Role of MRI in diagnosis of benign and malignant bone and soft tissue tumours

1. Role of MRI in diagnosis of benign and malignant bone and soft tissue tumours John-Henry Corbett Department of Radiology University of the Free State 05/2011

2. Conventional radiographs remain the initialimaging examination for bone and some soft tissue tumours • XR is invariably the most diagnostic • Best for establishing a differential diagnosis • Best in assesing activity of the lesion • Benign vs malignant • Other imaging modalities ( eg. MRI ) are superior in staging musculoskeletal neoplasms

3. Major advantages of MRI for musculoskeletal imaging • Excellent soft tissue contrast resolution • Multiplanar imaging capabilities • Various available contrast agents • Powerful imaging modality for abnormalities of • Fat, muscles, nerves, bone and bone marrow • Effective for use in • Neoplasms of tissues mentioned above • Response of neoplasms to neoadjuvant / posoperative chemotherapy and/or radiotherapy • Residual and/or recurrent tumour after surgery • Congenital and developmental musculoskeletal abnormalities • Traumatic lesions • Haemorrhage • Ischaemia / infarction of bone marrow / muscles / fat • Infectious and non-infectious inflammatory diseases

4. Longitudinal bone growth occurs by enchondral bone formation • A calcified cartilaginous matrix at the growth/physeal plate is remodelled into bone • Physeal plate contains four parallel zones perpendicular to the long axis of the bone • Active cartilage cell division and maturation in the proliferating and hypertrophic zones • Ostoid matrix formation and mineralization occurs in the ossification zone • Resting, Proliferating and Hypertrophic zones • Radiolucent on XR / CT • High signal on T2WI • Ossification zone • Mineralized bone on XR / CT • Low signal on T2WI

5. Axial bone growth occurs directly from the periosteum • E.g.: Diameter of long bones, facial bones • Outer fibrous layer and inner cellular layer (cambrium – osteoblastic activity) • Periosteum is loosely attached to the cortex of bones in children and firmly in adults • Periosteum is low signal on T1WI & T2WI • Reactivation of periosteum in adults • Trauma, infection or neoplasm • MRI can demonstrate periosteal elevation as well as subperiosteal abnormalities such as tumour, pus or haemorrhage

6. MRI signal in medullary portion of bone • Red (hematopoietic) marrow • 40% fat , 40% water & 20% protein • Intermediate T1WI signal – lower than subcut fat • Intermediate T2WI signal – similar to muscle • Predominant marrow in early childhood • Adults : Spine, flat bones, skull, proximal femur & humerus • Yellow (hematopoietically inactive) marrow • 80% fat, 15% water & 5% protein • Similar signal to subcutaneous fat on T1WI & T2WI • Later in childhood – progressive conversion of red to yellow marrow • Hands and feet • Distal long bones : diaphyseal regions in the first decade

7. Most pathological processes increase the T1 and T2 relaxation coefficients of involved tissue • Leads to ↓T1 signal and ↑T2 signal compared to surrounding normal tissue • Includes : ischaemia, infarction, inflammation, neoplasm • Haemorrhage : variable appearance according to age

8. Imaging evaluation of bone and soft tissue tumours • On XR most bone tumours are radiolucent • Osteolytic lesions may not be visible on XR until there is 30-50% loss of mineralization • MRI can detect marrow based tumours before they are evident on XR • MRI can also further characterize lesions with regards to extent and soft tissue extension

9. Features used to characterize bone and other tumours on XR • Lesion location • Epiphyseal/ metaphyseal / diaphyseal • Cortical / intramedullary / eccentric / central • Lesion size • Lesion density • Radiolucent / sclerotic / presence of matrix mineralization • Margins • Well defined geographic ± sclerotic borders / poorly defined • Moth eaten / permeative radiolucent patterns • Presence of cortical destruction • ± Extra osseous tumour extension • Presence of periosteal reaction • Interrupted vs non-interrupted pattern • Lamellated / onion skin appearance • Perpendicular-, sunburst pattern • Codman triangles

10. Features used to characterize bone and soft tissue tumours on MRI • Lesion location • Lesion size • Margins • Well-defined geographic ± low signal margins vs poorly defined • Signal of the lesion on • T1WI • PDWI with and/or without fat saturation • T2WI with and/or without fat saturation • STIR images • Enhancement after IV Gadolineum based contrast • Presence of cortical destruction

11. T1WI • Good contrast for identification of marrow , cortical and soft-tissueinvolvemement • Differentiation between fat (↑) and tumour (↓) • Definition of muscle plains and anatomic compartments • Longitudinal extent of the tumour can be seen on coronal or sagital T1WI • Gadolinium enhanced T1WI • Better characterize osseous & soft tissue involvement • Non-enhancing regions of tumour regarded as tumour necrosis • Useful for differentiating • Peritumoural oedema from underlying tumour • Recurrent tumour from scar / fibrosis • Dynamic contrast enhanced imaging has been used to determine response to chemotherapy • Good response shows reduced enhancement • Short time intervals should be used (similar in late phase enhancement)

