Enchondroma



Enchondroma


G. Petur Nielsen, MD

Andrew E. Rosenberg, MD










Enchondroma demonstrates classic “ring and arc” pattern corresponding to reactive bone rimming individual cartilage nodules. Spiculated radiodensities represent calcification of the hyaline matrix.






Well-circumscribed enchondroma shows that the tumor is composed of nodules of cartilage that vary in size and are gray-blue and glistening. The tan-white regions represent foci of matrix calcification.


TERMINOLOGY


Abbreviations



  • Enchondroma (ench)


Synonyms



  • Chondroma of bone


Definitions



  • Benign primary bone tumor composed of chondrocytes producing cartilage matrix that arises within medullary cavity


ETIOLOGY/PATHOGENESIS


Unknown



  • Likely results from genetic events in stem cells


CLINICAL ISSUES


Epidemiology



  • Incidence



    • 1 of more common primary bone tumors



      • 2nd in frequency to osteochondroma


    • Accounts for approximately 12-24% of primary benign bone tumors


    • Represents 3-10% of all primary bone tumors


  • Age



    • Usually presents during 3rd and 4th decades of life



      • Uncommon in children and elderly


  • Gender



    • Equal gender distribution


  • Ethnicity



    • No racial predilections


Site



  • Arise only in bones that form from process of enchondral ossification during embryologic development



    • Do not develop in bones that are intramembranous in formation


  • Almost 60% of solitary enchondromas arise in small tubular bones of hands and feet



    • Represents most common primary bone tumor of hand


  • Other frequent sites of involvement include long tubular bones (20-45%)



    • Frequently affected bones are femur, tibia, humerus, fibula



      • Metaphysis and proximal and distal potions of diaphysis


  • Uncommon for enchondroma to arise in flat bones and spine



    • < 3% develop in pelvis


Presentation



  • Vast majority are asymptomatic


  • Frequently detected as incidental finding during investigation of other conditions



    • Relatively common for enchondroma to be diagnosed in patients with pain associated with other abnormalities, such as osteoarthritis, torn menisci, or rotator cuff



      • Pain is erroneously attributed to enchondroma in periarticular bone


  • Almost 90% of enchondromas are solitary


  • Slow growing; may show no growth in adulthood


  • Infrequently painful except if fractured



    • Pain caused by generation of microfractures


    • Painful intraosseous hyaline cartilage tumor should raise possibility of chondrosarcoma


  • Fractures usually involve phalanges



    • Large tumors in long bones rarely present with dramatic pathologic fracture


Natural History



  • Slow limited growth that eventually ceases


  • Multiple lesions occur in syndromes: Ollier disease, Maffucci syndrome, metachondromatosis




    • Ollier disease: 2 or more enchondromas


    • Maffucci syndrome: 2 or more enchondromas associated with superficial soft tissue vascular tumors



      • Type of vascular tumor in Maffucci syndrome is spindle cell hemangioma


    • Metachondromatosis: Multiple enchondromas and osteochondromas (autosomal dominant mode of inheritance)


  • Malignant transformation of isolated lesion into chondrosarcoma very uncommon



    • Increased incidence of malignant transformation in enchondromatoses


Treatment



  • Most asymptomatic solitary enchondromas can be clinically followed


  • Determination of which tumor should be operated upon depends on clinical circumstances



    • Painful tumors may require therapy to alleviate symptoms and to exclude low-grade chondrosarcoma


    • Tumors with radiographic findings that raise suspicion of chondrosarcoma should be biopsied or curetted


    • Some patients may require treatment for psychological reasons


  • Surgical treatment is usually thorough curettage and packing with bone graft or cement


  • En bloc resection is performed on sizable lesions in expendable bones, such as proximal fibula or rib


Prognosis



  • Local recurrence following curettage is uncommon (3-4%)


  • Local recurrence should raise suspicion of chondrosarcoma


IMAGE FINDINGS


Radiographic Findings



  • Spherical or oblong in shape


  • Most tumors are lucent with scattered areas of increased radiodensity



    • Extent of mineralization varies considerably


    • Many tumors contain scattered dense stippled opacities


    • Represent irregular calcification of cartilaginous matrix


    • Rim of mineralized reactive bone surrounding individual radiolucent nodules of cartilage produce arcs, “O” or “C” ring-like mineralized structures


    • Progressive mineralization may occur over time and can be mistaken for enlargement of tumor


    • In older tumors, mineralized nodules coalesce and form solid, stone-like intraosseous density



      • Focal loss of calcification over time may indicate malignant transformation


  • Well-defined margins



    • Margins may or may not be associated with sclerosis


  • Tumor adjacent to inner cortex produces scalloping



    • Scalloping has smooth contours


  • Large tumors in small or flat bones can cause marked thinning of cortex or cortical resorption


