Tophaceous Gout Mimicking a Neoplasm of the Patella

• Abstract
• Case Description
• Discussion
• Key Radiologic Findings
• Conclusion
• Take-Home Points
• References

Abstract

Tophaceous gout of the patella and extensor apparatus of the knee can mimic a musculoskeletal neoplasm. Considering gout, correlation with clinical history and presentation, and meticulous analysis of imaging semiology are key to a correct diagnosis. The most useful signs are periarticular erosion with overhanging edges, increased soft tissue on radiography and computed tomography, the “snowstorm sign” on ultrasound, variable signal and enhancement, bandlike infiltration of tendons, and osseous erosions with no or little bone marrow edema on magnetic resonance imaging. Dual-energy computed tomography is both a sensitive and specific tool for noninvasive characterization of gout and for differentiating other crystal arthropathies.

Case Description

A 36-year-old obese man was referred for a second opinion about a suspected suprapatellar soft tissue neoplasm. The patient presented with an atraumatic 2-year history of swelling of the right knee, night pain, locking, instability, and morning stiffness. He had shown no response to nonsteroidal anti-inflammatory drugs. Physical examination revealed joint effusion and supra- and prepatellar swelling.

Conventional radiography (CR) demonstrated joint effusion and sclerotic delineated osteolysis at the patellar base ([Fig. 1]). Magnetic resonance imaging (MRI) showed a bandlike infiltration in the quadriceps tendon respecting its anatomical borders. There was cortical breakthrough at the patellar base and a well-delineated area of bone marrow replacement without adjacent bone marrow edema. The lesion was isointense to muscle on T1-weighted images, of heterogenous signal on T2-weighted images, and it showed vivid heterogeneous enhancement ([Fig. 2]).

Following discussion by the multidisciplinary tumor board, an imaging diagnosis of tophaceous gout was suggested. Ultrasound (US)-guided aspiration confirmed the diagnosis by demonstrating monosodium urate (MSU) crystals.

Discussion

Gout is an inflammatory arthropathy due to MSU crystal deposition in periarticular soft tissue including tendons and in joints with a predilection for cartilage–tendon and tendon–bone interfaces.[1]

The etiology of gout is multifactorial. Risk factors include medical comorbidities (obesity, hypertension, diabetes mellitus), pharmacologic treatment (chemotherapy), genetic predisposition, and intake of high-purine foods (meat, shellfish, alcohol), resulting in an increase of serum urate concentrations. When concentrations exceed 6.8 mg/dL and production exceeds excretion, the risk of MSU crystal deposition is increased.[2]

Inflammation around MSU deposits causes increased osteoclast and reduced osteoblast activity, resulting in bony erosions at the tophus–bone interface.[3]

Key Radiologic Findings

CR is the mainstay to evaluate chronic joint involvement. Typically, CR shows dense soft tissue tophi, preservation of joint space until late in the disease, joint effusion, and punched-out erosions with sclerotic margins and sometimes overhanging edges.

US confirms joint effusion, synovial thickening, hyperemia, soft tissue tophi, snowstorm appearance consisting of multiple hyperechoic MSU deposits floating within the synovial fluid, “double contour” sign ([Fig. 3]), and cortical erosions adjacent to tophi.[1] [4] [5] [6] [7] The double contour sign is a result of MSU deposition in the top layer of the articular cartilage in contrast to calcium pyrophosphate dihydrate depositions (CPPD) in the mid-depth of articular cartilage (“string of pearl sign”; [Fig. 3]), and cortical erosions adjacent to tophi.[1] [4] [5] [6] [7] US-guided aspiration of synovial fluid may be performed for microscopic detection of urate crystals.

