is an Assistant Professor of Radiology and
is a Professor of Radiology in the Department of Radiology,
University of Iowa Roy J. and Lucille A. Carver College of
Medicine, Iowa City, IA.
One of the important functions of a radiologist in interpreting
musculoskeletal radiographs is to identify a lytic lesion. But once
such a lesion is identified, a radiologist must also be able to
provide a definitive diagnosis or a reasonable differential
diagnosis for the lesion and provide appropriate recommendations to
the referring clinician. We will address each of these issues in
our approach to lytic bone lesions.
Identifying a lytic lesion
When a lytic lesion is suspected, the radiologist must keep in
mind the possibility of a normal variant, such as a pseudocyst.
Two common locations for pseudocysts are the humeral head and the
calcaneus. The pseudocyst of the humeral head is typically located
in the region of the greater tuberosity, while the pseudocyst of
the calcaneus is typically located anteriorly (Figures 1 and
A pseudocyst is a region of relatively low stress within a bone
resulting in trabecular bone formation that is not as pronounced as
in higher stress areas. This area of relatively lower stress
develops into an apparent lytic lesion, which is actually an area
of trabecular rarefaction. When this area of trabecular rarefaction
is visually compared with the surrounding bone that contains more
prominent trabeculae, one sees an apparent lytic lesion or the
On magnetic resonance imaging (MRI), a pseudocyst has normal marrow
signal, since it is a normal variant.
Another useful tool in identifying subtle lytic lesions is to
compare current studies with previous radiographs or to compare
them with images of the contralateral side. Comparison with prior
films may help to identify subtle focal changes, which, for the
less experienced radiologist, aids in the identification of a new
lytic lesion. Literature has also shown that comparison with prior
studies improves the diagnostic accuracy of the interpretation.
Comparison with the contralateral side should also be made when
these radiographs are readily available. Examples of studies with
readily available contralateral structures include pelvic
radiographs and skeletal surveys. On radiographs of the pelvis, one
hemipelvis can be readily compared with the other to more easily
and confidently identify subtle lytic lesions, cortical
destruction, or periosteal reaction. When interpreting skeletal
surveys, a radiologist should also use available studies of the
contralateral extremity for comparison purposes.
One of the most important first steps in deriving a differential
diagnosis when evaluating a lytic lesion is to know the age of the
patient. This is an important piece of information in
musculoskel-etal radiology. Typically, only certain lesions occur
within any given age range; therefore, the age of the patient must
be considered in order to generate a correct differential
diagnosis. Some of the lytic lesions that are largely confined to
certain age groups are: metastatic neuroblastoma in the infant and
young child, metastasis and multiple myeloma in the middle-aged and
elderly, Ewing's sarcoma and simple bone cyst in the long bones in
children and young teenagers, and giant cell tumor in the young to
middle-aged adult (20 to 50 years of age).
The next step is to examine the lesion to see if it has a
pathognomonic appearance and/or location. Some lytic lesions have a
characteristic radiographic appearance (including matrix) and/or
location that are inherently diagnostic. A few examples include: a
corduroy vertebral body (hemangioma; Figure 3), a fallen fragment
sign (simple bone cyst; Figure 4), intralesional gas in a
juxta-articular lesion (subchondral cyst, such as a degenerative
cyst or intraosseous ganglion cyst; Figure 5), an enlarged bone
with coarsened trabeculae and a thickened cortex (Paget's disease;
Figure 6), chondroid matrix in a geographic lytic lesion in the
hand (enchondroma; Figure 7), vertebra plana in an otherwise
healthy child (Langerhan's cell histiocytosis; Figure 8), and the
cockade sign in the calcaneus (intraosseous lipoma; Figure 9). One
must become familiar with characteristic pathognomonic radiographic
signs and appearances of lytic lesions.