  • Progressively enlarging tumors in small and flat bones can result in significant expansion of bone



    • Marked asymmetric bone expansion is uncommon and known as enchondroma protuberans


  • Cortical thinning, bone expansion, and periosteal reaction in combination are usually harbingers of malignancy when associated with cartilage tumors in flat or large tubular bones


  • Periosteal reaction usually absent unless fracture has occurred


  • No soft tissue extension or mass


MR Findings



  • High signal intensity on T2WI


  • Low to intermediate signal intensity on T1WI


  • Mineralized cartilage produces signal void


  • Marrow surrounding tumor is usually normal, except if there has been fracture



    • Presence of surrounding marrow edema raises possibility of chondrosarcoma



CT Findings



  • Well-circumscribed lobulated tumor


  • Stippled calcifications


  • Arcs, rings, and C-shaped patterns of mineralization


  • Scalloped endosteum with cortical thinning


  • No periosteal reaction unless associated with fracture


Bone Scan



  • May be negative


  • Actively calcifying tumors show moderate activity


  • Fractured tumors show marked activity


PET Scan



  • Enchondroma has SUV of < 2 with 18-FDG PET


MACROSCOPIC FEATURES


General Features



  • Firm-to-hard; grittiness depends on amount of matrix mineralization and reactive bone formation


  • Composed of coalescing pearly white or gray nodules that are usually 3-5 mm in diameter



    • Gray glistening nodules of hyaline cartilage


    • White areas represent mineralized matrix


  • Scalloping of endosteal surface may be present


  • Well demarcated from surrounding bone


Sections to Be Submitted



  • Process entire tumor in curettage specimen


  • Resections: Minimum of 1 section per cm



    • Concentrate on noncalcified regions


    • Submit closest bone and soft tissue margins


Size



  • Relatively small; ranges from 1-5 cm


  • Tumors in small bones may cause deformity of bone


  • Uncommon for tumor in long bone to be large enough to produce visible distortion


MICROSCOPIC PATHOLOGY


Histologic Features



  • Composed of variably sized nodules of hyaline cartilage



    • Fibrocartilage differentiation is rare


    • Elastic cartilage differentiation extraordinarily rare


  • Nodules of cartilage well circumscribed and have sharp margin with surrounding bone


  • Cartilage is hypo- to moderately cellular


  • Contains chondrocytes that have uniform, small, round, hyperchromatic (lymphocyte-like) nuclei


  • Occasionally, cells are binucleate and have fine chromatin and small nucleolus


  • Matrix is usually hyaline type and rarely fibrocartilaginous



    • Most prominent component of lesion


  • Myxoid matrix is uncommon



    • Should raise suspicion for chondrosarcoma


  • Hyaline matrix frequently calcifies



    • Calcification appears as amorphous purple or basophilic granular material


    • Chondrocytes undergo necrosis in zones of calcification


  • Periphery of nodules often undergoes endochondral ossification



    • Bone rims nodules of cartilage


    • No encasement of preexisting trabecular bone (infiltration), which is feature of chondrosarcoma


    • At periphery of tumor, remnants of cartilage may be in center of broad bony trabeculae


  • Enchondromas arising in digits are frequently hypercellular and demonstrate mild cytologic atypia


  • Enchondromas in Ollier disease and Maffucci syndrome may be hypercellular and exhibit cytologic atypia, and matrix may be focally myxoid


ANCILLARY TESTS


Immunohistochemistry



  • Chondrocytes strongly express vimentin and S100 but do not stain for keratin


Cytogenetics



  • Abnormalities involving chromosomes 5, 6, 7, 12, and 17


DIFFERENTIAL DIAGNOSIS


Low-Grade Chondrosarcoma



  • Grows with infiltrative pattern


  • Greater degree of cellularity


  • Increased nuclear atypia


Chondromyxoid Fibroma



  • Contains myxoid and fibrous elements


  • Lacks well-formed hyaline cartilage


DIAGNOSTIC CHECKLIST


Pathologic Interpretation Pearls



  • Well-circumscribed tumor composed of nodules of hyaline cartilage


  • Cartilage hypo- to moderately cellular


  • Chondrocytes cytologically banal



SELECTED REFERENCES

1. Eefting D et al: Assessment of interobserver variability and histologic parameters to improve reliability in classification and grading of central cartilaginous tumors. Am J Surg Pathol. 33(1):50-7, 2009

2. Romeo S et al: Benign cartilaginous tumors of bone: from morphology to somatic and germ-line genetics. Adv Anat Pathol. 16(5):307-15, 2009

3. Bell WC et al: Molecular pathology of chondroid neoplasms: part 1, benign lesions. Skeletal Radiol. 35(11):805-13, 2006

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Jul 6, 2016 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Enchondroma
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