Synovial chondromatosis (SC) is a locally aggressive neoplasm consisting of multiple hyaline cartilaginous nodules. This neoplasm typically manifests as multiple intra-articular calcified or uncalcified nodules, whereas the extraarticular form is particularly rare. We herein present a case of solitary extraarticular SC arising in the hand and correlate the imaging findings with pathologic findings. A male patient in his 60s presented with a progressively enlarging mass in his left hand over a period of three years. Radiograph showed a lobulated calcified mass adjacent to the first metacarpal bone. Computed tomography (CT) revealed ring and arc calcification, indicating cartilaginous lesion. No continuity with bone was observed. In magnetic resonance imaging (MRI), the signal of the mass was heterogeneous low to high intensity on both T1- and T2-weighted images. High intensity reflecting fat on T1-weighted image and marked high intensity reflecting cartilage on fat-suppressed T2-weighted image were shown in the mass. After gadolinium administration, the enhancement of the mass was faint. An en bloc excision of the mass was performed, and the tumor was histologically diagnosed as extraarticular SC. Microscopically, the tumor consisted of fibrous tissue, mature fat tissue, and lobules of cartilage. Extraarticular SC should be taken into consideration when cases of lobulated soft tissue mass with ring and arc calcification and a fat component (T1 hyperintense) in the hand are encountered.
Synovial chondromatosis is a locally aggressive neoplasm consisting of multiple hyaline cartilaginous nodules [1]. This neoplasm usually appears as multiple intra-articular calcified/uncalcified nodules. Although any joint can be affected, the extra-articular form of synovial chondromatosis is particularly rare. We herein present a case of solitary extra-articular synovial chondromatosis arising on the hand of a patient and correlate the imaging findings with the pathologic findings.
Clinical Presentation
A 60-year-old male presented with a gradually enlarging mass on his left hand that had been present for at least three years. The mass was located between the first and second finger, causing mild discomfort but no functional limitation. No history of trauma, systemic symptoms, or prior significant medical conditions were reported by the patient.
Imaging Findings
A radiograph revealed a soft-tissue swelling over the dorsolateral aspect of the thumb, with rounded multinodular calcifications, including a ring-and-arc pattern indicative of a cartilaginous lesion (Figure 1). The adjacent joint and bone were normal without any bony scalloping or erosion. Computed tomography (CT) revealed a lobulated mass with characteristic ring-and-arc calcifications, adjacent to the first metacarpal bone (Figure 2 A).
The anteroposterior radiograph of the left hand shows a soft-tissue swelling over the dorsolateral aspect of the thumb with rounded multinodular calcifications including ring-and-arc pattern indicative of a cartilaginous lesion. The adjacent joint and bone were normal without any bony scalloping or erosion.
Magnetic resonance imaging (MRI) showed an intermuscular lobulated mass in the divided left first dorsal interosseous muscle (Figure 2 B, C; asterisks). The signal of the mass was heterogeneous low to high intensity on both the T1- and T2-weighted images (T1WI and T2WI). High intensity on T1WI indicating fat were shown within the calcified portion of the mass (Figure 2 B-D; arrows). There were spotty areas of marked high signal intensity in the mass, which could be considered to reflect cartilage on the fat-suppressed T2WI (Figure 2 D; arrowheads). Faint patchy enhancement was seen after gadolinium administration (Figure 2 E; arrows).
Computed tomography (CT) revealed a lobulated mass with characteristic ring-and-arc calcifications (A). MRI showed an intermuscular lobulated mass in the divided left first dorsal interosseous muscle (B, C asterisks). The signal of the mass was heterogeneous low to high intensity on both T1- and T2-weighted image (T1WI and T2WI). High intensity indicating fat on T1WI were shown within the calcified portion of the mass (B-D arrow). There were spotty areas of marked high signal intensity in the mass, which could be considered to reflect cartilage on fat-suppressed T2WI (D arrowheads). Faint patchy enhancement was seen after gadolinium administration (E arrows).
Treatment Outcome
The tumor was surgically removed en bloc without complications. It was a white elastic hard mass with adhesion to the surrounding muscle. No evidence of recurrence was observed during a one-year follow-up period. The patient maintains full restoration of hand function without residual pain or discomfort.
Histopathological Findings
A photomicrograph (Figure 3) showed that the mass was comprised of adipose tissue, cartilage tissue, and bone tissue, considered to be osteochondroma. The adipose tissue was predominantly located in the central region of the mass. Islands-like distribution of cartilage tissue was also observed adjacent to the tendon tissue. The photomicrograph revealed an indistinct boundary between the tumor cartilage tissue and the tendon tissue. The excised mass was histologically diagnosed as extra-articular synovial chondromatosis.
