Introduction

This review covers three clinical scenarios which feature the single kidney. The first category concerns patients who are born with only one kidney: they have congenital solitary functioning kidney, either caused by unilateral renal agenesis or regression of a malformed rudiment. After addressing the definition, incidence and diagnosis of this disorder, three aspects will be discussed: the putative developmental etiologies of this disorder; the occasional familial nature of the disorder suggesting a genetic basis to the disorder, and the long-term outcome of these individuals in terms of risk of subsequent disease in the kidney and the occurrence of hypertension (the “renal prognosis”).

The second category concerns patients who, in childhood or adulthood, have had either a unilateral nephrectomy or a subtotal nephrectomy for intrinsic renal disease. The latter subgroup have had one kidney and a fraction of the contralateral organ removed and are said to have a “remnant kidney.” I will discuss the clinical evidence which addresses the renal prognosis of these individuals. The third category concerns the renal prognosis of the single kidney in otherwise healthy renal transplant donors.

Renal agenesis and the congenital single kidney

Definition

Renal agenesis implies the total absence of the kidney and can be considered as part of the spectrum of renal malformations which also include: (i) renal hypoplasia, a disorder in which the kidney is small and contains fewer nephrons than normal; (ii) renal dysplasia in which the kidney contains undifferentiated tissue; (iii) the multicystic dysplastic kidney in which the dysplastic organ contains massive cysts and; (iv) renal aplasia which describes a tiny dysplastic organ.