Differentiating Between Benign And Malignant Bone Tumors
Lower extremity bone lesions can have an intricate presentation as well as overlapping characteristics shared by benign and malignant bone tumors. Given these challenges, these authors discuss the pros and cons of different imaging modalities, and offer key insights on a variety of bone lesions ranging from osteosarcomas and fibrosarcomas to osteoblastomas and unicameral bone cysts.
The evaluation of bone tumors can be a challenge to any practitioner. The goal is to discern the benign bone lesion from the malignant bone lesion in the office or hospital setting. When evaluating a patient with a bone lesion, it is important to take multiple factors into consideration. One usually can narrow the probability of a tumor being benign or malignant based on the patient’s age, location of the lesion in the body, the lesion’s location within the bone and radiographic findings.1
However, it is important to note that this is not always uniformly true. Aggressive lesions may tend to be malignant although certain benign tumors may also display similar characteristics.2 It is also equally important to try to determine whether a lesion is a “primary” tumor or a “secondary” bone tumor, which has metastasized from another region of the body. Characteristically, many malignant tumors have clinical symptoms of pain associated with the lesion but this also can be true of some benign tumors.
The most useful modality for evaluating a bone lesion is the plain film radiograph. The advantage of radiographs is that they can provide essential information and characteristics as to the bone tumor’s size, location and aggressiveness when you are evaluating a primary lesion.1,3,4 Radiographic findings can certainly aid in the differential diagnosis and directing attention to the pattern of bone destruction and periosteal response is important.
After determining a suspected lesion is likely aggressive and possibly malignant, utilize other imaging modalities. Magnetic resonance imaging (MRI) is considered the “modality of choice” when the lesion in question is likely malignant.1 The advantage of MRI is the ability to evaluate bone marrow changes and the extent of a lesion. The disadvantage of MRI is that it may lack specificity due to many lesions having findings of a low T1 and high T2 signal, which can represent “edema, pus and tumor” infiltrate.1
Computed tomography (CT) scans can also be beneficial in observing bony changes that are more subtle than plain radiographs can represent. Computed tomography scans can also be useful in bone biopsies.1,5
Particularly when it comes to cases of metastatic lesions, bone scintigraphy is another imaging technique, which is very sensitive in detecting bone turnover with Tc-99m bisphosphonate.6 If any doubt remains, confirm the definitive diagnosis of a bone lesion via bone biopsy.
A Guide To Radiographic Presentations Of Aggressive And Benign Bone Lesions
The radiographic appearance of bone lesions and their pattern of bone destruction can yield clues to the aggressive versus benign state of a particular lesion. Periosteal reactions can be a guide to the aggressiveness of the lesion as well. However, benign and malignant bone lesions can have a “high degree of overlap” and aggressive lesions can have relatively “benign appearing periosteal reaction or none at all.”1,7 This also holds true for patterns of bone destruction in relation to lesions that appear less aggressive.
There are three types of bone destructive patterns: geographic, moth-eaten and permeative.