Study Type - Therapy (prospective cohort) Level of Evidence 2b What's known on the subject? and What does the study add? Stone density on non-contrast computed tomography (NCCT) is reported to be a prognosis factor for extracorporeal shockwave lithotripsy (ESWL). In this prospective study, we determined that a 970 HU threshold of stone density is a very specific and sensitive threshold beyond which the likelihood to be rendered stone free is poor. Thus, NCCT evaluation of stone density before ESWL may useful to identify which patients should be offered alternative treatment to optimise their outcome.
OBJECTIVE: To evaluate the usefulness of measuring urinary calculi attenuation values by non-contrast computed tomography (NCCT) for predicting the outcome of treatment by extracorporeal shockwave lithotripsy (ESWL).
PATIENTS AND METHODS: We prospectively evaluated 50 patients with urinary calculi of 5-22 mm undergoing ESWL. All patients had NCCT at 120 kV and 100 mA on a spiral CT scanner. Patient age, sex, body mass index, stone laterality, stone size, stone attenuation values (Hounsfield units [HU]), stone location, and presence of JJ stent were studied as potential predictors. The outcome was evaluated 4 weeks after the ESWL session by NCCT. ESWL success was defined as patients being stone-free (SF) or with remaining stone fragments of <4 mm, which were considered as clinically insignificant residual fragments (CIRF).
RESULTS: Our survey concluded that 26 patients (52%) were SF, 12 (24%) had CIRF and 12 (24%) had residual fragment on NCCT after a one ESWL treatment. Stones of patients who became SF or had CIRF had a lower density compared with stones in patients with residual fragments [mean (sd) 715 (260) vs 1196 (171) HU, P < 0.001]. The Youden Index showed that a stone density of 970 HU represented the most sensitive (100%) and specific (81%) point on the receiver-operating characteristic curve. The stone-free rate for stones of <970 HU was 96% vs 38% for stones of ≥970 HU (P < 0.001). A linear relationship between the calculus density and the success rate of ESWL was identified.
CONCLUSION: The use of NCCT to determine the attenuation values of urinary calculi before ESWL helps to predict treatment outcome, and, consequently, could be helpful in planning alternative treatment for patients with a likelihood of a poor outcome from ESWL.
© 2012 THE AUTHORS. BJU INTERNATIONAL © 2012 BJU INTERNATIONAL
BJU Int. 2012 Feb 28. doi: 10.1111/j.1464-410X.2012.10964.x. [Epub ahead of print]
PMID: 22372937 [PubMed - as supplied by publisher]
Analysis of treatment outcome of one ESWL session was carried out. The conclusion was that for an HU-value above 970 the stone-free rate was low compared with that recorded for HU levels below 970. This result confirms the well-known fact that hard and dense stones are more difficult to disintegrate and might require repeated treatment sessions for satisfactory fragment size. It is of note that all patients in this study were treated with a shockwave frequency of 90/min and that the majority of the patients (58%) had their stones in the renal pelvis. For stones close to the spine shockwave power might have been reduced by interference with skeletal structures. Such a factor might have been particularly important for poor disintegration of the hard stones. Nothing is mentioned about the energy levels used.
In terms of stone location there was obviously no difference in success since there were 33% failures for both lower calyx and upper/mid calyx stones.
My interpretation of this report is that for stones with HU above 970 more shockwave energy and repeated session should be anticipated in order to get a satisfactory result with ESWL.