The solitary kidney--a nephrological perspective.

The solitary kidney (SK) is of special interest for practitioners because of the reduced number of nephrons as compared to persons who have 2 kidneys. It undergoes adaptive phenomena of hypertrophy and hyperfiltration that allow long-term evolution, but pathological situations might occur in the remnant kidney. In some persons with a SK, the adaptive phenomena can be associated with proteinuria, arterial hypertension (AH) and diminished Glomerular Filtration Rate (GFR). In very rare situations, diminution of renal function in patients with a SK can progress to end-stage renal disease (ESRD) and, totally exceptionally, it requires renal replacement therapy. The SK can be congenital or acquired. At present patients with a SK address themselves more and more frequently to nephrology services which monitor the evolution of both the congenital and the surgically acquired SK. The congenital SK possesses a higher number of nephrons (75%, as compared to 2 functional kidneys in a healthy person) than the surgically acquired SK - 50% nephrons. This makes adaptive phenomena differ. Secondary lesions sometimes appear later in case of the congenital SK. In other situations, no significant differences between the evolution of the congenital or acquired SK are registered. The congenital solitary kidney is often associated with congenital abnormalities of the kidney and of the urinary tract (CAKUT). This association increases the risk for chronic kidney disease and for evolution towards chronic renal failure. The congenital SK is also often associated with gynaecological and other abnormalities. The acquired solitary kidney can be due to nephrectomy on a pathological kidney which could not be conservatively treated or due to donation of a kidney for renal transplantation. The SK itself sometimes requires partial nephrectomy intervention, for example sparing surgery. Although the evolution is in most cases favorable, it requires attentive monitoring.