Gout and Pseudogout

KEY FACTS

Terminology

• Inflammatory arthropathy due to urate crystal deposition (gout) or calcium pyrophosphate dihydrate (CPPD) crystal deposition (pseudogout)

Imaging

• US signs usually specific enough to make diagnosis without joint aspiration
• Tophi

Soft tophi (hyperechoic with no acoustic shadowing) → hard tophi (hyperechoic with intense acoustic shadowing)

– Quite well-defined irregular margins with variable hypoechoic halo (“wet clumps of sugar”)

– Multiple grouped tophi are common
• Tendons and ligaments

Probably most frequent site of gouty crystal deposition

Microdeposits with small hyperechoic foci → large hyperechoic foci with intense acoustic shadowing
• Synovial fluid

Hyperechoic foci or cloudy areas in synovial fluid

Fine punctuate echogenicity (“urate sand”)

Large echogenic aggregates (snowstorm appearance)

Pseudogout: Fewer echogenic foci in synovial fluid
• Hyaline (articular) cartilage

Gout: Thin echogenic band on surface of cartilage (“urate icing” or double-contour sign)

– Most sensitive sign for diagnosis of gouty arthritis

Pseudogout: Thin echogenic band in mid zone of cartilage (CPPD deposition); hyaline cartilage distribution has high disease specificity
• Fibrocartilage

Pseudogout: Punctuate echogenic foci within hypoechoic fibrocartilaginous disc (wrist) or menisci (knee) due to CPPD deposition
• Joint aspiration

Send fresh specimen (since crystals dissolved by water, alcohol, or formalin)

TERMINOLOGY

Synonyms

• Gouty arthropathy, crystalline arthropathy, metabolic arthritis, tophaceous gout, podagra, gouty tophi

Definitions

• Inflammatory arthropathy due to urate crystal deposition (gout) or calcium pyrophosphate dihydrate (CPPD) crystal deposition (pseudogout)

IMAGING

General Features

• Best diagnostic clue

Identification of echogenic foci (crystals) in joint or soft tissues
• Location

Gout: 1st metatarsophalangeal (MTP) joint (podagra) (50%) > ankle > midfoot > knee > wrist

– Helix of ear, olecranon bursa, tendons (especially patellar and triceps), knee and ankle ligaments

Pseudogout: Any joint, especially knee, wrist, scapho-trapezium-triquetral joints

– Extrachondral involvement (synovium, tendons, ligaments, soft tissues) is less common in pseudogout than in gout
• Size

Gouty tophi range from few mm to 5 cm
• Morphology

Monoarticular swelling → deforming polyarthropathy

– Tophi lead to hard, discrete nodules in subcutaneous, paraarticular, and other tissues

Radiographic Findings

• Eccentric soft tissue hyperdense swelling ± calcific tophi
• Asymmetrical arthropathy

Absence of osteopenia

Joint space preserved until late

Marginal erosions with overhanging edges and thin sclerotic edge

– Larger than erosions of rheumatoid arthritis

CT Findings

• Dual-energy CT has diagnostic accuracy close to 100% for gout with excellent reader agreement

Can automatically quantify urate volume

MR Findings

• T1WI

Tophi: Well-defined masses, isointense to muscle
• T2WI

Tophi: Low to high signal intensity

– Variable intensity reflects amount of urate deposition, edema, and maturity of granulation tissue

– Paucity of bone marrow edema suggests how pathophysiology of gouty erosions differs from other inflammatory arthropathies
• T1WI C+

Tophi: Honeycomb-like heterogeneous to near-homogeneous enhancement

– Honeycomb appearance is due to avascular urate surrounded by vascularized granulation tissue

Ultrasonographic Findings

• Tophi

Soft tophi (hyperechoic with no acoustic shadowing) → hard tophi (hyperechoic with intense acoustic shadowing)

Quite well-defined irregular margins with variable hypoechoic halo (“wet clump of sugar”)

Multiple grouped tophi are common
• Tendons (and ligaments)

Probably most frequent site of crystal deposition in gout

Ranges from microdeposits with small, hyperechoic foci within tendon to large, hyperechoic foci with intense acoustic shadowing

– Fibrillar pattern is disrupted, tendon is stretched and displaced

– ± tendon rupture (uncommon)

– Acoustic shadowing with larger (> 5-mm) masses
• Synovial fluid

Gout: Variable appearance of joint fluid

– Hyperechoic aggregates in synovial fluid

Fine punctuate echogenicity (“urate sand”)

Large echogenic aggregates (snowstorm appearance)

Pseudogout produces fewer echogenic aggregates in joint fluid
• Articular cartilage

Gout: Thin echogenic band on surface of cartilage (“urate icing” or double-contour sign)

– Most sensitive sign for diagnosis of gouty arthritis

Pseudogout: Thin echogenic band in mid zone of cartilage (CPPD deposition)

– No acoustic shadowing
• Fibrocartilage

Pseudogout: Punctuate echogenic foci within hypoechoic fibrocartilaginous disc (wrist) or menisci (knee) due to CPPD deposition
• Bone

Marginal erosions

– Invariably associated with overlying tophus
• Subcutaneous tissue

Gouty panniculitis, which is lobular panniculitis, particularly of lower extremities

Imaging Recommendations

• Best imaging tool

US best 1st-line investigation for gout

More accurate than clinical examination or radiography at detecting gout, though less accurate than DECT

Conflicting results, though overall sensitivity of US seems to be slightly less than DECT, particularly for extraarticular disease

– 1st MTP joint, 2nd MTP joint, ankle, knee, wrist, and patellar or triceps tendons all common sites of involvement

Screening 1st MTP joints and either knees or ankles is comparable to screening all areas

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Apr 9, 2020 | Posted by admin in MUSCULOSKELETAL IMAGING | Comments Off

KEY FACTS

Terminology

TERMINOLOGY

Synonyms

IMAGING

General Features

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Gout and Pseudogout

Gout and Pseudogout

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