E1986. Don't Forget the Basics: Radiographic Evaluation of Common Benign and Malignant Bone Tumors
Primary bone tumors are rare, with bone sarcomas representing only 0.2% of all malignant tumors. The classification includes primary tumors, secondary tumors arising from a benign lesion and metastases. Pseudotumors behave like tumors in diagnostic imaging, but their etiology is non-neoplastic, usually metabolic. The purpose of this review is to illustrate the main bone tumor findings in a step by step evaluation.
Educational Goals / Teaching Points
1. To learn the most important features that differentiate benign and malignant bone lesions.
2. To understand the benefits of using radiographs as the initial imaging method to study bone tumors.
3. To guide the analysis of the bone tumor findings in a step by step algorithm.
Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
First step. The age of the patient is crucial for further characterization. In children, benign tumors are the most common type. Some authors prefer a division under and over 30-years-old because in the latter metastasis are a common differential.
Next step. The number of lesions can aid to determine if we are dealing with a primary tumor, metastasis or a metabolic underlying condition.
Third step. Location in the body and within the bone is important given that some tumors arise in specific zones. For example, the parosteal osteosarcoma usually arises in the distal metaphysis of the femur.
Next step. The transition zone is one of the most important features. It’s important to assess whether it’s wide or narrow and to correlate with its margins. There are 3 types of margins: well-defined and sclerotic, well-defined and non-sclerotic, and ill-defined.
Fifth step. Bone destruction can be classified in 3 types, according to Lodwick et al: geographic (type I), moth-eaten (type II), and permeative (type III).
Next step. Bone matrix. Osteoid matrix is a dense, amorphous, cotton-like calcification seen in osteosarcoma. Cartilage matrix is seen as punctate, irregular, and curvilinear calcifications (rings and arches); this pattern is typical of enchondromas and osteochondroma. The fibrous matrix is seen as a uniform increase in density with a ground-glass appearance like seen in bone dysplasia.
Seventh step. Evaluate the periosteal reaction. Check if it’s continuous or interrupted. The continuous periosteal reaction can be classified as solid, single-layered, lobulated, and eggshell. The interrupted periosteal reaction can be classified as wedge-shaped, onion skins, the hair on end, sunburst, and Codman triangle.
Final step. Determine if the tumor has invaded the soft tissues. A cortical break can be the first sign.
Benign bone tumors are usually intraosseous, with well-defined or sclerotic borders, continuous periosteal reaction, and without a cortical break or soft-tissue mass. Malignant tumors tend to be poorly delimited, with cortical break and erosion, aggressive periosteal reaction, and soft-tissue involvement.
A well-detailed radiographic analysis and a good medical history will allow an accurate diagnosis and reduce the list of differentials to guide for better clinical decisions.