In the hands of the experienced examiner, ultrasonography represents a suitable means of differentiating solid and fluid-filled soft tissue formations. However, a specific diagnosis cannot be made by sonographic examination alone, therefore sonography has no particular significance in musculoskeletal tumor diagnosis except for image-guided fine-needle biopsy of soft tissue masses.

Conventional radiographs remain the most important diagnostic tool in bone tumor imaging. A great deal of information can be obtained easily, inexpensively, and with low radiation exposure from x-rays. Many useful informations can be obtained from conventional radiographs including findings on the topography of the lesion (localization in the foot skeleton and in the individual bone area), boundaries of the bone lesion, type of osteodestruction and periosteal reaction, radiological appearance of the tumor matrix (composition of the tumor tissue, e.g., dystrophic calcifications), and behavior and extent of soft tissue involvement.
The affected bone should always be visualized in the center of the x-ray and plain radiographs should include the adjacent structures and neighbouring joints. X-rays should always be taken in at least two planes. Depending on the symptoms and risk for a pathological fracture, weight-bearing radiographs in the standing position can additionally be performed in order to obtain additional information on the statics of the foot. The oblique image of the foot is a useful addition to the standard settings (dorsoplantar/a.p. and strictly lateral) to limit overlays of the foot skeleton.

Even soft tissue lesions can cause changes in the conventional x-ray image depending on their biological behavior. It is not uncommon to find superficial pressure erosions of the bone in slow-growing soft tissue tumors adjacent to the bone. Calcifications and ossifications of the tumor tissue can also provide helpful information on the potential tumor entity.

Lodwick’s classification offers an important tool to determine the growth rate of tumor-associated bone lesions. The bone reactions created by osseous tumors visible on plain radiographs are an index for the biological behaviour of both benign and malignant bone tumors. Thus, the Lodwick classification offers an important aid in the decision-making and initiation of further diagnostics (cross sectional imaging, biopsy) and the subsequent therapy, even if a definitive assessment on the dignity cannot be made.

Magnetic resonance imaging (MRI) allows the exact assessment of the intramedullary and extraosseous tumor extension including the reactive zone and localization in regard to neighbouring neurovascular structures as well as a differentiation between vital versus necrotic tumor portions. This is particularly important for the planning of a biopsy to obtain representative tumor tissue for a histopathological analysis.
Depending on the suspected tumor entity, additional MRI sequences may be performed (e.g., HEM /SWI sequences in pigmented villonodular synovitis). Certain tumor entities can be diagnosed by MRI examination alone based on their typical signal behavior. However, due to the rarity and the great heterogeneity of musculo-skeletal tumors, detailed knowledge of specific differential diagnoses of benig and maligant bone and soft tissue neoplasms is rare even amongst many experienced musculoskeletal radiologists. Therefore, it is recommended to seek advice from dedicated specialists at a tumor orthopedic center. (LINK https://www.kssg.ch/orthopaedie/leistungsangebot/tumororthopaedie UND https://www.kssg.ch/orthopaedie/ueber-uns/fachbereiche/fusssprunggelenk)

Despite the increasing accuracy of imaging studies, even a radiolgy specialist for musculoskeletal tumors can often only offer a differential diagnosis. If a specific benign diagnosis cannot be made clinically and radiologically, a biopsy should be performed. The definitive diagnosis must be confirmed by the pathologist based on an analysis of biopsy material. The site and type of the biopsy are dictated by the location of the tumor. Prior to a biopsy, the definitive surgical access route for subsequent tumor resection must be determined by the the interventional radiologist and the surgeon performing the definite tumor resection. The decisive factor for the localization of the tumor biopsy is not necessarily the shortest possible route to the tumor, but rather the sparing of tumor-free compartments and structures relevant for limb preservation. Basically, osseous lesions should be biopsied from the dorsum of the foot, whereas a direct approach is indicated for most soft tissue lesions. Contamination of tumor-free anatomical compartments by biopsy must be strictly avoided. In addition to obtaining tumor specimens for histopathological workup, specimens should always be obtained for microbiological analysis (DD osteomyelitis / abscess). Particularly in the foot, a pathological fracture should be prevented by non-weightbearing of the affected limb after bone biopsy.
Various methods are available for obtaining biopsies, such as fine needle aspiration cytology (FNA), percutaneous core needle biopsy (mostly CT-guided) or open surgical biopsy, all of which are associated with different advantages and disadvantages.