Radiology of the Urinary Tract

Radiological Examinations of the Urinary Tract

• The radiological examinations of the urinary tract are: • Ultrasound • Intravenous urography (IVU) • Computed tomography (CT) • Radionuclide examinations • Magnetic resonance imaging (MRI) • Arteriography • Studies requiring catheterization or direct puncture of the collecting systems

Imaging Technique: Ultrasound

• The main uses of ultrasound are: • To investigate patients with symptoms thought to arise from the urinary tract • To demonstrate the size of the kidneys and exclude hydronephrosis in patients with renal failure • To diagnose hydronephrosis, renal tumors, abscesses, and cysts, including polycystic disease • To assess and follow-up renal size and scarring in children with urinary tract infections • To assess the bladder and prostate

• Normal renal ultrasound: • The kidneys should be smooth in outline • The parenchyma surrounds a central echo-dense region, known as the central echo complex • The normal adult renal length, measured by ultrasound, is 9-12 cm • Renal length varies with age, being maximal in the young adult • Normal ureters are not usually visualized due to overlying bowel gas • The urinary bladder should be examined in the distended state, with sharply defined and barely perceptible walls

Urography

• Urography is the term used to describe the imaging of the renal tract using intravenous iodinated contrast medium

• There are two types of urography: • The traditional intravenous urogram (IVU) • CT urography

• The principles of both techniques are similar: • Firstly, 'non-contrast' imaging of the renal tract is required to identify all renal tract calcifications • In some cases, where the clinical question relates to renal calculi, the non-contrast CT may be sufficient (known as the 'CT KUB')

• The main indications for urography are: • To investigate patients with symptoms thought to arise from the urinary tract • To demonstrate the size of the kidneys and exclude hydronephrosis in patients with renal failure

IVU Study

• Plain film in intravenous urogram: • Used to identify all calcifications • Decide if they are in the kidneys by relating them to the renal outlines • Calcification seen in the line of the ureters or bladder must be reviewed with post-contrast scans to determine whether the calcification lies in the renal tract

• Films taken after injection of contrast medium: • Kidneys:

  • Check that the kidneys are in their normal positions
  • Identify the whole of both renal outlines
  • Measure the renal lengths • Calices:
  • The calices should be evenly distributed and reasonably symmetrical
  • The shape of a normal calix is 'cupped' and when it is dilated it is described as 'clubbed' • Pelvis and ureters:
  • The normal renal pelvis and pelvi-ureteric junction are funnel-shaped
  • The ureters are usually seen in only part of their length on any one film of IVU • Bladder:
  • The bladder is a centrally located structure that should have a smooth outline
  • It often shows normal smooth indentations from above owing to the uterus or the sigmoid colon, and from below by muscles of the pelvic floor

Computed Tomography Urography

• CT is initially performed without intravenous contrast medium (non-contrast CT or 'CT KUB') to identify calcification
• Indications and include: • The early renal cortical enhancement phase • The homogeneous nephrogram phase • The delayed urographic phase, obtained several minutes later to demonstrate contrast within the collecting systems

Magnetic Resonance Imaging

• Magnetic resonance imaging gives similar anatomical information to CT, with the advantage of being able to obtain scans directly in multiple planes

• It is generally used in selected circumstances, including: • To demonstrate renal artery stenosis • Inferior vena caval extension of renal tumors • To clarify problems not solved by ultrasound or CT • To assess the extent of bladder or prostate cancer prior to consideration for surgery

• Normal magnetic resonance imaging: • The renal contours should be smooth • Corticomedullary differentiation is best seen on T1-weighted images • The renal collecting systems, ureters, and bladder are best seen on T2-weighted images, as the fluid returns a high signal intensity

Special Techniques

• Retrograde and antegrade pyelography: • The techniques of retrograde and antegrade pyelography involve direct injection of contrast material into the pelvicaliceal system or ureters through catheters placed via cystoscopy or percutaneously into the kidney via the loin • The indications are limited to those situations where the information cannot be achieved by less invasive means
• Voiding cystourethrography (micturating cystogram) and videouro dynamics: • In voiding cystourethrography, the bladder is filled with iodinated contrast medium through a catheter and films are taken during voiding • The entire process is observed fluoroscopically to identify vesicoureteric reflux • Videourodynamic examination combines voiding cystourethrography with bladder pressure measurements • It is indicated in the investigation of patients with incontinence, obstructive symptoms, and neurogenic bladder
• Urethrography: • The urethra is visualized during voiding cystourethrography • For full visualization of the male urethra, an ascending urethrogram with contrast medium injection via the external urethral meatus is necessary • The usual indications for the examination are to identify urethral strictures and to demonstrate extravasation from the urethra or bladder neck following trauma