and Yeasts

As few as one bacterium per hpf in a strict, properly collected specimen indicates bacteriuria.

Urine Culture

The presumptive diagnosis of a urinary tract infection based on symptoms, and urinalysis should be confirmed by culture. Culture of a properly collected urine specimen (as described earlier) will provide identification, quantification, and specific antimicrobial sensitivities for the offending pathogen.

Bacterial Count

Infection is defined as 10³ to 10⁵ bacteria per milliliter in a properly collected specimen.

Technique for Urine Specimen Localization

Collecting the urine specimen in specific segmented samples is useful for localizing the source of a urinary tract infection or inflammatory process in male patients. Ensure that the patient has a full bladder and that the glans is properly prepared. Collect each specimen into a separate sterile container.

• VB1 collect the first 10 mL voided (urethral sample)

• VB2 collect a midstream sample after patient has voided about 200 mL (bladder sample)

• Stop voiding

• EPS massage prostate and collect drops of prostate secretions (prostatic sample)

• VB3 again have patient void immediately and collect first 10 mL (prostatic sample)

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Laboratory Tests

Serum Creatinine

Serum creatinine is a simple measurement that accurately reflects the glomerular filtration rate (GFR). Creatinine is a metabolic product of creatine phosphate in skeletal muscle. The daily production is relatively stable for a given individual and is proportional to muscle mass. Creatinine clearance occurs mainly by glomerular filtration (90%) and, to a lesser extent, by tubular secretion (10%). Thus creatinine clearance approximates the GFR, and a doubling of serum creatinine indicates a 50% reduction in GFR. As individual nephrons (of the 1,000,000/kidney) are lost to disease, the remainder hypertrophy, and the single-nephron GFR increases to maintain the overall GFR. A loss of 40% to 50% of renal mass is required before the GFR begins to decrease and creatinine increases. Note: a normal creatinine in a term infant is only 0.1 to 0.4 mg/dL because of low muscle mass.

Blood Urea Nitrogen

Urea is a metabolic product of protein catabolism that is excreted by the kidneys. Blood levels tend to reflect the GFR but can be influenced by dietary protein intake, hydration, gastrointestinal bleeding, and glucocorticoids. The BUN/creatinine ratio, which is normally 10:1, can be a useful indicator.

Conditions with Elevated BUN/Creatinine Ratio

• Dehydration

• Prerenal azotemia

• Urinary tract obstruction

• Blood in gastrointestinal tract

• Increased tissue catabolism

• Increased dietary protein intake

• Treatment with glucocorticoids

Prostatic Acid Phosphatase

Acid phosphatase is an enzyme produced by various body tissues; however, the prostate is noted to be the most concentrated source. Human prostatic acid phosphatase (PAP) is a glycoprotein of 102,000 MW. Routine enzymatic serum assays specific for PAP use thymolphthalein phosphate as substrate. Blood samples

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Causes of False-Positive Serum Prostatic Acid Phosphatase

• Serum samples taken within 24 hours of prostatic massage or transurethral resection of the prostate

• Serum samples that contain red cell hemolysis

• Serum samples from patients with fever

Prostate-Specific Antigen

Prostate-specific antigen (PSA) is a 34-kDa glycoprotein found only in the cytoplasm of prostatic epithelial cells. It is believed to function as a neutral serine protease that lyses seminal coagulum. It can be detected in the semen and serum of men with prostate tissue. It cannot be detected in women. PSA is the most useful test for prostate cancer.

PSA is specific only for prostate tissue and cannot differentiate benign from malignant prostate conditions. However, serum PSA levels above the normal range of 0 to 4 ng/mL correlate well with the presence of prostate cancer. In addition to prostate cancer, serum PSA levels can be elevated by acute prostatitis, vigorous prostatic manipulation or surgery, and markedly enlarged benign prostate glands. Serum PSA has been used extensively in prostate cancer for early detection, staging, and monitoring response to therapy. Serum PSA screening has become the best means for detecting early prostate cancer. PSA levels greater than 10 ng/mL are highly suggestive of the presence of prostate cancer, even in men with a normal digital rectal examination. The level of serum PSA tends to correlate with age and the volume of prostate cancer.

The percentage of free PSA is a useful assay for differentiating a benign from malignant source of PSA when the PSA level is between 4.0 and 10.0 ng/mL. A low percentage of free PSA (<15%) increases the likelihood that prostate cancer is present.

