**3.3 MRI**

Magnetic resonance imaging does not have a great diagnostic value in bone neoplasms, but it is the best test for local staging and surgical planning [17]. Evaluating structures adjacent to the lesion, such as the extension to soft tissues (most important sign of bone malignancy [16]) and the involvement of neurovascular structures, as well as the extent of spinal cord involvement and the presence of "skip" metastases (present in 25% of osteosarcomas) [14]. The examination should always include the two joints adjacent to the host bone (**Figure 2**) [10].

MRI is useful in assessing the response to chemotherapy, radiotherapy, and postoperative follow-up to detect mainly local recurrence [20, 21].

*Perspective Chapter: Bone Tumors – How to Make a Diagnosis? DOI: http://dx.doi.org/10.5772/intechopen.106673*

### **Figure 3.**

*(A) scintigraphy of a patient with Ewing's sarcoma affecting the entire femur, (B) patient with large-volume diaphyseal osteosarcoma, and (C) conventional osteosarcoma of the distal end of the femur.*

### **3.4 Scintigraphy**

Bone scintigraphy is routinely requested in the evaluation of malignant bone neoplasms, the exam measures changes in bone metabolism (increased turnover and osteoblastic activity), it is quite sensitive, but nonspecific (**Figure 3**) [16, 22].

Evaluation of bone metastases by scintigraphy is very useful since it can evaluate the skeleton in a complete way. The drug is well tolerated (technetium-99 m methylene diphosphonate [17]) and its analysis is not interfered with by metallic implants.

Osteoblastic lesions are easier to identify, while osteolytic lesions need a certain size to be detected [22]; examples of this are multiple myeloma and renal cell carcinoma metastases, which are usually negative in scintigraphy [23]. Non-neoplastic changes may appear in regions, for example, of degenerative disease in vertebrae and joints [22].

### **3.5 PET-CT**

Corresponding to a procedure that combines the images of a positron emission tomography (PET) and a computed tomography (CT), there is no contraindication to the test, except in pregnant or breastfeeding patients. PET and CT scans are performed at the same time with the same machine using 18F-fluorodeoxyglucose (18F-FDG, surrogate analog in glucose metabolism) as a marker. The SUV (standard uptake value), calculated at the end of the exam, provides semi-quantitative

### **Figure 4.**

*Patient with Ewing's sarcoma in the diaphysis of the right femur, there is only uptake of the radiopharmaceutical in the region of the bone lesion, with no other changes in the exam.*

information on glucose metabolism in the evaluated tissues, with a cut-off between 2.0 and 2.5 for defining benign and malignant lesions. PET-CT is evaluated for staging and monitoring the response to treatment of tumors, including detection of metastases and recurrence. Studies indicate that PET-CT shows sensitivity, specificity, and accuracy superior to scintigraphy to find metastases [24]. However, if it works according to the histological diagnosis, different results are observed. To screen for bone metastases in Ewing's sarcoma, PET-CT has better sensitivity than scintigraphy, whereas in osteosarcoma they are similar [25], although it has better accuracy than scintigraphy for the detection of approaching the growth plate in osteosarcoma [26]. PET-CT as a predictor of oncological response presents better results in Ewing's sarcoma than those presented in osteosarcoma [25] (**Figure 4**). In benign cartilaginous neoplasms, such as enchondromas or osteochondromas, the SUVmax value is generally less than 2, while in chondrosarcomas, most have values above 2, which represents a good tool for diagnostic differentiation [27, 28]. Patients with primary bone lymphoma and multiple myeloma have good applications for PET-CT for staging, follow-up, and prognostic evaluation [29].
