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

• Ollier's disease
• Maffucci's syndrome

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.