Renal parenchymal diseases: Is characterization feasible with ultrasound?

Ultrasound (US) imaging of the kidneys has greatly improved in recent years with introduction of wideband transducers and advances is beamformer technology. US is often the first imaging technique to be employed in patients with renal failure, haematuria or proteinuria, after clinical and laboratory evaluation. After conventional US evaluation, Doppler US (DUS) and resistive indices (RIs) analysis provide renal functional evaluation. Anyway, both sensitivity and specificity of conventional US and DUS in renal parenchymal disease evaluation remains low. In the initial or mild clinical stages of renal parenchymal diseases, kidneys may present normal US morphological appearance and normal RIs values, whereas different renal parenchymal diseases may reveal similar appearance on US and DUS evaluation. Besides, different renal parenchymal diseases may present some distinct features on conventional US and DUS with colour Doppler (CD) and power Doppler (PD) evaluation, even though percutaneous renal biopsy is often necessary to reach definite diagnosis. Renal vasculitides and tubular-interstitial nephropathies are more frequently identified by conventional US and DUS than glomerular nephropathies, since glomerular component accounts only for 8% of the renal parenchyma, whereas the highest percentage is occupied by vascular and tubulo-interstitial component. Follow-up of acute renal failure, during and after medical treatment, is the most useful field of employment of conventional US and DUS techniques, since a progressive lowering of RIs is correlated to a progressive recovery of renal function.