The role of renal dual-energy computed tomography in exploring the gouty kidney: the RENODECT study

Abstract

Objective: The objective of this study was to explore the ability of dual-energy computed tomography (DECT) to detect monosodium urate (MSU) crystal deposits in the kidneys and renal artery walls, and uric acid urolithiasis, in patients with gout and chronic kidney disease (CKD).

Methods: Patients with gout and with stage 2-4 CKD were prospectively included in this cross-sectional study. Patients underwent renal, knee and feet DECT scans. Renal DECT scans were read for MSU-coded lesions in the kidneys, renal artery walls, and urinary tract using different post-processing settings. Characteristics of patients with and without DECT-positive lesions were compared, and the DECT parameters of these lesions were measured.

Results: A total of 27/31 patients with had renal DECT scans and were included in the analysis (23/27 men, mean (standard deviation) 73 (9) years old, mean eGFR 45.3 mL/min/1.73 m2 (21.0), volumes of MSU in the knees and feet ranging from 0.11 to 475.0 cm³). None of the patients exhibited deposition of MSU crystals in the kidneys. One case of calyceal calculi and one case of ureterolithiasis were observed, wrongly coded as MSU in default post-processing settings for gout but identified as uric acid in the "kidney stone" settings. Five patients had MSU-coded plaques in the renal arteries, which had DECT parameters consistent with early calcified plaques rather than MSU, and had no association with volumes of peripheral MSU deposition.

Conclusion: DECT is unable to detect genuine monosodium urate crystal deposits in kidneys and renal artery walls, and but can characterize chronic asymptomatic urolithiasis.

Keywords: Gout; chronic kidney disease; dual-energy computed tomography; monosodium urate; uric acid.

Figure 1.

Presence of monosodium urate (MSU)-coded plaque in the right renal artery in default “gout” (2.5 mm) (a), and submillimetric in optimized (b) settings in a 60-year-old patient with moderate MSU deposits in the knees (c) and feet (d). Absence of any renal or vascular MSU deposits (e) in a 61-year-old patient with extensive MSU crystal deposits in the knees (f) and feet (g). Presence of calyceal calculi in (H) native conventional CT images, coded as monosodium urate (MSU) crystals in default “gout” settings (i), uncoded in optimized “gout” settings (j), and coded as uric acid in “kidney stones” settings (k).

Figure 2.

Combined effects of volumetric mass density (Rho) and effective atomic number (Zeff) on CT numbers at 80 and 140 kV on tophi, arterial plaques and urinary tract deposits. Each dot representing a combined value of attenuations at 140 and 80 kV will be coded as MSU (green) if above 150 HU and loosely (default settings) or closely (optimized settings) around the line where attenuations at both energies are equal (isoattenuation). Dots below the isoattenuation line will be coded as uric acid in “kidney stones” mode, while those above the line (higher Zeff) will be coded as containing calcium if in sufficient concentration. Typical MSU deposits (tophi) are distributed closely to the isoattenuation line. MSU: monosodium urate, HU: Hounsfield unit.