Soft tissue chondroma (extraskeletal chondroma) of the hand: Report of three cases

Abstract

Soft tissue chondroma, also known as extraskeletal chondroma or soft tissue osteochondroma, is a rare benign tumor composed of chondrocytes and a hyaline cartilage matrix. Imaging plays a fundamental role in its diagnosis, with the primary finding being a soft tissue mass devoid of any adjacent bone connections. Calcifications or ossifications are typically observed, although they are not mandatory for diagnosis. In this article, we present three cases of this rare entity manifesting in the hand, accompanied by comprehensive imaging findings obtained through radiography, ultrasound, computed tomography (CT), and magnetic resonance imaging (MRI), as well as the corresponding macroscopic and histopathological examinations. We will describe the key clinical, imaging, and pathological features of this condition.

Introduction

Soft tissue chondroma (STC), also known as extraskeletal chondroma or soft tissue osteochondroma, is a rare benign neoplasm composed of chondrocytes within a hyaline cartilage matrix. Originating from extraosseous and extra-synovial tissues, it is classified as a chondro-osseous tumor according to the most recent World Health Organization classification of soft tissue and bone tumors [1,2]. In earlier reports, extra-skeletal cartilage-producing tumors with focal calcifications were referred to as extra-skeletal chondromas. If they exhibited more ossifications, they were termed extra-skeletal osteochondromas. At the time, it was a source of debate whether these represented the same entity [3]. Although they can manifest in various locations and affect individuals of all ages and both genders, their primary site of occurrence is the hands and feet in individuals between the ages of 30 and 60. Typically, the clinical presentation is a painless, hard, and slowly growing nodular soft tissue lesion that may also cause symptoms [4,5]. In this study, we present three cases of STC, detailing their typical clinical and imaging features [6].

Case reports

Case number one

A 30-year-old male presented with a palpable, firm, painless nodule on the radial aspect of the left wrist approximately three years prior to presentation. There were no reports of trauma associated with the nodule. The patient had no relevant past medical or surgical history, no family history of musculoskeletal tumors, and no constitutional symptoms. Laboratory investigations, including complete blood count and inflammatory markers, were within normal limits. The diagnostic evaluation commenced with radiographic imaging and ultrasound (US) (Figs. 1A–C).

Fig. 1.

Radiographs of the left wrist, front view (A) showed soft tissue prominence and increased density within the radial soft tissues of the hand at the site of the clinical complaint, with multiple ossifications (circle). US demonstrated a heterogeneous soft tissue mass (B), which was mainly hypoechogenic, with areas of posterior shadowing suggestive of calcifications (arrows). There was no significant flow on Color Doppler (C). MRI of the wrist in Coronal T1-weighted (D), T2-weighted fat suppressed (E), T2*GRE (F) and T1-weighted fat suppressed post gadolinium (G) demonstrated a well-circumscribed deep juxta-articular soft tissue mass along the radial aspect of the carpus, extending toward the scaphotrapeziotrapezoidal joint space. The lesion was extraosseous and extra-synovial, located in intimate relationship with the adjacent joint capsule and insinuating between the first and second extensor compartments. The lesion demonstrated predominantly intermediate T1 signal intensity with internal foci of high T1 signal (arrow in D), heterogeneous high signal on T2-weighted imaging, and predominantly peripheral enhancement following gadolinium administration (arrow in G). Mild compression of the radial neurovascular bundle and adjacent superficial venous branches was present. The intra-operative image (H) shows a well circumscribed mass in the radial soft tissue of the hand. Histopathological image (I, H&E, 4x) shows a mature lamellar bone with endochondral ossification (arrowhead), fat marrow and a hypocellular hyaline cartilage cap (+).

Based on the radiographic findings, the possibility of a supernumerary carpal bone was raised. US showed a heterogeneous soft tissue mass with areas of posterior shadowing and no flow on color Doppler. MRI (Figs. 1D–G) showed a soft tissue mass with internal high T1 signal areas and foci of heterogeneous enhancement.

