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Synovial Chondromatosis

Synovial chondromatosis is a locally aggressive neoplasm consisting of multiple hyaline cartilaginous nodules involving the joint space, subsynovial tissue, or tenosynovium (extra-articular subtype). A small subset of cases are malignant.

Symptoms & Causes

Introduction

Synovial chondromatosis is a joint disorder characterized by the formation of multiple cartilaginous nodules within the joint space or surrounding tissues, which can sometimes become malignant.

Reference
WHO Classification of Tumours Editorial Board. Soft tissue and bone tumours [Internet]. Lyon (France): International Agency for Research on Cancer; 2020 [cited 2024 09 11]. (WHO classification of tumours series, 5th ed.; vol. 3). Available from: https://tumourclassification.iarc.who.int/chapters/33.

Related Terminology
Not recommended: synovial osteochondromatosis; synovial chondrosis; Reichel syndrome; synovial chondrometaplasia.

Subtype(s)
Extra-articular synovial chondromatosis (tenosynovial chondromatosis)

Localization

Most cases involve the large joints, with approximately 60–70% of cases affecting the knee. Any joint can be affected, including the temporomandibular and intervertebral joints. Some cases are entirely extra-articular and termed tenosynovial chondromatosis, typically arising in the hands and feet.

Symptoms

Signs and symptoms include pain, swelling, and mechanical symptoms (including locking, crepitus, and reduced range of movement). Palpable nodules can be detected on examination. Malignant change is associated with persistent and increased pain.

Imaging

Radiographs show a calcified mass in 75–90% of cases, showing either chondroid mineralization (punctate, ring and arc, so-called feathery calcification) or ossified nodules, typically of similar size and shape. The joint space is usually maintained, but pre-existent or resultant osteoarthritis may be present. Pressure erosion occurs where joint capacity is restricted, for example the hip. Although CT shows subtle calcification that can be missed on radiographs, approximately one third of patients lack calcifications on CT. Other imaging features common to well-differentiated cartilaginous neoplasms are shown using cross-sectional imaging. On MRI, the mass may consist of lobulated areas of low signal intensity (calcification and ossification), T2 hyperintensity (cartilage), or fatty signal (mature bone marrow). Septal and peripheral enhancement is seen on MRI and CT after contrast administration. MRI also frequently shows synovial thickening, effusions, and bone erosion. Tenosynovial chondromatosis is suggested by an elongated mineralized mass within a tendon sheath, with otherwise similar imaging appearances to intra-articular chondromatosis and eroding the adjacent bone in as many as 43% of cases. Tumors with similar imaging appearances can occur at the site of a known bursa. Multiple osteochondral loose bodies due to severe degenerative joint disease typically vary in shape and size on radiographs, but they may show similar appearances to synovial chondromatosis.

Epidemiology

Synovial chondromatosis is a rare neoplasm, with an estimated incidence of about 1.8 cases per 1 million person-years. It typically occurs in the third to fifth decades of life and is twice as common in males as in females.

Etiology

Unknown

Diagnosis & Treatment

Staging

Not clinically relevant

Pathogenesis

FN1-ACVR2A and ACVR2A-FN1 fusions, as assessed by FISH, are found in at least 50% of benign synovial chondromatosis, as well as in cases of malignant synovial chondromatosis. It is not clear whether it is the FN1 or ACVR2A altered gene that drives tumor development, because both FN1-ACVR2A and ACVR2A-FN1 are predicted to be in-frame. Both genes have been implicated in the development of other neoplasms.

Macroscopic Appearance

Synovial chondromatosis appears as multiple greyish-white, smooth or irregular, uniform or variably sized nodules, usually in the form of intra-articular loose bodies but sometimes embedded within or attached to synovium.

Histopathology

Nodules consist of hypercellular hyaline cartilage, in which chondrocytes are typically clustered. Nodules are often surrounded by a rim of residual synovial tissue. Calcification and/or endochondral ossification may be seen in longstanding lesions.

Differential Diagnosis

Primary synovial chondromatosis must be distinguished from multiple osteochondral loose bodies within the synovium seen in severe degenerative joint disease, as well as from soft tissue chondromas. Formation of concentric layers of cartilage and a uniform, more orderly distribution of chondrocytes is suggestive of osteochondral loose bodies. Benign lesions can exhibit atypia, and making a diagnosis of malignancy requires observation of unequivocal substantial nuclear enlargement, pleomorphism, hyperchromasia, and loss of chondrocyte clustering. Permeative infiltration of adjacent cortical or cancellous bone, conspicuous and/or atypical mitotic figures, and merging with a high-grade non-chondroid sarcoma are strong indicators of malignancy.

Cytology

Not clinically relevant

Prognosis and Prediction

The disease recurs in 15–20% of patients, with higher rates reported for tenosynovial cases. Malignant transformation is uncommon, occurring in 5–10% of cases, usually in large tumors and in longstanding cases after multiple local recurrences over several years. However, malignant cases may present de novo. Early and rapid growth of a local recurrence after treatment should raise suspicion for malignancy.

Clinical Features

Diagnostic Molecular Pathology

FISH can be used to detect FN1-ACVR2A rearrangements but will not distinguish benign from malignant. IDH1 and IDH2 mutations are absent.

Essential and Desirable Diagnostic Criteria

Essential: nodular cartilaginous tumor within synovium or loose in joint space; clustering of chondrocytes; minimal atypia and increased cellularity; malignancy is defined by unequivocal nuclear atypia, loss of chondrocyte clustering, bone invasion, conspicuous and/or atypical mitotic figures, or merging with a high-grade non-chondroid sarcoma.

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