17. Imaging of the urinary system. Indications, diagnostic strategy. Renal inflammatory diseases, nephrolithiasis.

Imaging of the urinary tract

A variety of imaging modalities are used in the evaluation of the urinary tract.

CT urography

CT urography refers to a contrast CT taken in a phase where the contrast has entered the urinary system. It's one of the most commonly used procedures used to image the upper urinary tract (renal pelvis and ureters).

• Procedure
  • A non-contrast CT is taken
  • IV contrast is injected
  • Several CT scans are taken afterwards when the contrast is in the urinary system
• Is generally used instead of regular x-rays and IV urography
• Indications
  • Gold standard for stones and renal masses
  • Staging of renal and bladder cancers
  • Hydronephrosis
  • Trauma
  • Retroperitoneal masses
  • Retroperitoneal lymph nodes
  • Adrenal masses

Ultrasound

Ultrasound is also widely used in the evaluation of the urinary tract. It may be used to evaluate the kidneys, look for kidney stone, measure bladder volume, and evaluate the testicles. When a transrectal probe is used, the prostate can be evaluated as well.

• Indications
  • Renal tumour
  • Renal cysts
  • Nephrolithiasis (not as good as CT)
  • To guide kidney biopsy or intervention
  • Hydronephrosis
  • Bladder stone
  • Urinary retention
    • Ultrasound can measure the amount of urine remaining in the bladder after urination
  • Testicular torsion
  • Cryptorchidism
  • Epididymitis
• Can also evaluate
  • Kidney
    • Size
    • Shape
    • Location
    • Masses
    • Cysts
  • Bladder
    • Size
    • Wall thickness
    • Colour doppler allows visualization of the ureteral jet
  • Prostate
    • Using transrectal probe
    • Size
    • Shape
    • Masses
  • Scrotum
    • Presence/absence
    • Cryptorchidism in the inguinal canal
    • Inguinal lymph nodes

Kidney stone disease

Kidney stone disease, also called nephrolithiasis or urolithiasis, refers to the presence of symptomatic kidney stones in the urinary tract. When stones are present in the ureter it may be called ureterolithiasis, while stones in the bladder are usually simply called bladder stones or bladder calculi. It's a relatively common condition, with a lifetime prevalence of 10 - 20 percent.Whether imaging is necessary in case of uncomplicated (no fever or sign of infection, pain can be controlled with NSAIDs, mild-moderately decreased kidney function) is controversial. In Norway, no imaging is obtained during the initial presentation; imaging is obtained after 3 - 4 weeks. According to most other guidelines however, CT is indicated urgently to assess for obstruction.

Imaging

A low-dose non-contrast CT is usually the first choice as this has little radiation exposure and can detect the majority of stones. Ultrasonography is a reasonable alternative first choice, especially in pregnant and children, but many stones are not visible on ultrasound (70% sensitive and specific). Kidney, ureter, bladder (KUB) radiography was previously widely used, but it is not sensitive and so is rarely used nowadays.

If the stone causes urinary obstruction, one may see hydronephrosis and dilated proximal ureters.

Acute kidney injury

Acute kidney injury (AKI) is a clinical syndrome which is characterised by an acute decrease kidney function (GFR) (over hours or days), as evidenced by elevated creatinine. There may also be accumulation of urinary waste products and oliguria/anuria, but not always. The cause may be prerenal, renal, or postrenal, but the most common causes are prerenal and acute tubular necrosis. AKI is a common problem in critically ill patients in the intensive care unit.

During the evaluation it’s important to determine whether it’s really acute or chronic, and to determine the underlying cause. Management includes treating the cause and correcting severe electrolyte disturbances. In some cases, renal replacement therapy may be required.

The condition is nowadays called acute kidney injury rather than acute renal failure.

Diagnosis and evaluation

In case of AKI, the kidney is usually enlarged, which can be visualised on ultrasonography. Ultrasound may also reveal an underlying cause and is therefore usually the first choice imaging modality for AKI.

Chronic kidney disease

Chronic kidney disease (CKD), previously called chronic renal failure is defined as the presence of either kidney damage or decreased kidney function for more than 3 months. Decreased kidney function is measured by decreased GFR.

Diagnosis and evaluation

Kidneys with CKD have abnormal morphology. On ultrasound the following features are seen:

• Decreased size of kidney (< 100 mm)
• Thinning of cortex (< 10 mm)
• Irregular surface

Renal scintigraphy may be used to precisely determine the kidney function of each kidney.

Glomerulonephritis

Glomerulonephritis refers to a disease affecting the glomeruli, even though inflammation itself (-itis) is not necessarily present. Glomerulonephritis is rare, and it can cause severe symptoms and chronic kidney disease.

Diagnosis and evaluation

On ultrasonography, the kidney is enlarged and has hyperechoic parenchyme.