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Differential Diagnosis of Musculoskeletal Disorders

Role of Radiologist!!navigator!!

  1. Is there a lesion?
  2. Is it a bone tumor?
  3. Is the tumor benign or malignant?
  4. Is a biopsy necessary?
  5. Is histologic diagnosis consistent with radiographic image?

Assessment of Bone Tumor

A systematic approach is imperative for assessment of a bone tumor with attention to size, number, and location of lesions; margins and zone of transition; periosteal reaction; matrix mineralization; soft-tissue component.

  1. Age (and gender) of patient
  2. Precise tumor location
    1. transverse: medullary, cortical, juxtacortical
    2. longitudinal: epi-, meta-, diaphyseal
  3. Pattern of bone destruction / aggressiveness
    1. nonaggressive
      • well-defined sharp margins
      • smooth solid-appearing periosteal reaction
    2. aggressive infiltrative osseous process
      • broad zone of transition
      • poorly defined borders
      • disrupted / “sunburst” appearance
      • DDx: destructive metabolic / infectious process
  4. Lesion matrix
    • “rings-and-arcs” appearance = chondral origin
    • opaque cloud-like matrix = osseous mineralization
    • osteolytic lesion → FEGNOMASHIC
    • CT for cortical continuity / disruption

Action Following Bone Tumor Assessment

  1. BENIGN
    1. Diagnosis certain: no further work-up necessary
    2. Asymptomatic lesion with highly probable benign diagnosis may be followed clinically
    3. Symptomatic lesion with highly probable benign diagnosis may be treated without further work-up
  2. CONFUSING LESION
    not clearly categorized as benign or malignant; needs staging work-up
  3. MALIGNANT: needs staging work-up
    Staging work-up:
    • Bone scan: identifies polyostotic lesions (eg, multiple myeloma, metastatic disease, primary osteosarcoma with bone-forming metastases, histiocytosis, Paget disease)
    • Chest CT: identifies metastatic deposits + changes further work-up and therapy

Local staging with MR imaging:

  1. Margins: encapsulated / infiltrating
  2. Compartment: intra- / extracompartmental
  3. Intraosseous extent + skip lesions
  4. Soft-tissue extent (DDx: hematoma, edema)
  5. Joint involvement
  6. Neurovascular involvement

Local assessment with CT imaging:

  • matrix / rim calcifications

Vessel and Nerve Involvement

  • tumor encasement of neurovascular bundle by
    • 180–360° = indicates infiltration by tumor
    • 90–180° = indeterminate for infiltration by tumor
    • 0–90° = infiltration by tumor unlikely

Tumorlike Conditions!!navigator!!

  1. Solitary bone cyst
  2. Juxtaarticular (“synovial”) cyst
  3. Aneurysmal bone cyst
  4. Nonossifying fibroma; cortical defect; cortical desmoid
  5. Eosinophilic granuloma
  6. Reparative giant cell granuloma
  7. Fibrous dysplasia (monostotic; polyostotic)
  8. Myositis ossificans
  9. “Brown tumor” of hyperparathyroidism
  10. Massive osteolysis

Pseudomalignant Appearance

  1. Osteomyelitis
  2. Aggressive osteoporosis

Pattern of Bone Tumor Destruction / Aggressiveness!!navigator!!

  1. GEOGRAPHIC BONE DESTRUCTION
    • Cause:
      1. slow-growing usually benign tumor
      2. rarely malignant: plasma cell myeloma, metastasis
      3. infection: granulomatous osteomyelitis
    • well-defined smooth / irregular margin
    • narrow zone of transition
  2. MOTH-EATEN BONE DESTRUCTION
    • Cause:
      1. rapidly growing malignant bone tumor
      2. osteomyelitis
    • less well-defined / demarcated lesional margin
    • broad zone of transition
    • mnemonic: H LEMMON
      • Histiocytosis X
      • Lymphoma
      • Ewing sarcoma
      • Metastasis
      • Multiple myeloma
      • Osteomyelitis
      • Neuroblastoma
  3. PERMEATIVE BONE DESTRUCTION
    • Cause: aggressive bone tumor with rapid growth potential (eg, Ewing sarcoma)
    • poorly demarcated lesion imperceptibly merging with uninvolved bone
    • broad zone of transition

Size, Shape, and Margin of Bone Tumors!!navigator!!