Alkaline Phosphatase

Alkaline phosphatase is an enzyme produced by many tissues, especially bone, liver, intestine, and placenta. Most enzyme present in normal serum is derived from metabolic activity in bone. Prostate cancer metastatic to bone causes an elevation in alkaline

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24-Hour Urine Collection

A 24-hour collection is often necessary for the workup of stone-forming patients and for an accurate assessment of renal function or proteinuria in a patient with renal disease. The most common reason for inaccuracy of values obtained from a 24-hour urine collection is incomplete collection. An incomplete collection is suggested by an inadequate amount of total creatinine in the sample because the total amount of creatinine excreted in 24 hours is dependent on muscle mass and is generally constant. The normal production of creatinine is 1.0 mg/kg per hour.

Stone Workup

A 24-hour urine collection for calcium, phosphorus, oxalate, magnesium, citrate, and uric acid is standard in the evaluation of the repeated stone former.

Creatinine Clearance

Creatinine clearance can be calculated from a 24-hour urine collection by knowing the volume of urine in milliliters per 24 hours (V), urine creatinine concentration in milligrams per milliliter (U_c), plasma creatinine concentration in milligrams per milliliter (P_c), and the following formula: (1,440 min/24 hr)

Creatinine clearance can be estimated without a 24-hour urine collection simply by knowing the patient's age, sex, weight, and serum creatinine and using the following formula.

Multiply answer by 0.85 for females.

This formula is invalid in the setting of acute renal failure because its application requires a stable serum creatinine (steady state).

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Proteinuria

Normal 24-hour protein excretion is less than 200 mg. Heavy proteinuria (>2 g/day) is suggestive of glomerular disease.

Urinary Electrolytes

Spot urinary sodium (Na) and potassium (K) measurements can be a valuable tool in diagnosing hypovolemia or prerenal azotemia. The kidney has an impressive capacity to hold onto sodium.

Human Chorionic Gonadotropin

Human chorionic gonadotropin (hCG) is a 38,000-MW double-chain glycoprotein with - and -subunits normally secreted by the syncytiotrophoblastic cells of the placenta. hCG is elevated in all patients with choriocarcinoma, in 40% to 60% of embryonal carcinomas, and in 5% to 10% of pure seminomas. Its -subunit is similar to those of luteinizing hormone, follicle-stimulating hormone, and thyroid-stimulating hormone; therefore, antibodies to the -subunit must be used for measurement. It has a metabolic half-life of 24 hours, and normal adult levels should be less than 5 mIU/mL (see Chapter 26).

-Fetoprotein

-Fetoprotein (AFP) is a 70,000-MW single-chain glycoprotein normally secreted by the fetal yolk sac. It also is produced by trophoblastic cells of embryonal carcinoma and yolk sac tumors. It is not made by pure choriocarcinoma or seminoma. Elevated AFP is found in 50% to 70% of nonseminomatous testis tumors. It has a half-life of 4 to 6 days, and normal adult levels should be less than 40 ng/mL (see Chapter 26).

Imaging Techniques

Roentgen Rays and Radiation

X-rays are electromagnetic waves of energy created when high-speed electrons hit the tungsten target of an x-ray tube. They fluoresce and expose photographic film while having great penetrating ability. An x-ray is ionizing energy owing to its ability to liberate electrons from atoms. The radiation dose is measured in

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Radiation Exposure Hazard

• A linear relationship exists between dose and carcinogenicity for doses of more than 1 Gy.

• A whole-body dose of 5 Gy can be fatal.

• Radiation dose is cumulative over a person's lifetime.

• Scatter radiation is the principal source of hazard to x-ray personnel and urologists using fluoroscopy.

• A chest radiograph has an effective dose of 0.02 mSv (1 mSv = 1 mGy for radiographs).

• An IVU is equivalent to 125 chest radiographs or close to 1 year of natural background radiation.

• An abdominal CT scan is equivalent to 500 chest radiographs or 3.3 years of natural background radiation.

• Eye exposure causes cataracts.

How to Avoid Scatter Radiation Exposure

• Use lead aprons, thyroid shields, and lead eyeglasses when in the same room as the active x-ray source.

• Maximize your distance from the x-ray source (remember the inverse-square law: exposure rate decreases with square of the distance).

• Minimize fluoroscopic times.

• Use fluoroscopic machines only with the x-ray tube under the table.

Contrast Media

Use of iodinated contrast media greatly enhances radiographic studies of the urinary tract. Sodium or methylglucamine salts of

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Adverse Effects of Iodinated Contrast Media

Vasomotor Effects

Vasomotor effects, including a sensation of warmth or flushing, nausea, vomiting, or a metallic taste, occur in up to 50% of patients and are of no clinical significance.

Anaphylactoid Reactions

Allergic reactions usually occur immediately or within 5 to 10 minutes and are characterized by hypotension and tachycardia when severe. Mild to moderate erythema and urticaria occur in up to 5% of patients and can be treated with 50 mg diphenhydramine (Benadryl) IM, if necessary. Severe urticaria or any respiratory distress, including burning or tightness of the throat, change in voice, laryngeal edema, bronchospasm, or apnea, occurs in up to 1 in 1,000 patients and should be treated with immediate epinephrine (1:1,000) 0.3 to 0.5 mg SC, followed by the usual resuscitation efforts, as needed.