In regard to matrix, mineralization of both chondroid and
osteoid matrix can be visible on radiographs. Mineralization of
chondroid matrix is seen as dot-like, popcorn-like, arcs and rings
of calcifications within the bone tumor, while osteoid matrix has a
cloud-like, wispy appearance (Figures 10 and 11). Some lesions that
can have radiographically visible chondroid matrix include
enchondroma, chondroblastoma, and chondrosarcoma. Osteoid matrix
can be seen in osteosarcoma and osteoid osteoma/osteoblastoma.
If the appearance of the lytic lesion is not pathognomonic, such
that one cannot give a definitive diagnosis or a succinct
differential diagnosis, then the radiologist must determine the
aggressiveness of the lesion. Generally speaking, benign lesions
can have a quiescent or aggressive appearance, while malignant
lesions have an aggressive appearance. Two radiographic
characteristics we have found useful in determining the
aggressiveness of a lytic lesion are the appearance of the lesion
based on the Lodwick classification system and the type of
periosteal reaction present.
The authors use the revised Lodwick classification system when
evaluating the appearance of a lytic lesion because this has been
shown to be a reliable and accurate method of determining that
certain lesions have a very high likelihood of not being malignant
based on their radiographic appearance.
This is a fairly versatile classification system in that multiple
factors important in evaluating lytic bone tumors can be
incorporated into a single grading system. The factors incorporated
into the revised Lodwick classification system include soft-tissue
involvement, pattern of bone destruction, size of lesion, zone of
transition, margin sclerosis, and host response.
The revised Lodwick classification system consists of five
grades labeled IA, IB, IC, II, and III. The grading of a lesion is
performed in a sequential four-step manner.
The first step is to determine the type of bone destruction
present in the lesion. A lesion with geographic destruction would
be defined as a lesion having a sharp, clearly defined margin
(grade I; Figure 12). Moth-eaten destruction is similar to
moth-eaten clothes with holes of destroyed bone. Permeative
destruction is an ill-defined, diffuse, somewhat subtle destructive
process of bone. Those lytic lesions that are entirely moth-eaten
and/or permeative are grade III (Figure 13). Any lytic lesion that
is a combination of geographic with moth-eaten and/or permeative
destruction is a grade II lesion (Figure 14). If the lesion is
grade II or III, then that lesion is classified and is considered
malignant until proven otherwise. If the lesion is grade I, then
classification proceeds to the second step. Lodwick often found it
difficult to differentiate between grade II and III lesions, but it
does not really matter because both grades indicate an aggressive
lesion that needs further evaluation and/or treatment.
The second step is to re-evaluate the margin of the lesion,
including any cortex that the lesion abuts. If any of the margins
are indistinct, then the lesion is classified as grade IC (Figure
15). Margins that are indistinct should not be confused with
moth-eaten/permeative destruction (grade II or III). If the lesion
cannot be classified as grade IC, then classification proceeds to
the third step.
In the third step, the lesion is evaluated for expansion. If an
expanded cortical shell is present and it exceeds 1 cm, then the
lesion is classified as grade IB (Figure 16). The fourth step
consists of evaluating the lesion for the presence of a
circumferential sclerotic margin. If the lesion has a sclerotic
margin, it is classified as grade IA (Figure 12). Those with a
nonsclerotic margin are classified as grade IB.
Usually, the authors recommend follow-up imaging for lytic
lesions that are asymptomatic, have a grade IA appearance, and are
found in an otherwise healthy patient. Nonspecific and
nonpathognomonic lytic lesions that are grade IB, IC, II, III, or
are symptomatic warrant further work-up at the time of discovery.
Based on previous studies, the likelihood of malignancy using the
revised Lodwick classification (disregarding patient symptoms and
whether the lesion is pathognomonic in appearance) is as follows:
grade IA is 6%, grade IB is 48%, grade IC is 36%, grade II is 97%,
and grade III is 100%.
If pathognomonic lesions are excluded from the results of these
studies, the likelihood of malignancy of grade IA lesions falls to
2% to 4%.
If periosteal reaction is present, we classify it as either
solid or interrupted (Table 1).
Solid periosteal reaction is described as a single layer of new
bone thicker than 1 mm and uninterrupted throughout its extent.
