**5. Diagnosis**

Detection of bone metastases is essential for accurate staging and optimal treatment. There is no standard approach for the detection of bone metastases in patients with cancer, so the choice of imaging should be guided by the clinical presentation.

**Radiographs** are fast, cheap, and widely available and are recommended for the initial evaluation of symptomatic areas, particularly of the extremities [10]. The typical radiographic appearance of a lytic metastasis is a permeative lesion of the diaphysis or metadiaphysis of a proximal long bone or bone of the axial skeleton, while osteoblastic lesions are usually sclerotic in appearance, sometimes admixed with lytic elements. Although it can be specific, for a destructive lesion in trabecular bone to be recognized, it must be >1 cm in diameter with loss of approximately 50% of the bone mineral content, so the sensitivity is low [10, 13]. Therefore, if the clinical suspicion is high, then computed tomography (CT) or magnetic resonance imaging (MRI) should be done.

**CT** produces images with excellent tissue and contrast resolution [13]. Compared to MRI, it is superior in terms of the evaluation of structural integrity of the bone, and it can be used to diagnose bone metastases in situations in which MRI is contraindicated or not available. However, differentiation between metabolically active from inactive bone lesions cannot be made, limiting its use for the evaluation of treatment effect [13].

In general, **MRI** is more sensitive than CT to detect bone metastases, allows better delineation of the extent of tumor, and is particularly useful for patients with spine metastases to evaluate the extent of medullary and extraspinal disease [10, 14, 15]. Metastatic lesions display decreased signal on T1-weighted sequences, reflecting the replacement of normal fatty marrow with water-containing tumor, while on T2-weighted images, they usually have a higher signal than the surrounding normal bone marrow [14–16].

Whole-body skeletal evaluation with Tc-99 m **skeletal scintigraphy**, generally referred to as **bone scan**, is the most widely used method to detect bone metastases because it provides visualization of the entire skeleton [5, 15]. However, it lacks specificity, it has low sensitivity for tumors with little to no osteoblastic activity, and it is inferior to MRI on the evaluation of vertebral metastases [1, 10, 14, 15, 17].

*Perspective Chapter: Bone Metastases of Solid Tumors DOI: http://dx.doi.org/10.5772/intechopen.108607*

**Positron emission tomography** (PET) scan is based on the preferential uptake of 18-fluorodeoxyglucose (18FDG) by tumor cells because of their increased glucose metabolism, so it detects the presence of tumor directly by quantifying the metabolic activity [5, 10, 16]. Therefore, it has high sensitivity and specificity for the diagnosis of distant metastases, including the bone, and it's use in initial staging and further evaluation for metastatic disease is increasing.

Definitive diagnosis requires histologic examination of **biopsy**. However, in patients with known cancer, a skeletal lesion with a typical appearance on imaging studies may be presumed to be metastatic, and there is no need for tissue diagnosis. For patients with bone-only disease, especially when there are few lesions or imaging tests are equivocal, histological confirmation of metastatic disease is strongly recommended [13]. The same holds true for patients with an unknown primary cancer who present with bone metastases and the initial evaluation fails to identify the primary site, where a biopsy is generally indicated to both confirm the malignant nature of the bone lesion and provide histologic information about likely primary sites. CT-guided fine needle aspiration biopsy (FNA) is easy to perform and accurate to document the presence of metastatic disease; however, it may not indicate the most likely site of the primary malignancy. Therefore, in this setting, a core biopsy may be needed, as it has higher diagnostic accuracy for determining the type, grade, and specific diagnosis of musculoskeletal tumors [18]. An open biopsy is required in a residual number of cases and may be done opportunistically in the operating room prior to possible internal fixation.