Vagal Reactions

Vagal reactions are characterized by hypotension and bradycardia when severe. Early signs are confusion, apprehension, and diaphoresis. Severe bradycardia (heart rate <50 beats/min) and hypotension (systolic blood pressure <80 mm Hg) should be treated with intravenous fluids, leg elevation, and 0.5 to 1.0 mg atropine IV push to increase heart rate.

Nephrotoxicity

Nephrotoxicity is believed to be dose related and is therefore dependent on extracellular fluid volume and renal function. It usually manifests as a decrease in urine output and a modest increase in serum creatinine within 24 hours, which peaks 2 to 5 days after the procedure. Patients with type I insulin-dependent diabetes and a serum creatinine of greater than 1.5 have been noted to be at high risk of nephrotoxicity. Diabetics taking Glucophage should discontinue medication for 48 hours after IV

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Cardiovascular Toxicity

Hypertonicity and direct chemotoxic effects can result in intravascular volume expansion, hemodilution, and hypotension in patients with cardiac risk factors.

Risk Factors for Adverse Effects from Contrast Media

• Diabetes (type I, juvenile) with renal insufficiency (creatinine >1.5 mg/dL)

• Renal insufficiency (creatinine >1.5 mg/dL)

• Diabetics taking metformin (Glucophage)

• Dehydration

• History of a previous reaction to contrast media

• History of allergic diseases [e.g., hayfever, asthma, food (especially shellfish) allergies]

• Congestive heart failure (effective volume depletion)

• Multiple myeloma

Prevention of Adverse Effects of Contrast Media

• Identify high-risk patients.

• Keep patient well hydrated (avoid use of strong laxatives).

• Premedicate with steroids (hydrocortisone 100 mg PO or prednisone 20 mg PO q6h 3 doses before study and diphenhydramine 50 mg PO) those patients who are at increased risk of an allergic-like reaction.

• Use nonionic contrast agents (Omnipaque).

• Hold Glucophage for 48 hours after contrast administration.

Ultrasound

Ultrasound is an extremely desirable method of imaging many urologic structures in a quick, cost-efficient, and noninvasive manner, without radiation or other known hazards. The advent of high-frequency, gray-scale, B-mode real-time scanning has greatly improved ultrasound images; however, they remain somewhat operator dependent. Bone and air are poor conductors of sound and thus block images of structures behind them. Fat also limits conduction; thus obese patients are difficult to image. Water conducts well and appears sonolucent. Sound is reflected whenever it encounters an interface of different tissue densities. Color-flow

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Renal Ultrasound

Renal ultrasound is especially useful when evaluating the kidney for cysts, solid masses, abscesses, hydronephrosis, stones, perirenal masses, and transplant rejection. The right kidney can be imaged with the patient supine, by using the liver as an acoustic window, or posteriorly. The left kidney is generally viewed posteriorly or with the patient in a right lateral decubitus position by using the spleen as an acoustic window.

Criteria for a Simple Benign Cyst

• No echoes within mass

• Good through transmission acoustic enhancement distal to lesion

• Sharply marginated, smooth posterior wall

Criteria for Transplant Rejection

• Enlargement from edema

• Indistinct corticomedullary junction

• Loss of central renal-sinus fat echo

Indications for Renal Ultrasound

• Differentiate a cystic from solid mass (95% accurate)

• Evaluate for obstruction (98% sensitivity and 90% specificity in detecting hydronephrosis)

• Evaluate renal transplants for evidence of rejection or obstruction

• Look for stones

Bladder Ultrasound

Bladder ultrasound can be performed transabdominally, transurethrally, or transrectally. It is used to assess bladder filling and to estimate postvoid residual urine.

Prostate Ultrasound Transrectal Ultrasound of Prostate

Transrectal ultrasound of the prostate (TRUSP) cannot differentiate benign from malignant prostate tissue. It is not a screening test for detection of prostate cancer. The primary reasons to use TRUSP are to guide prostate needle biopsies and to measure the size of the prostate (see Chapter 22).

Scrotal Ultrasound

Scrotal ultrasound is most valuable in differentiating intratesticular from extratesticular processes with an accuracy of 90% to

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Radiographs

Chest Radiograph

Chest radiographs should be a part of every metastatic workup.

Plain Film

Plain film [also referred to as flat plate, scout film, or kidney, ureter, and bladder (KUB)] is an invaluable aid in diagnosis and should not be underestimated. Pay careful attention to the size and shape of the renal outlines, and look for the presence of calcifications or air patterns.

