What's the Diagnosis - Case 38

History 63 year old man with right knee and progressive left hand pain.

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Findings Radiographs of the knee demonstrate a well defined lucency of the anterior aspect of the patella along the course of the extensor mechanism. MRI, demonstrates an intermediate to hyperintense mass of the extensor mechanism causing erosion of the anterior patella. Imaging of the hand, demonstrates progressive soft tissue mass at the PIP of the 4th digit. The mass demonstrates subtle density and a subtle erosion of the subjacent bone.

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Diagnosis Gout is an arthropathy based on urate crystal deposition. The deposition is typically in a juxta-articular location but may also be within tendons particularly within certain tendons such as the Achilles or knee extensor mechanism. On radiographs, gout produces classically juxta-articular erosions with well defined margins or overhanging edges related to the long standing process and subsequent bone repair. The soft tissue mass or tophus may become dense or frankly calcified related to dystrophic calcification within abnormal tissue.

On MRI, the lesions are classically defined as having low signal intensity on all pulse sequences, but as seen in this example, mild hyperintensity may be encountered. The overall constellation of findings must be taken into account to make the diagnosis. In this case, the soft tissue mass of the left hand was resected and urate crystals were identified via microscopic analysis.

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Resources

• Resnick. Diagnosis of Bone and Joint Disorders. 4th Ed. 2002.

• Intra-articular gouty tophi of the knee: CT and MR imaging in 12 patients.

Chen CK, Yeh LR, Pan HB, Yang CF, Lu YC, Wang JS, Resnick D. Skeletal Radiol. 1999 Feb;28(2):75-80.

• Imaging of intraarticular masses. Sheldon PJ, Forrester DM, Learch TJ. Radiographics. 2005 Jan-Feb;25(1):105-19. Review.

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