Synovial Chondromatosis Imaging

Synovial chondromatosis, or synovial osteochondromatosis, is a benign condition characterized by synovial membrane proliferation (demonstrated in the images below) and metaplasia. The synovial lining of a joint, bursa, or tendon sheath undergoes nodular proliferation, and fragments may break off from the synovial surface into the joint.[1] There, nourished by synovial fluid, the fragments may grow, calcify, or ossify. The intra-articular fragment may vary in size from a few millimeters to a few centimeters.[2, 3, 4]

Malignant transformation of synovial chondromatosis to synovial chondrosarcoma (CHS) is recognized to be a rare event.[5] In a study of 78 patients who presented with primary synovial chondromatosis, 5 went on to develop malignant change (incidence of 6.4%). The mean age at first diagnosis of synovial chondromatosis was 28 years, and the median time from original diagnosis to malignant transformation was 20 years (range, 2.7 to 39 years).[6]

Radiographs should be obtained first.[7, 8, 9, 10, 11]  Radiographic findings are frequently diagnostic but may not demonstrate noncalcified bodies. CT scans and CT arthrograms may also be used, especially for demonstrating noncalcified intra-articular bodies. CT scans may not demonstrate the full extent of proliferating synovial disease. MRI usually helps establish the diagnosis, and the images demonstrate the true extent of the disease.[12, 13]  MRI scans should then be obtained preoperatively. When MRI is not readily available, CT arthrography may be performed. Ultrasonographic examination may be used to investigate accessible joints. Synovial chondromatosis may be confused with pigmented villonodular synovitis (PVNS) if only MRI scans are available, and plain radiographs may help in such cases.[14]

(The images below present a detailed view of synovial chondromatosis of the shoulder.)

Plain radiograph of a 19-year-old man who initially presented with a history of shoulder pain of insidious onset. The patient was found to have synovial osteochondromatosis. Frontal radiograph of the shoulder shows multiple rounded, calcified bodies in the axillary recess and in the subscapularis bursa.

Magnetic resonance imaging (MRI) scan of a 19-year-old man who initially presented with a history of shoulder pain of insidious onset. The patient was found to have synovial osteochondromatosis. Coronal T1-weighted image of the shoulder shows multiple hypointense foci in the axillary recess and in the subacromial space. Note the hypointense foci deep to the deltoid in the subdeltoid bursa. The foci result from the presence of osteocartilaginous bodies in these areas. Cartilage bodies may be present in the sleeve of the biceps tendon.

Magnetic resonance imaging (MRI) scan of a 19-year-old man who initially presented with a history of shoulder pain of insidious onset. The patient was found to have synovial osteochondromatosis. Oblique sagittal proton density– and T2-weighted images show multiple, rounded, hypointense foci in the subscapularis bursa projecting underneath the coracoid process. Note the high signal intensity simulating the presence of surrounding fluid from the joint effusion. Some of the high signal intensity results from edematous proliferating synovium. The synovium is dissecting the body of the scapula and the infraspinatus. Note the solitary osteochondral body in that location.

Magnetic resonance imaging (MRI) scan of a 19-year-old man who initially presented with a history of shoulder pain of insidious onset. The patient was found to have synovial osteochondromatosis. Oblique sagittal proton density– and T2-weighted images show multiple, rounded, hypointense foci in the subscapularis bursa projecting underneath the coracoid process. Note the high signal intensity simulating the presence of surrounding fluid from the joint effusion. Some of the high signal intensity results from edematous proliferating synovium. The synovium is dissecting the body of the scapula and the infraspinatus. Note the solitary osteochondral body in that location.

Image from a 19-year-old man who initially presented with a history of shoulder pain of insidious onset. The patient was found to have synovial osteochondromatosis. Some of the multiple stones were removed from the patient's shoulder during surgery. Note the lamellate pattern to the chondral bodies.