Although not performed in our case, dual-energy CT (DECT) is diagnostic, obviating the need for fluid aspiration ([Fig. 4]). Using two different energies, DECT may differentiate MSU crystals from other crystal diseases such as CPPD disease and basic calcium deposition disease (previously designated as hydroxyapatite deposition disease) that contain calcium. Differentiation between MSU and CPPD cannot be made merely on adjustment of the thresholds of acquired DECT data, but rather by the distinct absorption/interaction properties of the atomic number of calcium and urate that makes DECT a specific tool for diagnosing gout.[1] [8] [9] Subsequently, color coding is assigned to visualize MSU depositions on the acquired computed tomography (CT) images. In addition, DECT is the modality of choice to assess multifocality and to quantify deposits.[10] [11]

On MRI, gout tophi are iso- to slightly hypointense to muscle tissue on T1-weighted images and of variable, usually heterogeneous, signal with hypointense areas on T2-weighted images. Tophi show heterogeneous enhancement. These findings, however, are nonspecific, and characterization of gout cannot be done on MRI alone.[12]

Gout of the patella and extensor tendons of the knee may be mistaken for a neoplastic process. Previous cases with a similar imaging appearance were reported in the literature.[13] [14] [15] [16] [17] It is of utmost importance to interpret the imaging findings with knowledge of the clinical history and presentation. A history of previous painful attacks, particularly at the great toe with intercritical periods, awareness of risk factors, and hyperuricemia are clues to suggest the correct diagnosis. Of note, serum uric acid level may be normal or decreased in acute gout flares.[18]

Our case was particularly challenging because the patient's age was younger than usual for gout, and his clinical presentation was less typical ([Table 1]). The differential diagnosis of the sclerotic delineated osteolytic defect in the patella included an intraosseous ganglion or giant cell tumor of the bone, but the extensive extraosseous component on MRI did not match with these alternative diagnoses. A soft tissue sarcoma was also considered, but the sclerotic margins of the osseous lesion in the patella on CR, as well as the absence of invasion of tissues beyond the quadriceps tendon, made this diagnosis less likely.

Conclusion

Gout of the patella and extensor tendons of the knee can be a diagnostic challenge on imaging, particularly if the clinical presentation is atypical. CR and MRI may mislead the clinician and radiologist if gout is not considered. Performing DECT or a US-guided fluid aspiration may solve the diagnostic dilemma.

Take-Home Points

• Gout may mimic bone and soft tissue tumors on imaging.

• A high clinical index of suspicion is a prerequisite for a correct diagnosis. Age > 40 years, male sex, and preferential joint involvement should raise the possibility of gout. However, atypical clinical presentation may occur. Risk factors should be considered.

• Meticulous analysis of imaging semiology is key. The most useful signs include periarticular erosion with overhanging edges, increased soft tissue density (CR), relative sparing of the joint space (CR), the “snowstorm” and “double contour” signs (US), and variable signal and enhancement and bandlike infiltration of tendons (MRI).

• DECT is a very useful tool for noninvasive characterization of gout and for differentiation from other crystal arthropathies.

Conflict of Interest

None declared.

Acknowledgments

Our special thanks to Uta E. Flucke, Department of Pathology, Radboud University Medical Center, Nijmegen, the Netherlands, for providing [Fig. 2d].