Interrupted periosteal reaction is simply the laying down of new
bone that is interrupted-that is, not continuous or solid. Some
examples include sunburst and Codman's triangle. Interrupted
periosteal reaction indicates that the associated lesion is
Those lesions that are not pathognomonic in appearance and have an
interrupted periosteal reaction also warrant further work-up
because of their higher likelihood of malignancy.
It is important to remember that interrupted periosteal reaction is
sometimes seen with osteomyelitis.
Further work-up recommendations for the aggressive, nonspecific
lytic lesion typically consist of MRI and/or computed tomography
(CT), a whole-body nuclear medicine bone scan, or even a biopsy.
Further work-up is also performed on those lesions that are
aggressive and pathognomonic in appearance for malignancy, such as
osteosarcoma (osteoid matrix) and chondrosarcoma (chondroid
matrix). It should be remembered that further work-up with MRI and
nuclear medicine studies is primarily used for lesion staging
and/or prebiopsy work-up. In the vast majority of cases, the key to
the diagnosis is in the plain radiographic appearance of the
At our institution, we obtain an MRI of an aggressive,
nonspecific lytic lesion to evaluate its full extent, to aid in
prebiopsy/preoperative planning, and, occasionally, to aid in
diagnosis. If there is any concern that the lesion might be an
osteosarcoma or Ewing's sarcoma, then the entire length of the
involved bone must be imaged, including any joints with which the
involved bone articulates. The reason the entire length is imaged
is to detect any skip lesions, which can be seen with osteosarcoma
and Ewing's sarcoma.
A skip lesion is a separate area of disease involvement from the
originally discovered lesion. The separate area of involvement will
have intervening normal marrow between it and the original lesion
(Figure 17). Identification of a skip lesion changes the treatment
and, possibly, the prognosis. When evaluating the extent of marrow
involvement, T1-weighted sequence images should be used, as these
have been shown to most accurately reflect the true extent of
MRI will also aid in establishing which compartments and
structures are involved.
The determination of which compartments are involved is important
in the decision of the type of treatment or surgery necessary, as
well as to determine a biopsy path. In general, a biopsy path
should avoid any compartments that are not grossly involved by the
Occasionally, an MRI or a CT examination of a nonspecific lytic
lesion will narrow the differential diagnosis. An example of this
would be the presence of fluid-fluid levels, which are most
commonly found in an aneurysmal bone cyst.
Another example would be a fatty tumor seen on MRI in the anterior
calcaneus, which is consistent with an intraosseous lipoma (Figure
In patients who are claustrophobic or who have a
contraindication for MRI, a CT examination is used to evaluate the
extent of the lesion. CT is also useful in the evaluation of
lesions located in anatomically complex osseous structures, such as
the pelvis, scapula, or spine (Figure 3). CT is also useful in
identifying mineralization of a matrix. For example, CT would be
used to identify chondroid matrix in a suspected chondroblastoma
A nuclear medicine bone scan is performed to look for a
polyostotic process. If the process is polyostotic, then the
differential diagnosis of a nonspecific lytic lesion can be
narrowed. For example, the vast majority of polyostotic lytic
processes in the elderly would represent either metastasis or
A bone scan may also identify other lesions that may be more
appropriate to biopsy; therefore, the bone scan also plays a role
in prebiopsy evaluation.
If the lesion is still nonspecific after thorough imaging,
image-guided biopsy of the lesion can be performed. The biopsy
pathway should be selected in conjunction with the surgeon so that
any uninvolved compartments can be avoided and any seeding along
the biopsy path can be easily resected during surgery without
worsening the patient's outcome or prognosis if the lesion is a
primary bone malignancy. Finally, percutaneous needle biopsy of a
chondrosarcoma should be avoided.
Lytic bone lesions are frequently encountered in a general
radiology practice. A rational and systematic approach can often
result in a specific diagnosis or a short differential diagnosis.
Based on this, a reasonable diagnostic work-up can be