Computed tomography window affects kidney stones measurements

Vol. 45 (5): 948-955, September – October, 2019

doi: 10.1590/S1677-5538.IBJU.2018.0819


ORIGINAL ARTICLE

Alexandre Danilovic 1, Bruno Aragão Rocha 2, Giovanni Scala Marchini 1, Olivier Traxer 3, Carlos Batagello 1, Fabio Carvalho Vicentini 1, Fábio César Miranda Torricelli 1, Miguel Srougi 1, William Carlos Nahas 1, Eduardo Mazzucchi 1
1 Departamento de Urologia do Hospital das Clínicas da Faculdade de Medicina da Universidade de São Paulo, SP, Brasil; 2 Departamento de Radiologia do Hospital das Clínicas da Faculdade de Medicina da Universidade de São Paulo, SP, Brasil; 3 Sorbonne Université, GRC n 20 Lithiase Renale, AP-HP, Hôpital Tenon, F-75020 Paris, France. University, Paris, France University, Paris, France

ABSTRACT

Objectives: Measurements of stone features may vary according to the non-contrast computed tomography (NCCT) technique. Using magnified bone window is the most accurate method to measure urinary stones. Possible differences between stone mea­surements in different NCCT windows have not been evaluated in stones located in the kidney. The aim of this study is to compare measurements of kidney stone features between NCCT bone and soft tissue windows in patients submitted to retrograde intra­renal surgery (RIRS).

Materials and Methods: Preoperative and 90th postoperative day NCCT were performed in 92 consecutive symptomatic adult patients (115 renal units) with kidney stones be­tween 5 mm to 20 mm (< 15 mm in the lower calyx) treated by RIRS. NCCT were evalu­ated in the magnified bone window and soft tissue window in three axes in a different time by a single radiologist blinded for the measurements of the NCCT other method.

Results: Stone largest size (7.92±3.81 vs. 9.13±4.08; mm), volume (435.5±472.7 vs. 683.1±665.0; mm3) and density (989.4±330.2 vs. 893.0±324.6; HU) differed between bone and soft-tissue windows, respectively (p<0.0001) 5.2% of the renal units (6/115) were reclassified from residual fragments > 2 mm on soft tissue window to 0-2 mm on bone window.

Conclusion: Kidney stone measurements vary according to NCCT window. Measurements in soft tissue window NCCT of stone diameter and volume are larger and stone density is lesser than in bone window. These differences may have impact on clinical decisions.

Keywords: Kidney Calculi; Nephrolithiasis; Patient Outcome Assessment

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