Nephrostomy is a procedure of many functions, but the most common is providing urinary drainage in case of obstruction of the ureter when retrograde access is impossible.
The drainage is built by a catheter, stent or tube. Those devices reach renal pelvis or a calyx, passing through the body wall and renal parenchyma and are then connected to a bag outside the body that collects the urine.

Nephrostomy has also application among other procedures by dissolving or removing renal calculi; getting access to the upper urinary tract for many endourologic procedures or supplying chemotherapeutic substances to the renal collecting system.
Nephrostomy Author: Stefan H Hautmann, MD, PhD Professor of Urology, Director, Department of Urology and Pediatric Urology, Luedenscheid Hospital, Academic Hospital of the University of Bonn, Germany
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Gale Encyclopedia of Surgery: A Guide for Patients and Caregivers | 2004 | Davidson, Tish; Laberge, Monique
COPYRIGHT 2004 The Gale Group Inc.
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Drain Guard is a device applicable by anchoring nephrostomy catheter inserted into the renal pelvis or the bladder from a position on the lower back.

National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health