X-ray plain films remain essential for the primary assessment of bone tumors, even in the era of tomographic and molecular imaging; however, lytic lesions, principally occurring in Ewing’s sarcoma, remain undetectable on plain films until demineralization has reached 30–50 %. Some features that should be investigated on plain radiographs and may aid in the differential diagnosis include an assessment of the primary tumor matrix, presence or absence of margins around the primary bone lesion, presence of corticalis destruction, presence and configuration of periosteal reaction, and presence of new bone formation. OS (Fig. 14.2a–i) usually occur in the epiphysis, ES usually in the meta- and diaphysis (Fig. 14.3a–r). The 3-phase bone scan is still occasionally employed in the initial work-up of suspected bone tumors. Unfortunately, the findings are not specific although most malignant tumor will present with increased tracer uptake in all 3 phases of the scan. In particular in patients with OS, a whole-body bone scan may detect possible osseous metastases, as well as soft tissue metastases that contain a sufficient amount of osseous matrix leading to tracer retention. Whole-body scans are obtained 2–4 h after injection of Tc99m MDP. The amount of injected activity is based on body weight or body surface area. Guidelines for appropriate activities have been published by both EANM and SNM. Standard planar images of the torso can be supplemented by spot views of regions of interest if clinically necessary. SPECT or SPECT/CT is rarely performed because the yield of new and clinically relevant finings is low. The main imaging tests for malignant bone tumors are CT, MRI, and, increasingly, FDG PET. CT and MRI define the local extent of the primary tumor, any soft tissue involvement, and the relationship to neurovascular structures. However, peritumoral edema may lead to uncertainty in defining the exact tumor margins [4]. High-resolution CT of the lungs remains the most sensitive test for the detection of pulmonary metastases. High-pitch CT may reduce breathing and pulsation artifacts and may also lower the radiation dose to the patient [5]. FDG PET shows a high sensitivity for primary and recurrent tumors with sensitivities in the 85–95 % range [6, 7]. A recent meta-analysis studying the role of FDG PET and PET/CT in ES showed a high overall pooled sensitivity of 96 % and specificity of 92 % for both primary staging and restaging [8]. SUV numbers for OS and ES vary widely, from as low as 3.0 to as high as 20 [9]. However, it should be noted that aggressive benign bone lesions cannot be distinguished from sarcomas on PET alone. Some benign lesions, such as giant cell tumors, may show very high FDG uptake and SUV; conversely, some malignant tumors, in particular chondrosarcomas, show relatively low FDG uptake. Moreover, false-positive FDG uptake may occur at fractures, sites of infections, or inflammations (such as periostitis). Thus, the primary purpose of FDG PET lies in the evaluation for distant disease, in detection of possible recurrence, and increasingly in monitoring the response to neoadjuvant and adjuvant chemotherapy.

With very few exceptions (so-called osteosclerotic variant), ES is an osteolytic tumor and marrow-infiltrating tumor. Therefore, bone scans, which are generally more sensitive for osteoblastic lesions, may not be very informative in ES. Instead, distant disease is assessed better by FDG PET/CT or PET/MRI. In contrast, bone scans are quite sensitive for OS metastases because of the intense osteoid production and osteoblast activity in these lesions.

Nowadays, FDG scans are performed as PET/CT with 3D PET. If a dedicated CT scan of the torso has been ordered, it should be done in the same setting as the PET scan, using higher (as appropriate for patient age) dose settings. In this case, the usual low-dose CT of the PET/CT can be eliminated, and the data from the dedicated CT are used for PET attenuation correction, thus reducing overall radiation burden to the patient. The PET field of view should extend from the skull base to the proximal thighs unless the primary tumor is located more distally. Routine imaging of the lower extremities is not necessary in patients with primary tumor in the head and neck region or trunk [10] because the diagnostic yield is extremely low. The application of combined PET/MRI [11] in pediatric patients is of growing interest because this may lower the radiation dose from medical imaging [12] and possibly enable us to address a series of diagnostic and prognostic questions in one setting.