Dr. Cronin is a Resident Physician in the Department of Radiology, and Dr. Hughes
is a Professor of Radiology, Residency Program Director, Department of
Radiology, University of California San Diego, San Diego, CA.
Bone tumors are a relatively infrequent finding in musculoskeletal
radiology. When evaluating osseous lesions, the radiologist’s main goal
is to assess whether the lesion is benign or aggressive in appearance
and whether further workup is required. The list of potential osseous
lesions is extensive; this review of bone tumors does not include
metabolic or degenerative lesions. To provide a meaningful differential
diagnosis to the referring clinician, several characteristics of every
osseous lesion should be routinely assessed.
radiographic features of a bone lesion should be examined. Five of
these include: zone of transition (ZOT), presence or absence of
periostitis, location in the bone, pattern of osseous destruction, and
age of the patient, along with associated symptoms.1-3
Additionally, determining if the process is mono-ostotic or polyostotic
can be very helpful. Because these characteristics are so important to
properly classifying bone tumors, more should be said about each.
zone of transition is that outer margin of the lesion that represents
the change from pathologic to normal bone. A wide ZOT is said to be
present when the lesion cannot be clearly circumscribed; this is usually
associated with an aggressive lesion. Malignancies such as Ewing’s
sarcoma and osteosarcoma typically show this pattern of involvement;
however, infection and other benign processes, such as eosinophilic
granulomas (EG) (Figure 1), can have wide margins. A wide ZOT does not
equate to malignancy, but it is very rare for a narrow ZOT (a
geographic lesion) to be associated with anything other than a benign
The location of the lesion in the bone, both
transversely and longitudinally, can also be useful in narrowing the
differential. For example, a select group of lesions is eccentrically
located and involves the cortex (osteoid osteoma, parosteal
osteosarcoma, and nonossifying fibroma) (Figure 2). Other lesions almost
always involve the epiphysis (giant cell tumor after physeal closure
(Figure 3), chondroblastoma). Some lesions, such as solitary bone cysts
(Figure 4), enchondromas (Figure 5), EG and Ewing’s sarcoma, tend to be
The number of osseous lesions can
also provide clues to etiology. Several lesions that can be polyostotic
include multiple hereditary exostoses, enchondromas, fibrous dysplasia
and, occasionally, eosinophilic granulomas.3 Of course,
metastatic disease and multiple myeloma (Figure 6) are common causes of
multiple lesions, but a few bony metastases can present as solitary
lesions—especially in renal or thyroid carcinoma.3,5
information from periosteal changes can be relatively more difficult.
Periostitis is often subtle and can mislead the radiologist attempting
to classify a lesion as benign or aggressive. Classic,
aggressive-appearing periostitis is described as having an “onion-skin,”
“sunburst” (Figure 7), or “hair-on-end” appearance.2,3 A
Codman triangle pattern is another aggressive configuration. Benign
patterns are those that, in theory, have had sufficient time to organize
and, thus, show solid thick or wavy unilamellar periosteal changes. Use
caution when assessing periosteal reactions, as many benign lesions
such as infection, EG (Figure 1), and aneurysmal bone cysts can result
in an aggressive-appearing periostitis. Regardless, recognizing
periosteal reaction of any type remains important, as this effectively
excludes several lesions from the differential. If periostitis is
present, fibrous dysplasia, solitary bone cyst, nonossifying fibromas,
and enchondromas can be removed from consideration unless complicated by
Two additional pieces of information that
can be extremely helpful are the age of the patient and the presence or
absence of pain. Some lesions, such as Ewing’s sarcoma and primary
osteosarcoma, are seen overwhelmingly only in the pediatric, adolescent,
and young adult populations. Likewise, EG, chondroblastoma, solitary
and aneurysmal bone cysts are rarely seen in adults >30 yrs.
Moreover, while infection, metastatic lesions, and aneurysmal bone cysts
typically present with pain, discomfort is rare (in the absence of
trauma) with fibrous dysplasia, enchondromas, and solitary bone cysts.
Several other characteristics, such as the presence of sclerotic
margins, soft tissue involvement, a pattern of bony destruction,
endosteal scalloping, and the pattern of matrix calcification, can also
aid in diagnosis.
Although plain radiographs, computed
tomography (CT), magnetic resonance imaging (MRI), and radionuclide
studies may each provide additional information, suspected soft-tissue
extension of an osseous lesion should be evaluated further with
contrast-enhanced MRI to determine not only tumoral extent but also the
risk of complications like neurovascular compromise. Also, MRI may help
narrow the list of differential considerations by demonstrating cystic
or necrotic components, encapsulation, contrast enhancement and the
presence of fluid levels (Figures 2, 8, 9) or peritumoral edema on MRI.
Dedicated CT may show occult, pathologic fracture in an otherwise
benign-appearing but painful lesion.
Scintigraphy with Tc99m
–MDP bone scan can determine whether a lesion is mono-ostotic versus
nature. The following is a brief description of each of the 15 most
common benign and malignant osseous lesions the radiologist is most
likely to encounter.
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)
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
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.
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
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.
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.
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.
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
Malignant bone lesions
In patients <30 years,
osteosarcoma and Ewing’s sarcoma are the most common primary malignant
tumors of bone. Osteosarcoma can be subdivided into medullary,
parosteal, periosteal and telangiectatic, all of which carry different
prognoses and treatment options.