  • Primary malignant tumors are larger than benign tumors
  • elongated lesion (= greatest diameter of >1.5 times the least diameter): Ewing sarcoma, histiocytic lymphoma, chondrosarcoma, angiosarcoma
  • sclerotic margin (= reaction of host tissue to tumor)

Tumor Position in Transverse Plane!!navigator!!

  1. CENTRAL MEDULLARY LESION
    1. Enchondroma
    2. Solitary bone cyst
  2. ECCENTRIC MEDULLARY LESION
    1. Giant cell tumor
    2. Osteogenic sarcoma, chondrosarcoma, fibrosarcoma
    3. Chondromyxoid fibroma
  3. CORTICAL LESION
    1. Nonossifying fibroma
    2. Osteoid osteoma
  4. PERIOSTEAL / JUXTACORTICAL LESION
    1. Juxtacortical chondroma / osteosarcoma
    2. Osteochondroma
    3. Parosteal osteogenic sarcoma

Tumor Position in Longitudinal Plane!!navigator!!

  1. EPIPHYSEAL LESION
    1. Chondroblastoma (prior to closure of growth plate)
    2. Intraosseous ganglion, subchondral cyst
    3. Giant cell tumor (originating in metaphysis)
    4. Clear cell chondrosarcoma
    5. Fibrous dysplasia
    6. Abscess

    mnemonic: CAGGIE
    • Chondroblastoma
    • Aneurysmal bone cyst
    • Giant cell tumor
    • Geode
    • Infection
    • Eosinophilic granuloma [after 40 years of age throw out “CEA” and insert metastases / myeloma]
  2. METAPHYSEAL LESION
    1. Nonossifying fibroma (close to growth plate)
    2. Chondromyxoid fibroma (abutting growth plate)
    3. Solitary bone cyst
    4. Osteochondroma
    5. Brodie abscess
    6. Osteogenic sarcoma, chondrosarcoma
  3. DIAPHYSEAL LESION
    1. Round cell tumor (eg, Ewing sarcoma)
    2. Nonossifying fibroma
    3. Solitary bone cyst
    4. Aneurysmal bone cyst
    5. Enchondroma
    6. Osteoblastoma
    7. Fibrous dysplasia

    mnemonic: FEMALE
    • Fibrous dysplasia
    • Eosinophilic granuloma
    • Metastasis
    • Adamantinoma
    • Leukemia, Lymphoma
    • Ewing sarcoma

Tumors Localizing to Hematopoietic Marrow!!navigator!!

  1. Metastases
  2. Plasma cell myeloma
  3. Ewing sarcoma
  4. Histiocytic lymphoma

Diffuse Bone Marrow Abnormalities in Childhood

  1. REPLACED BY TUMOR CELLS
    1. metastatic disease
      1. Neuroblastoma (in young child)
      2. Lymphoma (in older child)
      3. Rhabdomyosarcoma (in older child)
    2. primary neoplasm
      1. Leukemia
  2. REPLACED BY RED CELLS
    = red cell hyperplasia = reconversion
    1. severe anemia: sickle cell disease, thalassemia, hereditary spherocytosis
    2. chronic severe blood loss
    3. marrow replacement by neoplasia
    4. treatment with granulocyte-macrophage colony stimulating factor
  3. REPLACED BY FAT
    1. Myeloid depletion = aplastic anemia
  4. REPLACED BY FIBROUS TISSUE
    1. Myelofibrosis

Incidence of Bone Tumors!!navigator!!

  • 80% of bone tumors are correctly determined on the basis of age alone!

