Morphological Biomarkers Of Kidney Function

Actually, there is a growing interest in validating accurate and reproducible methods for calculation of renal volume, which may be an index of functional renal parenchyma (4). Follow-up of chronic nephropathies would be simplified for patients by such measurements. Today, the most widely used marker is the renal length, which is measured with sonography. However, its correlation with renal size is far from perfect (5,6). Measurement of parenchymal thickness has received little attention (7,8),

Figure 2 Parenchymal hypointensity on T2w images: (A) Paroxysmal nocturnal hemoglobinuria. Axial T2w image obtained at 2 T shows that the SI of the renal cortex is decreased, whereas it remains normal in the medulla. (B) Acute ischemic nephropathy. Decrease of SI on a T2w image within the outer medulla on axial view. Pathologic examination of the outer medulla showed iron in the interstitium compatible with hemosiderin deposition. Abbreviations: T2w, T2-weighted; SI, signal intensity. Source: Part (A) from Ref. 3.

Figure 2 Parenchymal hypointensity on T2w images: (A) Paroxysmal nocturnal hemoglobinuria. Axial T2w image obtained at 2 T shows that the SI of the renal cortex is decreased, whereas it remains normal in the medulla. (B) Acute ischemic nephropathy. Decrease of SI on a T2w image within the outer medulla on axial view. Pathologic examination of the outer medulla showed iron in the interstitium compatible with hemosiderin deposition. Abbreviations: T2w, T2-weighted; SI, signal intensity. Source: Part (A) from Ref. 3.

and its reproducibility is hampered by its heterogeneity throughout each kidney. The best method would be a volumetric technique applied to the entire parenchyma, excluding the sinus, or to the cortex. Coulam et al. (9) reported an excellent correlation between MRI measurement of total renal parenchymal volume and autopsy volume and weight, using coronal multiphasic contrast-enhanced three-dimensional (3-D) sequences in pigs. However, the segmentation was manual, done slice-by-slice. The cortical volume seems to be the most useful parameter because it is directly related to the filtration capabilities of the kidney. In our institution, we developed an automatic segmentation technique of the renal cortex applied to a contrast-enhanced 3-D dataset obtained at the vascular phase. This technique demonstrated its feasibility (unpublished data) but still requires validation.

New medical therapies for inherited polycystic diseases are emerging, with encouraging results in animal models (10). These treatments are able to slow established diseases, indicating that clinical trials should be considered. Increased renal volume predicts and is associated with loss of renal function in autosomal-dominant polycystic kidney disease (11), and renal cystic volume predicts renal outcome more reliably than the total renal volume (12). Therefore, measurement of renal cystic volume would be worthwhile to follow the effect of treatment. Computer-assisted detection software will be necessary for that purpose, with automatic detection of cyst walls and automatic volume calculations based on 3-D datasets, and used as an accurate surrogate marker, mostly when renal function is still preserved (11).

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