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Renal impairment

¹ Consultant Nephrologist, Renal Unit, ² Consultant Radiologist, Department of Radiology, Western Infirmary, Dumbarton Road, Glasgow G11 6NT, UK

• Approximately 5% of the adult population has chronically reduced kidney function.
  
• In the UK, guidelines have been implemented to identify patients with CKD by targeted screening so that measures can be taken to reduce the increased cardiovascular risk and slow the rate of deterioration in kidney function.
  
• There is a direct relationship between renal length and parenchymal thickness; both are generally reduced in renal impairment. Ultrasonic renal length is normally 10–12 cm; less than 9 cm is generally pathological. Increased renal cortical echogenicity on ultrasound is a good indicator of renal parenchymal disease.
  
• The principal types of acute kidney injury (AKI) are pre-renal, parenchymal or post-renal; a pre-renal aetiology is the most common. Ultrasound should usually be performed early to exclude obstruction. If a parenchymal aetiology of AKI is suspected, then kidney biopsy is required.
  
• In patients with CKD, renal artery stenosis (RAS) should be suspected in those with hypertension and stigmata of widespread atheromatous disease. Magnetic resonance angiography (MRA) and CT angiography are usually useful in patients suspected of having RAS.
  

Renal impairment represents a huge healthcare issue not just within the UK but also worldwide. Both the incidence of acute kidney injury and, with the ageing population, chronic kidney disease are increasing. This article will review the normal anatomy (in particular, the normal ultrasonic anatomy) of the kidney and highlight the main physiological roles of the kidney in order to enable a better understanding of how, once these functions fail, the clinical consequences arise. We will address the investigation and management of patients with both acute and chronic disease, as well as the aetiology, investigation and imaging options available. The classification of chronic kidney disease and its relationship with the estimated glomerular filtration rate will be discussed. The pivotal role of ultrasound in the imaging armamentarium will be highlighted. Finally, the risks of contrast-induced nephropathy, as well as the recommendations for MRI use to reduce any risk of nephrogenic systemic fibrosis, will be discussed.