Laboratory Studies
Routine blood investigations are performed only as part of preoperative studies. Otherwise, radiologic investigations are the mainstay of the diagnosis and follow-up of chondromas.
Radiography
Enchondroma
Enchondromas produce a localized radiotranslucent defect with punctate or stippled calcifications. The amount of lucency or opacity depends on the degree of calcification. Hence, some lesions may not have radiologically visible calcification and appear lytic on radiographs, whereas other lesions may show mainly irregular calcification.
Most enchondromas are metaphyseal. This observation is consistent with the theory that these lesions are remnants of embryonic physeal cartilage that fail to ossify. Enchondromas of short tubular bones are diaphyseal, but extension to the epiphyses is frequent.
In long bones, enchondromas typically do not show distinct outlines (see the images below). This is in contrast to their appearance in short tubular bones. The contour of short tubular bones is commonly expanded, with thinning of the cortices. If a cortical breach is present along with soft-tissue extension and periosteal bone reaction, malignant transformation should be suspected.
Plain radiograph reveals chondroma in left proximal femur (A) and low-grade chondrosarcoma in right superior pubic ramus and symphysis (B).
Because enchondromas are benign, their radiologic appearance should not grow or change in an adult. If a change is observed, particularly decreasing calcification or the development of translucency in the calcified lesion, chondrosarcoma or malignant transformation should be suspected. [9] The reason is that calcification occurs in resting cartilage and not in the actively dividing malignant chondrocytes of a chondrosarcoma.
Periosteal (juxtacortical) chondroma
The typical radiographic appearance of a periosteal chondroma is that of a well-defined surface lesion with stippled or punctate calcifications. Erosion of the underlying cortex may be noted, [10] and some long-standing tumors may be associated with subchondral sclerosis. Elevation of the periosteum overlying the lesion is a characteristic finding; on plain radiographs, this finding appears as solid buttresses of mature subperiosteal bone.
To differentiate chondromas from chondrosarcomas, clinicians should recognize that chondromas typically do not change or increase in size, shape, lucency, or calcification as seen on serial radiographs. [11]
CT and MRI
Computed tomography (CT) is useful because it can depict subtle radiographic changes in calcification and thereby indicate early malignant transformation. Positron emission tomography (PET)-CT may prove to be an effective means of distinguishing chondroma from intraosseous chondrosarcoma in long bones. [12] Single photon emission CT (SPECT)/CT may also be useful for this purpose. [13]
Magnetic resonance imaging (MRI) is indicated for assessing noncalcified intramedullary chondroid lesions. These tumors have low signal intensity on T1-weighted images and high signal intensity on T2-weighted images. With periosteal chondromas, MRI can show the overlying fibrous periosteum. Low signal intensity is expected on pulsed-sequence MRI images in areas where calcified chondroid matrix is demonstrated on plain radiographs.
MRI is also useful in assessing the thickness of the cartilaginous cap in osteochondroma; a cap thicker than 5 mm is grounds for concern about malignant change. Further MRI is helpful for evaluating soft-tissue extension and intramedullary extension in chondrosarcoma (see the image below). Dynamic contrast-enhanced (DCE)-MRI appears useful for differentiating enchondroma from low-grade chondrosarcoma, and it has been suggested that the combination of DCE-MRI with standard MRI may be more accurate for differentiating these cartilaginous tumors. [14]
Biopsy
If the diagnosis is in doubt, biopsy is indicated. Two approaches are used.
The usual practice is to perform biopsy first and defer definitive resection. However, biopsy is not appropriate for cartilaginous lesions that are clinically and radiologically benign and is not routinely performed or advised for these lesions. Furthermore, histologic examination may not always help in correctly differentiating benign lesions from malignant ones, and it should not be relied on in isolation from the clinical and radiologic findings.
The second approach, employed in rare cases, is to plan definitive resection simultaneously with biopsy and to confirm the diagnosis by examining frozen sections.
Histologic Findings
Gross findings
Enchondromas are composed of subcentimeter-sized lobules. [15] Variable penetration of the lobules into the marrow produces an irregular periphery. Satellite lesions may be present. Calcifications appear ivory white on cross-section.
Periosteal chondromas appear as lobulated, cartilaginous masses with a covering of fibrous tissue from the periosteum. The inner margin produces smooth excavation in the cortex (crater effect). Thickened cortical bone clearly separates the medullary cavity of the bone.
Microscopic findings
The lesions consist of lobules of mature hyaline cartilage with varying cellularity. Cellular tumors may contain chondrocytes with plump or double nuclei. In general, the chondrocytes are similar to those seen in hyaline cartilage. Normal marrow separates the cartilaginous lobules, which may be partially encased in mature lamellar bone. Within the lesion, one may observe areas of myxoid change or focal necrosis. Foci of fine or coarse calcifications may be seen. In addition, areas of enchondral ossification may be present.
Synovial chondromas
Synovial (soft-tissue) chondromas can be diffuse or localized. The former are characterized by multiple nodules that involve the entire synovium, whereas the latter are characterized by a discrete mass from a coalescence of metaplastic cartilage. In the rare nodular variety of synovial chondromatosis, a polypoidal pedunculated mass protruding into the joint may also be a feature. The large cartilaginous masses have multinodular granular surfaces, and individual nodules may range in size from less than 1 mm to 1-2 cm.
-
Enchondroma of proximal femur.
-
Plain radiograph reveals chondroma in left proximal femur (A) and low-grade chondrosarcoma in right superior pubic ramus and symphysis (B).
-
MRI showing chondroma (A) and low-grade chondrosarcoma (B).
