In this review, we will describe the spectrum of usual and unusual imaging findings in the chronic gout in common and rare sites. The most common sites of presentation are (in decreasing order of frequency) feet, ankles, knees, hands and elbows.

IMAGING FINDINGS IN CR

Radiographs of affected joints have little utility in acute gouty arthritis because generally many patients will not manifest abnormalities radiographic until many years later. After of several years of intermittent episodic arthritis, patients that have chronic tophaceous gout will show characteristic features on radiography, and sometimes pathognomonic (no matter what joint is involved), mainly by tophus erosion of the underlying bone. Periarticular erosions with overhanging edges and adjacent tophi with amorphous calcifications are pathognomonic.

1- Soft tissue alterations: tophi are eccentric juxtaaarticular soft tissue masses usually see after several years of chronic disease (see Fig. 1). Tophi may also be intraosseous (may mimic bone infarcts or enchondromas), intraarticular, or extraarticular. They may show an increased density by calcium precipitation to varying degrees (Fig. 2, Fig. 3). However, calcification of a tophus is an unusual finding.

2- Eccentric bony erosions: are key features. Erosions are typically punched out and they have been described as a “mouse bite”, occurring in an outward direction, with overhanging edges and sclerotic borders (Fig. 4). Occasionally, with longstanding disease, erosions may be mutilating as those of psoriatic arthritis or rheumatoid arthritis.

3- Proliferative bony changes: are manifestations of chronicity. Bone apposition may cause diaphyseal thickening, expansion of ends of bones, sclerotic rims, overhanging edges, irregular bone spicules at sites of tendon and ligament attachment, and joint changes that may result in osteoarthritis secondary (Fig. 5, Fig. 6, Fig. 7).

4- Joint space preserved: is preserved until late in the course of the disease (see Fig. 1,  Fig. 3, Fig. 4).

5- Normal mineralization: preservation of normal bone mineral density until the late stages of the disease (see Fig. 1,  Fig. 3, Fig. 4, Fig. 7). It is unusual to see a juxtaarticular osteoporosis (only in extremely longstanding disease due to disuse).

IMAGING FINDINGS IN CT

CT has begun to be used in the evaluation of gout until recently. Nodular lesions with Hounsfield units of 160 or above on CT may suggest the diagnostic of gout. CT imaging is very useful for identifying paraarticular calcifications when present (Fig. 8). CT also will allow for very good visualisation of bone erosion.

IMAGING FINDINGS IN MR

MR imaging is very useful to evaluate the extent of disease and involvement of soft tissues and synovium. MRI also is of particular interest for investigation of spinal involvement in gout.

At MR imaging, tophi have a wide spectrum of variable appearance, depending on the degree of hydration and calcification (hyperintensity has been attributed to the presence of high water content, whereas tophi with calcium, crystal and fibrous tissue appear hypointense). Tophi usually show low-signal intensity on both T1-weighted and T2-weighted images and a variable enhancement pattern (Fig. 9), with homogenous enhancement being the most common appearance (Fig. 10), indicating hypervascularity of the tophus. Peripheral enhancement has also been reported (Fig. 11).

The typical manifestations of acute inflammation are periarticular edema, synovitis, joint effusions and enhancement of the periarticular soft tissue structures, but these imaging findings may be seen in other inflammatory arthropathies.

COMMON JOINT DISTRIBUTIONS

1- Foot: the first metatarsophalangeal joint is the most commonly affected in gout (see Fig. 1, Fig. 3 Fig. 9). The imaging findings more common are tophi that cause erosions on the medial and dorsal aspect of the head of the first metatarsal and the adjacent proximal phalanx (see Fig. 4; Fig. 12, Fig. 13) with an asymmetrical distribution. Tophi and erosions may be recognized in a lateral view of the first metatarsophalangeal joint (see Fig. 7) and may be associated with hallux valgus deformity (see Fig. 12). It is important to know that any of the metatarsophalangeal joints may also be affected (see Fig. 6) mainly the fifth metatarsophalangeal joint (Fig. 14). Occasionally interphalangeal joints are areas of involvement (Fig. 15), frequently the first interphalangeal (see Fig. 4). Erosive changes may be seen in tarsometatarsal (Fig. 16) or intertarsal joints with retrocalcaneal bursitis.

2- Ankles: often associated with others joints affected by gout. The typical manifestations are tophi and periarticular erosions with sclerotic borders (Fig. 17).

3- Hands: the most common sites of presentation are (in decreasing order of frequency) the distal interphalangeal joints, the proximal interphalangeal joints, and the metacarpophalangeal joints. Frequently, these areas of involvement present an asymmetrical distribution. Erosive changes, sclerotic borders, tophi and proliferative bony changes may be seen in these sites (see Fig. 5, Fig. 10; Fig. 18, Fig. 19 , Fig. 20).

In wrists all of the imaging findings described previously may be identified, mainly in the carpometacarpal joints and ulnar styloid (Fig. 21, Fig. 22).

4- Elbows: swelling soft tissues may be seen around the elbow mainly over the extensor surface with associated olecranon bursitis (Fig. 23). Bilateral olecranon bursitis usually suggests the diagnosis of gout. Erosive or proliferative bony changes in the olecranon process have been reported in many patients (Fig. 24).

5- Knees: erosions of the medial or lateral tibial and femoral condyles or the anterior tibial tubercle with joint space preserved are manifestations that may be observed in the knee (see Fig. 11; Fig. 25). There is a predilection for tophaceous deposits around the prepatellar bursa, but tophi may be widespread being visualized anywhere in the knee (see Fig. 2). Tophus intraosseous may appear as focal cysts simulating neoplasm.

UNUSUAL JOINT DISTRIBUTIONS

1- Joint sacroiliac: is manifested by subchondral cyst formation, erosions and bony sclerotic changes. These imaging findings present an asymmetrical distribution and they are more frequently visualized in the early stages of the disease.

2- Hip, glenohumeral, sternoclavicular, acromioclavicular, and temporomandibular joints: are rare localizations, but often are observed in patients with gout. Manifestations are similar to others affected joints by gout (Fig. 26).

3- Spine: is a very infrequent localization, but erosions of the odontoid, vertebral bodies and end plates have been described. Tophaceous deposits may cause paraplegia in the spine by compression.