Calcifications on Plain Film

• Urinary calculi 90% are opaque (70% 90% of ureteral calculi can be found on KUB)

• Parenchymal calcifications within cysts or tumors (calcification increases likelihood of malignancy)

• Nephrocalcinosis (hyperparathyroidism, renal tubular acidosis, medullary sponge kidney)

• Tuberculosis of kidney

• Adrenal calcifications (suggests a history of adrenal hemorrhage)

• Phleboliths

• Calcified lymph nodes

• Gallstones (10% are calcified)

• Appendicolith (fecalith helpful if acute appendicitis is suspected)

• Calcified costal cartilages

• Calcified uterine fibroids

• Prostatic calcifications (suggests chronic prostatitis)

• Aortic calcifications

• Pancreatic calcification (suggests pancreatitis)

Air under Diaphragm

• Ruptured hollow viscus (emergency)

• Postoperative

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Air within Kidney or Renal Pelvis

• Emphysematous pyelonephritis

Intravenous Urography

Intravenous urography (IVU, IVP) remains one of the best diagnostic methods for obtaining anatomic and functional detail of the urinary tract. Routinely, 50 to 100 mL of contrast media is rapidly injected by IV push, followed by 1-, 5-, 10-, and 20-minute films, which are carefully monitored by a radiologist, and a postvoid film. The IVU is the gold standard for evaluating the patient with hematuria, and it is more sensitive than ultrasound in diagnosing acute hydronephrosis and in detecting ureteral or renal calculi.

Tomograms

Tomograms of the kidney during IVU are essential to obtain maximal detail of renal anatomy and are usually performed after the 1-minute film of a standard IVU.

Retrograde Urography

Retrograde urography can be performed only during cystoscopy. It is an extremely valuable procedure, when indicated, because it gives excellent definition of upper-tract anatomy. Technique will vary depending on whether a pyelogram or ureterogram is of primary interest. Generally an opaque whistle-tip or open-ended ureteral catheter can be passed up the ureter, or a bulb or acorn-tipped catheter can be placed in the ureteral orifice, followed by injection of 4 to 8 mL of half-strength Renografin into the catheter. Care must be taken to eliminate air bubbles. Appropriate films are taken, followed by a drainage film 10 minutes after removing the

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Indications for Retrograde Pyelography

• Poor renal function

• Poor visualization on IVU

• Equivocal findings on IVU

• Patients at high risk for contrast reactions

• Localizing level of ureteral obstruction

Anterograde Urography

Percutaneous studies are valuable when excretory or retrograde studies are contraindicated, particularly in infants and children, or when a nephrostomy tube is already in place. The contrast agent is directly injected into the collecting system via a percutaneous puncture through the patient's flank. Antibiotic coverage should be used. Contraindications include a bleeding diathesis, a nondilated collecting system, or local skin infection.

Retrograde Urethrogram

Retrograde urethrogram is used to demonstrate the anterior urethra (penile, bulbar, and membranous portions). A 12 F Foley catheter is placed into the urethra just until the base of the balloon disappears through the meatus. The balloon is then filled with 1 to 2 mL water, just enough to keep the catheter within the fossa navicularis with gentle resistance. Films are taken in the right posterior oblique position while injecting 30 to 50 mL half-strength standard contrast media.

Voiding Cystourethrogram

Voiding cystourethrogram (VCUG) is used to demonstrate the posterior urethra (bladder neck and prostatic urethra) or for demonstration of vesicoureteral reflux. It also is valuable in demonstrating the bladder and bladder-neck function in women with incontinence. The bladder is first filled, after urethral catheterization or suprapubic puncture. Dilute (15%) standard contrast medium is dripped by gravity from 45 cm above the level of the bladder until a sensation of discomfort is experienced. Films are taken in the right or left posterior oblique position while the

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Indications for Voiding Cystourethrogram

• Urinary tract infections in children and recurrent or persistent infections in adults

• Suspicion of vesicoureteral reflux

• Suspicion of posterior urethral valves

• Posterior urethral strictures

• Hydronephrosis in children

• Neurogenic bladders

• Urinary incontinence (cystocele, residual urine)

Computed Tomography

Computed tomography (CT) scans use computer-generated images of cross-sectional anatomy by interpretation of x-ray derived attenuation values through finite portions of a body slice. The CT picture is composed of tiny picture elements (pixels) to which 16 shades of gray are assigned. Each pixel actually represents a volume element (voxel) of tissue within a slice. Voxels are represented by an arbitrary scale of CT numbers or Hounsfield units (HU) from -1,000 to +1,000, with 0 HU equal to water. Because only 16 pixel shades are available to represent 2,000 HU, many voxels will appear the same shade of gray in the CT picture. Soft-tissue definition in body CT scans is routinely improved by limiting the range of HUs represented to 400 (-200 to +200). This is performed by setting the window width to 400 HU while maintaining a center of 0 HU. Use of both oral and intravenous contrast agents enhances CT images. New helical (spiral) CT scanners are faster and more accurate and minimize partial-volume artifacts seen in axial scanning.

