The two most important aspects of evaluating a bone tumor are the location of the tumor and the age of the patient.
Most bone tumors, regardless of whether they are benign or malignant, often occur in a characteristic location in the skeleton (ie, axial vs appendicular skeleton or long vs flat bone).
Epiphyseal lesions &medullary and peripheral :Chondroblastoma,giant cell tumor,osteomyelitis(fungus &TB) and aneurysmal bone cyst.
Epiphyseal & articular:Articular osteochondroma(trevors disease).
Metaphyseal & medullary:Enchondroma ,chondrosarcoma,simple bone cyst , fibrosarcoma,fibrous dysplasia and osteomyelitis(pyogenic).
Metaphyseal & cortical : Osteochondroma and osteosarcoma.
Metaphyseal & juxta-cortical : Fibrous cortical defect , non ossifying fibroma.
Diaphyseal & medullary : Fibrous dysplasia.
Diaphyseal & medullary & peripheral :Round cell tumor , langerhan cell histiocytosis.
Diaphyseal & cortical :Adamentinoma,osteofibrous dysplasia.
Diaphyseal & juxta-cortical : Osteoid osteoma,stress fracture,chronic osteomyelitis.
MARGIN
Bone lesions may range from a discrete well-defined abnormality to an ill-defined infiltrative process. The margin of the lesion and the zone of transition between lesion and adjacent bone are key factors in determining if a lesion is aggressive. A lesion with sharp margins and a narrow transition zone is radiographically considered nonaggressive, particularly when the margins have a sclerotic border.
A focal discrete lesion is called “geographic.” Geographic lesions are classified as type 1 and can be further categorized as type 1a (well-defined border with sclerotic rim) , type 1b (well-defined border but without sclerotic rim) , and type 1c (focal lytic lesion with ill-defined border) . On the other hand, an infiltrative lesion has ill-defined margins and a broad zone of transition, and its pattern of bone destruction may be “moth-eaten” (type 2) or “permeated” (type 3) , which refer to small, patchy, ill-defined areas of lytic bone destruction.
The classification of a lesion is not as important as an understanding of the radiographic features that make the abnormality look innocuous or aggressive. Type 1a lesions are at one end of the spectrum as the most innocuous and nonaggressive appearing, and type 3 lesions are at the other end of the spectrum as the most aggressive appearing. However, while a nonaggressive appearance suggests a benign process and an aggressive appearance suggests a malignant one, this is not always the case: Osteomyelitis and localized Langerhans cell histiocytosis are benign processes that can have an aggressive permeated appearance, and a giant cell tumor may look well defined but be locally aggressive and, on rare occasions, may even metastasize.
The permeated appearance is typical of a class of malignant lesions called the “small round blue cell group” because of these lesions' histologic appearance on hematoxylin and eosin stained specimens . Osteomyelitis and localized Langerhans cell histiocytosis also look “blue” on hematoxylin and eosin stained specimens. Although they are not histologically the same as the malignant small round blue cell lesions, they may also cause a permeated or moth-eaten radiographic appearance .
PERIOSTEAL REACTION
The presence and appearance of periosteal reaction are also important radiographic features that help characterize a bone lesion. Solid or unilamellated periosteal reaction is a nonaggressive appearance, since it indicates that the underlying lesion is slow growing and is giving the bone a chance to wall the lesion off . A multilamellated or “onionskin” appearance suggests an intermediate aggressive process, such as one that waxes and wanes or one that the bone is continually trying to wall off but cannot . Interruption (ie, regional disruption) of either the uni- or multilamellated periosteal reaction suggests an aggressive process that has broken through the periosteum. A spiculated, or “hair-on-end” (perpendicular to the cortex) or sunburst pattern, is the most aggressive appearance and is highly suggestive of malignancy . A Codman triangle refers to elevation of the periosteum away from the cortex, with an angle formed where the elevated periosteum and bone come together ; although the Codman triangle is often associated with conventional osteosarcoma, any aggressive process that lifts the periosteum may produce this appearance, even benign entities such as infection and subperiosteal hematoma. Sometimes periosteal reaction occurs as a result of pathologic fracture through a bone tumor and not because of the tumor itself, such as in the case of a simple bone cyst.
OPACITY AND MINERALIZATION
Tumors may be lytic, sclerotic, or mixed and usually have a typical opacity. For example, simple bone cysts and giant cell tumors are lytic, bone islands are sclerotic, and adamantinomas are often mixed. Lucency and sclerosis associated with true neoplasms are due to stimulation of osteoclasts or osteoblasts, respectively, by the tumor. Sometimes the destructive process will cause a fragment of bone to become sequestered within the lytic region; such a sequestrum may be seen in both benign and malignant processes .
Occasionally, the trabecular pattern within the lesion is the clue to its diagnosis. For example, an aneurysmal bone cyst and a desmoplastic fibroma may have a honeycomb appearance , and Paget disease can have coarsened trabeculae. A hemangioma in a long bone may have a sunburst or spoke-and-wheel pattern of trabeculation, while this same entity in a vertebral body will have a vertically oriented, coarsened, “corduroy” trabecular pattern.
