Rare disease
CASE REPORT
Tophaceous calcium pyrophosphate dihydrate deposition disease of the knee mimicking an aggressive soft tissue tumour Christopher Watura, Asif Saifuddin Department of X-ray, Royal National Orthopaedic Hospital NHS Trust, Middlesex, Stanmore, UK Correspondence to Christopher Watura, [email protected] Accepted 25 May 2014
SUMMARY Calcium pyrophosphate crystal deposition disease (CPPD), previously pseudogout, is the second most common crystal arthropathy after gout. There is increased radiographic prevalence associated with age, trauma and several metabolic disorders. Tophaceous CPPD (T-CPPD) is a rare form of CPPD which, though non-neoplastic, mimics a bone or soft tissue malignancy. T-CPPD usually presents as a mass in the temporomandibular joint and occasionally in the paraspinal tissues, but rarely in the joints of the extremities. We present an exceptionally rare case of TCPPD that was subtle on plain radiography, presenting as a soft tissue mass in the knee joint.
BACKGROUND Calcium pyrophosphate crystal deposition disease (CPPD), previously pseudogout, is the second most common crystal arthropathy after gout.1 The prevalence of CPPD is unknown, though there is increased radiographic prevalence associated with age, trauma and several metabolic disorders. The knee is the most commonly involved joint, followed by the wrist, ankle, elbow, toe, shoulder and hip.2 The disease is usually limited to articular cartilage (chondrocalcinosis); although, less commonly it occurs in the meniscus, ligamentum flavum and intervertebral disc.3 Tophaceous CPPD (T-CPPD), also known as tumoural CPPD, is a rare form of CPPD which although non-neoplastic, may mimic a bone or soft tissue tumour.4 T-CPPD usually presents as a mass in the temporomandibular joint or occasionally in the paraspinal tissues, but rarely in the joints of the extremities.2 3 5–7 We describe an exceptionally rare case of T-CPPD in the knee with a subtle appearance on plain radiography which did not detect calcifications.
a heterogeneous soft tissue mass measuring 4.5×4×2.6 cm arising in the lateral subgastrocnemius recess of the posterior capsule (figure 2A–C). There was associated scalloping of the lateral femoral condyle, bone marrow oedema-like signal in the middle and posterior thirds of the lateral femoral condyle and a small joint effusion. A radial tear of the lateral meniscus and mild patellar chondromalacia were also noted. The differential diagnoses from the referral centre included a complex ganglion or synovial mass. The patient was recalled for gadolinium-enhanced MRI, which confirmed the findings of the previous investigation and showed marked heterogeneous enhancement of the mass (figure 2D). Differential diagnosis now included an aggressive soft tissue lesion and referral to a specialist soft tissue tumour centre was advised. The favoured diagnosis at the Specialist Centre was nodular pigmented villonodular synovitis (PVNS) and the patient underwent ultrasound guided needle biopsy for confirmation of this. Histological examination of the biopsy sample demonstrated cores of ligament/tendon-type tissue
CASE PRESENTATION A 50-year-old man presented to his general practitioner with a 2-year history of left lateral knee pain, swelling and decreased range of motion. He denied any history of trauma and was otherwise healthy. On physical examination, there was a firm, non-tender, 4×4 cm mass in the lateral aspect of the popliteal fossa. To cite: Watura C, Saifuddin A. BMJ Case Rep Published online: [please include Day Month Year] doi:10.1136/bcr-2014203998
INVESTIGATIONS Plain radiographs were performed and a noncalcified soft tissue mass was seen at the posterior aspect of the left knee (figure 1). MRI demonstrated
Watura C, et al. BMJ Case Rep 2014. doi:10.1136/bcr-2014-203998
Figure 1 Lateral plain radiograph of the knee demonstrating a small soft tissue mass (arrows) posterior to the lateral femoral condyle. 1
Rare disease
Figure 2 MR images (A) and (B) showing a well-defined intermediate soft tissue mass (arrows) measuring 4.5×4×2.6 cm (mediolateral × superoinferior × anteroposterior) in the lateral subgastrocnemius recess of the right knee, (C) showing the associated cortical erosion (arrow) and marrow oedema-like signal and (D) demonstrating heterogeneous enhancement of the mass (arrows) postcontrast. (A) Sagittal T1-weighted spin echo (T1W SE), (B) axial fat suppressed protein density weighted fast spin echo (PDW FSE), (C) sagittal fat suppressed PDW FSE and (D) postcontrast fat suppressed sagittal T1W SE.
