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Enchondroma

Tumor biology and incidence

  • Generally a benign latent cartilage lesion except in phalanges where pain or fracture may be presenting features
  • Probably arises from a "rest" of physeal cartilage that migrates to metaphysis
  • Considered benign active if painful or if there is cortical erosion
    • When active, lesion must be differentiated from low-grade chondrosarcoma on analysis of clinical, radiographic, and pathologic features.
    • Differentiation can prove to be difficult in many cases.
  • Common benign bone tumor, with active lesions and incidental findings accounting for about 15% of all benign bone tumors
    • Incidence is probably higher, as most enchondromas are asymptomatic

Age

Most commonly present from ages 15-40 years

Gender

M:F = 1:1

Associated syndromes

Presentation

  • Lesions in long bones generally asymptomatic and discovered incidentally
    • Often discovered as the result of injury or non-neoplastic orthopaedic complaints (chondromalacia or rotator cuff tendonitis)
    • Active lesions in long bones are rare and are defined by pain
  • Lesions in the hand or, less commonly, the foot more commonly active
    • Erode cortical bone with resulting pain, bony mass, or pathologic fracture

Physical findings

  • Often no findings, but may be local tenderness at site of an active lesion
  • Expansile lesions in the hand may cause a palpable bony mass

Plain films

  • History, physical examination, and plain x-rays must be considered together and are the most valuable modalities for identification of an enchondroma.
  • Worrisome features for chondrosarcoma
    • Endosteal scalloping/ erosion in a long bone lesion
    • Permeative lucency within or surrounding an otherwise typical long bone enchondroma
Site
  • In long bones, enchondroma occurs in meta-diaphysis; most common in femur, humerus
  • In short, tubular bones of hand, enchondromas are commonly diaphyseal (proximal phalanx > metacarpals> mid phalanx> distal phalanx)
Size
  • Variable: 3-5 cm
    • Smaller in hands or feet.
Tumor effect on bone
  • Generally little endosteal erosion seen except in hands
  • Minor degree of endosteal scalloping secondary to a lobular growth pattern
  • Hand lesions may be quite erosive
    • May have a very aggressive x-ray appearance and still remain benign
Bone response to tumor

Geographic pattern but little endosteal response

Matrix
  • Matrix commonly described as "comma-shaped," "popcorn," or "stippled" calcification
  • Calcification more prominent in long bones; uncommon in hands and feet
  • Often radiolucent in the hands
Cortex
  • May see erosion and expansion of the cortex of the hand or foot bones
  • Usually no cortical erosion in long bones (unless pathologic fracture)
Soft tissue mass
  • No soft tissue mass
  • Lesion may erode through cortex with associated soft tissue mass, though rare
    • Called "enchondroma protuberans"; observed mainly in the hand

Bone scan

  • Benign latent lesions often show modest increased uptake on bone scan
  • Enchondroma may be quite "hot" on occasion
  • Not a good test for differentiating benign and malignant cartilage tumors
  • Multiple lesions on bone scan suggest Ollier's disease

CT scan

  • Evaluation of calcifications
  • Evaluation of endosteal scalloping/erosion and lucency within the lesion in differentiating chondrosarcoma from enchondroma

MRI

  • Calcification shows absence of signal intensity on both T1 and T2 sequences
  • Hyaline (not calcified) cartilage is bright on T2 weighted imaging due to high water content of cartilaginous matrix
  • MRI not definitive for differentiating benign and malignant lesions unless it demonstrates a soft tissue mass or other aggressive features

Differential diagnosis

  • Medullary bone infarct (especially in long bones)
    • Infarcts have "smoke rising from a chimney" appearance; can be difficult to differentiate from enchondroma
  • Giant cell tumor
    • May affect metacarpals, rarely phalanges in hand
  • Fibrous dysplasia
    • In long bonesm minimally calcified enchondroma may resemble fibrous dysplasia
  • Unicameral bone cyst, in long bones
  • Chondrosarcoma, in long bones
    • Cortical erosion, permeative changesm and lytic regions seen in malignant lesions

Natural history

  • Growth of lesion is rare after skelatal maturity
  • Malignant transformation can occur in 1% of solitary lesions
  • Patients with Ollier's disease (multiple enchodromas) have significant risk of malignant transformation – up to 30%
  • Patients with Maffucci's syndrome (multiple enchondromas and associated soft tissue lesions, most commonly hemangiomas) reported to have 100% risk of malignant transformation

Pathology

  • Gross: Well circumscribed lobules of cartilage.
  • Microscopic: Nodules of hyaline cartilage containing chondrocytes with small, condensed nuclei
    • Low cellularity, minimal nuclear atypiam and absence of binucleate cells distinguishes enchondroma from low-grade chondrosarcoma
    • Differentiation from low-grade chondrosarcoma may be difficult; consider the clinical and radiologic data with histological appearance when making diagnosis
  • More cellularity and nuclear atypia may be observed in lesions located in hand or foot.

Diagnosis and treatment

  • In latent lesions, diagnosis confirmed by initial plain x-ray and follow up x-rays showing lack of progression
  • Avoid biopsying lesions; pathologic diagnosis may be difficult unless:
    • The lesion changes over time
    • There is persistent pain without other clinically evident cause
    • There are worrisome x-ray findings of endosteal erosion, permeative lysis.
  • If lesion appears benign, observation is appropriate
  • Wait 3 months for repeat x-ray.
    • If no changes, repeat in 6 months and 1 year
  • If lesion is symptomatic, curettage and bone graft usually curative
    • Most commonly necessary in the hand or, less frequently, the toes.

Complications

  • Pathologic fracture, especially in the hand and, less frequently, the foot
  • Malignant transformation to secondary chondrosarcoma rare in solitary lesions

Recommended reading

Oncology and Basic Science. Ed: Timothy A. Damron. Orthopedic Surgery Essentials Series, 576pp, Philadelphia, PA, Lippincott Williams & Wilkins, 2007. 

Orthopaedic Knowledge Update: Musculoskeletal Tumors 2. Herbert S. Schwartz, MD, Editor. American Academy of Orthopaedic Surgeons, Rosemont Il, 2007

Flemming DJ, Murphey MD: Enchondroma and Chondrosarcoma. Semin Musculo Radiol 2000;4:59-71.

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