Arriving at Diagnosis

Imaging Modalities for Diagnosis of Bone & Soft Tissue Tumors

1. Plain Radiographs (X Ray)

• Plain radiograph is the first imaging test performed on presentation.
• It is simple, takes less time, less radiation compared to computed tomography.
• It provides in depth detail about the nature of the tumor, stage, progression, effects of the tumor on host bone or soft tissue, reaction of host to the tumor and also modality of surgery.

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2. Computed Tomography (CT)

• Provides enhanced details of bone anatomy, cortical continuity, cancellous bone integrity and periosteal reactions.
• Expensive compared to Plain radiographs, higher radiation exposure, and better detail.
• It has an advantage in axial imaging.
• Used for staging- thorax/chest to look for metastasis (HRCT).

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Ultrasound (USG)

• Can help characterize soft tissue tumors with respect to solid or cystic components.
• Can be used as a guide to biopsy soft tissue tumors, allowing to target the solid tumor site to aid pathological diagnosis.
• Used as an adjuvant in diagnosing bone and soft tissue tumors.

4. Magnetic Resonance Imaging (MRI)

• The most comprehensive and informative imaging modality for local staging of bone tumors
• It has several advantages and strengths such as no ionizing radiation, better contrast, multi-planar display and better delineation of tissues.
• Of special importance is the soft tissue contrast by MRI, which is better and allows differentiation between adjacent structures.
• The addition of gadolinium contrast or enhanced (diffusion weighted) MRI can further help in narrowing the diagnosis.
• Certain lesions in the same limb i.e. ‘Skip lesions’, akin to satellite lesions can be picked up.
• MRI also help in measuring the extent of tumor and help in reconstruction.

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Global picture of entire skeleton is obtained but it is highly sensitive and non-specific. Common radionuclide bone scans use technetium 99m (99mTc-MDP) during workup, which shows the primary tumor and also presence of any metastasis or skip lesions if present.

6. PET CT Scan

• Regional and distant spread occur in bone and soft tissue sarcomas, called as “Metastasis”.
• Most common site of spread is lungs followed by bone and other organs.
• Staging is procedure of assessing spread of sarcoma to other parts in the body and the recent emergence of PET has played a very important role.
• 18-FDG (fluorodeoxyglucose) PET CT is most commonly performed, followed by 18-NaF (sodium fluoride) PET CT to stage.

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