[Uric acid, a neglected molecule--the value of imaging]

Imaging plays a key role in two longterm effects of hyperuricemia: those on the urinary tract and on the skeletal system. This overview concentrates on the diagnosis of urinary stones and of musculoskeletal gout. Urinary stones are negative on radiography, i.e., they cannot be differentiated from the surrounding tissues, and even at intravenous urography only non specific filling defects are shown that may be hard to differentiate from blood clots and papillary necrosis whereas computed tomography without a contrast agent is highly sensitive in detecting all types of stones whether negative or positive at radiography. Gout of the musculoskeletal system usually manifests as an acute gouty arthritis after a long-standing asymptomatic hyperuricemia. An intercritical phase may follow before new acute attacks and--in up to 50%--chronic gout develop. During acute gouty arthritis imaging is non-specific. The distribution pattern, the relation of soft tissue changes and osteolytic paraarticular changes, calcifications and the lack of osteoporosis are a typical, nearly pathognomonic constellation of chronic tophaceous gout. In selected cases CT or MRI may add critical local information.