covered by hyperplastic synovium. There were diffuse deposits of amorphous calcified material containing rhomboid-shaped crystals on polarised light compatible with T-CPPD (figure 3). A subsequent CT study showed tiny focal areas of calcification (figure 4), consistent with the histological diagnosis of T-CPPD. 2
DIFFERENTIAL DIAGNOSIS The nodular form of PVNS is the commonest focal intra-articular soft tissue mass of the knee, but almost invariably does not calcify. Only two cases of atypical PVNS containing calcifications have been reported.8 9 The demonstration of calcification, either radiographically, or as in this case by CT, Watura C, et al. BMJ Case Rep 2014. doi:10.1136/bcr-2014-203998
Rare disease therefore has an impact on differential diagnosis. Recognised causes of calcified intra-articular soft tissue masses include synovial chondroma, synovial chondromatosis,10 synovial chondrosarcoma,11 synovial sarcoma,12 tophaceous gout and chronic Hoffa’s disease.13–15 Imaging appearances of differential diagnoses are described in table 1. The possibility of a calcified mass being sarcomatous emphasises the importance of diagnostic needle biopsy. However, there remains challenges for the diagnosing pathologists, particularly when calcifications are in the context of a mass lesion with hypertrophic chondrocytes. Noting the overall features including presence of characteristic crystals and absence of bone permeation is important to prevent the overdiagnosis of chondrosarcoma and subsequent overtreatment.16
Table 1 Imaging appearances of differentials in cases of non-radiographic tophaceous calcium pyrophosphate crystal deposition disease (T-CPPD) at the knee X-ray
Figure 4 Axial CT study demonstrating faint calcification within the lesion (arrow). Watura C, et al. BMJ Case Rep 2014. doi:10.1136/bcr-2014-203998
MRI
Heterogeneous Lobular soft tissue soft tissue mass mass. Intermediate T1 signal, heterogeneously bright on proton density fat saturation sequences. Gadolinium enhancement Hypoechoic or Characteristically Pigmented May be heterogeneous low-signal villonodular normal or soft tissue mass intensity on all synovitis8 show joint image sequences effusion. including T1 and Bone erosions T2. ‘Blooming’ on both sides artifact from of the joint haemosiderin on gradient echo images. Variable gadolinium enhancement Hypoechoic Ganglion Usually Cyst with fluid cyst normal. May (fluid density) signal cyst. May vary characteristics. be a soft in shape, for tissue High signal on T2 example, swelling and low signal discreet or on T110 lobulated. May have acoustic enhancement9 Variable signal Mixed Malignant Usually characteristics, soft tissue normal. May echogenicity, tumour can be may be solid tumour be a soft solid and cystic and cystic tissue components. May swelling and components enhance with bone gadolinium destruction Meniscal Usually May be normal Imaging modality cyst normal. May if intra-articular. of choice. Cyst be soft tissue Hypoechoic cyst with fluid signal swelling demonstrated if characteristics. extra-articular High signal on T2 and low signal on T1 T-CPPD
Figure 3 H&E, ×4 magnification, (A) synovial tissue with amorphous deposits of coarsely calcified material and (B) rhomboid-shaped crystals seen under polarised light.