Due to benign imaging features and the presence of significant symptoms, the orthopedic surgery team decided to resect the mass without prior biopsy. Marginal surgical excision was performed due to progressive local discomfort and the benign imaging appearance of the lesion. Histopathological study showed a well-defined multilobulated neoplasm, formed by moderately cellular cartilage, without atypia and showing internal areas of ossification. The final diagnosis was a STC. Figs. 1H and I show the intraoperative image and histopathology slides. Histopathological findings correlated with the imaging appearance by demonstrating a circumscribed osteocartilaginous lesion with endochondral ossification corresponding to the internal mineralized components seen on radiography and MRI. No significant cellular atypia, mitotic activity, infiltrative growth pattern, or synovial lining was identified, and the lesion was well circumscribed. At clinical follow-up, the patient remained asymptomatic without evidence of local recurrence.

Case number two

A 47-year-old male presented with a palpable mass in the palm of his right hand, which had been present for approximately one year prior to presentation. The mass subsequently became painful and was accompanied by numbness and tingling in his index and long fingers. The patient denied any history of trauma or systemic symptoms. The patient had no significant past medical or surgical history and no known family history of musculoskeletal neoplasms. Laboratory investigations were unremarkable, including inflammatory markers and routine blood tests. The diagnostic evaluation began with radiographs of the hand (Figs. 2A–C), followed by MRI (Figs. 2D–G), which showed an ossified mass in the volar myofascial planes of the hand. US examination was not performed.

Fig. 2.

Radiographs of the right hand showed an ossified mass (arrows in A,B and C) on the volar aspect of the hand, at the level of the third metacarpal shaft, corresponding to the area of clinical concern. MRI of the right hand in axial T1-weighted (D), axial PD-weighted fat-suppressed (E), coronal T1-weighted (F), and sagittal PD-weighted fat-suppressed (G) sequences demonstrated a deep extraosseous soft tissue mass within the central volar myofascial compartment of the hand. The lesion was extra-articular and intermuscular, located adjacent to the flexor tendons without evidence of tendon sheath invasion. The mass demonstrated predominantly high signal intensity on T1-weighted images, with central low signal intensity and peripheral high signal intensity on fluid-sensitive sequences, corresponding to internal ossified components and peripheral cartilaginous tissue, respectively. Mild surrounding edema and reactive marrow edema of the third metacarpal shaft (white arrows) were present, likely related to biomechanical stress. No osseous continuity or nerve compression was identified. Histopathological images (H, 1x; I, 2x) show a circumscribed lesion with bland hypocellular cartilaginous cap (*) and central mature lamellar bone with fatty marrow (+).

The patient underwent biopsy and subsequent resection of the lesion, and the histopathological study showed benign osteocartilaginous proliferation, consistent with the diagnosis of STC (Figs. 2H–I). Surgical excision was performed due to progressive pain and compressive symptoms affecting the adjacent digits. Histopathological examination demonstrated a well-circumscribed benign osteocartilaginous proliferation with central mature lamellar bone and fatty marrow corresponding to the ossified components identified on imaging. No significant atypia, mitotic activity, or any infiltrative features were present. Postoperatively, the patient experienced improvement of pain and sensory symptoms, without imaging evidence of recurrence during follow-up.

Case number three

A 12-year-old right-handed male presented with a slowly growing dorsal mass on his wrist that had started approximately one year prior to presentation. He was an active athlete and had observed a decrease in wrist extension and occasional pain while writing and playing basketball. The patient had no relevant medical or surgical history, no family history of bone or soft tissue tumors, and no constitutional symptoms. Laboratory investigations were within normal limits. Initially, the patient consulted an orthopedic surgeon, who suspected a dorsal ganglion cyst and obtained radiographs (Figs. 3A–C). Radiographs showed a dorsal ossified mass of the wrist. The patient then underwent CT and MRI (Figs. 3D–G), which showed the ossified mass in the dorsal soft tissues with surrounding edema and enhancement on MRI. US examination was not performed.

Fig. 3.

Radiographs of the right wrist (A, B and C) show an ossified mass (white arrows) in the dorsal aspect of the wrist, corresponding to the site of symptoms. CT in the axial plane with bone window settings (D) better demonstrated the ossified juxta-articular mass within the dorsal wrist soft tissues. MRI of the right wrist in axial T1-weighted (E), axial PD-weighted fat-suppressed (F), and T1-weighted fat-suppressed post-contrast (G) sequences demonstrated a deep juxta-articular extraosseous soft tissue mass along the dorsal aspect of the wrist, adjacent to the dorsal capsule and deep to the extensor tendons. The lesion demonstrated predominantly high signal intensity on both T1-weighted and fluid-sensitive sequences, corresponding to internal fatty marrow and cartilaginous components. Mild surrounding soft tissue edema and peripheral enhancement were present following gadolinium administration. No osseous continuity with the adjacent carpal bones was identified. Intraoperative image (H) shows a well-defined mass in the dorsum of the wrist. Histopathological slide show a circumscribed lesion (I, H&E, 1x) with a cartilaginous cap (*, J, H&E, 4x) with underlying enchondral ossification (+).

