summary Enchondromas are benign chondrogenic tumors composed of hyaline cartilage that typically occur in medullary cavity of the diaphysis or metaphysis, most commonly in the hands. Patients typically present between the ages of 20-50 with an asymptomatic lesion, discovered incidentally on radiographs. Diagnosis is made radiographically with the presence of a well-defined, lucent, central medullary lesion that is 1-10 cm, and often associated with "pop-corn" stippling, arcs, whorls, or rings. Treatment is observation as most lesions are asymptomatic. Epidemiology Incidence 2nd most common benign cartilage lesion (osteochondroma is most common) Demographics male:female ratio is 1:1 age bracket most common in 20-50 year olds Anatomic location usually found in the medullary cavity of the diaphysis or metaphysis the most common locations hand (60%) > feet the most common bone tumor in the hand is the enchondroma other locations include distal femur (20%) > proximal humerus (10%) > tibia rare in the pelvis, scapula, ribs suspect chondrosarcoma in these locations Etiology Pathophysiology enchondromas represent incomplete endochondral ossification chondroblasts and fragments of epiphyseal cartilage escape from the physis, displace into the metaphysis and proliferate there Associated conditions solitary enchondroma Ollier's disease (multiple enchondromatosis) sporadic inheritance with no genetic predisposition skeletal dysplasia with failure of normal endochondral ossification enchondromas throughout the metaphyses and diaphyses of long bones involved bones are dysplastic, with shortening and bowing risk of malignant transformation <30% Maffucci's syndrome sporadic inheritance with no genetic predisposition multiple enchondromas and soft-tissue angiomas radiographically, enchondromas in Maffucci's syndrome markedly expand the bone and angiomas are seen as small, round calcified phleboliths increased risk of visceral malignancies (astrocytoma, GI malignancy) overall risk of developing any malignancy up to 100% Classification Enneking Classification of Benign Lesions Grade Examples Stage 1 Latent lesions Enchondroma, non-ossifying fibroma Stage 2 Active lesions ABC, UBC, chondromyxoid fibroma, chondroblastoma Stage 3 Aggressive lesions Giant cell tumor of bone Presentation Symptoms asymptomatic, discovered incidentally on radiographs usually true for enchondromas in long bones and foot pathologic fracture often seen with enchondromas in the hand pain pain is uncommon when a patient presents with an enchondroma and pain in the adjacent joint, the cause of pain is often unrelated to the tumor unlike enchondroma, most chondrosarcomas have non-mechanical pain (rest pain and nocturnal pain) Physical exam shortening and angular deformities enchondromas may disrupt the growth plate multiple bluish angiomas in Maffucci's syndrome Imaging Radiographs recommended views skeletal survey if polyostotic disease is suspected findings well defined, lucent, central medullary lesions that calcify over time 1 to 10cm in size metaphyseal location when they first appear appear more diaphyseal as the long bone grows "pop-corn" stippling, arcs, whorls, rings minimal endosteal erosion (<50% width of cortex) cortical expansion and thinning may be present in hands, feet but not in long tubular bones (femur, tibia) may have purely lytic appearance (especially in hand) Ollier's disease enchondromas markedly expand the bone bones are dysplastic, with shortening and bowing Maffucci's syndrome enchondromas markedly expand the bone angiomas are visible as calcified phleboliths unlike enchondromas, chondrosarcomas display cortical thickening and destruction endosteal erosions and scalloping >50% of the width of the cortex are larger (>5cm) Bone scan indications to help differentiate chondrosarcoma from enchondroma to identify polyostotic disease rarely adds useful information only 20% have more uptake than ASIS most enchondromas are small, and easily identified as benign findings increased uptake, but less than chondrosarcoma because of continued remodeling within the lesion MRI indications usually not necessary for diagnosis identify size and intramedullary extent and soft tissue extension differentiate from chondrosarcoma findings lobular and bright on T2-weighted images no bone marrow edema or periosteal reaction may show steak of cartilage or "sled runner tracks" medullary fill >90% suggests chondrosarcoma instead Studies Core needle-biopsy from areas of bone scalloping or lysis prone to sampling error due to tumor heterogeneity chondrosarcomas may contain areas of benign hyaline cartilage often impossible to differentiate from low-grade chondrosarcoma Histology gross appearance blue gray, lobulated hyaline cartilage, with scattered calcifications microscopic solitary lesions in long bones hypocellular with bland, mature hyaline cartilage (blue balls of cartilage) separated by normal marrow differentiates from chondrosarcoma endochondral ossification encases cartilage with lamellar bone abundant extracellular matrix with no myxoid component solitary lesions in small tubular bones and fibula, Ollier's and Maffucci's syndromes hypercellular, with mild chondrocytic atypia characteristics of chondrocytes small, bland chondroid cells in lacunar spaces uniform staining nuclei no pleomorphism, mitoses, anaplasia, hyperchromasia or multinucleate cells unlike enchondromas, chondrosarcomas display hypercellularity, with plump nuclei multiple binucleate cells giant cells with clumps of chromatin Differential Bone infarct "smoke up the chimney" radiographic appearance MRI does not give high T2 signal enchondromas have high T2 signal because of high water content of cartilage Chondrosarcoma worsening pain large size deep endosteal scalloping >2/3 of cortical thickness periosteal reaction, cortical breakthrough rare in hands, feet, more common in pelvis, scapula, ribs the converse is true for enchondroma radiographic appearance differentiating low grade chondrosarcoma from enchondroma (see below) Treatment Nonoperative observation indications treatment for vast majority of asymptomatic enchondromas follow up serial radiographs at 6 months and 12 months to confirm radiographic stability long term follow-up for patients with multiple enchondroma syndromes Operative intralesional curettage and bone grafting indications lesion that shows any change on serial xrays symptomatic lesions pathologic fractures - immediate curettage and grafting is now favored no difference in outcomes between delayed and immediate curettage and grafting radiographs suspicious for low-grade chondrosarcoma large lesions at risk for recurrent fracture outcomes local recurrence is unusual Complications Malignant transformation risk of transformation of enchondroma to chondrosarcoma solitary enchondroma risk of malignant transformation is 1% Ollier's disease risk of malignant transformation is 25-30% Maffucci's syndrome risk of malignant transformation is 25-30%, but up to 100% risk of other visceral and CNS malignancies as well