• References

• 1 Sudoł-Szopińska I, Lanckoroński M, Teh J, Diekhoff T, Giraudo C, Chaudhary SR. Advanced imaging of gout and other inflammatory diseases around the knee. Semin Musculoskelet Radiol 2024; 28 (03) 337-351
  Thieme ConnectPubMedSearch in Google Scholar
• 2 Fernando A, Rednam M, Gujaranthi R. Gout. StatPearls. Available at: https://www-ncbi-nlm-nih-gov.accesdistant.sorbonne-universite.fr/books/NBK546606/ . Accessed November 22, 2024
  PubMed
• 3 Ray K. Crystal arthritis: tendon damage in gout—a role for MSU crystals?. Nat Rev Rheumatol 2014; 10 (06) 321-321
  CrossrefPubMedSearch in Google Scholar
• 4 Gitto S, Messina C, Vitale N, Albano D, Sconfienza LM. Quantitative musculoskeletal ultrasound. Semin Musculoskelet Radiol 2020; 24 (04) 367-374
  Thieme ConnectPubMedSearch in Google Scholar
• 5 Fodor D, Nestorova R, Vlad V, Micu M. The place of musculoskeletal ultrasonography in gout diagnosis. Med Ultrason 2014; 16 (04) 336-344
  PubMedSearch in Google Scholar
• 6 Lu CH, Li KJ. Snowstorm appearance of synovial fluid on musculoskeletal ultrasound. J Med Ultrasound 2019; 27 (03) 119-120
  CrossrefPubMedSearch in Google Scholar
• 7 Chowalloor PV, Siew TK, Keen HI. Imaging in gout: a review of the recent developments. Ther Adv Musculoskelet Dis 2014; 6 (04) 131-143
  CrossrefPubMedSearch in Google Scholar
• 8 Reijnierse M, Schwabl C, Klauser A. Imaging of crystal disorders: calcium pyrophosphate dihydrate crystal deposition disease, calcium hydroxyapatite crystal deposition disease and gout pathophysiology, imaging, and diagnosis. Radiol Clin North Am 2022; 60 (04) 641-656
  PubMedSearch in Google Scholar
• 9 Kravchenko D, Karakostas P, Brossart P, Behning C, Meyer C, Schäfer VS. The role of dual energy computed tomography (DECT) in the differentiation of gout and calcium pyrophosphate deposition disease. ACR Convergence 2020;OP0318
  PubMed
• 10 Chou H, Chin TY, Peh WC. Dual-energy CT in gout—a review of current concepts and applications. J Med Radiat Sci 2017; 64 (01) 41-51
  CrossrefPubMedSearch in Google Scholar
• 11 Becce F, Haavardsholm E. Crystal arthropathies. In: Jans L, Chen M. eds. Arthritis Imaging. Signs|Figures|Drawings|Patterns. Ghent, Belgium: Arthritis Imaging Publishing; 2021: 81-84
  Search in Google Scholar
• 12 Girish G, Glazebrook KN, Jacobson JA. Advanced imaging in gout. AJR Am J Roentgenol 2013; 201 (03) 515-525
  CrossrefPubMedSearch in Google Scholar
• 13 Hee LW, Singh VA, Jayalakshmi P. Can gout mimic a soft tissue tumour?. BMJ Case Rep 2010; bcr0920092266
  PubMedSearch in Google Scholar
• 14 Lameiras R, Figueiredo FD, Cruz J. et al. Gout arthropathy with tophaceous involvement of the knee and patella—a clinical case [poster]. European Society of Radiology-European Society of Musculoskeletal Radiology, 2018. Available at https://epos.myesr.org/poster/esr/essr2018/P-0155 . Accessed November 22, 2024
  PubMed
• 15 Giarraputo L, Savastano S, Santini S. et al. Patellar tophaceous gout involving the quadriceps femoris tendon. European Society of Radiology, 2013. Available at https://www.eurorad.org/case/11063 . Accessed November 22, 2024
  PubMed
• 16 Corpus-Zuñiga FM, Muramatsu K, Rayel MF, Tani Y, Seto T. Intra-osseous tophaceous gout of a bipartite patella mimicking aggressive bone tumour. Mod Rheumatol Case Rep 2021; 5 (02) 399-403
  CrossrefPubMedSearch in Google Scholar
• 17 Rose CW, Wallace AH. The great mimicker: atypical gout presentations from an orthopaedic oncology perspective. J Orthop Physician Assist 2021; 9: e21
  PubMedSearch in Google Scholar
• 18 Zhang J, Sun W, Gao F. et al. Changes of serum uric acid level during acute gout flare and related factors. Front Endocrinol (Lausanne) 2023; 14: 1077059
  CrossrefPubMedSearch in Google Scholar

Address for correspondence

Publication History

Article published online:
11 February 2025

© 2025. Thieme. All rights reserved.

Thieme Medical Publishers, Inc.
333 Seventh Avenue, 18th Floor, New York, NY 10001, USA