Photomicrograph (original magnification, 5; H-E stain) shows that the mass comprised adipose tissue (black arrows), cartilage tissue (white arrows), and bone tissue (black arrowheads).
Islands-like distribution of cartilage tissue (asterisks) is observed predominantly in the peripheral region of the mass. (original magnification, 5; H-E stain).
An indistinct boundary between the tumor cartilage tissue (white arrows) and the tendon tissue (black arrows) is shown in the peripheral area of the lesion (original magnification, 20; H-E stain)
Primary synovial chondromatosis represents a rare benign neoplastic disease with the formation of hyaline cartilage nodules in the subsynovial tissue of the joint, tendon sheath, or bursa [2]. The most common subtype of this disease involves the synovium of the joint, and most cases involve the large joints. It most commonly affects the knee joints, followed by the hip, shoulder, and elbow in approximately 60–70% of cases. It can occur in any joint, including temporomandibular and intervertebral joints. The disease occurs in a wide age range from childhood to late adulthood, with a predilection for the third to fifth decades, and in some series, has a higher incidence in men than in women [3]. Malignant transformation of synovial chondromatosis into chondrosarcoma has also been reported. McCarthy et al reported that malignant transformation was reported in 4 out of 155 cases (approximately 2.5%) of synovial chondromatosis [3]. Of these four cases, one occurred in the elbow joint and three in the hip joint.
Extra-articular synovial chondromatosis, also known as tenosynovial chondromatosis, is significantly less common than the intra-articular form of this disease, with the hands and feet being the most frequently affected sites [4–6]. Clinical symptoms of tenosynovial or bursal chondromatosis are most frequently a painless mass or one with mild tenderness upon palpation of the lesion. Given the location, trigger-finger or carpal-tunnel symptoms can occur [7]. Radiographs show a calcified mass in 75–90% of cases, showing either chondroid mineralization (ring and arc, punctate, so-called feathery calcification) or ossified nodules, as in our case [1, 2]. When calcified bodies are present, the radiographic findings often consist of multiple calcified nodules of relatively uniform size. CT can more clearly depict these findings. MRI demonstrates unmineralized bodies and synovial nodules as a lobulated, homogenous mass with low-to-intermediate intensity on T1WI and hyperintensity on T2WI [1]. Previous studies reported that calcified bodies are noted as focal areas of signal void. MRI also depicts the anatomy clearly, and an intimate relationship to the tendon sheath is seen in synovial chondromatosis. In some cases, however, as in ours, the continuity with the tendon may be unclear and difficult to distinguish from other soft tissue tumors [4, 6].
The pathophysiology of primary synovial chondromatosis is still unknown. In the secondary chondromatosis, the presence of intra or periarticular cartilaginous nodules is attributed to the pathomechanical sequelae of degenerative joint disease [8, 9] .
The gross pathological appearance of primary synovial chondromatosis consists of a bluish-white, multinodular, hyaline cartilage projecting hyperplastic synovium [10, 11]. The hyaline cartilage nodules detach from the synovium and present in the joint, bursa or tendon sheath. They may also reattach and be reabsorbed to the synovium. The chondral bodies are nourished by synovial fluid and may grow gradually. They are often numerous, and fusion or coalescence of multiple chondral bodies may occur. In long-term disease, the cartilage lobules often undergo peripheral enchondral ossification, which progresses to include a central yellow marrow [2].
The imaging findings in this case clearly reflected the pathological features of synovial chondromatosis. Our case presented as an extra-articular soft-tissue tumor with calcification, rather than multiple calcified nodules, on plain photographs and CT. The ring and arc calcifications indicated that the tumor contained cartilaginous components. Moreover, MRI showed a fat component within the calcified portion of the mass, which represents further maturation of the chondral fragments. In addition, spotty areas of marked high signal intensity reflecting hyaline cartilage were well depicted on fat-suppressed T2WI. These MR findings are considered to be characteristic MR findings suggestive of long-term extra-articular synovial chondromatosis. Therefore, recognition of the imaging findings correlated with the pathology is essential for proper preoperative diagnosis.
Extra-articular synovial chondromatosis should be considered in the differential diagnosis when cases of lobulated soft tissue masses in the hand, characterized by rings-and-arcs calcification and a fat component (T1 hyperintensity) are encountered.
The authors declare no conflicts of interest in association with this manuscript.
