Age / Sex : 54 / M

Chief complaint: palpable mass on the right knee

1) What is your impression?

Two weeks later, you can see the final diagnosis with a brief discussion of this case.

(Quiz는 quiz일 뿐이오니 답안은 한 개만 보내주시기 바랍니다)

Courtesy: 정선관 ( Juhng Seon Kwan), 원광의대 (Wonkwang University Hospital)

gouty tophus

Discussion

Findings:.

 Plain radiograph of the right knee shows a focal soft tissue swelling superficially on the pre-tibial region proximally.

MRI shows a lobulated superficial soft tissue mass having low signal intensity on all pulse sequences with contrast enhancement of peripheral portion and adjacent soft tissue. Differential Diagnosis:

Desmoid or extra-abdominal fibromatosis

Rheumatoid nodule

Organizing hematoma

Calcified soft tissue mass

Diagnosis:  

Gouty tophus

Discussion:

Traditionally, and even to this day, gout is largely diagnosed clinically, often by nonspecialists. Identification of monosodium urate crystals in the joint aspirate is considered the reference standard in the diagnosis of gout but may not be identifiable in up to 25% of acute gout cases

Radiography has historically been used to confirm suspected gout; however, classic findings seen on radiography, such as marginal erosions with overhanging edges and sclerotic margins, occur late in the disease process. Soft tissue nodules (tophi) are also a feature of longstanding gout.

The MRI features of gout are variable. Tophi have intermediate or low signal intensity

on T1-weighted images and heterogeneous signal intensity on T2-weighted or fluid-sensitive sequences, possibly because of the presence of variable amounts of calcium. Tophi can show uniform enhancement or show a nonenhancing center. Bone erosions adjacent to tophi can produce cortical destruction and variable bone marrow edema.

Ultrasound study with high-frequency transducers (12 MHz and higher) provide high-resolution imaging that is well-suited for the evaluation of gout.

CT allows to detect tophi as discrete masses with a density of 160–170 HU, which is higher than that of adjacent soft tissues. Tophi can be seen within the bone, about joints, within tendons, and in the soft tissues. CT also defines the well-demarcated corticated erosions with overhanging margin at intraarticular and extraarticular sites, which are often associated with tophi.

DECT is a useful diagnostic tool in the management of gout in the acute setting, can accurately assess deeper tophi, and, with the use of dedicated automated volume assessment software, can measure MSU crystal volumes in the extremities. Direct quantitative measurement of MSU volume can be made with DECT software, so reduction in actual MSU burden following successful treatment can be documented with serial DECT scans.

References:

Girish G, Glazebrook KN, Jacobson JA. Advanced imaging in gout. AJR 2013; 201:515–525

Choi HK, Burns LC, Shojania K, et al. Dual energy CT in gout: a prospective validation study.

Ann Rheum Dis 2012; 71:1466–1471

Choi HK, Al-Arfaj AM, Eftekhari A, et al. Dual energy computed tomography in tophaceous gout.

Ann Rheum Dis 2009; 68:1609–1612