Sagittal T1-weighted and sagittal short-tau inversion recovery (STIR) images of the ankle show proliferating synovium, which is seen as foci of increased signal intensity on the STIR images.

Sagittal T1-weighted and sagittal short-tau inversion recovery (STIR) images of the ankle show proliferating synovium, which is seen as foci of increased signal intensity on the STIR images.

The degree of calcification varies, and calcification may be seen as a few calcific specks or as foci of frankly ossified bodies.[15] The fragments may be found free within the joint cavity, or they may be embedded within the proliferating synovium, which may extend into the surrounding soft tissues. The natural history of synovial chondromatosis entails gradual progression of disease, joint deterioration, and secondary osteoarthritis. Essentially, the disease is a benign process, and although studies in the literature have reported malignant transformation, this finding is decidedly unusual.

Plain radiographs frequently show characteristic features, including multiple (usually >5) calcified or osseous bodies within the joint or bursa (see the images below). When fragments are not calcified, intrasynovial fragments may not be seen on plain images, and arthrographic studies are required to demonstrate the bodies. The differential diagnosis includes degenerative joint disease in which osteophytes have broken off into the joint; however, synovial chondromatosis tends to have a larger number of bodies in the joint. Other differential diagnoses include soft-tissue and intra-articular chondromas. In advanced stages of synovial chondromatosis, secondary degenerative changes are often observed.

Frontal radiograph of the knee shows multiple calcified bodies in the proximal tibiofibular joint in a patient with synovial osteochondromatosis.

Lateral radiograph of the knee shows multiple calcified bodies in the proximal tibiofibular joint in a patient with synovial osteochondromatosis.

Frontal radiograph of a patient with synovial osteochondromatosis of the knee joint. The bodies are located in the popliteal space of the knee.

Lateral radiograph of a patient with synovial osteochondromatosis of the knee joint. The bodies are located in the popliteal space of the knee.

Pressure erosions (saucerization, as demonstrated in the image below) and cyst formation can be seen in adjacent bone, although this is more typical for joints with lax capsules, such as the hip. A similar observation may be found in patients with pigmented villonodular synovitis (PVNS).

Lateral view of the ankle of a man who presented with ankle discomfort. Increased soft-tissue density is noted both anteriorly and posteriorly, simulating joint effusion. Note the stippled calcification seen posteriorly, resulting from calcification in some of the cartilage bodies. The anterior corner of the distal tibia is truncated as a result of pressure erosion. Similar pressure erosions may be seen in hip and knee joints in which synovial osteochondromatosis occurs. Note the mild osteopenia around the ankle; this is likely a result of hyperemia.

CT scanning is rarely necessary to make a diagnosis of synovial chondromatosis, and the features on CT scan are similar to findings on plain radiographs. CT scanning may show noncalcified bodies.

(CT scans of synovial osteochondromatosis are shown below.)

Axial computed tomography (CT) images of the elbow at the level of the radial ulna joint. Note the presence of osteocartilaginous bodies in the radial ulna joint and also posteriorly.

Sagittal reconstruction from a spiral computed tomography (CT) scan series of the elbow shows the distribution of the calcified bodies in the olecranon fossa and around the posterior and anterior aspects of the joint.

In synovial chondromatosis, T1-weighted and proton density–weighted images often demonstrate multiple rounded bodies that are isointense or hypointense relative to muscle. Some bodies demonstrate signal intensity (or lack of it) similar to that of cortical bone.[16]

(Magnetic resonance images of synovial chondromatosis are shown below.)

Magnetic resonance imaging (MRI) scan of a 19-year-old man who initially presented with a history of shoulder pain of insidious onset. The patient was found to have synovial osteochondromatosis. Coronal T1-weighted image of the shoulder shows multiple hypointense foci in the axillary recess and in the subacromial space. Note the hypointense foci deep to the deltoid in the subdeltoid bursa. The foci result from the presence of osteocartilaginous bodies in these areas. Cartilage bodies may be present in the sleeve of the biceps tendon.

