Spontaneous hydronephrosis in C57BL/KsJ mice

Spontaneous hydronephrosis was observed in 15 of 33 necropsied C57BL/KsJ mice. The gross and histological appearances of these lesions are described. Spontaneous hydronephrosis is rare in mice and has not been previously described in this strain. At least four different mutations are reported to cause hydronephrosis in the mouse; each is associated with a high incidence of severe skeletal defects. Because no skeletal malformations were observed in the present study, it is likely that either a multigenic trait which has been present for a long time but is expressed variably, or a mutation other than those previously described may be responsible for hydronephrosis in C57BL/KsJ mice.