Ultrasound
Normal or areas of calcification. May be soft tissue swelling
CT Lobular soft tissue mass with random focal or marginal areas of calcification7
Hypertrophic synovium and soft tissue mass. May be an effusion, and hyperdensity due to haemosiderin
May be difficult to visualise. Low-density (fluid density) cyst. Low Hounsfield units Variable density, may be mixed solid and cystic components Usually normal. Low-density (fluid density) cyst if large
3
Rare disease TREATMENT It was explained to the patient that this is a benign disease. His condition was medically managed and anti-inflammatories were prescribed.
OUTCOME AND FOLLOW-UP The patient was reviewed in clinic after 6 months. He reported a reduction in problems during activities of daily living and surgical intervention was deemed unnecessary.
DISCUSSION To our knowledge, there is only one case of T-CPPD without radiographic calcification in the existing literature.6 At the time of writing, only 30 cases in the joints of the extremities have been described in the literature. Most previous cases of T-CPPD in the extremities were radiographically misdiagnosed as bone or soft tissue tumours.7 17 Two cases have been previously reported in the knee joint.6 7 Only one of which was subtle on plain radiography,6 as was the case we present with also a similar clinical presentation and no history of trauma. In both cases, although plain radiographs did not demonstrate calcification in the mass, CT showed scattered focal areas of increased density compatible with calcification, demonstrating the potential value of carrying out CT. In the previous case, an excisional biopsy was performed and rhomboid-shaped, positively birefringent polarised light crystals compatible with CPPD were found.6 However, in our case the mass was much smaller and ultrasound guided needle biopsy was performed to confirm the histological diagnosis.
Contributors CW researched, wrote-up and submitted the case. AS provided the case material and edited the manuscript. Competing interests None. Patient consent Obtained. Provenance and peer review Not commissioned; externally peer reviewed.
REFERENCES 1 2 3 4 5
6
7
8 9 10
11 12
Learning points ▸ Tophaceous-calcium pyrophosphate crystal deposition is especially rare in the joints of the extremities. ▸ Nonetheless, this diagnosis should be considered in the case of an intra-articular calcifying soft tissue mass. ▸ Needle biopsy should be undertaken to confirm or exclude the presence of rhomboid crystals typical of calcium pyrophosphate.
13 14 15 16
17
Mukhopadhyay S, Guha A, Perera A. Monoarticular pseudogout of the hip presenting as septic arthritis: a case report. Acta Orthop Traumatol Turc 2011;45:200–2. Klippel JH. Primer on the rheumatic diseases. 13th edn. New York, USA: Springer, 2008. Ishida T, Dorfman HD, Bullough PG. Tophaceous pseudogout (tumoral calcium pyrophosphate dihydrate crystal deposition disease). Hum Pathol 1995;26:587–93. Lambrecht N, Nelson SD, Seeger L, et al. Tophaceous pseudogout: a pitfall in the diagnosis of chondrosarcoma. Diagn Cytopathol 2001;25:258–61. Bahk WJ, Chang ED, Lee AH, et al. Huge tophaceous pseudogout associated with tenosynovial chondromatosis arising from flexor digitorum tendon sheaths of the foot: a case report. Skeletal Radiol 2013;42:1755–9. Havitçioğlu H, Tatari H, Baran O, et al. Calcium pyrophosphate dihydrate crystal deposition disease mimicking malignant soft tissue tumor. Knee Surg Sports Traumatol Arthrosc 2003;11:263–6. Kato H, Nishimoto K, Yoshikawa T, et al. Tophaceous pseudogout in the knee joint mimicking a soft-tissue tumour: a case report. J Orthop Surg (Hong Kong) 2010;18:118–21. Baker ND, Klein JD, Weidner N, et al. Pigmented villonodular synovitis containing coarse calcifications. AJR Am J Roentgenol 1989;153:1228–30. Farrokh D. [Atypical form of pigmented villonodular synovitis of the knee containing calcifications]. J Belge Radiol 1996;79:203–5. Murphey MD, Vidal JA, Fanburg-Smith JC, et al. Imaging of synovial chondromatosis