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Pseudotumoral Presentation of Calcium Pyrophosphate Dihydrate Crystal Deposition Disease

To the Editor:

Chondrocalcinosis is a microcrystalline disease characterized radiographically by multiple foci of calcification in hyaline and fibrocartilage of the joints and intervertebral discs. Initially described by Zitnan and Sit'aj¹, it has recently been more appropriately designated calcium pyrophosphate dihydrate (CPPD) crystal deposition disease. This term also encompasses the tumorous form of the disease, designated tophaceous pseudogout.

We describe 2 cases of tophaceous pseudogout presenting as a single calcified soft-tissue mass with no evidence of CPPD crystal deposition disease in any other joint.

Case 1. A 76-year-old woman presented with a history of swelling and increasing pain of the right popliteal fossa leading to inability to bend the knee. In her history, she mentioned asthma in childhood and a Colles fracture 2 years before presentation. On examination, the overlying skin was normal. Palpation revealed a soft-tissue mass in the popliteal fossa associated with moderate pain. Laboratory findings were normal; in particular there was no inflammatory syndrome. Conventional radiographs and multidetector computed tomography (MDCT) showed a 3-cm nodular mass in the popliteal fossa, with multiple central or peripheral, arciform and annular calcific deposits suggesting a cartilaginous matrix. The mass was responsible for a large erosion of the adjacent bone, i.e., the posterior cortex of the femoral metaphysis. Considering the cartilaginous characteristics of the tumoral matrix and the presence of pain, which could not be explained by any associated intraarticular disorder, the diagnosis of subperiosteal chondrosarcoma was suspected and a surgical ablation of the tumor was performed.

Histopathologic analysis showed deposits of CPPD crystals bordered by a fibrous connective tissue presenting a lobulated pattern with areas of chondroid metaplasia. The crystals were short, rod-like to rhomboid, and birefringent under polarized light. A diagnosis of tumorous calcific collection with CPPD crystal deposition was made, also designated tophaceous pseudogout (Figure 1). Conventional joints including wrists, knees, and pubic symphysis were radiographed after the diagnosis to look for typical signs of intraarticular CPPD disease. Radiographs showed no calcific deposits on the hyaline or fibrocartilage.

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Figure 1. Case 1. Sagittal CT section shows well defined soft-tissue mass with arciform and annular calcification.

Case 2. A 41-year-old woman complained of gradually increasing pain of the hip for several years. She reported a major ski accident in the past (6 years previously) with a large hematoma of the anterior proximal portion of the thigh. She had no relevant medical or surgical history. Conventional radiographs, ultrasound, and high resolution MDCT showed a widely calcified and well circumscribed 4-cm mass of the iliopsoas tendon. The characteristics were those of a benign highly calcified lesion resembling a tumoral calcinosis. On magnetic resonance imaging (MRI), the lesion showed low signal intensity on T1-weighted images and high signal intensity on T2-weighted sequences with gadolinium enhancement. These MRI patterns are also those of the cartilaginous lesions. Because of recurrent pain and a slow increase of the size of the lesion, surgical ablation was performed.

Histopathologic and microscopic examination showed a calcified tumor with a fibrous stroma and broad areas of crystalline deposits associated with focal spots of chondroid metaplasia and giant cells. The crystals were rhomboid and birefringent under a polarized light. The diagnosis proposed was CPPD crystal deposition disease. Typically involved joints were screened to look for articular CPPD deposition.

Three years later, a soft-tissue mass developed in the hip again, with features similar to the previous episode. Needle biopsies and steroid infiltration were performed under MDCT control. Microscopic examination found similar patterns to those of 3 years before, and the diagnosis of pyrophosphate tophus recurrence was confirmed (Figures 2 and 3). She returned 6 months later with increasing pain of the same thigh and then underwent surgery. Complete ablation of the tumor was performed and the diagnosis of pyrophosphate tophus recurrence was confirmed.

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Figure 2. Case 2. MDCT axial native section shows a widely calcified mass in the psoas tendon. There is no intraarticular disorder.

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Figure 3. Case 2. Sagittal T2 fat-suppressed MR image taken simultaneously with that in Figure 2. There is edema within and adjacent to the lesion (+) involving the psoas muscle (arrow). The femoral head remains normal (*).

CPPD disease is characterized by the presence of crystal deposits in hyaline and fibrocartilage of the joints. CPPD crystal deposition disease is generally observed in middle-aged and elderly patients. Initial descriptions emphasized the occurrence of "pseudogout" attacks, but further investigations revealed multiple additional clinical patterns. These patterns emphasize the capacity of the disease to mimic a variety of other conditions including gout, rheumatoid arthritis, degenerative joint disease, neuropathic osteoarthropathy, and a rare condition described here, tophaceous pseudogout.