Most Frequent Benign Bone Tumor

  1. Osteochondroma 20–30%
  2. Enchondroma 10–20%
  3. Simple bone cyst 10–20%
  4. Osteoid osteoma
  5. Nonossifying fibroma
  6. Aneurysmal bone cyst 5%
  7. Fibrous dysplasia
  8. Giant cell tumor

Most Frequent Malignant Bone Tumor

  1. Bone malignancy
    1. Metastasis
  2. Primary bone malignancy
    1. Multiple myeloma
    2. Osteosarcoma
    3. Chondrosarcoma
    4. Ewing sarcoma
  3. Primary bone malignancy in children & adolescents
    1. Osteosarcoma
    2. Ewing sarcoma

Sarcomas by Age

mnemonic: Every Other Runner Feels Crampy Pain On Moving

  • Ewing sarcoma 0 –10 years
  • Osteogenic sarcoma 10–30 years
  • Reticulum cell sarcoma 20–40 years
  • Fibrosarcoma 20–40 years
  • Chondrosarcoma 40–50 years
  • Parosteal sarcoma 40–50 years
  • Osteosarcoma 60–70 years
  • Metastases 60–70 years

Ewing Sarcoma Family

  1. Ewing sarcoma of bone
  2. Extraskeletal Ewing sarcoma
  3. Primitive neuroectodermal tumor
  4. Askin tumor

Malignancy with Soft-tissue Involvement

mnemonic: My Mother Eats Chocolate Fudge Often

  • Metastasis
  • Myeloma
  • Ewing sarcoma
  • Chondrosarcoma
  • Fibrosarcoma
  • Osteosarcoma

Tumor Matrix of Bone Tumors!!navigator!!

Cartilage-forming Bone Tumors

  • centrally located ringlike / flocculent / flecklike radiodensity
  1. BENIGN
    1. Enchondroma
    2. Parosteal chondroma
    3. Chondroblastoma
    4. Chondromyxoid fibroma
    5. Osteochondroma
  2. MALIGNANT
    1. Chondrosarcoma
    2. Chondroblastic osteosarcoma

Bone-forming Tumors

  • inhomogeneous / homogeneous radiodense collections of variable size + extent
  1. BENIGN
    1. Osteoma
    2. Osteoid osteoma
    3. Osteoblastoma
    4. Ossifying fibroma
  2. MALIGNANT
    1. Osteogenic sarcoma

Fibrous Connective Tissue Tumors

  1. BENIGN FIBROUS BONE LESIONS
    1. cortical
      1. Benign cortical defect
      2. Avulsion cortical irregularity
    2. medullary
      1. Herniation pit
      2. Nonossifying fibroma
      3. Ossifying fibroma
      4. Congenital generalized fibromatosis
    3. corticomedullary
      1. Nonossifying fibroma
      2. Ossifying fibroma
      3. Fibrous dysplasia
      4. Cherubism
      5. Desmoplastic fibroma
      6. Fibromyxoma
      7. Benign fibrous histiocytoma
  2. MALIGNANT
    1. Fibrosarcoma

Tumors of Histiocytic Origin

  1. LOCALLY AGGRESSIVE
    1. Giant cell tumor
    2. Benign fibrous histiocytoma
  2. MALIGNANT
    1. Malignant fibrous histiocytoma

Tumors of Fatty Tissue Origin

  1. BENIGN
    1. Intraosseous lipoma
    2. Parosteal lipoma
  2. MALIGNANT
    1. Intraosseous liposarcoma

◊Lipomas follow the SI of subcutaneous fat in all sequences!

Tumors of Vascular Origin

<1% of all bone tumors

  1. BENIGN
    1. Hemangioma
    2. Glomus tumor
    3. Lymphangioma
    4. Cystic angiomatosis
    5. Hemangiopericytoma
  2. MALIGNANT
    1. Malignant hemangiopericytoma
    2. Angiosarcoma = hemangioendothelioma

Metastatic sites: lung, brain, lymph nodes, other bones

Tumors of Neural Origin

  1. BENIGN
    1. Solitary neurofibroma
    2. Neurilemmoma
  2. MALIGNANT
    1. Neurogenic sarcoma = malignant schwannoma

Bone Tumors with Fluid-Fluid Levels

  1. Aneurysmal bone cyst
  2. Telangiectatic osteosarcoma
  3. Giant cell tumor
  4. Chondroblastoma
  5. Fibrous dysplasia

Round Cell Tumor

Location: arises in midshaft

  • osteolytic lesion
  • reactive new bone formation
  • NO tumor new bone

mnemonic: LEMON

  • Leukemia, Lymphoma
  • Ewing sarcoma, Eosinophilic granuloma
  • Multiple myeloma
  • Osteomyelitis
  • Neuroblastoma

Outline