with radiologic–pathologic correlation. Radiographics 2007;27:1465–88. Schlachter TR, Wu Q, Matlyuk-Urman Z. AIRP best cases in radiologic–pathologic correlation: synovial chondrosarcoma. Radiographics 2011;31:1883–8. Wilkerson BW, Crim JR, Hung M, et al. Characterization of synovial sarcoma calcification. AJR Am J Roentgenol 2012;199:W730–4. Resnick D, Broderick TW. Intraosseous calcifications in tophaceous gout. AJR Am J Roentgenol 1981;137:1157–61. Park JH, Lee AH, Lee DH. An unusual presentation of Hoffa’s disease in an elderly patient with no trauma history: a case report. Acta Orthop Traumatol Turc 2011;45:195–9. Kidwai AS, Klassen C, Hemphill S, et al. Radiologic case study: intra-articular synovial lipoma. Orthopedics 2005;28:522, 611–13. Tan KB, Scolyer RA, McCarthy SW, et al. Tumoural calcium pyrophosphate dihydrate crystal deposition disease (tophaceous pseudogout) of the hand: a report of two cases including one with a previously unreported associated florid reactive myofibroblastic proliferation. Pathology 2008;40:719–22. Erhardt MA, Vetter SY, Suda AJ, et al. Mimicry in older patients: tophaceous pseudogout as a tumorlike lesion: a case report. J Am Podiatr Med Assoc 2011;101:462–5.
Copyright 2014 BMJ Publishing Group. All rights reserved. For permission to reuse any of this content visit http://group.bmj.com/group/rights-licensing/permissions. BMJ Case Report Fellows may re-use this article for personal use and teaching without any further permission. Become a Fellow of BMJ Case Reports today and you can: ▸ Submit as many cases as you like ▸ Enjoy fast sympathetic peer review and rapid publication of accepted articles ▸ Access all the published articles ▸ Re-use any of the published material for personal use and teaching without further permission For information on Institutional Fellowships contact [email protected] Visit casereports.bmj.com for more articles like this and to become a Fellow
4
Watura C, et al. BMJ Case Rep 2014. doi:10.1136/bcr-2014-203998
CASE REPORT
Tophaceous calcium pyrophosphate dihydrate deposition disease of the knee mimicking an aggressive soft tissue tumour Christopher Watura, Asif Saifuddin Department of X-ray, Royal National Orthopaedic Hospital NHS Trust, Middlesex, Stanmore, UK Correspondence to Christopher Watura, [email protected] Accepted 25 May 2014
SUMMARY Calcium pyrophosphate crystal deposition disease (CPPD), previously pseudogout, is the second most common crystal arthropathy after gout. There is increased radiographic prevalence associated with age, trauma and several metabolic disorders. Tophaceous CPPD (T-CPPD) is a rare form of CPPD which, though non-neoplastic, mimics a bone or soft tissue malignancy. T-CPPD usually presents as a mass in the temporomandibular joint and occasionally in the paraspinal tissues, but rarely in the joints of the extremities. We present an exceptionally rare case of TCPPD that was subtle on plain radiography, presenting as a soft tissue mass in the knee joint.
BACKGROUND Calcium pyrophosphate crystal deposition disease (CPPD), previously pseudogout, is the second most common crystal arthropathy after gout.1 The prevalence of CPPD is unknown, though there is increased radiographic prevalence associated with age, trauma and several metabolic disorders. The knee is the most commonly involved joint, followed by the wrist, ankle, elbow, toe, shoulder and hip.2 The disease is usually limited to articular cartilage (chondrocalcinosis); although, less commonly it occurs in the meniscus, ligamentum flavum and intervertebral disc.3 Tophaceous CPPD (T-CPPD), also known as tumoural CPPD, is a rare form of CPPD which although non-neoplastic, may mimic a bone or soft tissue tumour.4 T-CPPD usually presents as a mass in the temporomandibular joint or occasionally in the paraspinal tissues, but rarely in the joints of the extremities.2 3 5–7 We describe an exceptionally rare case of T-CPPD in the knee with a subtle appearance on plain radiography which did not detect calcifications.
