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Competing Interests: Competing interests: None declared.

The mammalian kidney consists of highly specialised cells that function in an integrated manner to maintain homeostasis of body fluids, electrolytes and nutrients. Formation of multicellular structures and differentiation of kidney cells are tightly regulated processes that begin during the fifth week and end by approximately 34 weeks of human gestation. This review focuses on the morphological, cellular and molecular steps required for kidney formation. Although some of this information is derived from studies of the human kidney, much has arisen from the study of genetic models of mammalian kidney morphogenesis. These models reveal mechanisms by which cell lineages are established in the embryonic kidney and the genetic pathways that are involved in their establishment and maintenance.

One percent of all pregnancies are found to have an antenatal abnormality; of these, 20% involve the genitourinary system. Today, controversy still exists regarding the postnatal management of some antenatal abnormalities detected by ultrasound. We present a case in which antenatal hydronephrosis initially detected by ultrasound appeared to resolve in utero. Postnatally, the child developed Citrobacter diversus urosepsis, meningitis, and cerebral abscess. Voiding cystourethrogram obtained after resolution of sepsis revealed grade IV reflux. This case underscores the importance of a full postnatal evaluation for all children with antenatal hydronephrosis and alerts clinicians to a virulent pathogen not commonly associated with urinary tract infection.

The investigation has been performed in 28 series of histological sections of human embryos and prefetuses (4-20 weeks of the intrauterine development) and in 17 fetal corpses by means of certain histological methods, preparation of graphic reconstructive models, microscopy and fine preparation. The structural form of the definitive organ renal pelvis is demonstrated to depend on the ramification type of the metanephric duct derivatives. This is stipulated by interinductive processes of the ureteral sprout and metanephrogenic tissue. Quantitative and qualitative characteristics of the diverticulum ramification of the mesonephric duct during embryonic period of the prenatal ontogenesis predetermine the number of the calyces renalis majors and minors in the metanephros.

The embryologic development of the metanephric kidney is a regulated and sequential growth process. The induction of the early precursors of the metanephric kidney (pronephros and mesonephric) are essential first steps for the later appearance of the metanephric kidney. The pathogenesis of cystic disease can now be reexamined in light of these unique but carefully programmed growth processes with the expectation that the specific nature of the several growth disorders responsible can be more clearly defined.