renal ultrasound

Indications

• assessment of renal size
  • large kidneys
  • hydronephrosis
  • amyloidosis
  • diabetes (early)
  • HIV nephtopathy
  • small or absent kidneys
  • nephrectomy
  • renal aplasia
  • renal artery stenosis (common in elderly)
  • renal damage from pyelonephritis, reflux nephropathy, glomerulonephritis (bilateral)
  • assessment of renal cortex thickness
• screen for urinary obstruction (may be negative early)
  • benign prostatic hypertrophy
  • nephrolithiasis
  • tumor (malignancy) obstructing urine flow
  • retroperitoneal fibrosis
• characterize mass lesions
  • angiomyolipoma
  • solid vs cystic
  • solid masses must be > 3 cm in size
• screen for polycystic kidney disease
• renal vein thrombosis
• evaluation of anuria (renal cortical necrosis)
• renal papillary necrosis

Contraindications

• NOT a screen for renal artery stenosis
• duplex ultrasonography of renal arteries has a sensitivity of > 90% for detection & degree of atherosclerotic renal disease, but is operator dependent

Clinical significance

• echogenicity generally refers to how bright or dark the kidney parenchyma appears in comparison to the liver
• fat & fibrous tissue are very echogenic
• the renal capsule consists of thin fibrous tissue, which is next to fat, thus the kidney often appears to be surrounded by a very bright rim on ultrasonography
• solid organs, such as the liver & spleen, have intermediate echogenicity
• the renal parenchyma, (renal cortex & renal medulla) is normally isoechoic or hypoechoic (darker) compared with the normal liver
• hyperechoic kidneys
  • fibrous tissue (glomerulosclerosis, interstitial fibrosis)
  • inflammatory infiltrates in acute interstitial nephritis & glomerulonephritis
  • proteinaceous casts (acute tubular necrosis)
  • calcium deposits & stones are very echogenic
    • medullary sponge kidney, hyperparathyroidism, renal tubular acidosis, vitamin D toxicity (9,10)
  • sickle cell disease, gout

Notes

• safe, non-invasive
• relatively inexpensive
• not dependent upon kidney function

More general terms

• ultrasound (US, UTZ)