a heterogeneous soft tissue mass measuring 4.5×4×2.6 cm arising in the lateral subgastrocnemius recess of the posterior capsule (figure 2A–C). There was associated scalloping of the lateral femoral condyle, bone marrow oedema-like signal in the middle and posterior thirds of the lateral femoral condyle and a small joint effusion. A radial tear of the lateral meniscus and mild patellar chondromalacia were also noted. The differential diagnoses from the referral centre included a complex ganglion or synovial mass. The patient was recalled for gadolinium-enhanced MRI, which confirmed the findings of the previous investigation and showed marked heterogeneous enhancement of the mass (figure 2D). Differential diagnosis now included an aggressive soft tissue lesion and referral to a specialist soft tissue tumour centre was advised. The favoured diagnosis at the Specialist Centre was nodular pigmented villonodular synovitis (PVNS) and the patient underwent ultrasound guided needle biopsy for confirmation of this. Histological examination of the biopsy sample demonstrated cores of ligament/tendon-type tissue
CASE PRESENTATION A 50-year-old man presented to his general practitioner with a 2-year history of left lateral knee pain, swelling and decreased range of motion. He denied any history of trauma and was otherwise healthy. On physical examination, there was a firm, non-tender, 4×4 cm mass in the lateral aspect of the popliteal fossa. To cite: Watura C, Saifuddin A. BMJ Case Rep Published online: [please include Day Month Year] doi:10.1136/bcr-2014203998
INVESTIGATIONS Plain radiographs were performed and a noncalcified soft tissue mass was seen at the posterior aspect of the left knee (figure 1). MRI demonstrated
Watura C, et al. BMJ Case Rep 2014. doi:10.1136/bcr-2014-203998
Figure 1 Lateral plain radiograph of the knee demonstrating a small soft tissue mass (arrows) posterior to the lateral femoral condyle. 1
Rare disease
Figure 2 MR images (A) and (B) showing a well-defined intermediate soft tissue mass (arrows) measuring 4.5×4×2.6 cm (mediolateral × superoinferior × anteroposterior) in the lateral subgastrocnemius recess of the right knee, (C) showing the associated cortical erosion (arrow) and marrow oedema-like signal and (D) demonstrating heterogeneous enhancement of the mass (arrows) postcontrast. (A) Sagittal T1-weighted spin echo (T1W SE), (B) axial fat suppressed protein density weighted fast spin echo (PDW FSE), (C) sagittal fat suppressed PDW FSE and (D) postcontrast fat suppressed sagittal T1W SE.
covered by hyperplastic synovium. There were diffuse deposits of amorphous calcified material containing rhomboid-shaped crystals on polarised light compatible with T-CPPD (figure 3). A subsequent CT study showed tiny focal areas of calcification (figure 4), consistent with the histological diagnosis of T-CPPD. 2
DIFFERENTIAL DIAGNOSIS The nodular form of PVNS is the commonest focal intra-articular soft tissue mass of the knee, but almost invariably does not calcify. Only two cases of atypical PVNS containing calcifications have been reported.8 9 The demonstration of calcification, either radiographically, or as in this case by CT, Watura C, et al. BMJ Case Rep 2014. doi:10.1136/bcr-2014-203998
Rare disease therefore has an impact on differential diagnosis. Recognised causes of calcified intra-articular soft tissue masses include synovial chondroma, synovial chondromatosis,10 synovial chondrosarcoma,11 synovial sarcoma,12 tophaceous gout and chronic Hoffa’s disease.13–15 Imaging appearances of differential diagnoses are described in table 1. The possibility of a calcified mass being sarcomatous emphasises the importance of diagnostic needle biopsy. However, there remains challenges for the diagnosing pathologists, particularly when calcifications are in the context of a mass lesion with hypertrophic chondrocytes. Noting the overall features including presence of characteristic crystals and absence of bone permeation is important to prevent the overdiagnosis of chondrosarcoma and subsequent overtreatment.16
Table 1 Imaging appearances of differentials in cases of non-radiographic tophaceous calcium pyrophosphate crystal deposition disease (T-CPPD) at the knee X-ray
