Imaging Principles

1. Introduction

• Imaging  plays a central role in the diagnosis, staging, and surgical planning     of musculoskeletal (MSK) tumors.

• Plain  radiography, CT, MRI, nuclear medicine scans, and      PET/CT remain the core modalities, often complemented by angiography     and ultrasound for specific indications.

• Selection of modality depends on tumor type, location, aggressiveness, and tissue      composition

2. Plain Radiography (X-ray)

• Serves as the first-line imaging tool and remains diagnostic in >80%      of bone tumor cases

• Reveals:

  • Tumor  location within the bone (epiphyseal, metaphyseal, diaphyseal).

  • Cortical  destruction or thickening, periosteal reactions (e.g., Codman       triangle, sunburst pattern).

  • Matrix  type — osteoid, chondroid, or fibrous.

  • Soft-tissue       calcification patterns suggesting tumor type.

• Limitation:  early detection in pelvic and spinal lesions is poor due to      overlapping structures.

3. Computed Tomography (CT)

• Preferred  modality for assessing extent of cortical destruction and 3D      anatomy.

• Helical CT with ≤1 mm slice thickness allows high-resolution multiplanar      and 3D reconstructions

• Contrast-enhanced  CT delineates:

  • Relationship of tumor to vessels and neurovascular bundles.

  • Vascular  invasion or distortion aiding surgical planning.

• 3D  reconstruction helps estimate need for en bloc vessel resection     or approach modification.

4. Magnetic Resonance Imaging (MRI)

• Superior  to CT for evaluating intramedullary spread and extraosseous      soft-tissue extension

• Advantages:

  • Multiplanar  imaging (axial, sagittal, coronal).

  • Excellent  contrast resolution for tumor–muscle–fat differentiation.

  • Contrast-enhanced       MRI defines vascular involvement, cystic components, and nerve proximity.

• MRI is essential for surgical margin planning and defining safe      resection limits.

• Characteristic  tumor appearances:

  • Lipomas, liposarcomas, PVNS, hemangiomas, and fibromatoses show distinctive       patterns.

• Pitfalls: Hemorrhagic high-grade sarcomas may mimic hematomas — clinical  follow-up is vital.

5. Bone Scintigraphy (Bone Scan)

• Used to detect metastatic spread or multifocal disease

Bone tumors imaging

• Three-phase      bone scan reflects tumor biologic activity:

  • “Tumor       blush” pattern — increased uptake during late flow phase in malignant       lesions.

• Also      used to monitor chemotherapy response by comparing uptake pre- and      post-treatment.

6. Angiography and Venography

• Angiography:

  • Demonstrates arterial displacement, occlusion, or encasement by tumors

  • CT   angiography is increasingly replacing conventional techniques.

  • Preoperative  embolization reduces intraoperative bleeding in hypervascular       metastases (e.g., renal carcinoma).

• Venography:

  • Shows  venous obstruction or compression by tumor mass.

  • Indirectly suggests neural invasion when adjacent vein occlusion is present.

7. Positron Emission Tomography / CT (PET/CT)

• Functional      imaging using FDG uptake proportional to tumor glucose      metabolism

• Applications:

  • Initial  staging, monitoring therapy response, and recurrence detection.

  • PET-CT       fusion combines functional and structural data — useful in detecting small       metastatic lesions.

• Standardized   Uptake Value (SUV) quantifies uptake, helping to distinguish      malignancy from infection or inflammation.

8. Ultrasonography (USG)

• Recommended  initial test for superficial soft-tissue masses (per ACR      Appropriateness Criteria)

• Benefits:

  • No       radiation, real-time vascular evaluation, dynamic movement analysis,       cost-effective.

• Evaluates      echogenicity, margins, vascularity, and cystic vs. solid composition.

• Diagnostic      accuracy: 77–93%, though specificity for malignancy is limited.

• Pitfall:     differentiation between lipoma and liposarcoma remains      challenging.

• Suspicious      features (pain, rapid growth) → further MRI required.

9. MRI

• Next-line      imaging if diagnosis remains uncertain after USG or radiographs

• Provides      superior soft-tissue contrast and local staging.

• Diagnostic      parameters:

  • Size       (>5 cm), deep location, heterogeneous T2 signal, ill-defined margins,       perilesional edema.

  • Necrosis,       bone or neurovascular invasion → suggest malignancy.

• Post-contrast  MRI enhances diagnostic accuracy:

  • Differentiates cystic vs. solid lesions.

  • Identifies necrotic areas and optimal biopsy sites.

• Reported  sensitivity and specificity for differentiating benign vs. malignant: 64–93%   and 82–85%, respectively.

10. CT and PET/CT in Soft-Tissue Tumors

• CT  acts as a second-line modality when MRI is nondiagnostic or      contraindicated (e.g., pacemaker, claustrophobia).

• Contrast-enhanced   CT evaluates bone involvement and surgical planning.

• PET/CT:

  • Not routine for primary diagnosis but valuable for metastatic work-up and treatment response evaluation.

  • Studies  suggest PET/CT may help differentiate benign and malignant tumors,  but ACR discourages routine use.

Key Findings

• Optimal MSK tumor imaging requires multimodal integration.

• Radiography and MRI form the diagnostic backbone, with CT and PET/CT for  staging and surgical planning.

• Ultrasound  remains useful for superficial masses, while angiography assists in vascular evaluation.

• Advances in functional imaging (PET/MRI) and 3D reconstruction  continue to enhance preoperative accuracy and individualized treatment  planning.

References

1. Rajakulasingam R, Stediuk K, Teh JJ, et al. Current progress and future trends in imaging of bone tumours. Eur Radiol Exp. 2021;5(1):27.

2. Shu H, Ma Q, Li A, et al. Diagnostic performance of US and MRI in predicting malignancy of soft tissue masses: using a scoring system. Front Oncol. 2022;12:853232.

3. Gitto S, Ippolito D, Bandiera E, et al. CT and MRI radiomics of bone and soft-tissue sarcomas. Insights Imaging.2024;15(1):16.