Magnetic resonance imaging (MRI) scan of a 19-year-old man who initially presented with a history of shoulder pain of insidious onset. The patient was found to have synovial osteochondromatosis. Oblique sagittal proton density– and T2-weighted images show multiple, rounded, hypointense foci in the subscapularis bursa projecting underneath the coracoid process. Note the high signal intensity simulating the presence of surrounding fluid from the joint effusion. Some of the high signal intensity results from edematous proliferating synovium. The synovium is dissecting the body of the scapula and the infraspinatus. Note the solitary osteochondral body in that location.

Magnetic resonance imaging (MRI) scan of a 19-year-old man who initially presented with a history of shoulder pain of insidious onset. The patient was found to have synovial osteochondromatosis. Oblique sagittal proton density– and T2-weighted images show multiple, rounded, hypointense foci in the subscapularis bursa projecting underneath the coracoid process. Note the high signal intensity simulating the presence of surrounding fluid from the joint effusion. Some of the high signal intensity results from edematous proliferating synovium. The synovium is dissecting the body of the scapula and the infraspinatus. Note the solitary osteochondral body in that location.

Sagittal T1-weighted and sagittal short-tau inversion recovery (STIR) images of the ankle show proliferating synovium, which is seen as foci of increased signal intensity on the STIR images.

Sagittal T1-weighted and sagittal short-tau inversion recovery (STIR) images of the ankle show proliferating synovium, which is seen as foci of increased signal intensity on the STIR images.

Some bodies may lie free, and some are completely intra-articular, whereas others may be adherent to the synovial surface. Some bodies may be found deep in the synovial lining, embedded in adjacent soft tissue.

T2-weighted images may show areas of high signal intensity consistent with joint effusion and synovial thickening.

In a study of 144 patients with synovial chondromatosis of the temporomandibular joint evaluated by MRI, 3 lesion types were visualized: loose body (32.6%), homogeneous mass (49.3%), and a mixture of the two (18.1%). Bony evaluations included 4 stages of erosion: without erosion, chondral breakdown, bony absorption, and bony perforation. Of the bony perforations, 80% were homogeneous masses and 20% were mixed loose body/homogeneous mass.[12]

The intravenous administration of a gadolinium-based contrast material usually enables the differentiation of joint effusion from hyperplastic synovium, which shows heterogeneous enhancement. Joint effusion may be hemorrhagic.

Gadolinium-based contrast agents have been linked to the development of nephrogenic systemic fibrosis (NSF) or nephrogenic fibrosing dermopathy (NFD). The disease has occurred in patients with moderate to end-stage renal disease after being given a gadolinium-based contrast agent to enhance MRI or magnetic resonance angiography scans. NSF/NFD is a debilitating and sometimes fatal disease. Characteristics include red or dark patches on the skin; burning, itching, swelling, hardening, and tightening of the skin; yellow spots on the whites of the eyes; joint stiffness with trouble moving or straightening the arms, hands, legs, or feet; pain deep in the hip bones or ribs; and muscle weakness.

When the presence of calcification is ambiguous, plain radiographs are useful adjuncts to MRI scans for establishing the diagnosis.

On MRI scans, synovial chondromatosis may appear similar to pigmented villonodular synovitis (PVNS), but the 2 conditions are easily differentiated by using plain radiographs.

The distinguishing feature of synovial chondromatosis  is calcification, which appears as signal voids in the synovium. This finding is optimally visualized when the intra-articular fragments are calcified.

Radionuclide studies (see the image below) may be obtained when the plain radiographic features are not clear. The affected areas usually show increased radionuclide uptake on technetium-99m bone scans.[17, 18]

Delayed bone scan shows diffusely increased uptake around the tibiotalar joint. This indicates increased metabolic activity and is consistent with synovitis around the ankle.