Figure 4 Axial CT study demonstrating faint calcification within the lesion (arrow). Watura C, et al. BMJ Case Rep 2014. doi:10.1136/bcr-2014-203998
MRI
Heterogeneous Lobular soft tissue soft tissue mass mass. Intermediate T1 signal, heterogeneously bright on proton density fat saturation sequences. Gadolinium enhancement Hypoechoic or Characteristically Pigmented May be heterogeneous low-signal villonodular normal or soft tissue mass intensity on all synovitis8 show joint image sequences effusion. including T1 and Bone erosions T2. ‘Blooming’ on both sides artifact from of the joint haemosiderin on gradient echo images. Variable gadolinium enhancement Hypoechoic Ganglion Usually Cyst with fluid cyst normal. May (fluid density) signal cyst. May vary characteristics. be a soft in shape, for tissue High signal on T2 example, swelling and low signal discreet or on T110 lobulated. May have acoustic enhancement9 Variable signal Mixed Malignant Usually characteristics, soft tissue normal. May echogenicity, tumour can be may be solid tumour be a soft solid and cystic and cystic tissue components. May swelling and components enhance with bone gadolinium destruction Meniscal Usually May be normal Imaging modality cyst normal. May if intra-articular. of choice. Cyst be soft tissue Hypoechoic cyst with fluid signal swelling demonstrated if characteristics. extra-articular High signal on T2 and low signal on T1 T-CPPD
Figure 3 H&E, ×4 magnification, (A) synovial tissue with amorphous deposits of coarsely calcified material and (B) rhomboid-shaped crystals seen under polarised light.
Ultrasound
Normal or areas of calcification. May be soft tissue swelling
CT Lobular soft tissue mass with random focal or marginal areas of calcification7
Hypertrophic synovium and soft tissue mass. May be an effusion, and hyperdensity due to haemosiderin
May be difficult to visualise. Low-density (fluid density) cyst. Low Hounsfield units Variable density, may be mixed solid and cystic components Usually normal. Low-density (fluid density) cyst if large
3
Rare disease TREATMENT It was explained to the patient that this is a benign disease. His condition was medically managed and anti-inflammatories were prescribed.
OUTCOME AND FOLLOW-UP The patient was reviewed in clinic after 6 months. He reported a reduction in problems during activities of daily living and surgical intervention was deemed unnecessary.
DISCUSSION To our knowledge, there is only one case of T-CPPD without radiographic calcification in the existing literature.6 At the time of writing, only 30 cases in the joints of the extremities have been described in the literature. Most previous cases of T-CPPD in the extremities were radiographically misdiagnosed as bone or soft tissue tumours.7 17 Two cases have been previously reported in the knee joint.6 7 Only one of which was subtle on plain radiography,6 as was the case we present with also a similar clinical presentation and no history of trauma. In both cases, although plain radiographs did not demonstrate calcification in the mass, CT showed scattered focal areas of increased density compatible with calcification, demonstrating the potential value of carrying out CT. In the previous case, an excisional biopsy was performed and rhomboid-shaped, positively birefringent polarised light crystals compatible with CPPD were found.6 However, in our case the mass was much smaller and ultrasound guided needle biopsy was performed to confirm the histological diagnosis.
Contributors CW researched, wrote-up and submitted the case. AS provided the case material and edited the manuscript. Competing interests None. Patient consent Obtained. Provenance and peer review Not commissioned; externally peer reviewed.
REFERENCES 1 2 3 4 5
6
7
8 9 10
11 12
Learning points ▸ Tophaceous-calcium pyrophosphate crystal deposition is especially rare in the joints of the extremities. ▸ Nonetheless, this diagnosis should be considered in the case of an intra-articular calcifying soft tissue mass. ▸ Needle biopsy should be undertaken to confirm or exclude the presence of rhomboid crystals typical of calcium pyrophosphate.
