A 48-year-old man presented with a 9-month history of the right ankle giving out. The patient had no history of trauma or other joint disease. The sensation of instability was associated with mild pain, and a variable degree of swelling was seen. Examination revealed diffuse swelling about the lateral aspect of the right ankle with a nontender 4.0 × 3.5-cm soft tissue mass. The mass was firm and immobile. Range of motion was from 5° dorsiflexion to 20° plantar flexion.
Radiographs revealed swelling in the soft tissue of the lateral aspect of the ankle and mineral densities (Fig 1A). Computed tomography scans revealed well-defined osteochondral lesions with well-demarcated cortical and trabecular structures around the talus (Fig 1B). Intraoperative findings at the time of the biopsy revealed dilatation of the ankle containing joint fluid and multiple osteochondral loose bodies. Loose osteochondral bodies were excised. Pathologic examination confirmed the diagnosis of synovial chondromatosis. The patient was followed up for 6 years, and has been free of pain and instability since excision of the lesion.
A 26-year-old woman presented with pain, swelling, and two discrete masses over the dorsum of the right foot. Her medical history and review of systems were unremarkable. Physical examination revealed two painless masses measuring 2.2 × 2.0 cm and 4.5 × 4.0 cm. Neurovascular function was intact.
Plain radiographs showed discrete mineral densities around the shafts of the second and third metatarsals with extensive remodeling of the metatarsal shaft. Magnetic resonance imaging scans showed the second metatarsal to be surrounded by a mass of cartilaginous consistency. A needle biopsy was done and a preliminary diagnosis of low-grade chondrosarcoma was made. Resection of the second ray of the right foot was done (Fig 3A). The histopathologic examination revealed findings consistent with synovial chondromatosis (Fig 3B). The patient was followed up for 5 years, and has returned to full physical activities since the excision.
Synovial chondromatosis rarely is found in the foot and only a few cases have been reported in the literature.7,16 The first reported case involved a patient who presented with pain, swelling, and paresthesia in the lateral aspect of the foot. Radiographs showed mineralized densities adjacent to the cuboid-metatarsal joint. Open synovectomy was done for synovial chondromatosis and the patient’s symptoms resolved.8 The other case of synovial chondromatosis occurred in the tarsometatarsal joints involving adjacent metatarsal bone.19 The current patients presented with a painful mass which showed mineralized densities around the joint on plain radiographs. The differential diagnosis of tumors of the foot is broad. Kirby et al 9 analyzed 83 cases of soft tissue tumors in the foot. Seventy-two (87%) of the lesions were benign, with ganglion cysts and plantar fibromatosis being the most common, and 11 (13%) were malignant tumors, five of which (45%) were synovial sarcomas. Chou and Malawer3 reviewed 33 patients with bone and soft tissue foot tumors. The most common diagnoses were fibromatosis (10 patients), aneurysmal bone cyst (four patients), synovial sarcoma (four patients), and chondrosarcoma (three patients).
It is important to obtain tissue for diagnosis before surgery when imaging studies do not provide specific diagnostic features. Diagnosis of chondrosarcoma in one of the current patients was made based on results of a needle biopsy. However, the specimens obtained from a needle biopsy did not represent the heterogeneous lesion appropriately. An open biopsy would be done if we had a similar case. Radiographic findings are often nonspecific. Magnetic resonance imaging scans were helpful because T2-weighted images showed a fluid lesion suggesting intraarticular pathologic features.9,17,20 Most of the patients (Patients 1, 2, 3, 5) did not have joint erosion imaging studies. In retrospect, the combined features of mineralized densities in the soft tissue mass on radiographs and intraarticular fluid-containing lesion seen on MRI scans supported the diagnosis of synovial chondromatosis in the foot. However, an incisional biopsy is recommended for these heterogeneous lesions in the absence of a specific radiographic diagnosis.
Metaplasia of cartilage in synovial chondromatosis produces multiple loose bodies in association with the synovial lining of the joint. The joints in the foot are not excluded from this metaplastic condition but are not affected as frequently as the larger joints, such as the knee. The cause of this disorder is not known. Metaplastic synovial cells are stimulated by an unknown mechanism that results in proliferation and differentiation into cartilaginous loose bodies. This cartilage can be mineralized and is visible on radiographs. Grossly, synovial chondromatosis appears as multiple well-circumscribed nodules of cartilage lying loosely in the joint cavity or embedded in the synovium.17,19,20 The underlying bone may be eroded and the lesion can invade outside the joint capsule.20 Microscopically, synovial chondromatosis is characterized by nodules of cartilage lined by synovial membranes. Histopathologic findings often reveal actively growing cartilage lobules and binucleate chondrocytes which can be interpreted as low-grade chondrosarcoma, as seen in Patient 4.20 Histopathologic findings should be interpreted after careful review of imaging studies which may suggest an intraarticular lesion. The disease process has been classified into three phases.10 The early phase is active synovitis without loose bodies in the joint. The second transitional phase shows nodular synovitis along with loose bodies in the joint. In the third phase, loose bodies are present, but the synovitis has resolved. The current patients had phase III disease. Synovial chondromatosis commonly presents with pain and swelling associated with the presence of intracapsular masses which can appear outside or adjacent to the joint of origin. The treatment of synovial chondromatosis involves removal of the loose bodies alone in phase III disease or removal of loose bodies in conjunction with synovectomy in the presence of active synovitis. The location of the synovial chondromatosis seems to be variable in joints of the foot. Synovial chondromatosis occurred in the tibiotalar, calcaneocuboid, naviculocuneiform, and metatarsophalangeal joints. Although synovial chondromatosis is rare in the foot, it should be included in the list of differential diagnoses of a juxtaarticular mass with mineralization.
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