Magnetic resonance imaging of tophaceous gout

Gouty arthritis is a common disease, and tophi represent the chronic phase of the disease process. A tophus consists of a core of monosodium urate (MSU) crystals surrounded by various degrees of vascularity of inflammatory tissue. We retrospectively reviewed the magnetic resonance (MR) images of 16 joints with tophaceous gout encountered in 14 patients. Totally 18 lesions of tophaceous mass were identified among the 14 patients. The MR images were evaluated for signal intensity characteristics and patterns of enhancement of tophi, and these findings were correlated with pathologic examinations in eight lesions. On T1-weighted images, signal intensity of tophi was low when compared with adjacent skeletal muscle in all 18 lesions. The signal intensity of tophi on T2-weighted images was more variable. Twelve of 18 lesions appeared as an area of high signal intensity, and as an area of low signal intensity in 6 of the 18 lesions, compared with adjacent skeletal muscle. Within the T2-weighted high-signal tophi, dot-like low-signal areas on both T1- and T2-weighted images were also noted in 11 of the 12 lesions. On post-enhanced images, all 12 high-signal tophi exhibited moderate, heterogeneous enhancement. In two of these 12, additional marginal enhancement was also noted in different regions of the lesions. Four of the six lesions with T2-weighted low-signal tophi underwent post-enhancement studies and showed poor enhancement in all lesions. The authors conclude that the signal intensity of tophi is constant on T1-but quite variable on T2- weighted and post-enhancement images. The presence of high signal intensity and enhancement could be related to the increased vascularity of adjacent affected synovium and hypervascular granulation tissues within the tophi.