13 14 15 16
17
Mukhopadhyay S, Guha A, Perera A. Monoarticular pseudogout of the hip presenting as septic arthritis: a case report. Acta Orthop Traumatol Turc 2011;45:200–2. Klippel JH. Primer on the rheumatic diseases. 13th edn. New York, USA: Springer, 2008. Ishida T, Dorfman HD, Bullough PG. Tophaceous pseudogout (tumoral calcium pyrophosphate dihydrate crystal deposition disease). Hum Pathol 1995;26:587–93. Lambrecht N, Nelson SD, Seeger L, et al. Tophaceous pseudogout: a pitfall in the diagnosis of chondrosarcoma. Diagn Cytopathol 2001;25:258–61. Bahk WJ, Chang ED, Lee AH, et al. Huge tophaceous pseudogout associated with tenosynovial chondromatosis arising from flexor digitorum tendon sheaths of the foot: a case report. Skeletal Radiol 2013;42:1755–9. Havitçioğlu H, Tatari H, Baran O, et al. Calcium pyrophosphate dihydrate crystal deposition disease mimicking malignant soft tissue tumor. Knee Surg Sports Traumatol Arthrosc 2003;11:263–6. Kato H, Nishimoto K, Yoshikawa T, et al. Tophaceous pseudogout in the knee joint mimicking a soft-tissue tumour: a case report. J Orthop Surg (Hong Kong) 2010;18:118–21. Baker ND, Klein JD, Weidner N, et al. Pigmented villonodular synovitis containing coarse calcifications. AJR Am J Roentgenol 1989;153:1228–30. Farrokh D. [Atypical form of pigmented villonodular synovitis of the knee containing calcifications]. J Belge Radiol 1996;79:203–5. Murphey MD, Vidal JA, Fanburg-Smith JC, et al. Imaging of synovial chondromatosis with radiologic–pathologic correlation. Radiographics 2007;27:1465–88. Schlachter TR, Wu Q, Matlyuk-Urman Z. AIRP best cases in radiologic–pathologic correlation: synovial chondrosarcoma. Radiographics 2011;31:1883–8. Wilkerson BW, Crim JR, Hung M, et al. Characterization of synovial sarcoma calcification. AJR Am J Roentgenol 2012;199:W730–4. Resnick D, Broderick TW. Intraosseous calcifications in tophaceous gout. AJR Am J Roentgenol 1981;137:1157–61. Park JH, Lee AH, Lee DH. An unusual presentation of Hoffa’s disease in an elderly patient with no trauma history: a case report. Acta Orthop Traumatol Turc 2011;45:195–9. Kidwai AS, Klassen C, Hemphill S, et al. Radiologic case study: intra-articular synovial lipoma. Orthopedics 2005;28:522, 611–13. Tan KB, Scolyer RA, McCarthy SW, et al. Tumoural calcium pyrophosphate dihydrate crystal deposition disease (tophaceous pseudogout) of the hand: a report of two cases including one with a previously unreported associated florid reactive myofibroblastic proliferation. Pathology 2008;40:719–22. Erhardt MA, Vetter SY, Suda AJ, et al. Mimicry in older patients: tophaceous pseudogout as a tumorlike lesion: a case report. J Am Podiatr Med Assoc 2011;101:462–5.
Copyright 2014 BMJ Publishing Group. All rights reserved. For permission to reuse any of this content visit http://group.bmj.com/group/rights-licensing/permissions. BMJ Case Report Fellows may re-use this article for personal use and teaching without any further permission. Become a Fellow of BMJ Case Reports today and you can: ▸ Submit as many cases as you like ▸ Enjoy fast sympathetic peer review and rapid publication of accepted articles ▸ Access all the published articles ▸ Re-use any of the published material for personal use and teaching without further permission For information on Institutional Fellowships contact [email protected] Visit casereports.bmj.com for more articles like this and to become a Fellow
4
Watura C, et al. BMJ Case Rep 2014. doi:10.1136/bcr-2014-203998
