Multimodality imaging of chronic tophaceous gout

The diagnosis of gout is usually based on clinical presentation and laboratory findings. Imaging plays a role in the assessment and grading of articular damage related to chronic, long-standing disease, which is characterized by granulomatous synovitis, tophi, and erosions. Multimodality imaging of chronic tophaceous gout may be useful in clinical practice for a variety of purposes, including assessment of disease-related anatomical changes and monitoring of articular and soft-tissue lesions over time, especially in response to urate-lowering therapy. Radiography remains the primary imaging technique. Ultrasonography may detect monosodium urate crystals on cartilage, is helpful to assess small joint effusion, to guide to joint aspiration, and to evaluate the volume of tophi. Computed tomography is considered to be more sensitive than plain radiography in the detection and evaluation of cortical bone erosions associated with tophi. MRI represents the only imaging modality which provides visualization of bone marrow oedema associated with erosions and may be useful to characterize and distinguish tophi from other soft tissue nodules

Imaging studies of crystalline arthritides

Gout, calcium pyrophosphate dihydrate (CPPD) deposition disease, and calcium hydroxyapatite deposition disease (HADD) are the three most common crystal-induced arthropathies. Multimodality imaging may help in their diagnosis, and is useful for a precise and comprehensive assessment and grading of the related osteoarticular damage. Plain film radiography, due to its low cost and wide availability, is the first imaging technique to be used in crystal deposition diseases, providing well-known and specific findings for CPPD deposition disease and HADD, while it may undergrade the early osteoarticular lesions in gouty patients. Ultrasonography (US) is a radiation-free approach that accurately depicts crystal deposits in cartilage, peri- and intra-articular soft tissues, but it does not give a panoramic view of the affected joints. Cross-sectional imaging techniques can examine crystal deposits in the spine and axial joints. CT has the potential to distinguish monosodium urate (MSU) crystals from calcium containing crystals, due to their different attenuation values. MRI may demonstrate synovitis, erosions and bone marrow edema in gouty patients and it may differentiate tophi from other soft tissue nodules due to its high contrast resolution and power of tissue characterization