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renal ultrasound

Indications: 1) assessment of renal size a) large kidneys a) hydronephrosis b) amyloidosis c) diabetes (early) d) HIV nephtopathy b) small or absent kidneys a) nephrectomy b) renal aplasia c) renal artery stenosis (common in elderly) d) renal damage from pyelonephritis, reflux nephropathy, glomerulonephritis (bilateral) [3] c) assessment of renal cortex thickness [2] 2) screen for urinary obstruction (may be negative early) a) benign prostatic hypertrophy b) nephrolithiasis c) tumor (malignancy) obstructing urine flow d) retroperitoneal fibrosis [2] 3) characterize mass lesions a) angiomyolipoma b) solid vs cystic c) solid masses must be > 3 cm in size 4) screen for polycystic kidney disease 5) renal vein thrombosis 6) evaluation of anuria (renal cortical necrosis) 7) renal papillary necrosis Contraindications: - NOT a screen for renal artery stenosis [1,3] - duplex ultrasonography of renal arteries has a sensitivity of > 90% for detection & degree of atherosclerotic renal disease, but is operator dependent [2] Clinical significance: - echogenicity generally refers to how bright or dark the kidney parenchyma appears in comparison to the liver [5] - 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

General

ultrasound (US, UTZ)

References

  1. Mayo Internal Medicine Board Review, 1998-99, Prakash UBS (ed) Lippincott-Raven, Philadelphia, 1998, pg 621
  2. Medical Knowledge Self Assessment Program (MKSAP) 11, 14, 16, 18. American College of Physicians, Philadelphia 1998, 2006, 2012, 2018
  3. ACCF/ACR/AIUM/ASE/ASN/ICAVL/SCAI/SCCT/SIR/SVM/SVS 2012 Appropriate Use Criteria for Peripheral Vascular Ultrasound and Physiological Testing Part I: Arterial Ultrasound and Physiological Testing J Am Coll Cardiol, (Published online 11 June 2012 PMID: 22694840 http://content.onlinejacc.org/cgi/content/full/j.jacc.2012.02.009
  4. Licurse A, Kim MC, Dziura J Renal ultrasonography in the evaluation of acute kidney injury: developing a risk stratification framework. Arch Intern Med. 2010 Nov 22;170(21):1900-7 PMID: 21098348
  5. Faubel S, Patel NU, Lockhart ME, Cadnapaphornchai MA. Renal relevant radiology: use of ultrasonography in patients with AKI. Clin J Am Soc Nephrol. 2014 Feb;9(2):382-94. Review. PMID: 24235286 Free PMC Article https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3913238/
  6. National Kidney Federation (UK) http://www.kidney.org.uk/Medical-Info/kidney-disease/small-singlekid.html