[Keratinizing squamous metaplasia (cholesteatoma) of the upper urinary tract].

Presentation of four cases of keratinizing squamous metaplasia (KSM), two of the renal pelvis, one pyelocaliceal and one ureteral. Nephrouretetectomy was performed in all cases. All our patients showed good evolution. A review of the literature is made discussing all the etiological, diagnostic and therapeutical aspects of the condition. Its benign evolution is highlighted as well as the current need, once a better knowledge of the condition's natural history is available, of using a conservative approach.