Division of Nephrology, St Louis University School of Medicine, St Louis, MO, USA
Sir,
Indwelling Double-J ureteral stents are used to maintain ureteral patency in a variety of benign and malignant conditions. Stents are placed intraoperatively, initially to prevent ureteral stricture and later to relieve obstruction. There are now additional applications for stents, including use in conjunction with extracorporeal shock wave lithotripsy (ESWL) and with various ureteral manipulations, such as calculus removal, dilatation, and medication infusion. Stents are available in a variety of chemical compositions. Stiff stents, originally made of polyethylene, were replaced by polyurethane which had less tendency to break and were easy to insert. Soft or siliconized stents are less irritating and more biocompatible than stiff stents, however, they are more difficult to introduce. Newer biosynthetics, such as C-flex and Percuflex, have the best properties of the older types and offer the advantages of ease of endoscopic insertion, exceptional patient tolerance, and improved resistance to encrustation. These stents have a radio-opaque coating allowing easy radiological visualization. Ureteral stents have to be exchanged or removed within 6 months after implantation because of stent encrustation and or alterations in their components.
Standard urology textbooks comment about visualizing stents by plain abdominal radiography and fluoroscopy, but do not comment about their visibility with ultrasound. Plain radiography consistently visualizes the stent, however, stents can rarely lose their radio-opaque coating with time [1] and not be visualized. Ultrasonography is widely used by the nephrologists, as opposed to radiography, for evaluation of renal diseases. However very little is mentioned in the medical literature about the visualization of ureteral stents with ultrasound. A total of 25 stent insertions under ultrasound guidance has been reported in the literature, claiming easy visualization of the stent in the renal pelvis with ultrasound [24]. Cases of overlooked or forgotten Double-J stents have been reported in the literature which were subsequently identified by plain abdominal radiograph [5]. We present a case where repeated ultrasonography missed an ureteral stent which on plain abdominal radiography was easily visualized extending in to the renal calyces. A subsequent ultrasound done with special attention to visualize the stent in the renal pelvis/calyces was able to identify the stent, which could have been easily mistaken for a calcified vessel.
Case.
A 54-year-old female with a history of diabetes and hypertension was admitted to our hospital with a diagnosis of meningitis, pneumonia and renal insufficiency. She was found to have a mild degree of right hydronephrosis on renal ultrasound. A Double-J ureteral stent (Microvasive, 6 Fr, 24 cm; Boston Scientific, Watertown, MA) was placed during the hospital stay with complete resolution of the hydronephrosis and some improvement in renal function. A renal ultrasound obtained during the outpatient follow-up showed no hydronephrosis and no evidence of stent in the renal pelvis or calyces (Figure 1A). As the patient reported that the stent had not been removed a repeat ultrasound was obtained which confirmed resolution of the hydronephrosis with no evidence of the stent in the renal pelvis or calyces. A urinalysis done at this time revealed 4000 RBC/hpf with 20 WBC/hpf suggesting the presence of an irritating foreign body in the genitourinary tract. A plain abdominal radiograph demonstrated that the stent was in a good position with one end in the upper renal calyces and the other end in the urinary bladder (Figure 1B
). A repeat ultrasound performed by an attending radiologist, with special attention to the renal pelvis and calyces obtaining special views, could visualize the stent as an echogenic double-line structure in the renal calyx (Figure 1C
) which could have been easily mistaken for a calcified vessel.
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Comment.
With the widespread use of ultrasonography, practising nephrologists must be aware of the fact that ultrasound could miss ureteral stents if not looked for diligently. Plain radiograph remains the best method to visualize the ureteral stent, whenever their presence or position is in question.
References