Bone Tumors and Tumor-like Conditions of Bone

Matthew V. Cronin, MD; Tudor H. Hughes, MBBS, MD, FRCR

Disclosures

Appl Radiol. 2012;41(10):6-15. 

In This Article

Benign Bone Lesions

Solitary Bone Cysts

As mentioned previously, solitary bone cysts tend to be centrally located, painless lesions occurring almost exclusively in patients <30 yrs These tumors appear lytic, have a narrow ZOT and are most often located in the proximal humerus and femur (Figure 4). There is no periostitis unless an associated fracture is present. A fracture through an SBC may show the classic "fallen fragment" sign, which is fractured bone that has fallen to the most dependent portion of the cyst.[3,4] As expected for a cystic structure, the MRI appearance of these lesions shows hypointense T1 and hyperintense T2 characteristics.

Aneurysmal Bone Cysts (ABC)

These metaphyseal lesions are seen almost exclusively in patients <30 years of age. In contrast to a unicameral or solitary bone cyst, an ABC is typically painful, can have periostitis (often aggressive) and is eccentrically located. The ZOT is usually narrow and an expansile bubbly appearance is common (Figures 2, 8). An ABC should be considered in the differential (along with osteoblastoma, tuberculosis, and osteoid osteoma) for lesions in the posterior elements of the spine. ABC often complicates other lesions, most notably chondroblastoma, osteoblastoma and giant cell tumor of bone. The MR and CT appearances may show fluid-fluid levels, which is a nonspecific finding and can be seen in other lesions, including chondroblastoma, giant cell tumor of bone, or telangiectatic osteosarcoma.[3,6–9]

Fibrous Dysplasia

This painless, typically metadiaphyseal lesion can be monoostotic or polyostotic. When polyostotic, fibrous dysplasia is overwhelmingly (90%) located on one side of the body.[3] The ZOT is narrow and the lesion itself can be quite heterogeneous with a lytic, sclerotic, or mixed appearance (Figure 10). When located in the pelvis, fibrous dysplasia can often appear lytic and bubbly while rib lesions may have a ground-glass appearance and be expansile. Involved tubular bones are expanded and demonstrate cortical thinning. In the hip, this can lead to varus angulation and a "Shepherd's crook" deformity of the femoral neck.[3,6,8,10] The skull base and calvarium are also common sites of involvement. There is no periostitis and the age range of affected patients is broad. The MRI appearance is nonspecific, typically showing T1 prolongation and variable T2 intensity.

Figure 10.

Fibrous dysplasia. (A) Frontal and (B) magnified view of (A), views of the left tibia/fibula in an 11-year-old boy. Note the mildly expansile nature of the dysplastic bone with cortical thinning and on the expanded view the ground-glass nature of the bone matrix.

Nonossifying Fibroma

This common lesion is cortically based and eccentrically located. Found in individuals between 2 and 30 years, the painless entity shows a narrow ZOT with sclerotic borders and an appearance that can range from lytic initially to entirely sclerotic in the latter stages of development, as they typically "heal" and appear ossified (Figure 2). There is no associated periostitis. The MR appearance is nonspecific, with low signal on T1-weighted images and variable T2 signal.[3,6–8]

Giant Cell Tumor

This geographic, lytic lesion is classically described as having 4 qualifying characteristics when found in the long bones. It is eccentrically located, has a sharp nonsclerotic ZOT, abuts subchondral bone, and almost always occurs in individuals with recently closed physes (Figure 3). The most common locations are distal femur, proximal tibia and distal radius. However, atypical locations such as the pelvis and calcaneus are also seen.[3,6,7,9,11] In these cases, giant cell tumors need not conform to the above criteria. These lesions are usually mono-ostotic; however, polyostotic tumors or satellite lesions are rarely seen and can be difficult to differentiate from metastatic GCT. Periostitis is not present. There is low signal on T1 and variable T2 MRI signal, which may include hyperintense regions or fluid levels secondary to aneurysmal bone cysts.

Eosinophilic Granuloma

Eosinophilic granuloma (EG) could also be called the great mimicker of osseous lesions. While EG typically is found only in patients<30 years, there are a few other discriminating characteristics. For example, EG may appear lytic, sclerotic, mixed or "moth-eaten" (Figure 1). The ZOT can be narrow or wide. Associated periostitis may cause this lesion to appear aggressive. Infrequently, a bony sequestrum may be present; however, this can also be seen in osteomyelitis, fibrosarcoma and primary lymphoma of bone.[3,6,8,12] Most EG lesions are monoostotic, but younger patients are at higher risk for developing polyostotic disease.

Enchondroma

Enchondromas are centrally located, geographic, and predominantly lytic-appearing lesions, which almost invariably contain a chondroid matrix when found in the long bones (Figure 5). These monoostotic, painless lesions may show endosteal scalloping; however, there is no associated periostitis. Enchondromas may be difficult to discriminate from low-grade chondrosarcomas, but the latter is more likely in a history of pain, cortical destruction or soft tissue extension.[13] Large or proximal lesions have an increased rate of malignant transformation. In contrast, enchondromas found in the hands and feet may be polyostotic, but they rarely undergo malignant transformation except in Ollier's disease or associated with soft-tissue hemangiomas, as in Maffucci's syndrome.[3,6] Chondroid matrix is conspicuously absent in these peripheral lesions.

Osteochondroma

This lesion arises from the metaphyseal region of the long bones as a bony excrescence contiguous with the medullary compartment that characteristically points away from the adjacent joint. Osteochondromas are typically solitary, appendicular lesions, which cease growing after the skeleton matures (Figure 11). Growth after this point, cortical erosion, or thickening of the associated cartilaginous cap is rare, but suggestive of malignant transformation into chondrosarcoma.[3,6,14,15] Multiple hereditary exostoses are a rare, autosomal dominant, polyostotic form of the disease that has an increased risk of malignant transformation.

Figure 11.

Osteochondroma. AP radiograph in a 25-year-old man shows the classic appearance of a metaphyseal lesion directed away from the adjacent joint with continuation of the medullary space into the lesion. These often cause mechanical problems and may develop an adventitial bursa.

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