Metastatic Lesions of the Bones

Metastatic Lesions of the Bones
Todd M. Blodgett, MD
Alex Ryan, MD
Hesham Amr, MD
Key Facts
Terminology
  • Bone metastases, metastatic lesions to bone, secondary bone tumors
Imaging Findings
  • More than 80% of metastases to bone are located in axial skeleton where red marrow blood flow is high
    • Vertebrae, ribs, and hips
  • FDG PET generally ineffective for tumors that are not FDG avid
    • Prostate cancer, highly mucinous tumors, occasionally renal cell carcinoma
    • Also limited in some sclerotic metastases
  • o Reveals marrow lesions in FDG-avid disease prior to cortical effects (often before bone scan becomes positive)
  • CT may miss many early infiltrative or osteolytic lesions
  • CT has higher sensitivity for osteoblastic/sclerotic bone metastases
  • F-18 NaF PET: Excellent PET bone agent, currently not reimbursed by Medicare and most third party payers
Top Differential Diagnoses
  • Degenerative Processes, Arthropathies
  • Healing Fracture or Bone Injury
  • Iatrogenic: Vertebroplasty, Kyphoplasty
  • Physiologic Activity
  • Primary Bone Tumors
Pathology
  • Most common childhood primaries: Neuroblastoma, Ewing sarcoma, rhabdosarcoma
Graphic shows a vertebral body image that has been completely replaced with metastatic disease.
Axial CECT shows lytic foci within a vertebral body image in a patient with multiple myeloma; one lesion erodes the posterior vertebral body cortex image.
TERMINOLOGY
Abbreviations and Synonyms
  • Bone metastases, metastatic lesions to bone, secondary bone tumors
    • Sclerotic/osteosclerotic metastases
    • Osteolytic metastases
Definitions
  • Malignant extension to bone, often by carcinoma, due to direct extension, retrograde venous flow, or hematogenous metastasis
IMAGING FINDINGS
General Features
  • Best diagnostic clue: Typical presentation includes scattered lesions in areas of osteoblastic or osteolytic activity
  • Location
    • Seeding occurs mostly in red marrow where blood flow is high
      • (80%) axial skeleton
      • Spine, pelvis, ribs, sternum, calvaria, proximal limb bones
      • Random distribution typical
      • More common proximally in long bones
    • Cortical involvement can occur secondary to direct invasion
  • Size: Ranges from small, solitary lesion to replacement of the entire marrow space
  • Morphology
    • Often infiltrating, elongated, or expansile
    • Focal or regional pattern more characteristic of fracture or arthropathy
    • May not be identifiable on CT
Imaging Recommendations
  • Best imaging tool
    • PET/CT very sensitive for detection of bone metastases
      • FDG PET sensitive for osteolytic lesions and CT sensitive for osteoblastic lesions
      • PET/CT more sensitive and specific than bone scan for delineation of disease and for surgical planning
    • Tc-99m whole body bone scan often used as initial screening due to low cost
      • Sensitivity 80-90%, better than plain radiograph or CT but nonspecific
      • More sensitive than FDG PET for osteoblastic lesions
      • Plain film correlation for further characterization/ambiguity; additional evaluation with CT or MR as necessary
  • Protocol advice
    • FDG PET/CT
      • Position arms above head for whole body scan
CT Findings
  • More sensitive for osteoblastic/sclerotic lesions
  • Insensitive for early infiltrative or osteolytic lesions
  • Early bone infiltration (before destruction) appears as increased attenuation of the normally fatty bone marrow
  • Increased attenuation of lesions generally correlates with lowered FDG uptake
  • Overall sensitivity for bone-seeking cancers: 71-100%
  • Spine
    • Posterior vertebral body almost always involved
    • 80% also in anterior body
    • Enhancement often not detectable
Nuclear Medicine Findings
  • General applications
    • FDG PET/CT more sensitive and specific than bone scan
      • Earlier detection of FDG-avid osteolytic marrow lesions (before cortical changes become evident)
      • Reveals 75% more metastases from breast cancer and to long bones
      • Exceptions include primaries with low FDG avidity, which are typically osteoblastic
      • Osteoblastic metastases include prostate, highly mucinous tumors, and occasionally renal cell carcinoma
      • Sclerotic metastases may not be FDG avid
    • Prediction of bone metastasis in the absence of associated CT findings is hindered by false positives
      • Especially with solitary foci
      • PPV of lesions with negative CT and positive FDG PET: 61%
      • PPV of lesions positive on CT but negative on PET: 17%
    • PET/CT may be cost-effective following screening bone scan for more detailed evaluation of bone metastases
  • Restaging
    • Overall rate of detection of recurrence for FDG PET and CT separately were 47% and 96%
    • Following therapy, “flare” phenomenon may present
      • Treated lesions may have increased FDG uptake during healing and osteoblastic remodeling
      • Bone pain may increase as well
      • Typically arises 4-6 weeks post-therapy and resolves within 3-6 months
      • May show “mixed” response, with a variety of resolved, stable, and new lesions
  • Response to therapy
    • Reduction in SUV of metastatic bone lesions following therapy is highly predictive of response
    • Total lesion glycolysis (TLG) changes were a poor indicator of response duration
      • Possibly due to lack of volume change in treated lesions
  • Findings/anatomy
    • Most common finding: Scattered osseous lesions focused in regions of red marrow, i.e., axial and proximal appendicular skeleton
      • Solitary lesions more likely inflammatory or degenerative than metastatic
      • Linear uptake along ribs (single focus of activity in ribs more likely fracture)
      • Vertebral mets often asymmetric and not confined to endplate
      • Proximal long bone involvement more common; distal long bone mets seen in lung, thyroid, and renal cell carcinoma
    • PET can detect tumors confined to marrow space
      • May have no detectable cortical remodeling and thus not be seen on bone scan
      • Multiple myeloma, lymphoma, leukemia
    • Aggressive tumors with overwhelming osteolytic/osteoblastic activity may be photopenic
      • Renal cell carcinoma, thyroid carcinoma, poorly differentiated anaplastic tumors
      • Occasionally lung, breast, neuroblastoma, myeloma
      • Lytic lesions may become photopenic following radiotherapy, often surrounded by reactive rim of activity
    • “Superscan” MDP bone scan
      • Diffusely increased activity due to disseminated bone lesions
      • May show relative absence of normal renal and soft tissue activity
      • Breast and prostate cancer most common causes
  • Findings by primary
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Sep 22, 2016 | Posted by in MAGNETIC RESONANCE IMAGING | Comments Off on Metastatic Lesions of the Bones

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