The lesion was fully resected, and the final diagnosis was a STC (Figs. 3H–J). Histopathological analysis confirmed a circumscribed benign osteocartilaginous lesion with endochondral ossification corresponding to the juxta-articular ossified dorsal wrist mass identified on radiography, CT, and MRI. No significant atypia, mitotic activity, or infiltrative growth pattern was identified. On follow-up, the patient had good recovery with a gradual return to sports activities.

Discussion

As seen in the three cases, imaging plays a pivotal role in the diagnosis of STC. Radiographs demonstrate absence of connection to the adjacent bone, distinguishing STC from cortical-based or periosteal-based lesions, such as osteochondromas and bizarre parosteal osteochondromatous proliferation (BPOP, also known as Nora’s lesion). Radiographs can also reveal erosion and remodeling of the underlying bone, as well as ossifications or chondroid-type calcifications, including discrete, irregular, ring-like, or curvilinear calcifications [1,[7], [8], [9]]. CT imaging provides superior visualization of a calcified soft tissue mass devoid of a bone connection [7]. US imaging can also demonstrate both the soft tissue component and calcifications, and Doppler studies can assess the presence of blood flow [5]. MRI is typically the best examination for these lesions, enabling a more comprehensive evaluation. MRI shows a well-defined lobulated mass exhibiting low or intermediate signal on T1-weighted and high signal on T2-weighted, corresponding to the high concentration of cartilage [7]. Areas of ossification can present as high T1 areas, as seen in all three cases. In the reported cases, multimodality imaging characteristics demonstrated these features. Notably, ossifications were present in all cases on conventional radiography, potentially leading to a misdiagnosis of a supernumerary carpal bone.

Macroscopic features include circumscribed, small tumors (usually smaller than 2 cm) with no connection to the bone. Microscopically, these masses present mature cartilage lobules with a matrix predominantly of hyaline cartilage, but with varying amounts of myxoid, fibrous or ossified cartilage. Atypical features such as hypercellularity have no prognostic significance, and immunohistochemistry can demonstrate chondrocyte expression of S100 and ERG, although these are not necessary for diagnosis [1]. These tumors also have recurrent FN1-FGFR2 and FN1-FGFR1 fusions in 50% of cases and show morphological and molecular overlap with phosphaturic mesenchymal tumor but have no association with fibroblast growth factor 23 expression or osteomalacia [2].

Despite the uncertain etiology, these tumors can originate from various soft tissues, including tendons, synovial sheaths, and the joint capsule. They exhibit a predilection for the hands and feet [5]. Simple excision is regarded as curative, although a recurrence rate of up to 20% has been observed [1]; therefore, clinical and imaging follow-up are recommended [7]. Different from synovial chondromatosis, there is no known risk of malignant transformation for STC [10,11].

In regard to the differential diagnoses, the possibilities of synovial chondromatosis (which typically affects larger joints and is arguably a related entity), extra-skeletal myxoid chondrosarcoma, myositis ossificans, BPOP, nuchal fibrocartilaginous tumor, chondroid lipoma, and calcifying aponeurotic fibroma should be considered [1]. Many of these entities may be indistinguishable by imaging, but the presence of a zonal reaction and peripheral ring calcification in a trauma context should direct the differential diagnosis towards myositis ossificans, while the relationship of the tumor to the cortical bone or the periosteum suggests a diagnosis of BPOP or osteochondroma [1,12]. Supernumerary bones may also be considered, particularly when complete ossifications are observed, as in cases #1 and #3.

In this study, we have presented three cases with imaging and pathological correlation of soft tissue chondromas. The most notable imaging feature is the presence of an ossified soft tissue mass without continuity with the adjacent bone. Whenever a radiologist encounters a soft tissue lesion, particularly in the hands or feet, that lacks continuity with the bone, STC should be included in the differential diagnosis.

Ethics approval and consent to participate

Consent to participate and IRB approval (number 86948325.5.0000.0071).

Patient consent

A written informed consent was obtained from the patient for the publication of this case report.