Medullary osteosarcoma (Figure
7) is the most common, occurring in adolescents and young adults
typically between the ages of 15 and 25 yrs. These are rapidly growing,
heterogeneous, metaphyseal lesions that show cortical destruction,
aggressive periostitis, and a wide ZOT. Osseous matrix formation is the
norm and a soft tissue component is often present. Evaluation with MRI
shows variable T1 and T2 signal characteristics secondary to varying
degrees of ossification. High T2 signal is often seen around the
periphery of the lesion, presumably related to adjacent edema.
Metastatic skip lesions are commonly seen and should be worked up with
Parosteal osteosarcoma (Figure 12)
originates from the parosteal soft tissues and is less aggressive than
the medullary form. This lesion typically occurs in older patients.
Growth is circumferential around the involved bone and typically does
not initially result in cortical destruction. As such the prognosis for
this lesion is more favorable. However, if intramedullary extension does
occur, the prognosis is more guarded.
osteosarcoma (Figure 9) has the potential to be misdiagnosed as a giant
cell tumor or chondroblastoma, as it is characteristically lytic and
deceivingly nonaggressive in appearance. Subtle cortical erosion or
periostitis may be present. Periosteal osteosarcomas are rarer than
those mentioned previously. Periosteal osteosarcoma is a surface lesion
that typically produces a sunburst or Codman’s triangle periostitis.
Adjacent cortical erosion is usually seen.3,4,7
sarcoma is the most prevalent primary malignancy of bone in children
and is second to osteosarcoma in adolescents and young adults.
Classically, Ewing’s is described as a diaphyseal-based, permeative
lesion with a wide ZOT and aggressive periostitis (Figure 13). An
associated soft tissue mass is invariably present. It should be noted,
however, that Ewing’s is not limited to a diaphyseal location; in fact ,
it is often found in metaphyseal or metadiaphyseal locations. This
lesion typically affects the appendicular skeleton in children but is
found more axially in adolescents. The radiographic appearance of
Ewing’s is nonspecific and can overlap that seen with infection or
eosinophilic granuloma. MRI characteristics show low signal on T1, high
signal on T2, and typically an adjacent soft-tissue mass that may be
heterogeneous in appearance secondary to focal necrosis.3,4,7
is typically a low-grade malignant osseous tumor found in adults. The
radiographic appearance can be misleading, as often few aggressive
features are present. This is a lytic, metaphyseal-based lesion, which
may have a “snowflake” chondroid matrix. However, completely lytic
lesions are not unusual (Figure 14). Cortical erosion, soft-tissue
extension, and pain may or may not be present. Low-grade chondrosarcoma
can be difficult, if not impossible, to differentiate from an
enchondroma, which is the primary alternative consideration in the
differential diagnosis. On MRI, low grade, differentiated
chondrosarcomas will appear bright on T2 imaging, with more homogeneous
signal than that of higher-grade lesions.3,4
Undifferentiated pleomorphic sarcoma (malignant fibrous histiocytoma) and fibrosarcoma
these two lesions have differing histologic appearances, they are
indistinguishable radiographically. These are relatively rare bone
tumors that may arise de novo or secondary to an underlying osseous
lesion, such as Paget’s disease, fibrous dysplasia, or nonossifying
fibroma, or at sites of prior radiation. This lesion has a permeative
appearance with an indistinct ZOT and may or may not have an associated
soft tissue component (Figure 15). The MRI appearance is again
nonspecific, with low T1 signal and heterogeneously bright signal on
Metastatic disease and myeloma
metastatic lesions have multiple appearances and therefore are often
included in the differential for atypically appearing sclerotic or lytic
lesions. Several metastatic lesions, such as renal cell, thyroid,
melanoma, and choriocarcinoma, are classically lytic in appearance.
However, other than renal cell cancer, this need not always be the case.
Metastatic prostate cancer (Figure 16) will typically show sclerotic
lesions, but breast, lung (Figure 17) and gastrointestinal malignancies
can also mimic this appearance. As is the case with other lesions, MRI
is useful for evaluation of soft tissue extent and staging; however,
biopsy is needed for diagnosis.3-5
Multiple myeloma is a
diffuse, permeative malignancy found in adults over the age of 35 to 40
yrs. While this lesion is typically lytic, a rare form of sclerotic
myeloma is seen in association with POEMS syndrome (Polyneuropathy,
Organomegally, Endocrinopathy, Monoclonal gammopathy and Skin changes).
In the early stages, myeloma may be preceded by a predominantly lytic
plasmacytoma that is usually found in the axial skeleton. Multiple
myeloma ultimately ensues, typically with a diffuse axial and
appendicular distribution. Multiple “punched out” lesions in the
calvarium and axial skeleton are a classic appearance of this disease
(Figure 6). Patients inevitably suffer from renal failure secondary to
Bence-Jones protein deposition or associated amyloidosis. Of note,
radionuclide studies with Tc99m-MDP are ineffective in demonstrating myelomatous lesions.3,4
article has reviewed the commonest benign and malignant bone tumors the
radiologist is likely to encounter. To construct a meaningful
differential diagnosis, an attempt should be made to characterize the
lesion as having either an aggressive or a benign appearance by
assessing such qualities as the zone of transition, periostitis, pattern
of lysis, and location. A careful and methodical analysis will help the
radiologist determine if the lesion is likely benign or if additional
workup or biopsy should be considered.
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