Imaging of Bone Neoplasms

Objectives 

• To describe the role of imaging in the evaluation of bone tumour

• To state the modes of imaging and their application and limitations

• To identify and differentiate between a aggressive (malignant) and non aggressive (benign)   bone tumour on imaging

• To correlate pathology of bone tumours with imaging

Role of imaging are three fold in the evaluation of bone tumours

• Diagnosis

• Exact estimation of the extent prior to surgical interventions

• Staging of tumours

Clues on imaging, which helps in diagnosis

• location

• appearance of lesion 

• type of periosteal reaction

• matrix of lesion

• density of lesion

• number of lesions

Clinical presentations of bone tumours
The clinical presentation is very nonspecific such as pain or swelling of a limb or any other region of the body, usually related to trauma. They may present with a pthological fracture or it may even be an incidental finding on imaging for other clinical problem.

Pathological fracture
Could occur at the site of a benign / malignant tumour.

                                  Fig 1 a- Pathological fracture in a Ewings Tumour

                                   Fig 1 b – pathological fracture in a bone cyst

Modes of imaging & applications

• Plain radiography

• MRI

• CT

• Nuclear imaging

Plain Radiography
Plain radiography remains the primary imaging modality. It detects the tumour, characterizes tumours but may not exactly estimate the extent of malignant lesions. It could differentiate a non aggressive ( fig 2) from aggressive tumour in most of the instances. Common non aggressive tumours are giant cell tumour, aneurismal bone cyst, enchondroma and osteochondroma (fig 3a,b,c).

Characteristics of  a non aggressive tumour on plain radiography
1.    Well defined, sclerotic margin
2.    Narrow zone of transition
3.    No breach of cortex
4.    No periosteal reaction
5.    Absence of an associated soft tissue mass

                               fig 2- Non aggressive (Benign) tumour on plain radiography

Common Benign bone tumours

                                                 Fig 2a - Giant cell tumour

                                                 2b- Aneurysmal bone cyst

                                                    2 c – Osteochondroma

Osteochondromas
Osteochondroma ( exostosis) are common benign tumours, which are seen in young adults, less than 20 year old. It has a M : F ratio of 1:3. They are composed of both osteoid tissues and a cartilage cap. The cartilage cap is only visualized on plain radiographs only when it is calcified.Their presentation can be just an incidental finding on imaging or a bony out growth or pain due to pressure effects on adjacent nerves or bursae causing bursitis. It occurs around knee in 40% of the cases. It may undergo malignant transformation, thus needs to follow up arises once it is diagnosed. Treatment is surgical resection and it is offered when they are symptomatic.

     Fig 3 – Osteochondroma at the fibula head causing pressure erosion on tibia


Aggressive (Malignant) bone tumour ( fig 4a,b)

They are characterized on plain radiography by,

• Wide zone of transition

• Periosteal reaction (Codmans trialgle , onion peel, sunray spicules)

• Soft tissue mass

• New bone formation

Types of periosteal reactions seen in malignant bone tumours ( fig 4a, b, c) showing an aggressive (Malignant ) tumour, osteogenic sarcoma on plain radiography with classic Codman triangle of periosteal  reaction sun ray apperance Onion peel periosteal reaction in an Ewing’s tumour.

                                                            Fig 4a AP view of femur

                                                                4 b -  lateral  view of femur

                                            Fig 4c – AP & lateral femur

Role of MRI in  Bone tumours
MRI detects the lesion and helps in characterizing the tumour. It gives an accurate estimate of  the extent of malignant tumours due to it’s inherent imaging characteristics and it’s ability to do multiplanar imaging. It is poor in detecting calcification or new bone formation. Role of  MRI in detecting the extent of the aggressive bone tumour is shown in the figure below.

                                                    Fig 5 – Coronal MRI -  Ewings




Role of CT in Bone tumours
CT is also used to detect extent of bone tumour as multiplanar imaging is feasible like in MRI( fig 6). It has an additional advantage of being able to characterize a bony lesion by identifying calcification and new bone formation. It is also used at the same time to detect  pulmonary metastases in a given case of suspected malignant bone tumour. Osteo chondroma, osteoid osteomas are easily characterized by CT, both being benign bone tumours of young.

          fig 6 - Osteochondroma on CT as an bony outgrowth on this  axial image of upper tibia


Role of Nuclear imaging in Bone tumours
Nuclear imaging studies detect lesions which are bone forming indicating the osteoblastic activity. They detect metastatic disease earlier than x –rays even not symptomatic. It is useful in the management of cancer, on staging and planning the management protocols. They identify metastatic bone disease in common malignancies such as carcinoma of breast, bronchus, prostate.

                    fig 8-  multiple bone metastases in  an isotope bone scan

Metastatic Disease of Bone
Bone metastases are imaged on plain radiography as a preliminary mode of imaging. They can be lytic or sclerotic. Former are more commoner. Sclerotic metastases are predominantly from carcinoma of prostate. In females carcinoma of breast after treatment may give rise to sclerotic or mixed metastases. Skeletal survey was done to detect metastases which is now mostly replaced by more sensitive isotope scanning with less radiation.

Imaging of multiple Myeloma
Is a malignant bone tumour of bone marrow of plasma cell origin. It may start off with plasmacytoma or as multiple myeloma from the beginning. Skeletal surveys were carried out for the diagnosis of multiple myeloma which is characterized by punched out lytic lesions.

Mimics of bone tumours
There are some mimics of bone tumours or rather pit falls in imaging suspected bone tumours. Acute osteomyelitis mimicking Ewing’s sarcoma and benign  Brown tumour or cystic tuberculosis mimicking metastases.