Relative Hounsfield Units for Various Tissues

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Common Problems in Interpreting Computed Tomography Scans

• Hounsfield units can be unreliable.

  • Variable calibration standards

  • Partial-volume effect

  • Patient-motion artifacts

  • Streak artifacts (bone, barium, metal clips, air fluid levels)

  • Computer-generated artifacts

• Intestinal lumen must be opacified with contrast.

• CT has limited value in identifying lymph node metastases (especially in transitional cell carcinoma and prostate cancer) because of poor sensitivity (60% 70%).

• CT cannot distinguish postoperative, postradiation, or postchemotherapy fibrosis from residual tumor.

• Very obese or very thin, emaciated patients do not scan well.

• Window width and center should be noted if the image is unusual.

• Anatomic variants may be present.

  • Gastric fundus posterior to pancreas

  • Prominent medial lobe of spleen

  • Accessory spleens

  • Renal lobulation

  • Left-sided or duplicated IVC

• CT cannot differentiate among an infected cyst, hemorrhagic cyst, abscess, area of infarction or tumor necrosis, and metastases.

Computed Tomography Criteria for a Benign Simple Renal Cyst

• Smooth, thin, invisible wall

• Homogeneous water density (0 HU 20)

• No contrast enhancement

• Sharp margination and interface with adjacent renal parenchyma

Specific Computed Tomography Scan Protocols

• Stone protocol helical (spiral) CT scanning of the abdomen and pelvis is performed without oral or N contrast for acute evaluation of colic for a suspected stone. Its advantage is speed, no need for contrast, and even radiolucent uric acid stones will be seen. If no stone or hydronephrosis is found, a stone can reliably be ruled out. However, it often fails to define the degree of obstruction. A follow-up IVU may be necessary.

• Renal protocol CT scanning to evaluate a renal mass must be performed first without and then with IV contrast. Hypodense lesions on noncontrast scans that enhance with IV contrast are solid and considered renal cell carcinoma until proven

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  otherwise. Fat within a solid renal mass is strong presumptive evidence for an angiomyolipoma.

Angiograms

Renal arteriography allows excellent anatomic visualization of the renal anatomy. In brief, the technique first involves placement of a catheter into the femoral artery by using the Seldinger method followed by an initial bolus aortogram. Next, selective renal arteriography may be performed for detail of the intrarenal vascular bed. The patient commonly receives 50 to 75 mL contrast agent during the entire procedure. Indications for renal arteriography have diminished considerably in recent years because of the remarkable advances in ultrasound, CT scans, and magnetic resonance imaging (MRI).

Complications of Renal Arteriography

• Contrast-related injury

  • Allergic reactions

  • Nephrotoxicity (acute tubular necrosis)

• Procedure-related injury

  • Local bleeding, hematoma

  • Arterial thrombosis

  • Arterial dissection

  • Thromboembolization to lower extremity

  • False aneurysm formation

  • Arteriovenous fistulae

Indications for Renal Arteriography

• Preoperative for renal vascular anatomy

• Renal trauma (when indicated)

• Living-donor renal transplants [digital subtraction angiography (DSA) generally preferred]

• Workup of renovascular hypertension (DSA preferred)

• Suspicion of renal artery aneurysm

• Renal tumors (before partial nephrectomy)

• Renal artery embolization

Digital Subtraction Angiography

DSA combines x-rays, contrast media, and digital computer technology to produce a high-quality angiographic image with certain technical advantages. In brief, a mask image is first made of the area of interest, before contrast enhancement, and it is digitally

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Two Types of Digital Subtraction Angiography

• Intravenous DSA (IV-DSA) is performed by peripheral or central venous injection of 40 to 50 mL contrast agent, usually central, followed by routine DSA. It is the procedure of choice in the initial evaluation of suspected renovascular hypertension and for evaluation of renal transplant donors. Advantages of IV-DSA are (a) it avoids the significant risks of arterial catheterization and (b) it is an outpatient procedure that does not require the expense of hospitalization.

• Intraarterial DSA (IA-DSA) uses arterial catheterization with DSA technology. Its chief advantage is that only minimal amounts of contrast agent are needed (<10 mL), making it particularly useful in patients with renal failure.

Venography

Renal Venography

Renal venography is helpful in detecting renal vein thrombosis with either clot or tumor thrombus. Renal vein catheterization also is used for measuring renal vein renin activity in patients with suspected renovascular hypertension.

