**9. Bone tumors**

For the diagnosis study of primary bone tumors prevails the importance of the morphological study to characterize the lesion and, in many cases, the initial plain films guides the diagnosis. In these cases, the usefulness of bone scintigraphy is lesser, but may be useful for detecting a lesion that is difficult to assess radiologically because of its location, and supporting the suspicion about the benignity or malignancy of the lesion. Characteristic patterns of uptake have been described in some primary bone tumors, but they are not reliable enough, given that there is an overlap in the scintigraphic characteristics of the benign and malignant bone lesions. The differential diagnosis of a solitary bone lesion usually depends more on morphologic imaging techniques, including radiographs, CT, and MRI, and on expert histologic analysis. In contrast, a larger role is developing for 18F-FDG-PET/CT for staging and response assessment of several bone tumors. Three-phase bone

into soft tissue, related with ectopic calcification. Focal skeletal abnormalities may represent

Renal osteodystrophy is secondary to a combination of bone disorders as a consequence of chronic renal dysfunction, and often shows the most severe cases of metabolic bone disease. It may include osteoporosis, osteomalacia, adynamic bone, and secondary hyperparathyroidism in varying degrees. The most frequent bone scan imagings are similar to a superscan from other metabolic bone disorders, and uptake of diphosphonate in areas of ectopic calcification also may be seen. A lack of bladder activity (secondary to the renal failure) may help in identification and differentiating this type of scintigraphic pattern from others. Aluminum toxicity from hemodialysis, rarely seen now, causes a poor quality bone scan with reduced skeletal uptake and increased soft-tissue activity, as aluminum blocks mineralization and hence the uptake of tracer, resulting in a pattern applicable to all forms of adynamic bone disease. Quantitative measurements of bone metabolism in renal osteodystrophy using 18F-fluoride have been compared with bone histomorphometry and have shown a close relationship between the net plasma clearance of 18F-fluoride to bone mineral and the histomorphometric indices of bone formation. The method was able to differentiate low turnover from high turnover states of renal osteodystrophy (Cook et al.,

Patients with osteomalacia usually demonstrate similar features of a bone scan as described in hyperparathyroidism, although in the early stages of the disease it may appear normal (Cook et al., 2010). The reason that osteomalacia shows these features is not fully understood. Tracer avidity may reflect diffuse uptake in osteoid, although more likely, it is due to the degree of secondary hyperparathyroidism that is present. In addition, the presence of focal lesions may represent pseudofractures or true fractures. Pseudofractures are characteristically found in the ribs, the lateral border of the scapula, the pubic rami, and the medial femoral cortices. Although osteomalacia is usually a biochemical and*/*or histologic diagnosis, the typical bone scan features can be helpful in suggesting the diagnosis. The detection of pseudofracutures with this technique is more sensitive than that

For the diagnosis study of primary bone tumors prevails the importance of the morphological study to characterize the lesion and, in many cases, the initial plain films guides the diagnosis. In these cases, the usefulness of bone scintigraphy is lesser, but may be useful for detecting a lesion that is difficult to assess radiologically because of its location, and supporting the suspicion about the benignity or malignancy of the lesion. Characteristic patterns of uptake have been described in some primary bone tumors, but they are not reliable enough, given that there is an overlap in the scintigraphic characteristics of the benign and malignant bone lesions. The differential diagnosis of a solitary bone lesion usually depends more on morphologic imaging techniques, including radiographs, CT, and MRI, and on expert histologic analysis. In contrast, a larger role is developing for 18F-FDG-PET/CT for staging and response assessment of several bone tumors. Three-phase bone

with radiography (Cook et al., 2010; as cited in Fogelman et al., 1977, 1978).

associated Brown tumors, although these are relatively uncommon.

**8.4 Renal osteodystrophy** 

2010; as cited in Messa et al., 1993).

**8.5 Osteomalacia** 

**9. Bone tumors** 

scintigraphy offers information about the vascularity of the bone lesion: Malignant tumors tend to be more vascularized and be uptake in all three phases of the scan, while benign bone tumors often do not show changes in the first two phases of the scintigraphy. Normal uptake, even in the third stage, is a sign for the mildness of the bone lesion. Osteoid osteoma is a benign bone tumor that constitutes an exception to this statement: It is highly vascular and provides uptake images in all three phases of the scan. In fact, a normal bone scan excludes its diagnosis. Aneurysmal bone cyst may show similar features. In patients with a benign tumor and a bone scan showing intense uptake, a fracture should be suspected.