• References

• 1 Sudoł-Szopińska I, Lanckoroński M, Teh J, Diekhoff T, Giraudo C, Chaudhary SR. Advanced imaging of gout and other inflammatory diseases around the knee. Semin Musculoskelet Radiol 2024; 28 (03) 337-351
  Thieme ConnectPubMedSearch in Google Scholar
• 2 Fernando A, Rednam M, Gujaranthi R. Gout. StatPearls. Available at: https://www-ncbi-nlm-nih-gov.accesdistant.sorbonne-universite.fr/books/NBK546606/ . Accessed November 22, 2024
  PubMed
• 3 Ray K. Crystal arthritis: tendon damage in gout—a role for MSU crystals?. Nat Rev Rheumatol 2014; 10 (06) 321-321
  CrossrefPubMedSearch in Google Scholar
• 4 Gitto S, Messina C, Vitale N, Albano D, Sconfienza LM. Quantitative musculoskeletal ultrasound. Semin Musculoskelet Radiol 2020; 24 (04) 367-374
  Thieme ConnectPubMedSearch in Google Scholar
• 5 Fodor D, Nestorova R, Vlad V, Micu M. The place of musculoskeletal ultrasonography in gout diagnosis. Med Ultrason 2014; 16 (04) 336-344
  PubMedSearch in Google Scholar
• 6 Lu CH, Li KJ. Snowstorm appearance of synovial fluid on musculoskeletal ultrasound. J Med Ultrasound 2019; 27 (03) 119-120
  CrossrefPubMedSearch in Google Scholar
• 7 Chowalloor PV, Siew TK, Keen HI. Imaging in gout: a review of the recent developments. Ther Adv Musculoskelet Dis 2014; 6 (04) 131-143
  CrossrefPubMedSearch in Google Scholar
• 8 Reijnierse M, Schwabl C, Klauser A. Imaging of crystal disorders: calcium pyrophosphate dihydrate crystal deposition disease, calcium hydroxyapatite crystal deposition disease and gout pathophysiology, imaging, and diagnosis. Radiol Clin North Am 2022; 60 (04) 641-656
  PubMedSearch in Google Scholar
• 9 Kravchenko D, Karakostas P, Brossart P, Behning C, Meyer C, Schäfer VS. The role of dual energy computed tomography (DECT) in the differentiation of gout and calcium pyrophosphate deposition disease. ACR Convergence 2020;OP0318
  PubMed
• 10 Chou H, Chin TY, Peh WC. Dual-energy CT in gout—a review of current concepts and applications. J Med Radiat Sci 2017; 64 (01) 41-51
  CrossrefPubMedSearch in Google Scholar
• 11 Becce F, Haavardsholm E. Crystal arthropathies. In: Jans L, Chen M. eds. Arthritis Imaging. Signs|Figures|Drawings|Patterns. Ghent, Belgium: Arthritis Imaging Publishing; 2021: 81-84
  Search in Google Scholar
• 12 Girish G, Glazebrook KN, Jacobson JA. Advanced imaging in gout. AJR Am J Roentgenol 2013; 201 (03) 515-525
  CrossrefPubMedSearch in Google Scholar
• 13 Hee LW, Singh VA, Jayalakshmi P. Can gout mimic a soft tissue tumour?. BMJ Case Rep 2010; bcr0920092266
  PubMedSearch in Google Scholar
• 14 Lameiras R, Figueiredo FD, Cruz J. et al. Gout arthropathy with tophaceous involvement of the knee and patella—a clinical case [poster]. European Society of Radiology-European Society of Musculoskeletal Radiology, 2018. Available at https://epos.myesr.org/poster/esr/essr2018/P-0155 . Accessed November 22, 2024
  PubMed
• 15 Giarraputo L, Savastano S, Santini S. et al. Patellar tophaceous gout involving the quadriceps femoris tendon. European Society of Radiology, 2013. Available at https://www.eurorad.org/case/11063 . Accessed November 22, 2024
  PubMed
• 16 Corpus-Zuñiga FM, Muramatsu K, Rayel MF, Tani Y, Seto T. Intra-osseous tophaceous gout of a bipartite patella mimicking aggressive bone tumour. Mod Rheumatol Case Rep 2021; 5 (02) 399-403
  CrossrefPubMedSearch in Google Scholar
• 17 Rose CW, Wallace AH. The great mimicker: atypical gout presentations from an orthopaedic oncology perspective. J Orthop Physician Assist 2021; 9: e21
  PubMedSearch in Google Scholar
• 18 Zhang J, Sun W, Gao F. et al. Changes of serum uric acid level during acute gout flare and related factors. Front Endocrinol (Lausanne) 2023; 14: 1077059
  CrossrefPubMedSearch in Google Scholar