Venacavography

Venacavography is often a useful adjunct to CT or MRI in defining the extent of involvement of the vena cava with renal tumor thrombus.

Lymphangiograms

Lymphangiograms are performed by direct catheterization of a lymphatic vessel on the dorsum of the foot with a fine (27- or 30-gauge) needle and injecting contrast media (Ethiodol). Lymphangiograms were more commonly used in the past to aid diagnosis of lymph node metastases in prostate, bladder, and testicular

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• Patients with stage I testicular germ cell tumors who are candidates for surveillance;

• Planning of radiotherapy portals.

Nuclear Scans

Nuclear scans use radioactive tracers, primarily technetium-99m (^99mTc) chelates and iodine-131 (¹³¹I) orthoiodohippurate, to derive functional images and data by using the Anger scintillation camera.

DMSA Renal Scan

^99mTc-DMSA is not filtered but binds to the basement membrane of proximal tubular cells (t_1/2, 6 hr). It is used to assess functional renal mass and differential or relative renal function between the two kidneys. Optimal scanning is performed 4 or 24 hours after injection of tracer.

Indications for DMSA Renal Scan

• Estimation of differential renal function

• Estimation of functioning renal mass

• Evaluation of a pseudotumor

• Assessment of pyelonephritis in children

DTPA Renal Scan (with or without Lasix)

^99mTc-DTPA is excreted principally in the urine by glomerular filtration (80%) and is not secreted or reabsorbed (t_1/2, 1.4 hr). It is used to assess renal blood flow, GFR, and the functional status of the collecting systems (i.e., obstruction). Patients must be well hydrated.

The renogram produced is a time activity curve of renal function consisting of three phases:

• Vascular phase represents primarily renal perfusion (normally a steep upward curve lasting <1 min);

• Tubular-uptake phase represents the gradual accumulation of activity in the parenchyma [transit time (i.e., time to peak activity) is normally 3 5 min];

• Excretory phase represents washout of activity that depends on rate of urine production and flow in the collecting system (normally a steep downward sloping curve with a washout t_l/2

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  of 10 minutes). By administering furosemide (Lasix) during the washout phase, a dilated, nonobstructed system can usually be differentiated from a truly obstructed system.

Indications for DTPA Renogram

• Evaluation of renal transplant function

• Diagnosis of upper-tract obstruction

• Evaluation of a renal mass in the newborn

MAG3 Renal Scan (with or without Lasix)

^99mTc-MAG3 is handled by almost exclusively (90%) tubular secretion. It is believed to be superior to DTPA for diuretic renography to determine the presence or absence of obstruction in the hydronephrotic kidney.

Indications for MAG3 Renogram

• To determine the presence or absence of obstruction in the hydronephrotic kidney

• To evaluate ureteropelvic junction obstruction

Hippuran Scan

¹³¹I-Hippuran (orthoiodohippurate) is excreted in the urine by tubular secretion (80%) and glomerular filtration (20%). It measures effective renal plasma flow, a more accurate indicator of excretory function. ¹³¹I-Hippuran should be used when looking for obstruction in the presence of significant renal failure, because glomerular function is affected earlier and to a greater extent than tubular function.

Radionuclide Cystography

Radionuclide cystography is effective for evaluation of vesicoureteral reflux in the pediatric patient. It is more sensitive than a VCUG and gives 50 to 200 times less radiation exposure. It is performed either by direct retrograde filling of the bladder with ^99mTc-pertechnetate in saline or indirectly after a routine DTPA renal scan (less accurate).

Testicular Flow Scan

Testicular flow scan using ^99mTc-pertechnetate for the differentiation of testicular torsion from epididymitis has a reported 95% sensitivity and 100% specificity.

Common Patterns

• Acute early torsion decreased perfusion to the involved side

• Late or missed torsion central photon deficiency with a halo or rim of reactive hyperemia on delayed images

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• Epididymitis increased perfusion to the involved side and a crescent of increased activity corresponding to the inflamed epididymitis

Bone Scan

A bone scan is the most sensitive means of detecting osseous metastases ( 97%). Positive bone scans often precede radiographic lesions by 3 to 6 months. ^99mTc-Methylene-diphosphonate, the most useful agent, is taken up in all areas of increased bone turnover, not just metastatic deposits. However, metastatic lesions characteristically are asymmetrical, multiple, and involve the axial skeleton. False negatives occur in 3% to 8% of cases. Normally, the kidneys are seen to take up isotope. Failure to visualize the kidneys indicates either inadequate tracer dose or that widespread metastatic disease has taken up all the isotope (superscan). Serial scans are often misleading in evaluating response to hormonal therapy or chemotherapy.