The radiographic opacity of a lesion can also be affected by the mineralization of its matrix. The term matrix refers to the type of tissue of the tumor—such as osteoid, chondral, fibrous, or adipose, all of which are radiolucent—and mineralization refers to calcification of the matrix. This concept of matrix mineralization is important to understand, because the pattern of mineralization can be a clue to the type of underlying matrix and, thus, the diagnosis. For example, calcification of chondral tissue often produces punctate, flocculent, comma-shaped, or arclike or ringlike mineralization, indicating that the lesion is cartilaginous, such as an enchondroma, chondrosarcoma, or chondroblastoma , but all of these lesions vary in the frequency of radiographically evident mineralization. Bone-forming tumors have fluffy, amorphous, cloudlike mineralization, causing an opaque radiographic appearance , but the distinction between chondral and osseous mineralization can sometimes be difficult. Some tumors are completely nonmineralized, making determination of their tissue of origin difficult. Faint mineralization in a lesion is best assessed by using CT, which is more sensitive than radiographs for differences in attenuation .
SIZE AND NUMBER
The size of a lesion can also be a clue to its diagnosis, since some entities have size criteria. For example, osteoid osteoma and osteoblastoma are histologically similar lesions, but they differ in size: The nidus of an osteoid osteoma is less than 1.5 cm in diameter, while the osteoblastoma is larger than 1.5 cm . Traditionally, a well-defined lytic lesion in the cortex of a long bone with a sclerotic rim has been termed a fibrous cortical defect if it is less than 3 cm in length and a nonossifying fibroma if it is larger than 3 cm , but some authors prefer to use the term fibroxanthoma for both of these lesions . A 1–2-cm chondral lesion in a long bone is most likely to be an enchondroma, while the risk of it being a low-grade chondrosarcoma increases if it is greater than 4 or 5 cm .
Primary bone tumors are solitary occurrences, while other abnormalities may be multiple . Multiple sclerotic lesions might represent metastatic disease or osteopoikolosis (multiple bone islands); the latter are usually similar in size and are centered around joints. The most common causes of multiple lucencies in someone older than 40 years are metastatic carcinoma, multiple myeloma, and metastatic non-Hodgkin lymphoma, but benign entities such as multiple brown tumors may look similar.
CORTICAL INVOLVEMENT
In addition to lesions that specifically arise within the cortex, the cortex may be affected by processes that originate in the medullary canal or the periosteum or surrounding soft tissue. For example, as a medullary process expands, it may cause erosion of the inner surface of the cortex, called endosteal scalloping . If the medullary lesion is so aggressive that it erodes the inner aspect of the cortex without giving the periosteum a chance to lay down new bone, the cortex will eventually be completely destroyed and breached by the lesion. On the other hand, if the bone has time to lay down new periosteum on the outer surface of the cortex as the inner surface is being eroded, the bone may look expanded owing to the outward ballooning of the cortex . Depending on the aggressiveness of the lesion, the ballooned cortex may have normal thickness or be thin. The ballooned cortex gives rise to the categories of lytic expansile and “soap bubble” lesions.
A process that starts on the outer surface of the cortex, either in the periosteum or adjacent soft tissue, may erode the outer surface of the cortex; this process is called saucerization. If the tumor is not mineralized, saucerization may be the only radiographic indication of its presence. Sometimes the periosteum will react at the site adjacent to the saucerization, giving a buttressed appearance but not necessarily indicating the benign or malignant nature of the lesion . The buttressed appearance may also occur when a slowly growing intramedullary process becomes more aggressive and breaks through (ie, interrupts) an area of solid periosteal reaction.
SOFT-TISSUE COMPONENT
The presence of a soft-tissue component with a bone lesion suggests a malignant process. The tumor may have frankly destroyed the cortex as it expanded, or it may have permeated through the haversian canals of the cortex to reach the surrounding tissue. The soft-tissue component may displace adjacent fat planes . Tumors that often have a soft-tissue component are osteosarcoma, Ewing sarcoma, and lymphoma .
ADVANCED IMAGING
While radiographs are often sufficient to enable a diagnosis, advanced imaging is sometimes needed. MR images and CT scans may provide additional information by virtue of their tomographic nature, multiplanar capability, and better soft-tissue contrast than radiographs. CT is useful for evaluating subtle mineralization in a lytic lesion, for demonstrating radiographically occult bone destruction , or for demonstrating the lucent nidus of an osteoid osteoma amid a large area of reactive sclerosis . MR imaging has become the standard for evaluating the local extent of a malignant process for the purposes of staging and assessing tumor response to chemotherapy . However, it must be stressed that CT and MR images should only be interpreted with concurrent radiographic correlation.
CONCLUSION
Despite the availability of advanced imaging methods such as CT and MR imaging, with their ever increasing number of detectors and strength of the magnetic field, the diagnosis of a tumor or tumorlike lesion of bone still depends on the conventional radiograph. By paying attention to the age of the patient, the location of the lesion, and the radiographic features of the lesion, the interpreter will be led to a short differential, if not the single correct, diagnosis.
ESSENTIALS
Tumors have a typical patient age range—<20,>40 years old—and a typical location in the skeleton—flat versus tubular bones, epiphyseal versus metaphyseal versus diaphyseal, or medullary versus cortical versus juxtacortical.
The margin of a lesion and type of periosteal reaction are indicators of lesion aggressiveness, but not necessarily of whether it is benign or malignant: A well-defined lesion with a sclerotic rim and thick unilamellar periosteal reaction is the most innocuous appearance, while a permeated pattern with spiculated periosteal reaction is the most aggressive.
The pattern of mineralization of the tumor matrix is often the clue to the type of tumor: Mineralization of chondral tissue is punctate, flocculent, or arclike, while mineralization of osseous tissue is fluffy and cloudlike.
No comments:
Post a Comment