[Polyomavirus infections of the urinary tract. Cytologic and ultrastructural features].

The cytopathology of viral infections has some limitations, since the cellular changes provide only an indirect evidence of the underlying disease, and the diagnosis should always be confirmed by virologic methods. We report here one case of Polyomavirus infection in a renal transplant recipient, in which the cellular changes observed in Papanicolaou-stained voided urine specimen were consistent with viral infection. Transmission electron microscopy (TEM) provided a simple and relatively quick identification of viral particles, whose size and morphology were typical for human Polyomavirus. Immunoelectron microscopy (IEM), using colloidal gold technique, confirmed the diagnosis. The morphological criteria used in differential diagnosis and the advantages and limitations of the method are discussed.