Indications for Bone Scan

• Initial evaluation of prostate cancer and neuroblastoma

• Skeletal pain or other evidence of metastases in prostate cancer, renal cell cancer, seminoma, neuroblastoma, and bladder cancer (rarely)

Gallium Scan

Gallium-67 citrate scans are useful in patients with a suspected abscess and a nondiagnostic ultrasound. Imaging must wait 48 to 72 hours after injection because of normal urinary excretion. It is reported to have a sensitivity of 90%, but a specificity of only 65%, meaning that many false-positive scans occur.

Indium-111 Leukocyte Scan

Indium-111 oxine labeled white blood cells require laboratory labeling of white cells; however, it is more sensitive and specific for localizing acute infections, and images can be made in less than 24 hours.

Positron Emission Tomography (PET) Scans

PET scans use a radioactive tracer, fluorodeoxyglucose (FDG). The scan tracks the uptake and utilization of FDG by cells about an hour after injection. It can be used to differentiate normal cells from malignant cells. PET scans have had limited use for urologic malignancies to date.

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Magnetic Resonance Imaging

MRI gives outstanding soft-tissue resolution that is well suited for renal and adrenal masses and vascular imaging. Radiofrequency pulses are used to excite briefly the hydrogen protons of the tissues and organs to be imaged. Nuclear magnetic resonance (NMR) signals are characterized by (a) spin density, (b) T₁ relaxation time, and (c) T₂ relaxation time. A computer transforms NMR signals into a visual image by using a gray scale that corresponds to the signal intensity. Fat gives off the highest-intensity signal and is represented by white, whereas bone and air give the lowest signals and are represented by black. MRI can be enhanced by use of an intravascular contrast agent such as gadolinium-DTPA. T₁-weighted images are best for defining anatomy, whereas T₂-weighted images are better for demonstrating pathology. Cysts appear much brighter than solid masses on T₂-weighted images.

Indications for MRI

• Characterization of renal masses as solid or cystic.

• Imaging adrenal masses; presence of fat favors adenoma rather than metastasis.

• Pheochromocytomas are extremely bright on T₂-weighted images.

• MR angiography of kidneys (renal vein and vena cava patency).

Contraindications to MRI

• Pacemakers

• Ferromagnetic intracranial aneurysm clips

• Claustrophobia

Endoscopy

The ability to visualize directly almost the entire urinary tract is one highlight of the specialty of urology. Modern fiberoptic light sources and wide-angle lenses provide a capability for precise diagnosis and follow-up that is unmatched by any specialty [note: French (F) scale; 3 F = 1 mm].

Urethroscopy

Urethroscopy is performed by using 0- or 30-degree lenses. Cystoscope sheaths range from 8 F to 26 F in caliber. Inspection for tumors, strictures, stones, diverticula, prostatic enlargement, and

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Cystoscopy

Cystoscopy is possible by passing the scope into the bladder. Complete visualization of the entire bladder can generally be performed with 30- and 70-degree lenses. Inspection of the ureteral orifices and bladder walls for tumors, diverticula, lesions, stones, foreign bodies, and general morphology (i.e., trabeculation) can be conducted. A flexible cystoscope is preferred for an awake male patient.

Ureteroscopy

Transurethral ureteroscopy can be performed with rigid or flexible ureteroscopes, allowing visualization of the entire ureter up into the renal pelvis and major calyces.

Nephroscopy

Nephroscopy can be performed percutaneously with a rigid or flexible instrument. Many procedures are possible through the instrument. A small-caliber flexible ureteroscope can be passed into the renal pelvis for visualization of the intrarenal collecting system.

Cyst Puncture

Although most renal cysts are benign, and more than 90% can be correctly diagnosed with ultrasound or CT, some will require a cyst puncture to make a final diagnosis.

Technique

Cyst puncture is performed with a thin needle guided by ultrasound or CT. Cyst fluid is aspirated and sent for histochemical and cytologic studies followed by double-contrast (air-contrast media) imaging of the cyst cavity, taking multiple radiographic views.

Interpretation

Benign Cysts

Benign cysts contain a clear, straw-colored fluid with low levels of fat and protein, no blood, and negative cytology.

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Malignant Cysts

Malignant cysts often have a murky or bloody fluid, with high concentrations of fat and protein, and positive cytology. Tumor nodules may be seen on the cyst walls.

Inflammatory Cysts

Inflammatory cysts have a murky or purulent aspirate with moderately elevated fat and protein concentrations and significant levels of amylase and lactate dehydrogenase. Cytology will show numerous inflammatory cells, and cultures will generally be positive.

Prostatic Needle Biopsy

Prostatic needle biopsy is essential for the diagnosis of prostate cancer. It is an easy, efficient, outpatient procedure that should be performed without hesitation for any suggestive areas found on digital rectal examination or with an elevated PSA (see Chapters 3 and 22). Ultrasound guidance should always be used if available. Two techniques are used: core-needle biopsy and fine-needle aspiration.