12. T2WI • Distinguish muscle from tumour • Increase diagnostic specificity of marrow infiltration • Seen as low signal on T1WI • Proton density- / T2WI- with fatsatorSTIR • Lesion iso-intense to adjacent tissue • T1WI, T2WI and T2WI fatsat / STIR • Axial images to delineate the relationship of the tumour to adjacent neurovascular structures and compartments • MR spectroscopy not routinely used

13. Not possible to distinguish benign from malignant lesions of bone and soft tissue on MRI signal characteristics alone • Malignant lesions tend to be more extensive • Involvement of cortex, marrow and soft tissues • Involvement of the neurovascular bundle • Perform MRI prior to biopsies to avoid postsurgical inflammation and oedema • Prolong T2 relaxation time of uninvolved tissues • Muscle oedema is non-specific • Associated with trauma, infection & vascular insults

14. On T1WI ↑ signal in surrounding muscles can be seen in atrophy with fatty infiltration orneuromuscular disorders • Not to be mistaken for tumour • Marrow inhomogeneity • Red to yellow marrow conversion • Especially middle aged obese women with smoking history / immature skeleton • Metaphyseal or diaphyseal low signal intensity (red marrow) • No extension over physeal scar • ↑Signal intensity on STIR images

15. T1WI : Normal ↓ signal meta-diaphyseal red marrow. Epihyseal region is uniformly yellow marrow STIR : ↑ signal red marrow This finding of marrow inhomogeneity is considered a normal variant.

16. Coronal T1WI Coronal STIR Red marrow heterogeneity in the femoral dyaphysis with no extension across the physeal scar

17. Staging of bone / soft tissue tumours • MRI is the imaging modality of choice • Should be used with conventional XR • MRI is accurate in determining • Local extent of the tumour – intra /extra osseus • Skip metastases • Involvement of muscle compartments, joints and neurovascular bundles • Local lymphadenopathy • Enneking staging system for bone and soft tissue tumours is most widely used • Based on tumour grade, site and metastases • Histologic, radiologic and clinical criteria

18. Benignlesion are considered grade 0 (G0) • Malignant lesions are either • Low grade (G1) • High grade (G2) • Site and extent of tumours • T0 : benign tumours confined in a true capsule and anatomic compartment of origin • T1 : aggressive benign or malignant lesion confined to its anatomic compartment • T2: spread beyond the anatomic compartment of origin • Metastatic disease • M0: no metastatic disease • M1: regional or distant metastases

21. Important points in reporting on bone tumours • What is the total intraosseous extent of the tumour • Is there involvement of the growth plate • Are there any “skip” metastases • Is the adjacent joint involved • What is the relationship to the neurovascular bundle • Important points in reporting on soft tissue tumours • Anatomical location of the tumour • Its relationship to the adjacent bone • Its relationship to the neurovascular bundle • Provisional diagnosis • Neoplastic or non-neoplastic • Benign or malignant

22. Suggested series for bone tumours ( 3 ) • Longitudinal T1WI • Covering the whole lesion • Include the adjacent joint • Intraosseous extent and relationship to the growth plate • Extremity coil if possible • Coronal T1WI • Body coil • Include the whole bone • Evaluation for skip metastases • Axial T2WI with FATSAT • Relationship to the neurovascular bundle • Extremity coil if possible • Include the whole lesion

23. Suggested series for soft tissue tumours ( 4 ) • Longitudinal T1WI • Longitudinal STIR • Coronal T1WI • Axial T2WI with FATSAT

24. Longitudinal T2WI • Adds nothing to intraosseous staging • Both tumour (osteosarcoma) and marrow are relatively high signal • Standard enhanced T1WI • Have not been shown to be of value in evaluating primary bone tumours • Axial T1WI • Adds nothing to extraosseous staging • Tumour mostly isointense to muscle

25. Sagittal T1W SE image of the whole femur in a patient with distal femoral osteosarcoma. A region of reduced signal intensity in the mid-diaphysis proved to be a ‘skip’ metastasis. Coronal T1W SE image of the distal femur in a patient with osteosarcomashowing intraosseous extent.

26. Axialdual-echo T2FSE sequence with fat saturation in a patient with distal femoral osteosarcoma. The relationship between extraosseous tumour and the neurovascular bundle is best demonstrated on the proton density image (right) since the neurovascular bundle is isointense to muscle on the T2W sequence (left). Peritumoural oedema is also clearly distinguished from fat by the addition of fat saturation.

27. WHO classification of soft tissue tumours

30. WHO classification of bone tumours

31. Incidence of soft tissue tumours

32. Incidence of soft tissue tumours

34. References • Aisen AM, Martel W, Braunstein EM et al. MRI and CT evaluation of bone and soft-tissue tumors. American Journal of Roengenology 1986; 146:749-756. • Kransdorf MJ & Murphey MD. Radiologic evaluation of soft-tissue masses: a current perspective. American Journal of Roengenology 2000; 175: 575-587. • Meyers SP. MRI of bone and soft-tissue tumours and tumour-like lesions. Thieme; 2008. • Saifuddin A, Twinn P, Emanuel R & Cannon SR. An audit of MRI for bone and soft-tissue tumours at referral centres. Clinical Radiology 2000; 55:537-541. • Stoller DW. MRI in orthopaedics and sports medicine. 3rd Ed. Lippincott, Williams & Wilkins; 2006.