Some of the most common cancer types, including breast cancer, prostate cancer, and lung cancer, show a predilection to metastasize to bone.
- Effects of bone metastasis:
- severe pain, bone fractures, spinal cord compression, hypercalcemia, anemia, spinal instability, decreased mobility.
- Renal cell
- Multiple myeloma
- Colonic carcinoma
- Bladder carcinoma
- Soft-tissue sarcoma.
The findings of sclerotic metastases virtually exclude an untreated renal tumor or hepatocellular carcinoma.
Bone metastases may be osteolytic, sclerotic, or mixed on radiographs. Lesions usually appear in the medullary cavity, spread to destroy the medullary bone, and then involve the cortex. Osteolytic metastases are encountered most frequently, especially in breast and lung carcinomas . The specific appearance of bone metastases is often useful in suggesting the nature of the underlying primary malignancy.
Metastases from certain primary sites (eg, renal cell or thyroid carcinomas) are almost always osteolytic, whereas those from other sites (eg, prostatic carcinoma) are predominantly sclerotic.
Other malignancies associated with sclerotic metastases include breast carcinoma, colonic carcinoma, melanoma, bladder carcinoma, and soft-tissue sarcoma. The findings of sclerotic metastases virtually exclude an untreated renal tumor or hepatocellular carcinoma.
In vertebrae, clues to metastatic involvement include pedicular destruction, an associated soft-tissue mass, and an angular or irregular deformity of the vertebral endplates.
The initial manifestation of healing in an osteolytic metastatic lesion is a sclerotic rim of reactive bone. With progressive healing, sclerosis increases and advances from periphery of the lesion to its center: The lesion shrinks and eventually resolves. For a mixed osteolytic-sclerotic lesion, a healing response to therapy is demonstrated as uniform lesional sclerosis, whereas increasing osteolysis indicates disease progression.
Purely sclerotic lesions are more difficult to assess. A sclerotic lesion that shrinks or completely disappears after therapy signifies disease regression, whereas one that grows and causes destruction implies progression.
FALSE NEGATIVES AND POSITIVES:
Osteolytic metastases can mimic osteoarthritis both clinically and radiographically; for example, they can mimic subchondral cysts and Schmorl nodes in the spine. Osteolytic foci may resemble amyloidosis, cystic angiomatosis, and infiltrative bone marrow lesions.
Sclerotic metastases may be difficult to distinguish from other sclerotic bone lesions such as bone islands, tuberous sclerosis, mastocytosis, and osteopoikilosis.
Role of nuclear medicine:
Indications for bone scintiscanning include staging in asymptomatic patients, evaluating persistent pain in the presence of equivocal or negative radiographic findings, determining the extent of bone metastases in patients with positive radiograph findings, differentiating metastatic from traumatic fractures by assessing the pattern of involvement, and determining the therapeutic response to metastases.
PET scanning can help in identifying bone metastases at an early stage of growth, before host reactions to the osteoblasts occur. FDG-PET scanning depicts early malignant bone-marrow infiltration because of the early increased glucose metabolism in neoplastic cells.Isotopic imaging methods depict bone metastatic lesions as areas of increased tracer uptake. The classic pattern appears as the presence of multiple randomly distributed focal lesions throughout the skeleton. Findings of a solitary scintigraphic abnormality or just a few lesions may present special problems in the interpretation of findings.
The differential diagnosis of multiple scintigraphic abnormalities includes metabolic problems (eg, Cushing syndrome), osteomalacia, trauma, arthritis, osteomyelitis, Paget disease, and infarctions. Some metastases may produce normal scintiscan findings. Cold or photopenic metastases may be found in association with lesions of highly aggressive anaplastic carcinomas. In diffuse metastatic disease, isotopic accumulation may be sufficiently uniform to produce a false-negative impression.