Core-Needle Biopsy

Core-needle biopsy is performed by using a spring-loaded Biopty needle via a transperineal or transrectal approach. Core biopsies yield good tissue samples for pathologic examination.

Transrectal

Transrectal ultrasound guided-needle biopsy is the standard for prostate biopsy. It allows accurate needle guidance and does not require an anesthetic. Six to 12 systematic random biopsies are taken under ultrasound guidance. Patients should hold aspirin and any anticoagulant or antiplatelet medications for approximately 5 to 7 days before biopsy. All patients should have a Fleets enema before biopsy and should have antibiotic coverage before and for 2 to 5 days after (generally a quinolone). Injection of lidocaine (Xylocaine) with a long needle into the periprostatic soft tissues at the prostate vesical junction will greatly eliminate most of the discomfort of the procedure. Complications include bleeding, infection, urosepsis, and urinary retention.

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Transperineal

Transperineal approach is less frequently used today. It does not conform with transrectal ultrasound as well and requires local anesthesia to the perineum. After local lidocaine (Xylocaine) infiltration of the perineum, the index finger of one hand is placed in the rectum to guide the needle held in the other hand toward the area in question.

Fine-Needle Aspiration

Aspiration by using a Franzen needle and transrectal approach has the lowest complication rate. Cells are aspirated through a thin 22-gauge needle for cytologic examination. It is performed as an outpatient procedure without anesthesia, and results can be available within hours.

Cytology

Cytology has expanded the capabilities of making early diagnosis from minimally invasive procedures. Cytologic examination can be performed on aspirates from the prostate, kidney, and lymph nodes; washings from the bladder, ureter, and renal pelvis; and voided urines. Well-preserved cells are essential for accurate interpretation. Difficulty most often arises in differentiating atypia from low-grade tumors.

Flow Cytometry

Flow cytometry utilizes a highly complex machine that can measure frequency, size, structure, and staining characteristics of thousands of cells per second. Studies have demonstrated significant associations between cell DNA ploidy and disease prognosis.

The Whitaker Test

The Whitaker test is a quantitative pressure flow study used to evaluate upper-tract obstruction as from a ureteropelvic junction obstruction or an obstructed megaureter. It is considered the definitive test for obstruction when other less invasive methods are equivocal.

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Procedure for a Whitaker Test

• A nephrostomy or pyelostomy tube is placed in the renal pelvis (percutaneous 20-gauge needle nephrostomy is commonly used), and a catheter is placed in the bladder.

• A constant-flow infusion is delivered to the renal pelvis at 10 mL/min.

• Manometers are attached to perfusion and bladder outflow catheters.

• Renal pelvis and bladder pressures are monitored once the collecting system is full.

• Differential pressures (renal pelvis minus bladder) of less than 15 cm H₂O indicate absence of obstruction.

Urodynamics

Urodynamics is the study of physiology and fluid mechanics of normal and abnormal micturition. It encompasses a large field of specialized tests and nomenclature. Elaborate urodynamic studies require special equipment and training for proper performance. The two most useful and commonly used urodynamic studies are the uroflow and cystometrogram (see also Chapter 21).

Uroflow

The urine flow rate is ideally obtained on an electronic uroflowmeter that produces a flow curve that plots the instantaneous stream flow rate against time, in addition to measuring peak and average flow rates, flow time, and volume voided (see Chapter 21). Uroflow is the single most valuable urodynamic study to evaluate voiding dysfunction. The peak flow rate and the flow curve can confirm a diagnostic suspicion and provide etiologic insight into the voiding problem.

Cystometrogram

The cystometrogram is a recording of detrusor function using either a gas (CO₂) or water cystometer. Intravesical pressures are recorded during passive filling and active contraction of the bladder. Subjective events (first desire to void, sensation of fullness, and discomfort) are noted on the graph. Bladder compliance can be calculated from the filling phase of the study ( V/ P).

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Normal Cystometrogram

See Chapter 21.

• Good accommodation during filling with pressures in the range of 10 cm H₂O

• No uninhibited contractions (involuntary pressure spikes of >15 cm H₂O)

• First desire to void at 100 to 200 mL

• Fullness at 300 to 400 mL

• Discomfort between 400 and 500 mL

• Good detrusor contraction with pressures reaching 30 cm H₂O in the female and 30 to 50 cm H₂O in the male patient

Sources of Error in Routine Cystometrogram

• Inability to differentiate detrusor pressure elevations from intraabdominal pressure

• Too fast a filling rate

• Urethral catheter irritation

• CO₂ can irritate the bladder mucosa

• Patient misunderstanding instructions

• Movement artifacts