Metastatic bone tumors are classified as osteolytic, osteogenic and mixed. The development of bone metastases is different, but the slower development can be seen as osteosclerosis around the tumor, mostly seen in thyroid cancer and kidney cancer metastases. Bone metastases from breast cancer and lung cancer develop more rapidly and show penetrating bone destruction, with bone expansion and extensive bone cortical destruction. Osteogenic metastases are mostly seen in bone metastases from hormone-producing tumors such as prostate cancer, breast cancer, and thyroid cancer. It is not possible to detect all bone metastases on conventional X-rays, as some bone destruction may not be visible. It has been assessed that bone metastases do not show up on X-rays until after 30 to 50% loss of minerals in the bone. The type of bone destruction can be map-like, worm-like and infiltrative. The borders may or may not be clear, and periosteal reaction and soft tissue masses may or may not be present, but the absence of periosteal reaction and soft tissue masses is more common. Radionuclide bone scans, including planar and single photon emission CT (SPECT) imaging, are the best screening method to identify early bone metastases, which can detect osteolytic and osteogenic lesions. CT scans can also show osteolytic, osteogenic, and mixed changes in the tumor. CT examinations can clearly demonstrate the extent of the lesion and are particularly good for diagnosing anatomically complex areas such as the spine and pelvis. MRI is extremely sensitive for bone metastasis examination. Usually, bone metastasis invades the medullary cavity and bone cortex, and the T1-weighted image shows low signal (long TE) and T2-weighted image shows high signal (long TR). Meanwhile, MRI can reflect the tumor reaction area in the medullary cavity, which helps to determine the scope of surgery.
Osteolytic lesions: the most common, accounting for about 75% of metastases. typical osteolytic bone destruction is seen in renal cancer, adrenal cancer, uterine cancer, gastrointestinal tumor, thyroid cancer, liver cancer, wilms tumor, pheochromocytoma, melanoma and squamous skin cancer. x-ray presentation: the margins can be clear (map-like bone destruction), more often seen as worm-like, chisel-like or penetrating bone defects with unclear boundaries. The margins are irregular and there is no sclerosis around. Residual bone trabeculae and bone cortex are seen in the osteolytic area, without periosteal reaction. In a few cases, there was cortical swelling, reflecting the different degrees of aggressiveness of the metastases. Most had no soft tissue mass shadow.
Figure 1: The patient was a male, 64 years old, with bone metastasis from lung cancer. x-ray showed osteolytic changes in the proximal tibia with no obvious periosteal reaction.
Figure 2: Wu, male, 33 years old, with bone metastasis from gastric cancer. x-ray showed osteolytic changes in the proximal humerus with soft tissue masses.
2. Osteogenic lesions: they account for about 15% of metastases, and the primary foci are mostly seen in prostate cancer and spermatogenic cell carcinoma in men, and mainly from breast cancer, uterine cancer and ovarian cancer in women. Uncommon are bronchopulmonary carcinoma, bladder cancer, nasopharyngeal carcinoma, gastric cancer, neural tube cell tumor and neuroblastoma. Osteogenic destruction X-ray shows nodular, speckled, diffuse lamellar hyperdensity, even ivory-like, bone trabeculae disorder, thickening, roughness, and the volume of affected bone may increase.
3.Mixed lesion: It accounts for about 10% of metastases, usually from lung cancer, breast cancer, cervical cancer, ovarian cancer and testicular tumor.
Metastases usually have no or mild periosteal reaction, unlike primary malignant bone tumors (characterized by extensive periosteal reaction, heliotropic, onionskin, or codman’s triangle). Rarely, periosteal reactions are also seen, most often in metastases from prostate cancer, gastrointestinal malignancies, retinoblastoma, and neuroblastoma.
Some metastases possess specific imaging features that can suggest the site of the primary focus, at least narrowing the differential diagnosis. For example, vesicular, highly distended, so-called balloon-like metastases are most often seen in bone metastases from kidney, liver, or thyroid cancer; renal cancer with bone distention is seen with characteristic segregation; and multiple round, dense foci, or diffuse increased bone density, are most often seen in bone metastases from prostate cancer, with an x-ray presentation similar to Paget’s disease, or osteosarcoma when solitary. The expansiveness of metastases is confirmed by nuclein enrichment.
Usually metastatic bone tumor lesions are characterized by the coexistence of bone resorption and bone formation, and radiographs can show the main course of the lesion. When osteolysis is predominant, the lesion appears osteolytic; when bone formation is predominant, the lesion appears sclerotic; multiple sclerosing metastases may appear focal (multiple snowball-like manifestations) or diffuse with increased bone density. Bone destruction is always achieved through the resorptive action of tumor-induced osteoclasts. Primary tumors causing simple osteolytic changes are often located in the kidney, lung, breast, thyroid, and gastrointestinal tract (e.g., Figures 3-A and 3-B); whereas primary foci causing osteogenic metastases are often located in the prostate. It must be noted that after treatment (radiation therapy, chemotherapy, hormonal therapy) purely osteolytic lesions can be transformed into sclerotic lesions.
Figure 3-A
Figure 3-B
Figure 3: A patient with hepatitis B for many years, admitted with upper arm pain. a, X-ray shows an osteolytic lesion with pathological fracture in the proximal segment of the right humerus, which was considered to be a bone metastasis from hepatocellular carcinoma, and later confirmed by pathology. b, MRI shows a T2-weighted coronal long TR manifestation in the proximal segment of the humerus with a surrounding soft tissue mass.
Scintigraphy was almost entirely positive in bone metastases. Increased radionuclide uptake is seen in both osteolytic and sclerotic lesions, probably due to increased bone transformation and reactive repair around the lesion. Radionuclide bone scans help to differentiate metastases from multiple myeloma, which often exhibit normal uptake of tracer. A few cases of bone metastases show positive x-ray performance and negative bone scintigraphy performance, which may be justified by the fact that bone density on x-ray, which represents the net metabolic result over a longer period of time, does not necessarily represent current metabolic activity, so a low metabolic rate and osteogenic lesions on x-ray may produce a negative bone nuclide scan result.
When a patient has an abnormal radionuclide bone scan presentation with a normal or suspicious x-ray presentation, CT examinations often clearly show foci of destruction within the bone, thus establishing the diagnosis of metastases, as well as concomitant soft tissue masses. MRI is more sensitive than technetium bone scan, and focal osteolytic metastases are characterized by a low signal on T1-weighted images and a high signal on T2-weighted images. Focal sclerosing metastases, such as those derived from breast cancer and prostate cancer, induce an osteogenic response to form new bone, so both T1- and T2-weighted images show low signal. (As shown in Figure 4)
Figure 4-A
Figure 4-B
Figure 4-C
Figure 4: Li, female, 49 years old, 1 year post-breast cancer. a. X-ray shows osteolytic changes in the intertrochanteric space of the left femur, with no obvious periosteal reaction or soft tissue mass. b. MRI axial T1-weighted image shows inhomogeneous signal in the intertrochanteric space and femoral neck, with homogeneous signal in the uninvolved femoral head and medullary cavity. c. MRI coronal T2-weighted image shows hyperintense signal in the femoral neck.