Soft-tissue calcified mass (tophaceous pseudogout) is a rare presentation of CPPD disease, as described^2-9. Some reports^3-6 describe highly calcified masses that are difficult to differentiate from tumoral calcinosis. Some others emphasized radiological similarities with benign or malignant cartilaginous lesions.

Our cases support these various data, as initial diagnosis was tumoral calcinosis in one case and subperiosteal chondrosarcoma in the other. Differentiation between the latter condition and pseudogout is difficult because of the presence of arciform and annular calcifications within the soft-tissue mass. Diagnosis can be made even more difficult by histological data that can show areas of chondroid metaplasia, sometimes associated with cellular atypia, simulating once again a cartilaginous lesion^4,10. Surgical ablation is therefore necessary to identify the CPPD crystals in the mass, in order to avoid misdiagnosis of benign or malignant cartilaginous lesion. In both our cases, metaplastic areas of cartilage were seen, but with no cellular atypia. In most reports, the soft-tissue masses were associated with calcifications within hyaline or fibrocartilage, making the diagnosis relatively easy. Lambrecht, et al¹⁰ reported the case of a well circumscribed mass of amorphous calcification located in the soft tissue adjacent to the lesser trochanter. In that case, calcific deposits were present in the symphysis pubis and the femoral head. In another case⁵ the tophaceous pseudogout of the sternoclavicular joint was also associated with severe pluriarticular chondrocalcinosis. Maugars, et al¹¹ reported large periarticular calcifications of the hips and pubis in a woman with diffuse primary chondrocalcinosis, symptomatic in the knees. Serial articular and periarticular biopsies showed CPPD in cartilage, synovia, capsula, tendon, and muscle. In contrast, in both our cases, no calcific deposits were found in other joints, making the diagnosis almost impossible as long as the typical radiological patterns were not present. This specific pattern makes us question the most appropriate term to designate this disease.

Based on literature data, the locations most commonly involved with tophaceous pseudogout are the wrist and digits^2,3,9, the infratemporal fossa, and the temporomandibular joint^4,7,8,12. However, many other locations can be involved, such as the para-ischial region¹⁰, the base of the neck, cervical spine^6,13, sternoclavicular joint⁵, and mitral valve¹⁴.

To our knowledge, our report is the first to describe CPPD disease involving the iliopsoas tendon. Lambrecht, et al¹⁰ described tophaceous pseudogout adjacent to the lesser trochanter, but the lesion was intimately associated with the semimembranous tendon. Sissons, et al⁹ also reported the presence of a highly cellular lesion adjacent to the right hip. The mass was located in the tissues adjacent to the bone and contained deposits of CPPD crystals.

Surgical ablation of these lesions is the rule, mainly because this diagnosis is usually not established and histopathologic confirmation is needed. Complete ablation is required, because the lesion is at risk of recurrence after partial and sometimes even complete ablation^15,16. We observed a recurrence in one of our cases, after complete excision of the mass located in the iliopsoas myotendinous junction. Three years after surgery, a 3.5-cm mass reappeared at exactly the same location.

Because of its unusual presentation, location, and histology, tumoral CPPD crystal deposition presenting as a single soft-tissue calcified tumor may be misinterpreted as a soft-tissue cartilaginous lesion or tumoral calcinosis. It is necessary to identify the CPPD crystal components on biopsy fragments to avoid misdiagnosis.

SEBASTIEN BRUNOT, MD; Unité d'Imagerie Ostéo-articulaire, Hôpital Pellegrin, CHU de Bordeaux; THIERRY FABRE, MD, Unité de Chirurgie Orthopédique, CHU Bordeaux; SEBASTIEN LEPREUX, MD, Service d'Anatomo-Pathologie, Université Victor Segalen, Bordeaux; FRANCOIS DIARD, MD, Unité d'Imagerie Ostéo-articulaire, Hôpital Pellegrin, CHU de Bordeaux; RICHARD MASSONNAT, MD, Service De Rhumatologie, Université Victor Segalen; NATHANAEL SABBAH, BA; OLIVIER HAUGER, MD, Unité d'Imagerie Ostéo-articulaire, Hôpital Pellegrin, CHU de Bordeaux.

Address reprint requests to Dr. S. Brunot, Université Victor Segalen Bordeaux 2, 146 rue Léo Saignat, 33076 Bordeaux cedex, France. E-mail: sebbrunot@hotmail.com

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