Imaging of tophaceous gout: computed tomography provides specific images compared with magnetic resonance imaging and ultrasonography

Abstract

Methods: Four male patients with chronic gout with tophi affecting the knee joints (three cases) or the olecranon processes of the elbows (one case) were assessed. Crystallographic analyses of the synovial fluid or tissue aspirates of the areas of interest were made with polarising light microscopy, alizarin red staining, and x ray diffraction. CT was performed with a GE scanner, MR imaging was obtained with a 1.5 T Magneton (Siemens), and ultrasonography with colour Doppler was carried out by standard technique.

Results: Crystallographic analyses showed monosodium urate (MSU) crystals in the specimens of the four patients; hydroxyapatite and calcium pyrophosphate dihydrate (CPPD) crystals were not found. A diffuse soft tissue thickening was seen on plain radiographs but no calcifications or ossifications of the tophi. CT disclosed lesions containing round and oval opacities, with a mean density of about 160 Hounsfield units (HU). With MRI, lesions were of low to intermediate signal intensity on T₁ and T₂ weighting. After contrast injection in two cases, enhancement of the tophus was seen in one. Colour Doppler US showed the tophi to be hypoechogenic with peripheral increase of the blood flow in three cases.

Conclusion: The MR and colour Doppler US images showed the tophi as masses surrounded by a hypervascular area, which cannot be considered as specific for gout. But on CT images, masses of about 160 HU density were clearly seen, which correspond to MSU crystal deposits.

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Figure 1 .

(A) Patient 2, left knee, lateral tophus. Two dimensional reconstruction coronal CT: lateral soft tissue thickening containing nodular opacities of 150–200 HU in density (a smaller medial tophus lesion is seen). (B) Coronal T₁ MRI with fat saturation after injection of gadolinium. The lateral tophus is intermediate in signal intensity. The periphery of the tophus is stained with contrast. (C) Colour Doppler view of the lateral aspect of the knee: the tophus is hypoechogenic with an hyperechogenic rim. Vessels are seen all around the tophus (coloured spots).

Figure 2 .

(A) Patient 3, left knee, prepatellar tophus. CT showing prepatellar soft tissue thickening and small nodular opacities of 150–200 HU in density. There are erosions with overhanging edges of the patella. Nodular opacities are also seen in the posterior part of the knee. (B) Transverse T₂ MRI with fat saturation. The soft tissue is intermediate in signal intensity. The nodular lesions are clearly seen. There is also joint fluid. (C) Colour Doppler transverse view of the medial aspect of the knee. The tophus appears as a hypoechogenic nodule surrounded by a hyperechogenic rim. Some vessels are visible within and around the nodule.