Computed tomography versus ureteroscopy in identification of renal tract stone with ureteral stent in situ

Abstract

Non-contrast helical computed tomography (CT) is well validated in diagnosing urinary tract stone disease. It has been shown that this technique is superior to all other imaging modalities with a 97% sensitivity and a 96% specificity in detecting renal tract calculi.1 Nevertheless, using CT to diagnose stones in the urinary tract with a ureteral stent in situ is more difficult due to the complexity in differentiating between the stent and stones. Tanrikut et al 2 and Yoshida et al 3 suggested that stone density has a Hounsfield unit value of between 400 and 1,600 whereas a ureteral stent has a Hounsfield unit value of over 2,000. When using abdominal window settings to analyse CT, it is difficult to differentiate between stent and stone because they would have a similar bright white appearance. By using bone window settings, however, there would be a visual distinction between the stent and stone. 2,3The method of using bone window settings in the diagnosis of a stone with a stent in situ has not yet been validated. In our study, we attempted to validate this method by comparing the results of CT and ureteroscopy in identification of renal tract stones with a ureteral stent in situ. Ureteroscopy is often perceived as the current 'gold standard' as it allows clinicians to directly visualise stones in the renal tract. In spite of this, it is still possible to miss small stones with ureteroscopy.If CT were proven to be as good as ureteroscopy, then clinicians could safely rely on CT to pre-operatively diagnose stone clearance with a stent in situ. This would have implications for the type of surgery offered to patients, namely local anaesthetic removal of ureteral stents versus the more invasive and more time consuming ureteroscopy procedure. This would ultimately offer improvements in theatre efficiency. MethodsAll patients who had stents inserted for renal tract stones and underwent non-contrast CT with the stent in situ followed by ureteroscopy between May 2008 and October 2009 at The Canberra Hospital, Australia, were analysed retrospectively.Helical CT was performed using a 1mm slice collimation without intravenous or oral contrast administration. CT was reported in bone window settings to determine the presence and size of stones by consultant radiologists from the same department. The aim of this study was to validate the use of non-contrast computed tomography (CT) with a ureteral stent in situ instead of ureteroscopy for identification of renal tract stones. METHODS All patients who had stents inserted for renal tract stones and underwent non-contrast CT with the stent in situ followed by ureteroscopy between May 2008 and October 2009 at The Canberra Hospital, Australia, were analysed retrospectively. Statistical analysis was performed to compare any differences between CT and ureteroscopy in the identification of stones. RESULTS Overall, 57 patients were included in the study. The difference between CT and ureteroscopy findings was statistically significant. CT identification of stones with a stent in sit...

The S.T.O.N.E. Score: A new assessment tool to predict stone free rates in ureteroscopy from pre-operative radiological features

“…Although CT may be the best imaging modality to evaluate presence and or burden of stone post treatment, certainly, it is not free of limitations. Furthermore, the presence of ureteral stents may obscure the presence of small stone fragments following URS (26). This pragmatic method of limiting postoperative imaging to questionable and complicated cases is commonly accepted and minimizes radiation and costs to the patient (9,27).…”

Comparative Evaluation of Diagnostic Quality in Native Low-dose CT without and with Spectral Shaping employing a Tin Filter in Urolithiasis with implanted Ureteral Stent

“…Unter Verwendung einer NI-Margin von 0,5 Bewertungsstufen resultierte eine Verwerfgrenze der NI-Hypothese in der Gruppe A von 2,73 und in Gruppe B von 3,65, jeweils basierend auf der durchschnittlichen Bewertung der Steinabgrenzbarkeit im Protokoll ohne Zinnfilter. Die 95 %-Konfidenzintervalle der Steinabgrenzbarkeit mit Zinnfilter in der Gruppe A waren [3,12] und in Gruppe B [4,47]. Die jeweilige Verwerfgrenze wurde von der unteren Grenze des Konfidenzintervalls mit Zinnfilter in keiner der Gruppen unterschritten, konsistent mit der Annahme einer NI des Untersuchungsprotokolls mit Zinnfilter.…”

“…Vorteile der CT gegenüber der Sonografie bestehen hierbei in der Untersucherunabhängigkeit, einer insgesamt geringeren Artefaktanfälligkeit, der vollständigen Abbildung des Harntraktes sowie der Option einer Bestimmung der Steinkomposition anhand seiner Densität. Unmittelbar an das Konkrement angrenzende Harnleiterschienen können dabei die Messbarkeit der Größe und Densität des Urolithen beeinträchtigen [3]. Harnleiterschienen sind zur Entlastung einer Harnstauung regelmäßig indiziert, sodass diese Konstellation eine häufig auftretende Herausforderung für den Diagnostiker ist [2].…”

“…The advantages of CT compared to sonography are the independence of the examiner, overall lower susceptibility to artifacts, complete imaging of the urinary tract, as well as the option of determining the stone composition based on its density. Ureteral stents directly adjacent to the calculus can thereby affect the measurability of the size and density of the urolith [3]. Ureteral stents are regularly indicated to relieve urinary retention, making this constellation a common challenge for the diagnostician [2].…”

Automated False Positive Reduction and Feature Extraction of Kidney Stone Object in 3D CT Images

“…Although a fair amount of research has been performing in segmentation of abdominal organs, such as the liver, kidneys, and spleen, from CT scan image, different organs and tissues have very similar gray levels, which consigns thresholding to limited utility [4]. Kidney stone segmentation on CT imaging has also difficult due to the complexity in differentiating the stone, the stent, calcification and bone which have similar gray levels [5] as shown in Fig. 1 (b).…”